DiVA - Academic Archive On-line

ARPD : Asynchronous random key predistribution in the LEAP framework for Wireless Sensor Networks

Andreas Achtzehn — Mon, 7 Jan 2008 16:58:00 +0200

In the LEAP framework for wireless sensor networks a set of keys is used to secure communication. LEAP distinguishes between unicast (pairwise) communication, group (cluster) communication and global (broadcast) communication. The keys used in pairwise communication are derived from an initial key KI that nodes are equipped with prior to deployment

and that is deleted after link setup. Further keys are distributed encrypted with these pairwise keys. If the initial key is ever disclosed, the whole network is compromised.

To lower the threat of KI disclosure, we present a novel KI -less scheme for key predistribution. Our scheme is based on random key redistribution, and proves to perform better in medium sized networks than previous proposals. It is resilient against node capture attacks and allows node to node authentication. Attacks against overlying protocols in the network are more difﬁcult with this scheme.

We have conducted computations to show the feasibility of our scheme for networks up to a size of 1000 nodes. By introducing a key reuse system we are able to increase the probability of a successful link setup. We have included a security analysis that discusses our scheme’s resistance against commonly known attacks.

Presentation of the VINN Excellence Center for Wireless Sensor Networks (WISENET)

Anders Ahlén — Wed, 2 Dec 2009 10:23:00 +0200

Development of Electroacoustic Sensors for Biomolecular Interaction Analysis

Henrik Anderson — Thu, 20 Aug 2009 13:36:00 +0200

Biomolecular interaction analysis to determine the kinetics and affinity between interacting partners is important for the fundamental understanding of biology, as well as for the development of new pharmaceutical substances. A quartz crystal microbalance instrument suitable for kinetics and affinity analyses of interaction events was developed. The functionality of the sensor system was demonstrated by development of an assay for relative affinity determination of lectin-carbohydrate interactions.

Sensor surfaces allowing for effective immobilization of one interacting partner is a key functionality of a biosensor. Here, three different surfaces and immobilization methods were studied. First, optimized preparation conditions for sensor surfaces based on carboxyl-terminated self assembled monolayers were developed and were demonstrated to provide highly functional biosensor surfaces with low non-specific binding. Second, a method allowing for immobilization of very acidic biomolecules based on the use of an electric field was developed and evaluated. The electric field made it possible to immobilize the highly acidic C-peptide on a carboxylated surface. Third, a method for antibody immobilization on a carboxyl surface was optimized and the influence of immobilization pH on the immobilization level and antigen binding capacity was thoroughly assessed. The method showed high reproducibility for a set of antibodies and allowed for antibody immobilization also at low pH.

Three broadly different strategies to increase the sensitivity of electroacoustic sensors were explored. A QCM sensor with small resonator electrodes and reduced flow cell dimensions was demonstrated to improve the mass transport rate to the sensor surface. The use of polymers on QCM sensor surfaces to enhance the sensor response was shown to increase the response of an antibody-antigen model system more than ten-fold. Moreover, the application of high frequency thin film bulk acoustic resonators for biosensing was evaluated with respect to sensing range from the surface. The linear detection range of the thin film resonator was determined to be more than sufficient for biosensor applications involving, for instance, antibody-antigen interactions. Finally, a setup for combined frequency and resistance measurements was developed and was found to provide time resolved data suitable for kinetics determination.

Resistance Electric Field Dependence and Time Drift of Piezoresistive Single Crystalline Silicon Nanofilms

Emil Anderås — Tue, 6 Apr 2010 08:26:00 +0200

Adding Mobility to Wireless Sensor Network Simulations : Poster Abstract

Nils Aschenbruck — Fri, 14 Jan 2011 16:01:07 +0200

Combined Secure Storage and Communication for the Internet of Things

Ibrahim Bagci — Tue, 9 Jul 2013 11:22:00 +0200

A social node model for realising information dissemination strategies in delay tolerant networks

Saeed Bastani — Wed, 9 Jan 2013 13:54:00 +0200

In Delay Tolerant Networks (DTNs) as an emerging content dissemination platform, mobile nodes opportunistically exchange content as they meet, with the intent of disseminating content among nodes that share common interests. During a meeting, nodes can exchange both content of direct interest to themselves as well as content that is of interest to a larger set of nodes that may be encountered in the future. The utility of DTN is governed by the content exchange opportunity (the amount of content that can be exchanged during a meeting) as well as the selection of content to be exchanged in order to maximise the interest nodes will have in information they are exposed to. Considering that there is a cost associated with the content exchange (e.g. battery usage, buffer occupancy or consumed transmission opportunity) the aim for nodes participating in content dissemination should be to maximise their payoff. In this paper, we contribute a generic framework for describing the characteristics of content exchange among participating nodes in a network. We incorporate a distributed information popularity measurement and the pairwise interaction of nodes modelled as a bargaining problem. The outcome of this process is the fair split up of dwelling time as a network resource and the selection of which content objects to exchange in order to maximise the nodes’ payoff. The framework is generally intended to be used as a capstone for investigation of content dissemination properties and various content exchange strategies in a DTN, a topic addressed in this paper and experiments conducted to validate the function and correctness of the proposed framework.

Measurements in opportunistic networks

Fredrik Bjurefors — Thu, 8 Mar 2012 00:00:00 +0200

Opportunistic networks are a subset of delay tolerant networks where the contacts are unscheduled. Such networks can be formed ad hoc by wireless devices, such as mobile phones and laptops. In this work we use a data-centric architecture for opportunistic networks to evaluate data dissemination overhead, congestion in nodes' buffer, and the impact of transfer ordering. Dissemination brings an overhead since data is replicated to be spread in the network and overhead leads to congestion, i.e., overloaded buffers.

We develop and implement an emulation testbed to experimentally evaluate properties of opportunistic networks. We evaluate the repeatability of experiments in the emulated testbed that is based on virtual computers. We show that the timing variations are on the order of milliseconds.

The testbed was used to investigate overhead in data dissemination, congestion avoidance, and transfer ordering in opportunistic networks. We show that the overhead can be reduced by informing other nodes in the network about what data a node is carrying. Congestion avoidance was evaluated in terms of buffer management, since that is the available tool in an opportunistic network, to handle congestion. It was shown that replication information of data objects in the buffer yields the best results. We show that in a data-centric architecture were each data item is valued differently, transfer ordering is important to achieve delivery of the most valued data.

Opportunistic Networking : Congestion, Transfer Ordering and Resilience

Fredrik Bjurefors — Thu, 15 May 2014 11:45:00 +0200

Opportunistic networks are constructed by devices carried by people and vehicles. The devices use short range radio to communicate. Since the network is mobile and often sparse in terms of node contacts, nodes store messages in their buffers, carrying them, and forwarding them upon node encounters. This form of communication leads to a set of challenging issues that we investigate: congestion, transfer ordering, and resilience.

Congestion occurs in opportunistic networks when a node's buffers becomes full. To be able to receive new messages, old messages have to be evicted. We show that buffer eviction strategies based on replication statistics perform better than strategies that evict messages based on the content of the message.

We show that transfer ordering has a significant impact on the dissemination of messages during time limited contacts. We find that transfer strategies satisfying global requests yield a higher delivery ratio but a longer delay for the most requested data compared to satisfying the neighboring node's requests.

Finally, we assess the resilience of opportunistic networks by simulating different types of attacks. Instead of enumerating all possible attack combinations, which would lead to exhaustive evaluations, we introduce a method that use heuristics to approximate the extreme outcomes an attack can have. The method yields a lower and upper bound for the evaluated metric over the different realizations of the attack. We show that some types of attacks are harder to predict the outcome of and other attacks may vary in the impact of the attack due to the properties of the attack, the forwarding protocol, and the mobility pattern.

Resilience and Opportunistic Forwarding : Beyond Average Value Analysis

Fredrik Bjurefors — Thu, 17 Apr 2014 11:31:00 +0200

Opportunistic networks are systems with highly distributed operation, relying on the altruistic cooperation of highly heterogeneous, and not always software and hardware-compatible, user nodes. Moreover, the absence of central coordination and control makes them vulnerable to malicious attacks. In this paper, we study the resilience of popular forwarding protocols to a representative set of challenges to their normal operation. These include jamming locally disturbing message transfer between nodes, hardware/software failures and incompatibility among nodes rendering contact opportunities useless, and free-riding phenomena. We first formulate and promote the metric envelope concept as a tool for assessing the resilience of opportunistic forwarding schemes. Metric envelopes depart from the standard practice of average value analysis and explicitly account for the differentiated challenge impact due to node heterogeneity (device capabilities, mobility) and attackers’ intelligence. We then propose heuristics to generate worst- and best-case challenge realization scenarios and approximate the lower and upper bounds of the metric envelopes. Finally, we demonstrate the methodology in assessing the resilience of three popular forwarding protocols in the presence of the three challenges, and under a comprehensive range of mobility patterns. The metric envelope approach provides better insights into the level of protection path diversity and message replication provide against different challenges, and enables more informed choices in opportunistic forwarding when network resilience becomes important.

Synthesis of highly textured thin piezoelectric AlN films with a tilted c-axis

Johan Bjurström — Fri, 11 Jan 2008 09:47:00 +0200

Design and Fabrication of Temperature Compensated Liquid FBAR Sensors

Johan Bjurström — Tue, 30 Jan 2007 13:48:00 +0200

Temperature compensation of liquid FBAR sensors

Johan Bjurström — Fri, 9 Mar 2007 14:22:00 +0200

In this work we demonstrate a practically complete temperature compensation of the second harmonic shear mode in a composite Al/AlN/Al/SiO₂ thin film bulk acoustic resonator (FBAR) in the temperature range 25 °C–95 °C. The main advantages of this mode are its higher Q value in liquids as well as its higher frequency and hence higher resolution for sensor applications. For comparative reasons the non-compensated fundamental shear mode is also included in these studies. Both modes have been characterized when operated both in air and in pure water. Properties such as Q value, electromechanical coupling, dissipation and sensitivity are studied. An almost complete temperature compensation of the second harmonic shear mode was observed for an oxide thickness of 1.22 µm for an FBAR consisting of 2 µm thick AlN and 200 nm thick Al electrodes. Thus, the measured temperature coefficient of frequency (TCF) in air for the non-compensated fundamental shear mode (1.25 GHz) varied between −31 and −36 ppm °C⁻¹ over the above temperature range while that of the compensated second harmonic shear mode (1.32 GHz) varied between +2 ppm °C⁻¹ and −2 ppm °C⁻¹ over the same temperature interval. When operated in pure water the former type shows a Q value and coupling coefficient, k²_t, around 180 and 2%, respectively, whereas for the second harmonic these are 230 and 1.4%, respectively.

Energy Constrained Wireless Sensor Networks : Communication Principles and Sensing Aspects

Erik Björnemo — Fri, 9 Jan 2009 11:11:00 +0200

Wireless sensor networks are attractive largely because they need no wired infrastructure. But precisely this feature makes them energy constrained, and the consequences of this hard energy constraint are the overall topic of this thesis. We are in particular concerned with principles for energy efficient wireless communication and the energy-wise trade-off between sensing and radio communication.

Radio transmission between sensors incurs both a fixed energy cost from radio circuit processing, and a variable energy cost related to the level of radiated energy. We here find that transmission techniques that are otherwise considered efficient consumes too much processing energy. Currently available sensor node radios typically have a maximum output power that is too limited to benefit from transmission-efficient, but processing-intensive, techniques. Our results provide new design guidelines for the radio output power. With increasing transmission energy -- with increasing distance -- the considered techniques should be applied in the following order: output power control, polarisation receiver diversity, error correcting codes, multi-hop communication, and cooperative multiple-input multiple-output transmissions.

To assess the measurement capability of the network as a whole, and to facilitate a study of the sensing-communication trade-off, we devise a new metric: the network measurement capacity. It is based on the number of different measurement sequences that a network can provide, and is hence a measure of the network's readiness to meet a large number of possible events. Optimised multi-hop routing under this metric reveals that the energy consumed for sensing has decisive impact on the best multi-hop routes. We also find support for the use of hierarchical heterogeneous network structures.

Model parameter uncertainties have large impact on our results and we use probability theory as logic to include them consistently. Our analysis shows that common assumptions can give misleading results, and our analysis of radio channel measurements confirms the inadequacy of the Rayleigh fading channel model.

On the energy-efficiency of cooperative MIMO in nakagami-fading wireless sensor networks

Erik Björnemo — Fri, 29 Aug 2008 14:48:00 +0200

Low-power radio communication in industrial outdoor deployments: the impact of weather conditions and ATEX-compliance

Carlo Alberto Boano — Fri, 14 Jan 2011 17:01:15 +0200

Controllable radio interference for experimental and testing purposes in wireless sensor networks

Carlo Alberto Boano — Fri, 14 Jan 2011 17:04:35 +0200

Demo Abstract: Generation of Controllable Radio Interference for Protocol Testing in Wireless Sensor Networks

Carlo Alberto Boano — Fri, 14 Jan 2011 16:36:42 +0200

The Impact of Temperature on Outdoor Industrial Sensornet Applications

Carlo Alberto Boano — Fri, 14 Jan 2011 14:45:50 +0200

Exploiting the LQI Variance for Rapid Channel Quality Assessment : Poster Abstract

Carlo Alberto Boano — Fri, 14 Jan 2011 17:10:38 +0200

Making Sensornet MAC Protocols Robust Against Interference

Carlo Alberto Boano — Fri, 14 Jan 2011 16:04:52 +0200

Hot Packets : A systematic evaluation of the effect of temperature on low power wireless transceivers

Carlo Alberto Boano — Mon, 10 Jun 2013 14:50:00 +0200

Temperature is known to have a significant effect on the performance of radio transceivers: the higher the temperature, the lower the quality of links. Analysing this effect is particularly important in sensor networks because several applications are exposed to harsh environmental conditions. Daily or hourly changes in temperature can dramatically reduce the throughput, increase the delay, or even lead to network partitions. A few studies have quantified the impact of temperature on low-power wireless links, but only for a limited temperature range and on a single radio transceiver. Building on top of these preliminary observations, we design a low-cost experimental infrastructure to vary the onboard temperature of sensor nodes in a repeatable fashion, and we study systematically the impact of temperature on various sensornet platforms. We show that temperature affects transmitting and receiving nodes differently, and that all platforms follow a similar trend that can be captured in a simple first-order model. This work represents an initial stepping stone aimed at predicting the performance of a network considering the particular temperature profile of a given environment.

