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Applications of active materials
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Energy efficiency is a vital key component when designing and miniaturizing self sustained microsystems. The smaller the system, the smaller is the possibility to store enough stored energy for a long and continuous operational time. To move such a system in an energy efficient way, a piezoelectrical locomotion module consisting of four resonating cantilevers has been designed, manufactured and evaluated in this work. The combination of a suitable substrate, a multilayered piezoelectric material to reduce the voltage, and a resonating drive mechanism resulted in a low power demand.

A manufacturing process for multilayer cantilever actuators made of P(VDF-TrFE) with aluminum electrodes on a substrate of flexible printed circuit board (FPC), has been developed. An important step in this process was the development of an etch recipe for dry etching the multilayer actuators in an inductive plasma equipment.

Formulas for the quasi static tip deflection and resonance frequency of a multilayered cantilever, have been derived. Through theses, it was found that the multilayered structures should be deposited on the polymer side of the FPC in order to maximize the tip deflection.

Both a large and a miniaturized locomotion module were manufactured and connected by wires to verify that the three legged motion principal worked to move the structures forward and backward, and turn it right and left. By touching and adding load, to a fourth miniaturized cantilever, its ability to act as a contact sensor and carry object was verified.

The presented locomotion module is part of a multifunctional microsystem, intended to be energy efficient and powered by a solar panel with a total volume of less than 25 mm3 and weight 65 mg. The whole system, consisting of a solar cell, an infra red communication module, an integrated circuit for control, three capacitors for power regulating, the locomotion module and an FPC connecting the different modules, was surface mounted using a state of the art industrial facility. Two fully assembled systems could be programmed both through a test connector and through optical sensors in the multifunctional