The Triangle Metric: Fast Link Quality Estimation for Mobile Wireless Sensor Networks : (Invited Paper)

Carlo Alberto Boano — Fri, 14 Jan 2011 15:40:06 +0200

Towards adaptive zero-knowledge protocols : A case study with Fiat–Shamir identification protocol

Volkan Cambazoglu — Wed, 5 Jun 2013 15:39:00 +0200

Interactive zero-knowledge protocols are used as identification protocols. The protocols are executed in rounds, with security being increased with every round. This allows for a trade-off between security and performance to adapt the protocol to the requirements of the scenario. We experimentally investigate the Fiat–Shamir identification protocol on machines and networks with different performance characteristics. We find that the delay of the protocol highly depends on network latency and upload bandwidth. Computation time becomes more visible, when the protocol transmits little amount of data via a low latency network. We also experience that the impact of the sizes of the variables on the delay of the protocol is less than the number of rounds', which are interior factors in the protocol.

The impact of trace and adversary models on location privacy provided by K-anonymity

Volkan Cambazoglu — Tue, 10 Apr 2012 13:42:00 +0200

Mode Switch : Adaptive use of delay-sensitive or energy-aware communication in IEEE 802.15.4-based networks

Feng Chen — Fri, 10 Dec 2010 19:41:00 +0200

Integrated Antenna Solutions for Wireless Sensor and Millimeter-Wave Systems

Shi Cheng — Thu, 7 Jan 2010 15:08:13 +0200

This thesis presents various integrated antenna solutions for different types of systems and applications, e.g. wireless sensors, broadband handsets, advanced base stations, MEMS-based reconfigurable front-ends, automotive anti-collision radars, and large area electronics.

For wireless sensor applications, a T-matched dipole is proposed and integrated in an electrically small body-worn sensor node. Measurement techniques are developed to characterize the port impedance and radiation properties. Possibilities and limitations of the planar inverted cone antenna (PICA) for small handsets are studied experimentally. Printed slot-type and folded PICAs are demonstrated for UWB handheld terminals.

Both monolithic and hybrid integration are applied for electrically steerable array antennas. Compact phase shifters within a traveling wave array antenna architecture, on single layer substrate, is investigated for the first time. Radio frequency MEMS switches are utilized to improve the performance of reconfigurable antennas at higher frequencies. Using monolithic integration, a 20 GHz switched beam antenna based on MEMS switches is implemented and evaluated. Compared to similar work published previously, complete experimental results are here for the first time reported. Moreover, a hybrid approach is used for a 24 GHz switched beam traveling wave array antenna. A MEMS router is fabricated on silicon substrate for switching two array antennas on a LTCC chip.

A concept of nano-wire based substrate integrated waveguides (SIW) is proposed for millimeter-wave applications. Antenna prototypes based on this concept are successfully demonstrated for automotive radar applications.

W-band body-worn nonlinear harmonic radar reflectors are proposed as a means to improve automotive radar functionality. Passive, semi-passive and active nonlinear reflectors consisting of array antennas and nonlinear circuitry on flex foils are investigated.

A new stretchable RF electronics concept for large area electronics is demonstrated. It incorporates liquid metal into microstructured elastic channels. The prototypes exhibit high stretchability, foldability, and twistability, with maintained electrical properties.

Array antenna for body-worn automotive harmonic radar tag

Shi Cheng — Sun, 6 Dec 2009 18:32:10 +0200

T-matched dipole antenna integrated in electrically small body-worn wireless sensor node

Shi Cheng — Sun, 6 Dec 2009 18:12:12 +0200

A 2.4 GHz antenna for an electrically small body-worn sensor node is presented. Usually, unbalanced antennas are used in such applications. Implementing a balanced antenna in a small node deployed on the body is problematic from the points of view of both design and characterisation. A solution using a T-matched dipole integrated in the node housing is presented. Techniques for characterisation both in free space and on the body are described. Besides antenna port impedance and radiation efficiency, radiated power and radiation patterns of the active antenna fed by a transceiver in a fully functional sensor node are measured. The benefits and drawbacks of the chosen antenna design and characterisation techniques are discussed.

Design and characterization methods for a balanced antenna integrated in a small sensor node

Shi Cheng — Fri, 19 Mar 2010 16:23:00 +0200

Liquid metal stretchable unbalanced loop antenna

Shi Cheng — Sun, 6 Dec 2009 18:16:00 +0200

We present a 2.4 GHz unbalanced loop antenna that can be stretched along multiple dimensions simultaneously. It was realized by incorporating room temperature liquid metal alloy into microstructured channels in an elastic material. The demonstrated prototype exhibits a stretchability of up to 40% along two orthogonal orientations as well as foldability and twistability. Port impedance and radiation characteristics of the nonstretched and stretched antenna were studied numerically and experimentally. Measured results indicate a radiation efficiency of more than 80%.

Foldable and stretchable liquid metal planar inverted cone antenna

Shi Cheng — Sun, 6 Dec 2009 18:27:09 +0200

A mechanically flexible planar inverted cone antenna (PICA) for ultrawideband (UWB) applications is presented. It can be both folded and stretched significantly without permanent damage or loss of electrical functionality. The antenna is manufactured with a process in which conductors are realized by injecting room temperature liquid metal alloy into micro-structured channels in an elastic dielectric material. The elastic dielectric material together with the liquid metal enables bending with a very small radius, twisting, and stretching along any direction. Port impedance and radiation characteristics of the non-stretched and stretched antenna are studied in simulations and experiments. The presented antenna has a return loss better than 10 dB within 3-11 GHz and a radiation efficiency of > 70% over 3-10 GHz, also when stretched. Tests verify that stretching up to 40% is possible with maintained electrical performance. The presented antenna is useful for example for body-worn antennas and in applications in harsh environments where mechanical flexibility helps improve durability.

A highly stretchable microfluidic meandered monopole antenna

Shi Cheng — Mon, 21 Dec 2009 10:05:00 +0200

Body Surface backed flexible antennas for 17 GHz wireless body area networks sensor applications

Shi Cheng — Wed, 23 Jan 2008 14:04:00 +0200

Satellite based wireless sensor networks: Global scale sensing with nano- and picosatellites

Walter Colitti — Mon, 17 Jan 2011 10:24:01 +0200

NETWORKING 2010

Tue, 21 Dec 2010 19:38:00 +0200

An adaptive communication architecture for wireless sensor networks

Adam Dunkels — Mon, 17 Jan 2011 10:58:58 +0200

Software-based sensor node energy estimation : Demo abstract

Adam Dunkels — Mon, 17 Jan 2011 10:56:18 +0200

Making sensor networks ipv6 ready

Mathilde Durvy — Mon, 17 Jan 2011 09:49:48 +0200

Fabrication of Electroacoustic Devices for Integrated Applications

Johannes Enlund — Fri, 24 Apr 2009 08:07:00 +0200

Electroacoustic technology has in many ways revolutionised the wireless telecommunication industry. The IC compatible fabrication technique of thin film electroacoustic devices has so far provided a considerable increase in device performance and reduction in size. At the moment, new areas where this technology can be of use is under investigation. In particular, thin film bulk acoustic wave resonators are promising candidates for biochemical and gravimetric sensor applications.

For bulk acoustic waves, the thesis addresses a number of aspects in the design, fabrication, characterisation, and integration of thin film electroacoustic devices. The object of the studies conducted in the thesis has been to improve on design and thereby optimise the performance of the device to fit a particular application of interest. For high frequency and high power applications, a conceptually new design of the solidly mounted resonator has been investigated. A 1 GHz plate wave resonator with a much higher Q factor than its surface acoustic counterpart have also been fabricated. A multi-chip-module 2 GHz microwave oscillator featuring a monolithically integrated solidly mounted resonator and a flip chip transistor have been fabricated and characterised with a phase noise of -125 dBc/Hz at 100 kHz. For sensor applications, the fabrication of shear mode solidly mounted resonators featuring c-axis inclined AlN films has been studied. A process for the bonding of a microfluidic system on top of the resonator has been realised. Further, the effect of conductive liquids on the resonator performance has been investigated.For surface acoustic wave devices, acoustic manipulation of particles in microfluidic channels has been studied. Two functional devices have been fabricated by bonding piezoelectric substrates to glass or fused silica superstrates. By generating an interface acoustic wave, that propagates along the bonded interface, manipulation of sub-micrometer particles was realised.

FBAR sensor array for in liquid operation

Johannes Enlund — Wed, 1 Sep 2010 12:11:39 +0200

This letter discusses the design of thickness shear mode thin-film bulk acoustic resonator (FBAR) sensor array for in liquid operation with respect to minimizing the observed Q-degradation and crosstalk.

Analysis of Q-degradation and Cross-Talk in BAW Sensor Arrays Operating in Conductive Liquid Media

Johannes Enlund — Fri, 19 Mar 2010 14:05:08 +0200

Solidly mounted thin film electro-acoustic resonator utilizing a conductive Bragg reflector

Johannes Enlund — Mon, 21 Jan 2008 08:28:00 +0200

A new design of a solidly mounted resonator (SMR) that utilizes an all-metal Bragg reflector eliminating thus the need for a bottom electrode is proposed. In this configuration, the role of the bottom electrode is taken by the Bragg reflector rendering the resonator “combined electrode-Bragg reflector SMR”. The main advantages of the proposed design are the substantially reduced electrode resistance (and hence higher Q), the utilization of the full piezoelectric coupling at high frequencies as well as expected improvement in power handling capabilities due to lower dissipation and improved heat conductivity. Resonators with the classical and the new design have been fabricated and evaluated. The measurements indicate that indeed the resonators with the new design demonstrate improved performance.

Detailed simulation of heterogeneous wireless sensor networks

Joakim Eriksson — Thu, 14 May 2009 00:00:00 +0200

Wireless sensor networks consist of many small nodes. Each node has a small microprocessor, a radio chip, some sensors, and is usually battery powered which limits network lifetime. Applications of wireless sensor networks range from environmental monitoring and health-care to industrial automation and military surveillance.

Since the nodes are battery powered and communication consumes more than computation much of the research focuses on power efficient communication. One of the problems is however to measure the power consumption and communication quality of the different solutions.

Simulation of sensor networks can greatly increase development speed and also be used for evaluating power consumption as well as communication quality. Simulation experiments typically give easier access to fine grained results than corresponding real-world experiments. The problem with simulators is that it is hard to show that a simulation experiment corresponds well with a similar real-world experiment.

This thesis studies how detailed simulation of wireless sensor networks can be validated for accuracy and also shows several important uses of detailed simulation such as power consumption profiling and interoperability testing. Both of them represent important topics in today's wireless sensor network research and development.

The results of the thesis are the simulation platform COOJA/MSPSim and that we show that MAC-protocol experiments performed in our simulator COOJA/MSPSim correspond well with experiments performed in our testbed. We also show that using COOJA/MSPSim any software running in the simulation can be power profiled.

Accurate power profiling for sensor network simulators

Joakim Eriksson — Mon, 17 Jan 2011 10:39:03 +0200

Accurate, network-scale power profiling for sensor network simulators

Joakim Eriksson — Mon, 17 Jan 2011 09:23:00 +0200

Towards Interoperability Testing for Wireless Sensor Networks with COOJA/MSPSim : Demo Abstract

Joakim Eriksson — Mon, 17 Jan 2011 09:42:16 +0200

COOJA/MSPSim:Interoperability Testing for Wireless Sensor Networks

Joakim Eriksson — Mon, 17 Jan 2011 09:13:07 +0200

Demo abstract: accurate power profiling of sensornets with the COOJA/MSPSim simulator

Joakim Eriksson — Fri, 14 Jan 2011 16:49:19 +0200

Self-organizing TDMA for multihop networks

Laura Marie Feeney — Fri, 9 Mar 2012 15:32:00 +0200

On the consistency of simulation results

Laura Marie Feeney — Wed, 12 Oct 2011 19:24:00 +0200

Exploring semantic interference in heterogeneous sensor networks

Laura Marie Feeney — Thu, 14 Aug 2008 13:28:00 +0200

Managing cross layer information in OMNeT++ simulations

Laura Marie Feeney — Thu, 23 Dec 2010 09:48:00 +0200

This paper describes a general approach to dealing with cross layer information in OMNeT++-based network simulations. Rather than prescribe a specific cross layer architecture, this work is intended to address the software engineering problem of passing information between simulation modules in a sound way. An XML-based mechanism for passing information between modules using OMNeT++'s controlInfo data structure is presented. Because XML is an intermediate format for the OMNeT++ network description language (NED), it is further suggested that allowing NED files to be annotated with information about cross layer interactions will enhance readability and reuse-ability. A further goal of this paper is to initiate discussion and collaboration in the Swedish (and international) OMNeT++ community.

Poster Abstract: A Testbed for Measuring Battery Discharge Behavior

Laura Marie Feeney — Tue, 27 Nov 2012 08:36:00 +0200

Poster Abstract: Using batteries wisely

Laura Marie Feeney — Tue, 27 Nov 2012 08:42:00 +0200

Multi-rate relaying for performance improvement in IEEE 802.11 WLANs

Laura Marie Feeney — Sat, 21 Jul 2007 11:08:00 +0200

Modeling Capacity in Ad Hoc Networks : Extended Poster Abstract

Laura Marie Feeney — Mon, 7 Jan 2008 16:51:00 +0200

We describe a simple network model for efficiently simulating the CBR flow capacity of a multi-hop wireless network. The model is particularly intended for studying the behavior of asynchronous protocols, particularly power save protocols, where it is useful to examine many scheduling variations as well as many topologies and network configurations.

We describe our experience using the model in some experiments in which we examine how the network performance is sensitive to the timing to scheduling variations induced by the operation of a simple power save protocol. We note that the model also seems seems suitable for combinatoric and probabilistic analysis, which is on-going work.

Poster abstract: The feasibility of leveraging a power save protocol to improve performance in ad hoc networks

Laura Marie Feeney — Mon, 7 Jan 2008 16:50:00 +0200

We discuss how the operation of an asynchronous power save protocol affects the scheduling of transmissions in an ad hoc network. We present simulation results that show that network capacity is sensitive to the random distribution of wakeup schedules. Finally, we discuss the implications of this result with respect to improving performance and speculate about potential new cross-layer architectures.

A model for evaluating asynchronous protocols in Ad hoc Networks

Laura Marie Feeney — Thu, 21 Dec 2006 10:12:00 +0200

Leveraging a power save protocol to improve performance in ad hoc networks

Laura Marie Feeney — Wed, 23 Jan 2008 16:40:00 +0200

Power save protocols reduce energy consumption in ad hoc and sensor networks by allowing nodes to put their network interface into a low power consumption sleep state. The power save protocol must allow neighboring nodes to establish intervals during which they are mutually awake and available to exchange traffic. Many such protocols are based on a coordinated election of a covering set that is responsible for buffering traffic for sleeping nodes, but uncoordinated (i.e. asynchronous) protocols have also proven an attractive option.

The impact of wakeup schedule distribution in asynchronous power save protocols on the performance of multihop wireless networks

Laura Marie Feeney — Mon, 7 Jan 2008 16:52:00 +0200

How do the dynamics of battery discharge affect sensor lifetime?

Laura Marie Feeney — Thu, 10 Apr 2014 17:07:00 +0200

Energy Framework : An extensible framework for simulating battery consumption in wireless networks

Laura Marie Feeney — Thu, 23 Dec 2010 09:42:00 +0200

Towards adaptive sensor networks

Niclas Finne — Mon, 30 May 2011 00:00:00 +0200

Wireless sensor networks consist of many small embedded devices that are equipped with sensors and a wireless communication unit. These devices, or sensor nodes, are typically low cost, resource constrained and battery-powered. Sensor network applications include environmental monitoring, industrial condition monitoring, building surveillance, and intelligent homes.

Sensor network applications today are often developed either using standard software components which enables simpler development but leads to far from optimal performance, or software customized for the specific application which complicates development, software updates, and software reuse.

We suggest that logic is separated from configuration and other information, for instance, network statistics and estimated power consumption. Software components publish their configuration and other information using a generalized programming abstraction. Configuration policies are separate modules that react on changes and reconfigure the sensor node as needed. These configuration policies are responsible for coordinating the configuration between the components and optimize the sensor network towards the application objectives.

One of our contributions is that we demonstrate the need for self-monitoring and self-configuration based on experiences from two deployed sensor networks. Our main contribution is that we devise a configuration architecture that solves the problem of cross-layer optimization for sensor network applications without tight coupling between components, thus enabling standard and easily replaceable components to be used. The configuration architecture makes it possible to reach the same level of performance as specialized cross-layer optimizations but without adding application-specific knowledge to the components.

Experiences from two sensor network deployments self-monitoring and self-configuration keys to success

Niclas Finne — Mon, 17 Jan 2011 10:47:51 +0200

Improving Sensornet Performance by Separating System Configuration from System Logic

Niclas Finne — Fri, 14 Jan 2011 16:07:29 +0200

Mobile system for establishing the lactate threshold by analysing the respiratory air

Mia Folke — Fri, 27 May 2011 15:11:00 +0200

Dynamic landscapes : A model of context and contingency in evolution

David V. Foster — Sat, 22 Jun 2013 11:05:00 +0200

Although the basic mechanics of evolution have been understood since Darwin, debate continues over whether macroevolutionary phenomena are driven by the fitness structure of genotype space or by ecological interaction. In this paper we propose a simple model capturing key features of fitness-landscape and ecological models of evolution. Our model describes evolutionary dynamics in a high-dimensional, structured genotype space with interspecies interaction. We find promising qualitative similarity with the empirical facts about macroevolution, including broadly distributed extinction sizes and realistic exploration of the genotype space. The abstraction of our model permits numerous applications beyond macroevolution, including protein and RNA evolution.

Adaptive random re-routing for differentiated QoS in sensor networks

Erol Gelenbe — Mon, 16 Nov 2009 21:42:00 +0200

Modeling an Electronically Switchable Directional Antennafor Low-power Wireless Networks : Poster abstract

Biruk Silase Geletu — Fri, 25 Nov 2011 09:31:19 +0200

Quadrotor UAV : Konstruktion och användbarhetsstudie av en UAV i sensornätverk

Erik Grafström — Tue, 25 Jan 2011 12:08:00 +0200

Quadrotor UAVs are self-stabilizing, autonomous flying machines that has recently become more popular than ever. Unmanned Aerial Vehicles have their roots in the military, where they were developed for use in reconnaissance and combat. During the last few years, advances in the fields of electronic sensors, electric motors and microcontrollers have enabled smaller designs and autonomic flight control even for private use. The quadrotor, which is the particular kind of UAV we are looking closer at in this paper, has 4 rotors in an X-like formation. This configuration has many advantages such as good lift capacity, non-complex mechanical structure and serviceability.

In this project we aquired a current overview of the domain and determine whether it is possible to construct a quadrotor UAV designed for use in a WISENET sensor network on a low budget and short time schedule.

Based on existing community project AeroQuad, a quadrotor is constructed with a budget of about 500 euro. Combining theoretical and practical analysis, we conclude that a quadrotor UAV can be constructed within the given specifications.

Wireless Sensor Network and Radio Wave Propagation in Harsh Environments

Mathias Grudén — Fri, 4 May 2012 11:33:00 +0200

This licentiate thesis cover two important subjects regarding the application of wireless sensor networks (WSNs). Both subjects are related to propagation mechanisms. The first subject is what the radio channel looks like and how it behaves. In this case three different, and extreme, environments are measured and characterized - a train, a half scale jet engine fan and a full scale military jet engine. The train environment is characterized by measure the path loss and fading over distance. For the case with the jet engines, difficulties were found to measure the path loss over distance, so in this case stationary antennas were used, but with the engine running. Each of these shows an extreme type of fading, also known as Rayleigh fading. For the case of jet engine at full speed (about 10 000 rpm), it was shown that the time between two consecutive fading dips where only 290 μs, which is about twice the length of a data package from the WSN involved in this project. The Rayleigh distributed amplitude fading occurs when there is a multipath environment, the radio waves propagate several different paths between the transmitter and receiver, which causes a superposition at the receiver. When having Rayleigh fading, the performance of the radio link is greatly reduced. When applying a WSN in this type of environment, the use of several antennas will improve the received power of the signal. This is done by adding extra antennas to a wireless system and in a clever way combine the signals, or select one of two signals from the antennas. In a book chapter and in a paper presented in the thesis, a new and low energy type of diversity is described. The performance of this new type of diversity is shown by having a two branch diversity and discretely shifting the phase of each branch before combining them. In this case, four relative phase shifts are performed during each symbol received. When performing a combining like this, the energy is saved by not having any decision circuitry. By using this type of diversity and using a 90 % signal reliability and an ideal environment, the diversity gain is 5.5 dB for an averaging detector and 10.3 dB for a peak detector. The drawback with this system is that it is only limited for systems using simple types of amplitude (ASK) or frequency (FSK) modulation.

Wireless Sensor Network Systems in Harsh Environments and Antenna Measurement Techniques

Mathias Grudén — Thu, 13 Mar 2014 11:06:00 +0200

Wireless sensor network (WSN) has become a hot topic lately. By using WSN things that previously were difficult or impossible to measure has now become available. One of the main reasons using WSN for monitoring is to save money by cost optimization and/or increase safety by letting the user knowing the physical status of the monitored structure. This thesis considers four main topics, empirical testing of WSN in harsh environments, antenna designs, antenna measurements and radio environment emulation.

The WSN has been tested in train environment for monitoring of ball bearings and inside jet engines to monitor strain of blades and temperatures. In total, two investigations have been performed aboard the train wagon and one in the jet engine. The trials have been successful and provide knowledge of the difficulties with practical WSN applications. The key issues for WSN are robust communication, energy management (including scavenging) and physical robustness.

For the applications of WSN in harsh environments antennas has to be designed. In the thesis, two antennas has been designed, one for train environment and one for the receiver in the jet engine. In the train environment, a more isotropic radiation pattern is preferable; hence a small dual layered patch antenna is designed. The antenna is at the limit of being electrically small; hence slightly lower radiation efficiency is measured. For the WSN in the jet engine, a directive patch array is designed on an ultra-thin and flexible substrate. The thin substrate of the antenna causes rather lower radiation efficiency. But the antenna fulfils the requirements of being conformal and directive.

In reverberation chambers are used to measure antennas, but there are difficulties to provide a realistic radio environment, for example outdoor or on-body. In this thesis, a large reverberation chamber is designed and verified. It enables measurement between 400 MHz and 3 GHz. Also, a sample selection method is designed to provide a post processing possibilities to emulate the radio environment inside the chamber. The method is to select samples from a data set that corresponds to a desired probability density function. The method presented in this thesis is extremely fast but the implementation of the method is left for future research.

Field Operational Testing for Safety Improvement of Freight Trains using Wireless Monitoring by Sensor Network

Mathias Grudén — Wed, 19 Feb 2014 09:52:20 +0200

Today, the majority of wagon failures on railroad systems are because of the poor maintenance of ball bearings, which causes emergent stops and delays. The existing stationary detectors, lack in predicting failures which cause troubles in scheduling maintenance. During the fall of 2011, a trial was performed by applying a wireless sensor network (WSN) aboard a train wagon with the objective to demonstrate a proof of concept for monitoring the temperature of ball bearings aboard the train wagon. This trial investigates several key aspects when applying sensor networks such as radio wave propagation, energy scavenging and performance of the WSN aboard the wagon. Two wireless links were used in the WSN. The aboard network communicates at 2.45 GHz, and the external communication is an 868 MHz radio frequency identification radio link. Since the energy in the WSN node is limited, appropriate energy scavenging devices are also presented and evaluated in a lab environment. Effort has been made to overcome these problems. The energy consumption in the network is still a problem; the most promising energy scavenging technique is piezoelectric harvesting by vibrations, which in the experiments scavenged 2.32 mW.

Diversity Techniques for Robustness and Power Awareness in Wireless Sensor Systems for Railroad Transport Applications

Mathias Grudén — Sun, 25 Sep 2011 21:12:54 +0200

Reliability Experiments for Wireless Sensor Networks in Train Environment

Mathias Grudén — Mon, 15 Mar 2010 11:07:00 +0200

Privacy-aware probabilistic sampling for data collection in wireless sensor networks

João Guerreiro — Wed, 7 Dec 2011 21:42:00 +0200

The rising popularity of web services and their applications to sensor networks enables real-time data collection and queries by users. Unlike traditional periodic data collection, the traffic patterns generated from real-time data collection may expose the interests of users or the locations of unusual events to the attackers. To provide privacy in data collection, we propose a novel probabilistic sampling mechanism that can hide user queries and unusual events in the network, while supporting both routine and on-demand data reporting. Our goal is to prevent attackers from locating the unusual events and identifying interests of users by eavesdropping and analyzing the network traffic. In our probabilistic sampling scheme, the data are carefully reported at random times in order to mask the unusual events and user queries. In the meantime, our scheme can provide users with high data accuracy at minimized communication overheads. Extensive simulations have been conducted to evaluate the security strength, data accuracy and communication overheads of the proposed scheme.

WISENET Wireless Sensor Networks VINN Excellence Center

Per Gunningberg — Mon, 9 Jun 2008 16:14:00 +0200

This broschure was produced for the inauguration of WISENET December 7, 2007. It decribes the future impact of WISENET, application areas and the 10 partners. The three research areas "Node Integration & Energy", "Networkning & Security" and "Wireless Communication" is briefly described as well as the application projects in "Water Sensing" and "Transport".

Efﬁcient Mobile Data Collection with Mobile Collect

Navid Hassanzadeh — Mon, 12 Nov 2012 09:33:02 +0200

The main task of most deployed wireless sensor networks is data collection. While a number of solutions have been designed for static networks, there are currently no widely used data collection algorithms for mobilesensor networks. In this paper, we concentrate on scenarios where many nodes, both data sources and sinks, move along a certain track in one direction, a scenario that is common in sports events. Rather than designing a new protocol from scratch, we extend an existing data collection protocol with lightweight mechanisms to make it efficient for mobility. Our extensive simulations and results in a test bed that includes mobile robots demonstrate that our solution is able to achieve high packet delivery rates at low energy consumption. For our target scenario, our solution more than doubles packet delivery rates when the network is sparse. Our solution also works well in scenarios with a higher degree of mobility where nodes move according to a more demanding random waypoint model.

Do Sensor Networks need Mobile MAC Protocols

Navid Hassanzadeh — Mon, 12 Nov 2012 09:36:45 +0200

Rethinking link-level abstractions for sensor networks

Zhitao He — Mon, 17 Jan 2011 10:27:46 +0200

Droplet : A New Denial-of-Service Attack on Low Power Wireless Sensor Networks

Zhitao He — Mon, 2 Dec 2013 12:37:00 +0200

Sensor Networks and Their Radio Environment : On Testbeds, Interference, and Broken Packets

Frederik Hermans — Wed, 24 Sep 2014 14:52:00 +0200

Sensor networks consist of small sensing devices that collaboratively fulfill a sensing task, such as monitoring the soil in an agricultural field or measuring vital signs in a marathon runner. To avoid cumbersome and expensive cabling, nodes in a sensor network are powered by batteries and communicate wirelessly. As a consequence of the latter, a sensor network's communication is affected by its radio environment, i.e., the environment's propagation characteristics and the presence of other radio devices. This thesis addresses three issues related to the impact of the radio environment on sensor networks.

Firstly, in order to draw conclusions from experimental results, it is necessary to assess how the environment and the experiment infrastructure affect the results. We design a sensor network testbed, dubbed Sensei-UU, to be easily relocatable. By performing an experiment in different environments, a researcher can asses the environments’ impact on results. We further augment Sensei-UU with support for mobile nodes. The implemented mobility approach adds only little variance to results, and therefore enables repeatable experiments with mobility. The repeatability of experiments increases the confidence in conclusions drawn from them.

Secondly, sensor networks may experience poor communication performance due to cross-technology radio interference, especially in office and residential environments. We consider the problem of detecting and classifying the type of interference a sensor network is exposed to. We find that different sources of interference each leave a characteristic "fingerprint" on individual, corrupt 802.15.4 packets. We design and implement the SoNIC system that enables sensor nodes to classify interference using these fingerprints. SoNIC supports accurate classification in both a controlled and an uncontrolled environment.

Finally, we consider transmission errors in an outdoor sensor network. In such an environment, errors occur despite the absence of interference if the signal-to-noise ratio at a receiver is too low. We study the characteristics of corrupt packets collected from an outdoor sensor network deployment. We find that content transformation in corrupt packets follows a specific pattern, and that most corrupt packets contain only few errors. We propose that the pattern may be useful for applications that can operate on inexact data, because it reduces the uncertainty associated with a corrupt packet.

Supporting Heterogeneous LCD/Camera Links

Frederik Hermans — Tue, 15 Apr 2014 00:00:00 +0200

Sensei-UU — a relocatable WSN testbed supporting repeatable node mobility

Frederik Hermans — Thu, 2 Dec 2010 19:26:00 +0200

A Lightweight Approach to Online Detection and Classification of Interference in 802.15.4-based Sensor Networks

Frederik Hermans — Thu, 23 Aug 2012 09:58:00 +0200

With a rapidly increasing number of devices sharing access to the 2.4 GHz ISM band, interference becomes a serious problem for 802.15.4-based, low-power sensor networks. Consequently, interference mitigation strategies are becoming commonplace. In this paper, we consider the step that precedes interference mitigation: interference detection. We have performed extensive measurements to characterize how different types of interferers affect individual 802.15.4 packets. From these measurements, we define a set of features which we use to train a neural network to classify the source of interference of a corrupted packet. Our approach is sufficiently lightweight for online use in a resource constrained sensor network. It does not require additional hardware, nor does it use active spectrum sensing or probing packets. Instead, all information about interferers is gathered from inspecting corrupted packets that are received during the sensor network’s regular operation. Even without considering a history of earlier packets, our approach reaches a mean classification accuracy of 79.8%, with per interferer accuracies of64.9% for WiFi, 82.6% for Bluetooth, 72.1% for microwave ovens, and 99.6% for packets that are corrupted due to insufficient signal strength.

SoNIC : Classifying interference in 802.15.4 sensor networks

Frederik Hermans — Thu, 11 Apr 2013 13:48:00 +0200

All is not lost : Understanding and exploiting packet corruption in outdoor sensor networks

Frederik Hermans — Fri, 29 Nov 2013 22:50:00 +0200

Poster Abstract : An Experimental Study of Attacks on the Availability of Glossy

Kasun Hewage — Mon, 2 Dec 2013 14:43:00 +0200

Glossy is a reliable and low latency flooding mechanism which makes use of constructive interference. Therefore, it is important to investigate what happens when attacks are mounted on Glossy that try to break constructive interference. In this chapter, we explore the effectiveness of different methods of breaking constructive interference in Glossy. Our results show that Glossy is quite robust to approaches where nodes do not respect the timing constraints necessary to create constructive interference. Changing the packet content, however, has a more tremendous effect on the packet reception rate.

Design of an Antenna for a Wireless Sensor Network for Trains

Malkolm Hinnemo — Tue, 10 Jan 2012 08:29:00 +0200

An antenna for a wireless sensor network for trains is designed and built. The network will monitor temperature and vibrations of the wheel bearings on the train wagons. Doing this will allow for an earlier detection of damaged wheels, which will ease planning of maintenance and reduce wear on the rails considerably. The requirement of the system is that it is to be installed without any cables attached to the sensor nodes. This calls for wireless communication, and that for that antennas are needed.A train is a difficult environment to transmit electromagnetic (EM) waves in. It is full of metal and EM-waves cannot pass through a conducting material. Having much metal in its vicinity also affects the function of the antenna. This needs to be taken into consideration when making the design.The constructed antenna is a small dual-layer patch antenna. Dual layer means that it is constructed out of two sheets known as substrates of isolating material with different characteristics. The lower one of these substrates is made in such a way that integration with a circuit board is possible. Such integration would reduce the production cost considerably. The antenna is designed for direct placement on a conducting surface. This surface could be part of the train. It uses the surrounding metal as a ground plane in order to reduce its size. The result is a small patch antenna with good radiation qualities in metallic surroundings. The longest side is 18.35 mm, equaling 14.9 % of the wavelength that the antenna is designed for.

Design of a Miniaturized Patch Antenna for Easy Deployment on Metal Surfaces

Malkolm Hinnemo — Wed, 2 Jan 2013 15:23:38 +0200

Continuous Monitoring of Train Wagons Using Wireless Sensor Network and Battery Assisted RFID Tags

Malkolm Hinnemo — Wed, 2 Jan 2013 15:35:56 +0200

Near field terahertz imaging for biological tissue measurements

J. Hjerdt — Mon, 20 Dec 2010 15:14:06 +0200

Skitracker: Measuring Skiing Performance using a Body Area Network

Thomas Homewood — Thu, 28 Feb 2013 12:46:00 +0200

Cross-country skiing is a technically demanding sport that requires the use of several distinct techniques. Typical research in this area involves testing in laboratory conditions using bulky equipment.

The goal of this project is to create a complete system that allows tests to be conducted on skiers in real conditions, using a network of wireless sensors to collect data.

We begin by outlining what data coaches and skiers want to see, before describing in detail our system, which comprises a set of networked wireless sensors mounted on the skier, a smartphone used as a base station, and a web interface viewing and editing recorded data.

We then conduct testing of the system on Swedish national team skiers, and use the data collected to compare the relative performance of these skiers in outdoor conditions. Finally the system is evaluated and future developments are discussed.

Skitracker : Measuring skiing performance using a body-area network

Thomas Homewood — Thu, 11 Apr 2013 13:56:40 +0200

A mote-in-the-loop approach for exploring communication strategies for sensor networks

Minyan Hong — Mon, 1 Nov 2010 15:19:57 +0200

Exploring Sensor Network Communication Strategies with the Mote-in-the-Loop Approach

Minyan Hong — Fri, 25 Nov 2011 09:27:10 +0200

Low-profile directive antenna using metamaterial slab for RFID tags

Xin Hu — Mon, 20 Dec 2010 15:09:58 +0200

A location-based publish/subscribe framework for wireless sensors and mobile phones

He Huang — Mon, 11 Jun 2012 21:15:00 +0200

Quality-of-Information Aware Data Delivery for Wireless Sensor Networks : Description and Experiments

Gregory Humber — Mon, 8 Feb 2010 22:42:00 +0200

Simulation and evaluation of unsynchronized power saving mechanisms in wireless ad hoc networks

Philipp Hurni — Wed, 20 Dec 2006 16:46:00 +0200

Power saving mechanisms in wireless ad hoc network nodes mainly switch off the transmission and reception hardware for a maximal amount of time and turn it on again within a given interval. Many approaches aim to synchronize the state changes of the nodes in the network through distributed beacon generation and introduce mechanisms where nodes synchronously wake up at designated points of time to exchange announcements about pending traffic. Synchronization however is difficult to achieve, in particular in ad hoc networks. This paper describes the simulation, evaluation and refinement of a recently proposed power saving approach based on asynchronous wake-up patterns and wake-up announcements integrated with AODV. We show that significant improvements of the connectivity under low wake ratios can be achieved by carefully designed forwarding strategies of AODV route request messages.

A wireless body area network (WBAN) based tracking and monitoring application system

Bestoon Jaff — Fri, 19 Mar 2010 16:10:00 +0200

Design and Performance of Diversity based Wireless Interfaces for Sensor Network Nodes

Magnus Jobs — Mon, 29 Apr 2013 10:37:00 +0200

The main focus of the work presented in this licentiate thesis concerns antenna design, adaptive antenna control and investigation on how the performance of small wireless nodes can be increased by inclusion of multiple antennas. In order to provide an end-user suitable solution for wireless nodes the devices require both small form factor and good performance in order to be competitive on the marked and thus the main part of this thesis focuses on techniques developed to achieve these goals. Two prototype systems have been developed where one has been used by National Defence Research Agency (FOI) to successfully monitor a test-subject moving in an outdoor terrain. The other prototype system shows the overall performance gain achievable in a wireless sensor node when multiple antennas and antenna beam steering is used. As an example of how to include multiple antennas in a wireless node the concept of using dual conformal patch antennas for wireless nodes is presented. The proposed antenna showed an excess of 10 dB gain when using a single driven antenna element as would be the case in a system utilizing antenna selection combining. When used as a 2-element phased array, up to 19 dB gain was obtained in a multiscattering environment. Using the second order resonance the proposed antenna structure achieves low mutual coupling and a reflection coefficient lower than -15 dB. The presented antenna design shows how a dual antenna wireless node can be designed using discrete phase control with passive matching which provides a good adaptive antenna solution usable for wireless sensor networks. The inclusion of discrete phase sweep diversity in a wireless node has been evaluated and shown to provide a significant diversity gain. The diversity gain of a discrete phase sweep diversity based system was measured in both a reverberation chamber and a real life office environment. The former environment showed between 5.5 to 10.3 dB diversity gain depending on the detector architecture and the latter showed a diversity gain ranging from 1 to 5.4 dB. Also the performance of nodes designed to be placed in a high temperature and multiscattering environment (the fan stage of a jet engine) has been evaluated. The work was carried out in order to verify that a wireless sensor network is able to operate in such a multiscattering environment. It was shown that the wireless nodes are able to operate in an emulated turbine environment based on real-life measured turbine fading data. The tested sensor network was able to transmit 32 byte packages using cyclic redundancy check at 2 Mbps at an engine speed of 13.000 rpm.

Wireless Interface Technologies for Sensor Networks

Magnus Jobs — Fri, 23 Jan 2015 10:32:00 +0200

The main focus of the work presented in this thesis concerns the development and improvement of Wireless Sensor Networks (WSNs) as well as Wireless Body Area Networks (WBANs). WSN consist of interlinked, wireless devices (nodes) capable of relaying data wirelessly between the nodes. The applications of WSNs are very broad and cover both wireless fitness monitoring systems such as pulse watches or wireless temperature monitoring of buildings, among others.

The topics investigated in the work presented within this thesis covers antenna design, wireless propagation environment evaluation and modeling, adaptive antenna control and wireless nodes system design and evaluation. In order to provide an end-user suitable solution for wireless nodes the devices require both small form factor and good performance in order to be competitive on the marked and thus the main part of this thesis focuses on techniques developed and data collected to help achieve these goals.

Several different prototype systems have been developed which have been used to measure data by the Swedish Defence Research Agency (FOI), GKN Aerospace Sweden AB, the Swedish Transport Administration. The system developed with GKN Aerospace was used to do real-time test measurements inside a running RM12 jet engine and required a substantial amount of measurements, environmental modeling and system validation in order to properly design a wireless system suitable for the harsh and fast fading environment inside a jet engine. For FOI improvements were made on a wearable wireless body area network initially developed during the authors master thesis work. Refinements included work on new generation wireless nodes, antenna packaging and node-supported diversity techniques.

Work and papers regarding the design of different types of antennas suitable for wireless nodes are presented. The primary constraints on the presented antennas are the limited electrical size. The types of antennas developed include electrically small helix antennas manufactured both on stretchable substrates consisting of a PDMS substrate with Galinstan as the liquid metal conductors, screen printed silver ink for helix antennas and conformal dual patch antennas for wireless sensor nodes. Other standard type antennas are included on the wireless sensors as well.

Performance Evaluation of a Conformal Dual Patch Antenna in an Indoor Environment

Magnus Jobs — Mon, 22 Apr 2013 10:57:00 +0200

The performance of a conformal dual patch antenna design for wireless sensor networks were measured and evaluated in a real world multi-scattering environment. Both simulated and measured radiation patterns when using the antenna as a two element phased array were measured and corresponded well. The environment was measured and show strong fading characteristics. The measured data shows that the proposed structure gives a distinct advantage to the nodes communication compared to single element antennas while keeping the form factor suitable for integration of embedded hardware.

Antenna diversity with opportunistic combining for ASk systems with single channel receivers

Magnus Jobs — Mon, 20 Dec 2010 15:29:38 +0200

Wireless body area networks (WBANs) and efficient energy conservative designs

Magnus Jobs — Mon, 20 Dec 2010 15:23:22 +0200

Wireless sensor networks for aircraft engines

Magnus Jobs — Mon, 20 Dec 2010 15:37:54 +0200

A Tunable Spherical Cap Microfluidic Electrically Small Antenna

Magnus Jobs — Fri, 19 Apr 2013 08:26:00 +0200

We present a novel microfluidic three-dimensional elec- trically small antenna (ESA). It is easy to construct simply by pneumatically inflating a planar stretchable liquid alloy microfluidic antenna into a spherical cap. Its center frequency is tuned when it is inflated; demonstrating combined high efficiency and a wide tunable frequency range around its hemispherical shape.

Wireless body area network (WBAN) monitoring application system (MASS) for personal monitoring

Magnus Jobs — Thu, 18 Mar 2010 13:55:00 +0200

Conformal dual patch antenna for diversity based sensor nodes

Magnus Jobs — Tue, 17 Apr 2012 14:36:51 +0200

A conformal antenna structure based on dual triangular patches is presented. The dual antennas are designed to be used in diversity based sensor node applications and are integrated in the enclosure of the node. The internal shielded enclosure houses the required electronics and power supply. Simulations and measurements show acceptable diversity performance and efficiency in the second resonance mode.

Undersökning av vissa beläggningars påverkan på antenners effektivitet i tågmiljö

Fredrik Johansson Holmbäck — Wed, 26 Jun 2013 17:36:00 +0200

For several years Uppsala University together with several companies has been involved in a WISENET project aimed at improving railway transport security. By placing a sensor system near the wheels of each wagon, the temperature of the bearings can be measured and transmitted to a collector placed centrally on the wagon. This in turn transmits the collected data to RFID receivers placed intermittently along the railway.

As the signals are transmitted wirelessly, problems may occur as the antennas get dirty or coated with ice and snow. To determine the effects of these coatings, several tests were performed examining the reflection coefficient S11, the impedance Z11 and the efficiency eta of an antenna, and how they varied when various coatings were placed over the antenna. Examined coatings were ice, snow and water to determine the effects of weather, and various metal-based coatings: powdered iron both pure and partially oxidized, and iron ore granules. Finally a sample coating taken directly from a car was tested to determine how closely the other coatings resembled what appeared in normal use.

Most of the coatings gave similar results; little or no loss of efficiency and a lowering of the resonance frequency by some 75 MHz, with both iron powder samples, the ore granules and the sample coating proved nearly identical in results. Thick layers of snow gave a noticeable drop in efficiency, as did the presence of any amount of water, which also greatly affected the resonance frequency.

Fixed link margins outperforms power control in energy-limited wireless sensor networks

Mathias Johansson — Wed, 23 Jan 2008 09:32:00 +0200

Recent developments in thin film electro-acoustic technology for biosensor applications

Ilia Katardjiev — Tue, 13 Mar 2012 11:41:52 +0200

The article reviews recent developments of the thin film electro-acoustic (TEA) technology in view of the design and fabrication of micro-acoustic transducers for biosensor applications. The use of the TEA technology leads to transducer miniaturisation, compatibility with the IC technology, possibility for multiplexing, decrease in fabrication cost, reduction of consumables, mass fabrication, etc. Focus lies on the design, fabrication and evaluation of the transducer performance in liquid media as judged by electro-acoustic behaviour and ultimately by mass and viscosity resolution. The analysis draws the conclusion that the thickness excited quasi-shear thin film bulk acoustic resonator technology is far ahead in its development with regard to other alternative approaches in terms of both performance and level of maturity. Consequently, the main aspects of the quasi-shear thin film bulk acoustic resonator (FBAR) technology from film synthesis and fabrication through to performance evaluation and demonstration are reviewed in detail.

A Passive Radio Triggered Switch with ID Functionality

Ilia Katardjiev — Sat, 5 Jan 2013 13:40:05 +0200

Recent advances in the thin film electro-acoustic technology

Ilia Katardjiev — Wed, 21 Nov 2012 13:38:34 +0200

Shear mode TFBARs

Ilia Katardjiev — Mon, 21 Jan 2008 07:55:00 +0200

Cooperative state estimation for preserving privacy of user behaviors in smart grid

Younghun Kim — Wed, 7 Dec 2011 21:43:42 +0200

A software radioempowered sensor network

Yafei Li — Mon, 17 Jan 2011 09:18:45 +0200

Multiple nanowire via interconnects in flexible printed circuit boards

Mikael Lindeberg — Mon, 21 Dec 2009 09:41:00 +0200

High aspect ratio “multiple wire” microvias in flexible PCBs

Mikael Lindeberg — Mon, 21 Dec 2009 09:04:00 +0200

A PCB-like Process for Vertically Configured Thermopiles

Mikael Lindeberg — Wed, 19 Mar 2008 14:35:00 +0200

Thermopiles are important components in infrared thermal detectors, thermoelectric generators and thermoelectric coolers. We present a thermopile structure with up to 224 vertically arranged thermocouple legs in a polyimide flex material. The thermopile is optimized for infrared thermal radiation detection and is fabricated using printed circuit board-like (PCB-like) processing. Each thermoelectric leg consists of a bundle of a few hundred sub-micrometre-sized strands of either antimony or nickel. These metal wire bundles were achieved by employing ion track technology on the polyimide foil, resulting in a porous dielectric material. Electrochemical methods were used to grow the thermoelectric materials in the pores. The plating mask was produced in a laminated dry photoresist. A small metal cross section, 20 mu m(2) (1 vol%), ensured a low heat exchange between the two surfaces of the flex. The typical resistance per thermocouple was 34 Omega. A responsivity to irradiance of 4.3 V mm(2) W(-1) was measured when heating with a white light source (irradiance 1 mW mm(-2)).

Design, Implementation, and Evaluation of Wireless Sensor Network Systems

Jiangchuan Liu — Thu, 26 May 2011 14:47:48 +0200

Seasonal Affective Disorder Monitoring System

Negar Makvandian — Tue, 1 Jan 2013 06:34:00 +0200

A glimpse of energy-efficient location-triggered mobile application design and implementation in data collection scenarios

Yemao Man — Tue, 18 Dec 2012 16:28:00 +0200

4th International Workshop on Real-World Wireless Sensor Networks : 4th International Workshop on Real-World Wireless Sensor Networks, REALWSN 2010, held in Colombo, Sri Lanka, in December 2010

Pedro Marron — Tue, 29 Mar 2011 08:53:10 +0200

Thick Silicides Synthesised With Smooth Surface for Integrated TFBAR Applications

David Martin — Mon, 26 Jan 2009 13:47:00 +0200

Optimisation of a smooth multilayer Nickel Silicide surface for ALN growth

David Martin — Fri, 17 Dec 2010 13:55:51 +0200

Optimisation of a smooth multilayer Nickel Silicide surface for ALN growth

David Martin — Mon, 26 Jan 2009 12:32:00 +0200

For use in thin film electroacoustic (TEA) technology a few hundred nanometrethick nickel silicide (NiSi) electrode would need to be fabricated. A complete fabrication process for the formation of over 200 nm thick silicide films has been optimised for use as an electroacoustic electrode. Optimisation of silicidation temperature and identification of the mono phase of silicide is demonstrated. Thick electrodes are formed by depositing multilayers of silicon and nickel pairs onto silicon (Si) substrates before rapid thermal annealing. The numbers of multilayers and relative material thicknesses are optimized for both surface roughness and electrical resistivity. The growth of textured aluminium nitride (AlN) has been investigated on the optimised surfaces.

Electro-Acoustic and Electronic Applications Utilizing Thin Film Aluminium Nitride

David Michael Martin — Wed, 29 Apr 2009 10:25:00 +0200

In recent years there has been a huge increase in the growth of communication systems such as mobile phones, wireless local area networks (WLAN), satellite navigation and various other forms of wireless data communication that have made analogue frequency control a key issue. The increase in frequency spectrum crowding and the increase of frequency into microwave region, along with the need for minimisation and capacity improvement, has shown the need for the development of high performance, miniature, on-chip filters operating in the low to medium GHz frequency range. This has hastened the need for alternatives to ceramic resonators due to their limits in device size and performance, which in turn, has led to development of the thin film electro-acoustics industry with surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters now fabricated in their millions. Further, this new technology opens the way for integrating the traditionally incompatible integrated circuit (IC) and electro-acoustic (EA) technologies, bringing about substantial economic and performance benefits.

In this thesis the compatibility of aluminium nitride (AlN) to IC fabrication is explored as a means for furthering integration issues. Various issues have been explored where either tailoring thin film bulk acoustic resonator (FBAR) design, such as development of an improved solidly mounted resonator (SMR) technology, and use of IC technology, such as chemical mechanical polishing (CMP) or nickel silicide (NiSi), has made improvements beneficial for resonator fabrication or enabled IC integration. The former has resulted in major improvements to Quality factor, power handling and encapsulation respectively. The later has provided alternative methods to reduce electro- or acoustomigration, reduced device size, for plate waves, supplied novel low acoustic impedance material for high power applications and alternative electrodes for use in high temperature sensors.

Another method to enhance integration by using the piezoelectric material, AlN, in the IC side has also been explored. Here methods for analysing AlN film contamination and stoichiometry have been used for analysis of AlN as a high-k dielectric material. This has even brought benefits in knowledge of film composition for use as a passivation material with SiC substrates, investigated in high power high frequency applications. Lastly AlN has been used as a buried insulator material for new silicon-on-insulator substrates (SOI) for increased heat conduction. These new substrates have been analysed with further development for improved performance indicated.

Buried Aluminum Nitride Insulator for SOI Substrates

David Martin — Mon, 7 Jan 2008 14:49:00 +0200

Supporting cyber-physical systems with wireless sensor networks : An outlook of software and services

Prasant Misra — Mon, 30 Sep 2013 12:33:00 +0200

Efficient RF voltage transformer with bandpass filter characteristics

Milena Moreira — Wed, 21 Nov 2012 13:55:00 +0200

A microwave bandpassfilter with a large ratio between the output andthe input impedance has been designed and fabricated. Consequently,it functions both as a voltage transformer and a bandpassfilter, or trans-filter for brevity. It represents a two-port micro-acoustic resonatoremploying Lamb waves in a thin piezoelectric AlNfilm grown ontoa Si carrier substrate with a centre frequency of around 887 MHz.The transfilter has a transformer ratio of 10 and a voltage efficiencyof over 80%. The component has a small size ( < 0.5 mm2) and isshown to sustain power levels of 250 mW. It can be used in avariety of cases where both voltage amplification and frequencyfilter-ing are required. Examples include: charge pumps in RFID tags,energy scavenging, remotely triggered switches, wake-up radios inwireless networks, stand-by units in home electronics etc.

Aluminum scandium nitride thin-film bulk acoustic resonators for wide band applications

Milena Moreira — Wed, 10 Aug 2011 15:25:07 +0200

Piezoelectric c-textured Al(1-x)ScxN thin films, where the Sc relative concentration, x, varies in the range 0-0.15 have been studied in view of radio frequency (RF) electro-acoustic applications. Thin film bulk acoustic wave resonators (FBARs) employing these films were fabricated and characterized as a function of the Sc concentration for the first time. The measured electromechanical coupling is found to increase by as much as 100% in the above concentration range. The results from this work underline the potential of the c-textured Al(1-x)ScxN based FBARs for wide band RF applications.

Synthesis of c-tilted AlN films with a good tilt and thickness uniformity

Milena Moreira — Sat, 5 Jan 2013 10:49:00 +0200

This communication describes a method for the deposition of thin piezoelectric AlN films with an inclined c-axis relative to the surface normal. Further, the tilt over the wafer is sufficiently uniform and exhibits a planar symmetry as well as good thickness uniformity. Careful control of both the nucleation and growth stages is needed to obtain tilted films with excellent quality. Thus in the nucleation state, it is argued that two independent mechanisms, namely seed layer texture and/or surface roughness, are mainly responsible for the subsequent titled growth. To achieve the latter, however, a certain directionality of the deposition flux is also necessary. The directionality of the deposition flux is achieved through the use of an array of linear magnetrons tilted under a certain angle with respect to the substrate normal.

Programming Storage-centric Sensor Networks with Squirrel

Luca Mottola — Fri, 14 Jan 2011 16:12:37 +0200

Not All Wireless Sensor Networks Are Created Equal: A Comparative Study On Tunnels

Luca Mottola — Fri, 14 Jan 2011 14:53:56 +0200

Electronically-switched Directional Antennas for Wireless Sensor Networks: A Full-stack Evaluation

Luca Mottola — Tue, 9 Jul 2013 11:11:00 +0200

Anquiro: Enabling Efficient Static Verification of Sensor Network Software

Luca Mottola — Fri, 14 Jan 2011 16:15:52 +0200

Seamless sensor network ip connectivity : Demo Abstract

Geoff Mulligan — Mon, 17 Jan 2011 09:36:25 +0200

On providing sink anonymity for wireless sensor networks

Edith C.-H. Ngai — Fri, 3 Dec 2010 18:26:00 +0200

On Providing Sink Anonymity for Sensor Networks

Edith C.-H. Ngai — Mon, 25 May 2009 17:42:00 +0200

Information-Aware Traffic Reduction for Wireless Sensor Networks

Edith C.-H. Ngai — Mon, 16 Nov 2009 16:30:00 +0200

Quality-of-Information aware data collection for mobile sensor networks

Edith C.-H. Ngai — Thu, 10 May 2012 06:39:00 +0200

Quality-of-information-aware data collection for mobile sensor networks

Edith C.-H. Ngai — Thu, 1 Aug 2013 20:34:00 +0200

Quality of information (QoI) in sensor networks measures information attributes such as precision, timeliness, completeness, and relevance of data ultimately delivered to users. It is a challenge to provide the required QoI in mobile sensor networks given the large scale and complexity of the networks with heterogeneous mobile and sensing devices. In this paper, we provide a comprehensive study on major QoI metrics for mobile sensor networks and discuss how QoI-aware data collection can be achieved. The cases with mobile sensors, mobile sinks, and mobile mules carrying data and their impact on QoI are discussed in detail. Mobility creates challenges in terms of timeliness but also opportunities in increased coverage and relevance. In a case study, we design a QoI-aware publish/subscribe system for mobile sensor networks. Users can subscribe to obtain information about events of interest by specifying the target area, sensing context, etc. The subscriptions and the sensing data are delivered to relevant sensors and users by location-based routing. We also discuss techniques that can be applied to further enhance the QoI in our publish/subscribe system. Simulation results demonstrate that the users can receive their subscribed data successfully with low communication overhead. Our publish/subscribe system can also handle mobility of clients smoothly without causing any data loss.

OppSense : Information sharing for mobile phones in sensing field with data repositories

Edith C.-H. Ngai — Wed, 7 Dec 2011 21:38:34 +0200

On providing location privacy for mobile sinks in wireless sensor networks

Edith C.-H. Ngai — Tue, 5 Jun 2012 10:32:00 +0200

On Providing Location Privacy for Mobile Sinks in Wireless Sensor Networks

Edith C.-H. Ngai — Mon, 16 Nov 2009 16:41:00 +0200

Context-aware sensor data dissemination for mobile users in remote areas

Edith C.-H. Ngai — Thu, 10 May 2012 21:46:00 +0200

Quality-of-Information Aware Data Collection for Mobile Sensor Networks

Tue, 18 Dec 2012 17:11:23 +0200

Protecting Receiver Privacy in Routing for Wireless Sensor Networks

Edith Ngai — Mon, 25 May 2009 17:05:00 +0200

Oscillators Based on Monolithically Integrated AlN TFBARs

Martin Norling — Tue, 31 Mar 2009 14:28:35 +0200

Oscillators based on AlN thin-film bulk acoustic resonators are designed, fabricated and measured. The circuits are realised as silicon-on-silicon multichip modules where SiGe transistors are flip-chip mounted on a novel carrier substrate which includes monolithically integrated resonators and passive components. The paper describes the development and processing of the carrier substrate and resonators, as well as the development of the oscillator circuits. The oscillators operate at 2 GHz. Measurements of the oscillators reveal a lowest phase-noise of -125 dBc/Hz at 100 kHz offset.

Storage-Centric Debugging of Performance Problems in Sensor Networks : Poster Abstract

Tony O'Donovan — Fri, 14 Jan 2011 16:10:48 +0200

Detailed Diagnosis of Performance Anomalies in Sensornets

Tony O'Donovan — Fri, 14 Jan 2011 15:48:42 +0200

Fabrication of wireless sensor flip-up antennas

Sam Ogden — Mon, 21 Dec 2009 09:24:42 +0200

Predictive power control for dynamic state estimation over wireless sensor networks with relays

Jan Ostergaard — Mon, 1 Nov 2010 15:10:47 +0200

Predictive power control and multiple description coding for wireless sensor networks

Jan Ostergaard — Mon, 28 Dec 2009 13:02:00 +0200

Selective Reprogramming of Mobile Sensor Networks through Social Community Detection

Bence Pasztor — Fri, 14 Jan 2011 16:23:12 +0200

An adaptive cross-layer design for prioritized traffic in wireless communications

Guduru K. Pradeep — Thu, 17 Feb 2011 18:35:00 +0200

A predictive power control scheme for energy efficient state estimation via wireless sensor networks

Daniel E Quevedo — Wed, 2 Dec 2009 12:27:00 +0200

Predictive power control of wireless sensor networks for closed loop control

Daniel E Quevedo — Wed, 2 Dec 2009 12:23:00 +0200

Predictive Power Control of Wireless Sensor Networks for Closed Loop Control

Daniel E Quevedo — Mon, 14 Dec 2009 14:37:00 +0200

On Kalman filtering over fading wireless channels with controlled transmission powers

Daniel E Quevedo — Mon, 27 Aug 2012 13:36:40 +0200

We study stochastic stability of centralized Kalman filtering for linear time-varying systems equipped with wireless sensors. Transmission is over fading channels where variable channel gains are counteracted by power control to alleviate the effects of packet drops. We establish sufficient conditions for the expected value of the Kalman filter covariance matrix to be exponentially bounded in norm. The conditions obtained are then used to formulate stabilizing power control policies which minimize the total sensor power budget. In deriving the optimal power control laws, both statistical channel information and full channel information are considered. The effect of system instability on the power budget is also investigated for both these cases.

Energy Efficient State Estimation With Wireless Sensors Through the Use of Predictive Power Control and Coding

Daniel E. Quevedo — Tue, 23 Nov 2010 13:42:22 +0200

We study state estimation via wireless sensors over fading channels. Packet loss probabilities depend upon time-varying channel gains, packet lengths and transmission power levels of the sensors. Measurements are coded into packets by using either independent coding or distributed zero-error coding. At the gateway, a time-varying Kalman filter uses the received packets to provide the state estimates. To trade sensor energy expenditure for state estimation accuracy, we develop a predictive control algorithm which, in an online fashion, determines the transmission power levels and codebooks to be used by the sensors. To further conserve sensor energy, the controller is located at the gateway and sends coarsely quantized power increment commands, only whenever deemed necessary. Simulations based on real channel measurements illustrate that the proposed method gives excellent results.

Innovation based state estimation with wireless sensor networks

Daniel E Quevedo — Mon, 28 Dec 2009 12:59:00 +0200

Dynamic controller allocation for control over erasure channels

Daniel E Quevedo — Wed, 2 Jan 2013 13:36:24 +0200

Design of Embedded Filters for Inner-Loop Power Control in Wireless CDMA Communication Systems

Daniel E. Quevedo — Wed, 1 Jun 2011 14:11:00 +0200

Distributed Computing in Sensor Systems : 6th IEEE International Conference, DCOSS 2010, Santa Barbara, CA, USA, June 21-23, 2010, Proceedings

Rajmohan Rajaraman — Tue, 29 Mar 2011 08:42:21 +0200

Security Considerations for the WirelessHART Protocol

Shahid Raza — Fri, 14 Jan 2011 17:07:17 +0200

Design and Implementation of a Security Manager for WirelessHART Networks

Shahid Raza — Fri, 14 Jan 2011 16:52:33 +0200

Experimental Challenges in Wireless Sensor Networks — Environment, Mobility, and Interference

Olof Rensfelt — Thu, 20 Sep 2012 11:08:00 +0200

Wireless sensor networks are used to collect sensor data in different applications such as environmental monitoring, smart building control, and health care applications. Wireless sensor nodes used are typically small, low-cost, and battery powered. The nodes are often hard to access after deployment, for example when they are in remote locations. Another property of wireless sensor networks is that their operation is dependent on the environment they operate in, both due to the specific sensor readings but also due to the effects on communication by factors such as fading and radio interference. This makes it important to evaluate a wireless sensor network in its intendent target environment before final deployment.

To enable experiments with wireless sensor networks in their target environment, we have designed and implemented a testbed called Sensei-UU. It is designed to allow WSN experiments to be repeated in different locations, thus exposing effects caused by the environment. To allow this, the testbed is designed to be easily moved between experimental sites.

One type of WSN applications Sensei-UU is aimed to evaluate is protocols where nodes are mobile. Mobile testbed nodes are low-cost robots which follow a tape track on the floor. The localization accuracy of the robot approach is evaluated and is accurate enough to expose a protocol to fading phenoma in a repeatable manner.

Sensei-UU has helped us develop a lightweight interference classification approach, SoNIC, which runs on standard motes. The approach only use information from a standard cc2420 chipset available when packets are received. We believe that the classification accuracy is good enough to motivate specific transmission techniques avoiding interference.

An Interactive Test-bed for Heterogeneous Wireless Sensor Networks.

Olof Rensfelt — Tue, 11 Jan 2011 10:31:26 +0200

Sensei-UU : a flexible testbed for heterogeneous wireless sensor networks

Olof Rensfelt — Mon, 13 Dec 2010 10:02:10 +0200

We present Sensei - a nomadic, relocatable, wireless sensor network (WSN) testbed with support for mobile nodes. The nomadism makes it possible to evaluate a WSN application in different environments ranging from lab environments to in- situ installations to prototype deployments. Other WSN testbeds are often static and can not be easily moved between sites. We also support reproducibility mobility in the testbed, using robots or humans as actuators with movement patterns defined in mobility scripts.

Repeatable experiments with mobile nodes in a relocatable WSN testbed

Olof Rensfelt — Mon, 13 Dec 2010 09:57:00 +0200

We present Sensei-UU, a testbed that supports mobile sensor nodes. The design objectives are to provide wireless sensor network (WSN) experiments with repeatable mobility and to be able to use the same testbed at different locations, including the target location. The testbed is inexpensive, expandable, relocatable and it is possible to reproduce it by other researchers. Mobile sensor nodes are carried by robots that use floor markings for navigation and localization. The testbed is typically used to evaluate WSN applications when sensor nodes move in meters rather than millimeters, eg. when human carries a mobile data sink (mobile phone) collecting data while passing fixed sensor nodes. To investigate the repeatability of robot movements, we have measured the achieved precision and timing of the robots. This precision is of importance to ensure the same radio link characteristics from one protocol experiment to another. We find that our robot localization is accurate to #x00B1;1 cm and variations in link characteristics are acceptably low to capture fading phenomena in IEEE 802.15.4. In the paper we show repeatable experiment results from three environments, two university corridors and from an anechoic chamber. We conclude that the testbed is relocatable between different environments and that the precision is good enough to capture fading effects in a repeatable way.

Repeatable experiments with mobile nodes in a relocatable WSN testbed

Olof Rensfelt — Mon, 18 Apr 2011 13:28:00 +0200

Many sensor network application scenarios include mobile nodes, such as a moving sink. Evaluatingsuch applications in a testbed is challenging since the testbed has to support mobile nodes. Wepresent Sensei-UU, a sensor network testbed that supports mobile sensor nodes. The testbedis inexpensive, relocatable and possible to reproduce by other researchers. Its primary designobjectives are to support experiments with repeatable mobility and to support relocating thetestbed deployment to different locations. Mobile sensor nodes are carried by robots that usefloor markings for navigation and localization. The testbed can be used to evaluate applicationsin which sensor nodes move in the order of meters rather than millimeters, e.g., when a humancarries a mobile phone that collects data while passing stationary sensor nodes. To investigate therepeatability of robot movements, we measure the achieved precision and timing of the robots, andfind that our robot localization is accurate to ±1 cm. Furthermore, we investigate variations inradio signal strengths between mobile and stationary nodes. We study the impact of imprecisemovements, external sources of interference, and environmental influences. We conclude thatSensei-UU supports experiments in which these variations are acceptably low to capture small-scalefading phenomena in IEEE 802.15.4.

Sensei-UU : a relocatable sensor network testbed

Olof Rensfelt — Mon, 13 Dec 2010 10:05:00 +0200

SoNIC : Classifying and Surviving Interference in 802.15.4-based Sensor Networks

Olof Rensfelt — Thu, 23 Aug 2012 10:07:00 +0200

Secure and Privacy-Aware Data Collection in Wireless Sensor Networks

Ioana Rodhe — Thu, 18 Oct 2012 09:10:00 +0200

A wireless sensor network is a collection of numerous sensors distributed on an area of interest to collect and process data from the environment. One particular threat in wireless sensor networks is node compromise attacks, that is, attacks where the adversary gets physical access to a node and to the programs and keying material stored on it.

Only authorized queries should be allowed in the network and the integrity and confidentiality of the data that is being collected should be protected. We propose a layered key distribution scheme together with two protocols for query authentication and confidential data aggregation. The layered key distribution is more robust to node and communication failures than a predefined tree structure. The protocols are secure under the assumption that less than n sensor nodes are compromised. n is a design parameter that allows us to trade off security for overhead. When more than n sensor nodes are compromised, our simulations show that the attacker can only introduce unauthorized queries into a limited part of the network and can only get access to a small part of the data that is aggregated in the network. Considering the data collection protocol we also contribute with strategies to reduce the energy consumption of an integrity preserving in-network aggregation scheme to a level below the energy consumption of a non-aggregation scheme. Our improvements reduce node congestion by a factor of three and the total communication load by 30%.

Location privacy of the users carrying mobile devices is another aspect considered in this thesis. Considering a mobile sink that collects data from the network, we propose a strategy for data collection that requires no information about the location and movement pattern of the sink. We show that it is possible to provide data collection services, while protecting the location privacy of the sink. When mobile phones with built-in sensors are used as sensor nodes, location information about where the data has been sensed can be used to trace users and infer other personal information about them, like state of health or personal preferences. Therefore, location privacy preserving mechanisms have been proposed to provide location privacy to the users. We investigate how a location privacy preserving mechanism influences the quality of the collected data and consider strategies to reconstruct the data distribution without compromising location privacy.

Query authentication and data confidentiality in wireless sensor networks

Ioana Rodhe — Wed, 11 Jun 2008 00:00:00 +0200

In this thesis we consider diﬀerent aspects of security in sensor networks, in particular query authentication and conﬁdential data aggregation. Authenticating the queries is important so attackers cannot modify existing queries because this would lead to wrong readings; or insert new queries into the network because this would lead to waste of energy. When answering to queries, in-network aggregation in sensor networks is an eﬃcient way to save energy. Nevertheless, node capture in hostile environments require protocols for data aggregation where the intermediate nodes contribute with their own values to the aggregated data without getting access to it.

Our contributions are two protocols for query authentication and conﬁdential data aggregation together with a common layered key distribution scheme. Both static and mobile base stations are supported. The proposed protocols use symmetric cryptography, which is preferred in sensor networks because of the sensor’s limited computational power, energy supply and memory storage. The results from our simulations show that, if an attacker captures a small number of nodes, the attacker can only introduce unauthorized queries into a limited part of the network and can only get access to a small part of the data that is aggregated into the network.

A study of the message complexity for integrity preserving aggregation schemes used in wireless sensor networks

Ioana Rodhe — Thu, 9 Dec 2010 16:21:48 +0200

n-LDA : n-Layers Data Aggregation in Sensor Networks

Ioana Rodhe — Fri, 29 Aug 2008 14:55:00 +0200

Secure Overlays : Making Static Key Distribution Schemes Work with Mobile Base Stations in WSNs

Ioana Rodhe — Thu, 9 Dec 2010 16:10:57 +0200

n-LQA: n-Layers Query Authentication in Sensor Networks

Ioana Rodhe — Fri, 29 Aug 2008 14:53:00 +0200

We present a protocol for query authentication in a sensor network where there is multi-hop communication and the queries are broadcasted by the base station into the network. Authenticating the queries is important so attackers cannot modify existing queries because this would lead to wrong

readings; or insert new ones into the network because this would lead to waste of energy. We propose a layered query authentication protocol that ensures that, in the presence of less than n captured nodes, unauthorized queries are stopped after a small number of hops. When more than n nodes are captured, the unauthorized queries will only spread in one direction with a limited angle. Message authentication codes (MACs) are used to protect the authenticity and integrity of the query. n MACs are

attached to the query message at the base station and the nodes replace MACs from this message in an interleaved manner.

On location privacy and quality of information in participatory sensing

Ioana Rodhe — Thu, 25 Oct 2012 10:50:00 +0200

Participatory sensing applications typically bind sensor data to locations. Location privacy preserving mechanisms protecting the location of users introduce therefore an uncertainty in the collected data distributions. We consider two strategies to reconstruct a data distribution after k-anonymity has been applied to the users' location information. We investigate how different parameters for the location privacy preserving mechanism influence both the quality of information and the location privacy of the users. Our results show that the cloak area resulted from applying k-anonymity has a higher impact on both the quality of information and the location privacy than the number of users, k, that are cloaked together.

Evaluating Battery Models in Wireless Sensor Networks

Christian Rohner — Fri, 30 Aug 2013 12:07:00 +0200

Wireless sensor deployment for collaborative sensing with mobile phones

Zheng Ruan — Wed, 2 Nov 2011 13:21:35 +0200

Wireless sensor networks : The greatest innovation since internet

Anders Rydberg — Mon, 20 Dec 2010 14:00:16 +0200

Antenna integrated wireless interfaces for sensor applications

Anders Rydberg — Wed, 2 Dec 2009 10:26:00 +0200

Integrated antennas for RF MEMS routers

Anders Rydberg — Wed, 2 Dec 2009 10:33:00 +0200

Selection Algorithms for Enhanced MIMOAntenna Measurements using Mode-Stirred Reverberation Chambers

Anders Rydberg — Wed, 2 Jan 2013 15:46:30 +0200

Wireless body area network (WBAN) systems for personal monitoring and biomedical regulation

Anders Rydberg — Mon, 20 Dec 2010 15:33:45 +0200

Techniques for communication robustness in train environment

Anders Rydberg — Mon, 20 Dec 2010 15:20:31 +0200

Towards small MEMS based wireless sensors

Anders Rydberg — Wed, 23 Jan 2008 13:08:00 +0200

Fabrication and characterization of a shear mode AlN solidly mounted resonator-silicone microfluidic system for in-liquid applications

Gunjana Sharma — Tue, 31 Mar 2009 14:48:00 +0200

A shear mode AlN solidly mounted resonator (SMR) microfluidic sensor system was fabricated and characterized. The AlN SMR fabrication process is fully IC compatible and uses reactive sputtering to deposit piezoelectric AlN thin films with a non-zero mean inclination of the c-axis, which allows in-liquid operation through the excitation of the shear mode. Silicone encapsulation bonded on top of the Si sensor chip includes a microfluidic system to transport the analyte and confine the flow to the active area of the sensor chip. The sensor operation in air, water, glycerol and acetone was characterized. The resonator had a resonance frequency of around 1.2 GHz and a Q value in water of around 100. Results concerning the stability and resolution are also presented. The results indicate a potential of highly sensitive low-cost microfluidic sensor systems for applications in, e.g. point-of-care testing.

Increasing ZigBee Network Lifetime with X-MAC

Pablo Suarez — Mon, 17 Jan 2011 10:51:44 +0200

Lower trees with fixed degrees : a recipe for efficient secure hierarchical aggregation in WSNs

Davor Sutic — Mon, 10 Jan 2011 14:22:00 +0200

We propose two strategies to reduce energy consumption for secure data aggregation in wireless sensor networks. While the purpose of data aggregation is to reduce energy consumption, secure data aggregation introduces an overhead making the total energy consumption comparable to naive secure non-aggregation. Another aspect is that the secure data aggregation has higher node congestion than non-aggregation schemes for networks of sizes up to about 100 nodes. Considering a secure data aggregation protocol, our strategies are to reduce the height of the aggregation tree and limit its node degree. The former results in fewer verification messages and a lower total communication load, and the latter reduces node congestion. The most heavily burdened node sends a third of the messages required in the original protocol, which for small networks is lower than with non-aggregation, and the total communication load is lowered compared to non-aggregation.

ESEM as a Tool for Studying High Temperature Electronics

Stefan Svensson — Wed, 21 Sep 2011 11:12:22 +0200

Researchers studying materials and processes at high temperatures are often restricted to do evaluation afterwards and at room temperature using e.g. scanning electron microscopy (SEM). Limited by high vacuum, outgassing and non-conducting samples are difficult to study with SEM. For such samples, environmental scanning electron microscope (ESEM) is an alternative that is particularly suited also for high temperature in-situ studies. The electron detector in the ESEM make use of otherwise unwanted scattering of electrons as an amplifier of the signal, and by using differential pumping, it is possible to introduce several mbar of either oxygen, water vapor, or a gas of choice into the sample chamber while still maintaining the high-vacuum in the electron column. The auxiliary gas neutralizes surface charges built up by the electron beam, which makes it possible to image non-conductive and outgassing samples, thus making it possible to study e.g. polymeric and high temperature materials. Our ESEM, FEI XL30, have a heating stage making it possible to reach temperatures up to 1500°C. Equipped with electrical feed- throughs, the instrument can be used to study high temperature phenomena on electrically activated components.

ESEM is an instrument that has found its use for biological and organic samples. However, less work has been done using it for high temperature processes. Here, we show real-time imaging of the sintering of dielectric and Ag thick-film prints on AlN substrates. The use of the electrical feed-throughs to activate electrical components and study them at high temperatures is also demonstrated. ESEM is a versatile tool for high temperature studies and in-situ analysis of electrical components, solder processes and different die-attach materials.

Significant configurational dependence of the electromechanical coupling constant of B0.125Al 0.875 N

Ferenc Tasnádi — Fri, 19 Mar 2010 11:55:12 +0200

Currently, AlN is the preferred material in electroacoustic applications but modern applications necessitate the synthesis of materials with a range of electroacoustic properties. Among the promising candidates are the wurtzite Boron-containing AlN alloys. In here we study theoretically some of the material properties of wurtzite B0.125Al0.875N. The results indicate that wurtzite B0.125Al0.875N exhibits a strong configurational dependence of the electromechanical coupling constant. It is further shown that the lattice parameters as well as the stiffness constants are less sensitive of the atomic configuration and comply well with the Vegard's rule.

A ubiquitous publish/subscribe platform for wireless sensor networks with mobile mules

Xiaoyu Tong — Mon, 2 Jul 2012 14:36:00 +0200

Enabling Large- Scale Storage in Sensor Networks with the Coffee File System

Nicolas Tsiftes — Fri, 14 Jan 2011 17:14:12 +0200

Efficient Sensor Network Reprogramming through Compression of Executable Modules

Nicolas Tsiftes — Mon, 17 Jan 2011 10:34:53 +0200

Low-Power Wireless IPv6 Routing with ContikiRPL : Poster Abstract

Nicolas Tsiftes — Fri, 14 Jan 2011 15:51:57 +0200

A Framework for Low-Power IPv6 Routing Simulation, Experimentation, and Evaluation : Demo abstract

Nicolas Tsiftes — Fri, 14 Jan 2011 16:26:32 +0200

Wireless activity monitor using 3D integration

Ric van Doremalen — Fri, 19 Mar 2010 16:37:00 +0200

Body surface backed flexible antennas and 3D Si-level integrated wireless sensor nodes for 17 GHz wireless body area networks

Piet van Engen — Thu, 18 Mar 2010 13:43:00 +0200

3D Si-level integration in wireless sensor node

Piet van Engen — Tue, 15 Dec 2009 14:10:00 +0200

Directional transmissions and receptions for high throughput burst forwarding

Ambuj Varshney — Tue, 3 Dec 2013 00:48:01 +0200

Many sensor network applications generate large amounts of sensed data. These often need to be delivered reliably to the sink node for further processing. In such applications, high communication throughput allows for more data to be sensed. Intra-path interference is a problem in reliable forwarding of data and affects the end-to-end throughput. We show that using antennas that allow directional transmissions and receptions significantly reduces intra-path interference and enables high throughput forwarding of packet bursts over multiple hops using only one wireless channel.

Using Directional Transmissions and Receptions to Reduce Contention in Wireless Sensor Networks

Ambuj Varshney — Tue, 3 Dec 2013 00:41:00 +0200

Electronically Switched Directional (ESD) antennas allow software-based control of the direction of maximum antenna gain. ESD antennas are feasible for wireless sensor network. Existing studies with these antennas focus only on controllable directional transmissions. These studies demonstrate reduced contention and increased range of communication with no energy penalty. Unlike existing literature, in this chapter we experimentally explore controllable antenna directionality at both sender and receiver. One key outcome of our experiments is that directional transmissions and receptions together considerably reduce channel contention. As a result, we can significantly reduce intra-path interference.

Interconnecting Smart Object with IP - The Next Internet

Jean-Philippe Vasseur — Fri, 14 Jan 2011 14:04:40 +0200

REALWSN 2008 : Proceedings of the 2008 Workshop on Real-World Wireless Sensor Networks

Fri, 22 Aug 2008 11:52:00 +0200

Towards comparable simulations of cooperating objects and wireless sensor networks

Thiemo Voigt — Fri, 14 Jan 2011 16:58:08 +0200

Understanding link dynamics in wireless sensor networks with dynamically steerable directional antennas

Thiemo Voigt — Fri, 19 Apr 2013 16:03:40 +0200

By radiating the power in the direction of choice, electronically-switched directional (ESD) antennas can reduce network contention and avoid packet loss. There exists some ESD antennas for wireless sensor networks, but so far researchers have mainly evaluated their directionality. There are no studies regarding the link dynamics of ESD antennas, in particular not for indoor deployments and other scenarios where nodes are not necessarily in line of sight. Our long-term experiments confirm that previous findings that have demonstrated the dependence of angle-of-arrival on channel frequency also hold for directional transmissions with ESD antennas. This is important for the design of protocols for wireless sensor networks with ESD antennas: the best antenna direction, i.e., the direction that leads to the highest packet reception rate and signal strength at the receiver, is not stable but varies over time and with the selected IEEE 802.15.4 channel. As this requires protocols to incorporate some form of adaptation, we present an intentionally simple and yet efficient mechanism for selecting the best antenna direction at run-time with an energy overhead below 2 standard omni-directional transmissions.

4th International Conference on Distributed Computing in Sensor Systems (DCOSS) : Proceedings for Work-in-Progress, Poster, and Demo Papers

Fri, 22 Aug 2008 11:44:00 +0200

CoReDac: Collision-free command-response data collection

Thiemo Voigt — Mon, 17 Jan 2011 10:44:28 +0200

Improving sensor network robustness with multi-channel convergecast

Thiemo Voigt — Mon, 17 Jan 2011 10:41:53 +0200

A Node-Link Perspective on the Impact of Local Conditions in Sensor Networks

Hjalmar Wennerström — Wed, 31 Aug 2016 14:47:00 +0200

Sensor networks are made up of small battery-powered sensing devices with wireless communication capabilities, enabling the network to monitor the environment in which it is deployed. Through their flexible and cable-free design these networks open up for new deployment scenarios that were previously not plausible such as during a natural disaster. Motivated by scenarios where centralized oversight is not possible the focus of this thesis is to equip nodes with further adaptability to changes in the links it has with other nodes. This is achieved through contributions in three areas focusing on observations from a node-link perspective.

First, the impact the local environment has on the nodes is explored by deploying a sensor network outdoors next to a meteorological station to correlate the variations in link quality to the changes in the environment. The work identifies temperature as the main factor, where through further investigations in a controlled setting, a linear relationship between the decrease in signal quality and the increase in temperature is described.

Secondly, the thesis address how nodes in a sensor network can be motivated to exchange data by modeling it as a game. The game theoretic design is motivated by the absence of any centralized control and focus on the nodes as individual users in the network. The presented design motivates the selfish nodes to participate in the exchange of sensor data, showing that it is the best strategy.

Lastly, by exploring and understanding how connections in a mobile sensor network occur, nodes are given more flexibility to determine how to send and sample sensor data. This adaptability to contact occurrences is shown to provide better ways of sending data by selecting higher quality links as well as making sampling more energy preserving by reducing the rate in the vicinity of other nodes.

Meteorological impact and transmission errors in outdoor wireless sensor networks

Hjalmar Wennerström — Tue, 17 Dec 2013 00:00:00 +0200

Wireless sensor networks have been deployed outdoors ever since their inception. They have been used in areas such as precision farming, tracking wildlife, and monitoring glaciers. These diverse application areas all have different requirements and constraints, shaping the way in which the sensor network communicates. Yet something they all share is the exposure to an outdoor environment, which at times can be harsh, uncontrolled and difficult to predict. Therefore, understanding the implications of an outdoor environment is an essential step towards reliable wireless sensor network operations.

In this thesis we consider aspects of how the environment influence outdoor wireless sensor networks. Specifically, we experimentally study how meteorological factors impact radio links, and find that temperature is most significant. This motivates us to further study and propose a first order model describing the impact of temperature on wireless sensor nodes. We also analyze transmission errors in an outdoor wireless sensor networks, identifying and explaining patterns in the way data gets corrupted. The findings lead to a design and evaluation of an approach for probabilistic recover of corrupt data in outdoor wireless sensor networks. Apart from the experimental findings we have conducted two different outdoor deployments for which large data sets has been collected, containing both link and meteorological measurements.

A long-term study of correlations between meteorological conditions and 802.15.4 link performance

Hjalmar Wennerström — Tue, 21 May 2013 13:14:00 +0200

A Long-Term Study on the Effects of Meteorological Conditions on 802.15.4 Links

Hjalmar Wennerström — Mon, 12 Nov 2012 09:41:49 +0200

Remote monitoring of natural phenomena using wireless sensor networks requires these networks to successfully operate while being exposed to the surrounding environment. Weather conditions are an essential aspect of the environment, therefore it is important to understand the effects of weather on sensor networks. This understanding is especially important since weather varies strongly over time and affects the communication between sensor nodes. In our ongoing work we study how different meteorological conditions influence radio links in outdoor wireless sensor networks that use IEEE 802.15.4 for communication. We deploy an experimental setup next to a meteorological research station and aim to run experiments over several months in order to capture both short- and long-term changes in the link characteristics. We show some initial measurements of the deployment, highlighting influences on packet reception rate and signal strength.

Transmission errors in a sensor network at the edge of the world

Hjalmar Wennerström — Tue, 11 Jun 2013 13:28:00 +0200

The performance of an outdoor wireless sensor network for remote monitoring is dictated by its ability to deliver sensed data to a sink. The often isolated location means that radio interference is typically low and with different patterns in transmission errors compared to an indoor deployment. To better understand these processes, we investigate packet errors in such a network. Specically, we study characteristics of decoding errors within 802.15.4 transmissions.

We describe the experimental deployment of an outdoor sensor network, located above the Arctic circle, where we log both successfully received and broken packets. Results indicate that a substantial amount of received packets contain errors, where the errors in each packet are typically few. We distinguish between transmission errors and payload errors, and find that transmission errors are equally probable over all positions of a packet, whereas bit errors in the payload are not. This results in some bits having a 25% higher risk of being corrupted than others.

A Study of Packet Errors on Outdoor 802.15.4 Links

Hjalmar Wennerström — Mon, 10 Jun 2013 13:53:58 +0200

Thin Film Electroacoustic Devices for Biosensor Applications

Gunilla Wingqvist — Fri, 6 Mar 2009 09:21:00 +0200

Biosensors are today important devices within various application areas.

In this thesis a new type of label-free biosensor device is studied, which is fabricated using the same processes used for the fabrication of integrated circuits. This enables tighter integration and further sensors/biosensor miniaturization. The device is a so-called Thin Film Bulk Acoustic Resonator (FBAR). Within this thesis a low temperature reactive sputtering process for growing AlN thin films with a c-axis inclination of 20-30^o has been developed. This enables shear mode FBAR fabrication suitable for in-liquid operation, essential for biosensor applications. Shear mode FBARs were fabricated operating at frequencies above 1GHz exhibiting Q values of 100-200 in water and electromechanical coupling factors k_t² of about 1.8%. This made it possible to move the thickness excited shear mode sensing of biological layers into a new sensing regime using substantially higher operation frequencies than the conventionally used quartz crystal microbalance (QCM) operating at 5-20MHz. Measured noise levels of shear mode FBARs in contact with water showed the resolution to be in the range 0.3ng/cm² to 7.5ng/cm². This demonstrated the FBAR resolution without any averaging or additional stabilization measures already to be in the same range as the conventional QCM (5ng/cm²), suggesting that FBARs may be a competitive and low cost alternative to QCM. The linear thickness limit for sensing of biomolecular layers was concluded to be larger than the thickness of the majority of the molecular systems envisaged for FBAR biosensor applications. A temperature compensated shear mode FBAR composite structure was demonstrated with retained coupling factor and Q-value by utilizing the second mode of operation. Understanding has been gained on the sensor operation as well as on how the design parameters influence its performance. Specifically, sensitivity amplification utilizing low acoustic impedance layers in the FBAR structure has been demonstrated and explained. Further, temperature compensated Lamb mode (FPAR) devices were also studied and demonstrated with optimized electromechanical couplings.

Temperature Compensation of Thin Film Resonators utilizing the Lowest order Symmetric Lamb mode

Gunilla Wingqvist — Mon, 17 Jan 2011 15:19:05 +0200

Micromachined thermally compensated thin film Lamb wave resonator for frequency control and sensing applications

Gunilla Wingqvist — Thu, 12 Feb 2009 16:57:00 +0200

Micromachined thin film plate acoustic wave resonators (FPAR) utilizing the lowest order symmetric Lamb wave (S0) propagating in highly textured 2μm thick Aluminum Nitride (AlN) membranes have been successfully demonstrated [1]. The proposed devices have a SAW-based design and exhibit Q factors of up to 3000 at a frequency around 900MHz as well as design flexibility with respect to the required motional resistance. However, a notable drawback of the proposed devices is non-zero temperature coefficient of frequency (TCF) which lies in the range -20 ppm/K to –25 ppm/K. Thus, despite the promising features demonstrated, further device optimization is required. In this work temperature compensation of thin AlN film Lamb wave resonators is studied and experimentally demonstrated. Temperature compensation while retaining at the same time the device electromechanical coupling is experimentally demonstrated. The zero TCF Lamb wave resonators are fabricated onto composite AlN/SiO₂ membranes. Q factors of around 1400 have been measured at a frequency of around 755 MHz. Finally, the impact of technological issues on the device performance is discussed in view of improving the device performance.

Shear mode AlN thin film electro-acoustic resonant sensor operation in viscous media

Gunilla Wingqvist — Wed, 4 Apr 2007 09:06:00 +0200

A shear mode thin film bulk acoustic resonator (FBAR) operating in liquid media together with a microfluidic transport system is presented. The resonator has been fabricated utilizing a recently developed reactive sputter-deposition process for AlN thin films with inclined c-axis relative to the surface normal with a mean tilt of around 30°. The resonator has a resonance frequency of around 1.2 GHz and a Q value in water of around 150. Sensor operation in water and glycerol solutions is characterized. Theoretical analysis of the sensor operation under viscous load as well as of the sensitivity and stability in general is presented. The theoretical predictions are compared with experimental measurements. The results demonstrate clearly the potential of FBAR biosensors for the fabrication of highly sensitive low cost biosensors, bioanalytical tools as well as for liquid sensing in general.

Mass Sensitivity of Thin Film Resonator Device

Gunilla Wingqvist — Fri, 17 Dec 2010 14:13:32 +0200

Thin film bulk acoustic resonators (FBARs) for biosensor applications

Gunilla Wingqvist — Tue, 1 Dec 2009 15:33:44 +0200

Mass sensitivity of multilayer thin film resonant BAW sensors

Gunilla Wingqvist — Tue, 9 Dec 2008 15:00:00 +0200

Abstract: A systematic study of the mass sensitivity and its dependence on the material's properties and thicknesses in composite multilayer Thin Film Bulk Acoustic Resonators (FBAR) is presented. The Mason transmission line model has been employed in combination with the acoustic energy balance principle for the determination of the FBAR mass sensitivity. The results have been experimentally verified. Further, the mass sensitivity dependence on various parameters has been studied and correlated with wave reflection and interference within the composite structure in addition to the well-known dependence on resonator acoustic impedance and operation frequency. The mass sensitivity for both the fundamental and the second harmonic mode of operation has been studied in view of their practical relevance. In particular, sensitivity amplification induced by the presence of an on-top deposited low acoustic impedance layer has been identified for the first harmonic and its potential applicability discussed in terms of gas and in-liquid sensing. Optimized structures for both sensing applications are suggested by considering the overall sensor resolution defined by both the mass sensitivity and the FBAR performance.

Improved properties of AlON/4H-SiC interface for passivation

M Wolborski — Fri, 11 Jan 2008 13:04:00 +0200

Improved Properties of AlON/4H-SiC Interface for Passivation Studies

M. Wolborski — Tue, 14 Apr 2009 16:57:46 +0200

Aluminium oxynitride (AlON) films of variable composition were grown by reactive sputter deposition in a N₂/O₂ ambient at room temperature and studied for device passivation. The films were deposited on Si and 4H-SiC substrates as well as on SiC PiN diodes. The AlON/SiO₂/SiC stack provided superior interface properties compared to the AlON/SiC structure. Samples with 8% oxygen content, in the AlON film, and subjected to a UV exposure prior to deposition, exhibited the smallest net positive interface charge. A large net negative interface charge was observed for samples with 10% oxygen content and for the samples with 8% oxygen content and subjected to a RCA1 surface clean, prior to deposition. Diodes passivated with AlON films demonstrated reduced leakage current compared to as-processed diodes.

RealProct : Reliable protocol conformance testing with real nodes for wireless sensor networks

Junjie Xiong — Wed, 7 Dec 2011 21:45:05 +0200

Fundamentals of the grating-assisted surface acoustic wave-plate bulk acoustic wave interaction

V. Yantchev — Fri, 9 Oct 2009 13:27:56 +0200

The resonant interaction between Rayleigh surface acoustic waves (SAWs) and Lamb modes in a plate [in general, plate bulk acoustic waves (plate BAW)] through the loading effect of an infinite periodical grating defined on the plate surface is theoretically described and its fundamental characteristics revealed. Further, the eigenmodes along with amplitude ratios inside such types of gratings are determined. Analytical expressions describing the interaction have also been derived. The analysis performed in here represents the first fundamental description of the problem. In this work, only the case of isotropic elastic medium is considered, thus illuminating the fundamentals of the interaction itself, excluding the effects of crystal anisotropy. The modes' dispersion is found to exhibit a complex stopband structure. In the vicinity of the resonance condition the interaction of the waves generates new three-component eigenmodes. Specifically, two independent eigenmodes have been found to coexist in the structure due to the presence of the coupler, i.e., the periodic grating. One of them is represented by two contrapropagating SAWs coupled to a plate BAW, while the other one is represented by a near-onset Lamb mode generating two contrapropagating SAWs. Three general cases of the interaction representing Lamb modes with cutoff frequencies equal, smaller, and grater than the second Bragg frequency of the grating are considered, respectively. Analogies can be found with other interwave interactions as, for example, between light and optical phonons in solids.

Coupled Mode approach to the analysis of thin film S0 lamb wave resonators

Ventsislav Yantchev — Fri, 23 Oct 2009 23:07:00 +0200

Thin AlN film resonators utilizing the lowest order symmetric lamb mode: Further developments

Ventsislav Yantchev — Mon, 21 Jan 2008 08:01:00 +0200

Thin film plate acoustic wave resonators utilizing thelowest order symmetric Lamb wave (S0) propagating in highlytextured 2μm thick Aluminum Nitride (AlN) membranes weresuccessfully demonstrated for the first time [1]. Further theutilization of fast lateral modes in thin films has recently beingtargeted independently by other groups as well [2,3]. Theunperturbed S0 mode in thin film AlN has an acoustic wavevelocity in excess of 10 000 m/s with a weak dispersion andsufficient coupling. Q factors of around 1800 were demonstratedfor 890 MHz one-port synchronous resonators operating in thevicinity of the upper stopband edge [1]. In this work anexperimental study on the resonators’ performance vs variety ofdesign parameters is performed. Devices operating in thevicinity of the stopband center offering a Q of up to 3000 at afrequency of around 875 MHz are demonstrated. Further,micromachined 2-port longitudinally coupled thin filmresonators utilizing the S0 mode are demonstrated for the firsttime.

Analysis of Resonant SAW -Plate BAW Interaction in Periodical Couplers

Ventsislav Yantchev — Mon, 26 Jan 2009 10:43:00 +0200

Surface acoustic waves (SAW) scattering into asemi-infinite solid have been studied since the early 60-ies. Inthe case of a substrate with finite plate-like dimensions thescattering into bulk waves (BAW) is transformed intoscattering to bulk plate modes. There have been some attemptsto model the phenomenon but the most interesting case ofinteraction of SAW with BAW resonator, i.e. scattering in aquasi-perpendicular direction was not considered. Theresonant interaction between Rayleigh SAW and near-onsetPlate Waves in isotropic solids, through the coupling effect ofan infinite periodical grating defined on the plate surface istheoretically described and its characteristics revealed. Theanalysis proposed is based on the Bloch theorem. The gratingboundary conditions are considered assuming a weak surfaceperturbation. Further, the eigenmodes along with amplituderatios inside such types of gratings are determined. Initialresults on Gulyaev-Bljustein wave (GBW) – thickness shearmode (TSM) interaction are also presented.

Micromachined Thin Film Plate Acoustic Resonators Utilizing the Lowest Order Symmetric Lamb Wave Mode

Ventsislav Yantchev — Mon, 17 Nov 2008 12:38:00 +0200

Thin film integrated circuits compatible resonant structures using the lowest order symmetric Lamb wave propagating in thin aluminum nitride (AlN) filmmembranes have been studied. The 2-μm thick, highly coriented AlN piezoelectric films have been grown on silicon by pulsed, direct-current magnetron reactive sputter deposition. The films were deposited at room temperature and had typical full-width, half-maximum value of the rockingcurve of about 2 degrees. Thin film plate acoustic resonators were designed and micromachined using low resolution photolithography and deep silicon etching. Plate waves, having a 12-μm wavelength, were excited by means of both interdigital (IDT) and longitudinal wave transducers using lateralfield excitation (LW-LFE), and reflected by periodical aluminum-strip gratings deposited on top of the membrane. The existence of a frequency stopband and strong grating reflectivity have been theoretically predicted and experimentally observed. One-port resonator designs having varying cavity lengths and transducer topology were fabricated and characterized. A quality factor exceeding 3000 has been demonstrated at frequencies of about 885 MHz. The IDT based film plate acoustic resonators (FPAR) technologyproved to be preferable when lower costs and higher Qs are pursued. The LW-LFE-based FPAR technology offers higher excitation efficiency at costs comparable to that of the thin film bulk acoustic wave resonator (FBAR) technology.

Efficient Application Integration in IP-Based Sensor Networks

Dogan Yazar — Fri, 14 Jan 2011 16:32:13 +0200

Augmenting Reality with IP-based Sensor Networks : Demo Abstract

Dogan Yazar — Fri, 14 Jan 2011 15:55:54 +0200

Substrate integrated waveguides in flexible PCB

H Yousef — Wed, 2 Dec 2009 11:23:00 +0200

High Aspect Ratio Microstructures in Flexible Printed Circuit Boards : Process and Applications

Hanna Yousef — Wed, 19 Mar 2008 14:35:00 +0200

Flexible printed circuit boards (flex PCBs) are used in a wide range of electronic devices today due to their light weight, bendability, extensive wiring possibilities, and low-cost manufacturing techniques. The general trend in the flex PCB industry is further miniaturization alongside increasing functionality per device and reduced costs. To meet these demands, a new generation of low cost manufacturing technologies is being developed to enable structures with smaller lateral dimensions and higher packing densities.

Wet etching is today the most cost-efficient method for producing a large number of through-foil structures in flex PCBs. However, conventional wet etch techniques do not allow for through-foil structures with aspect ratios over 1 – a fact that either necessitates thin and mechanically weak foils or puts severe limitations on the packing density. The fabrication techniques presented in this thesis allow for through-foil structures with higher aspect ratios and packing densities using wet etching. To achieve high aspect ratios with wet etching, the flex PCB foils are pre-treated with irradiation by swift heavy ions. Each ion that passes through the foil leaves a track of damaged material which can be subsequently etched to form highly vertical pores. By using conventional flex PCB process techniques on the porous foils, high aspect ratio metallized through-foil structures are demonstrated.

The resulting structures consist of multiple sub-micrometer sized wires. These structures are superior to their conventional counterparts when it comes to their higher aspect ratios, higher possible packing densities and low metallic cross-section. Furthermore, metallized through-foil structures with larger areas and more complicated geometries are possible without losing the mechanical stability of the foil. This in turn enables applications that are not possible using conventional techniques and structures. In this thesis, two such applications are demonstrated: flex PCB vertical thermopile sensors and substrate integrated waveguides for use in millimeter wave applications.

Plated Through-Hole Vias in a Porous Polyimide Foil for Flexible Printed Circuit Boards

Hanna Yousef — Wed, 19 Mar 2008 14:35:00 +0200

A fabrication process for high aspect ratio plated through-hole vias is presented for flexibleprinted circuit boards. A 75 μm thick porous Kapton foil that allows direct definition of highaspect ratio through-hole vias by dry photoresist film lithography and electrodeposition ispresented. Pretreatment with swift heavy ion irradiation and wet etching define the poredensity and porosity of the foil, similar to ion-track-etched filter membranes. Thin filmmetallization of a seed layer and lithography of a laminated dry photoresist film define the viasizes and positions. Subsequent through-hole electrodeposition produces vias consisting ofmultiple wires, where each open pore defines one wire. The via geometries are characterizedby scanning electron microscopy. The electrical properties of the vias are characterized byresistance measurements. Vias with an aspect ratio over 2 and a side length of 33 μm showhigh yield with low resistance and low variation in resistance.

Vertical Thermopiles Embedded in a Polyimide-Based Flexible Circuit Board

Hanna Yousef — Wed, 19 Mar 2008 14:35:00 +0200

A fabrication process for vertical thermopiles embedded in a 75-mu m-thick polyimide foil has been developed for flexible printed circuit boards (flex PCBs). The vertical connections consist of electrodeposited antimony- and nickel-plated through-hole vias. The plated through-hole vias consist of multiple wires, with a total metal content that is 1% of the total via volume. The via fabrication technique is similar to standard flex PCB wet etch and metallization processes. The main difference is that the foils are pretreated with ion irradiation to induce highly selective vertical etch rates. The thermopiles were characterized by measuring their voltage response to an applied temperature difference across the foil thickness.

Ion track enabled multiple wire via interconnects in printed circuit boards

Hanna Yousef — Thu, 14 Aug 2008 13:40:00 +0200

Ion track technology for electronics manufacturing

Hanna Yousef — Thu, 14 Aug 2008 13:43:00 +0200

Ion Track Enabled Multiple Wire Microvia Interconnects in Printed Circuit Boards

Hanna Yousef — Wed, 19 Mar 2008 14:35:00 +0200

As the call for higher wiring density in packaging and vertical microvia interconnections (microvias) rapidly evolves, the need for smaller lateral dimensions in printed circuit boards (PCB) microvias must be met. The ion track lithography described in this paper allows for high throughput micromachining of small, deep, vertical microvias in flexible PCB and all-polymer laminates.

Ion track lithography makes use of swift heavy ion irradiation to enhance the selectivity and directionality of chemical etching. Within the areas exposed to the ion irradiation, small sub-micron pores (capillaries) are created, one for every ion. If etching is prolonged, the pores become merged. Electrodeposition from a metallic seed layer is used to fill these structures with metal. The lithography masks define either the areas where the ion tracks are developed or where the tracks are metallized. The smallest achievable size of the microvias is only limited by the resolution of the mask; microvias below 10 μm in diameter can also be achieved also in thick polyimide foils.

Since each impinging ion forms one track, the foil’s porosity can be controlled by adjusting the irradiation dose, as well as by etching the pores to a suitable size. Depending on the porosity and material, the resultant metallized microvia consists of either individual or interlaced wires (like strands in a bundle wire), or is a solid. As an individual sub-micron wire may have an aspect ratio of several hundreds, this allows for the fabrication of truly vertical microvia structures, allowing ultra-high density microvia batch production.

Demonstrator microstructures with highly vertical microvias have been fabricated in foils up to 125 μm thickness. Several components integrated in flexible PCB have been presented by us, e.g. magnetoresistive sensors, thermopile IR-sensors and microwave components like inductor elements.

Information Quality Aware Sensor Network Services

Sadaf Zahedi — Mon, 25 May 2009 15:48:00 +0200

Rapid Convergecast on Commodity Hardware: Performance Limits and Optimal Policies

Haibo Zhang — Fri, 14 Jan 2011 16:29:32 +0200

Wireless Sensor Networks for Permanent Health Monitoring of Historic Constructions

Daniele Zonta — Fri, 14 Jan 2011 14:32:57 +0200

Approaching the maximum 802.15.4 multihop throughput

Fredrik Österlind — Mon, 17 Jan 2011 10:30:57 +0200

Sensornet checkpointing: “Enabling repeatability in test-beds and realism in simulators.”

Fredrik Österlind — Mon, 17 Jan 2011 09:27:50 +0200

Cooja TimeLine: A Power Visualizer for Sensor Network Simulation

Fredrik Österlind — Fri, 14 Jan 2011 15:01:23 +0200

Strawman: Resolving Collisions Through Collisions

Fredrik Österlind — Mon, 10 Oct 2011 13:46:09 +0200

Integrating Symbolic Execution with Sensornet Simulation for Efficient Bug Finding

Fredrik Österlind — Fri, 14 Jan 2011 15:34:06 +0200

StrawMAN: Making Sudden Traffic Surges Graceful in Low-Power Wireless Networks

Fredrik Österlind — Fri, 14 Jan 2011 15:44:39 +0200

Smart Antennas Made Practical: The SPIDA Way

Erik Östrom — Fri, 14 Jan 2011 16:19:08 +0200

Evaluation of an Electronically Switched Directional Antenna for Real-world Low-power Wireless Networks

Erik Öström — Fri, 14 Jan 2011 16:45:06 +0200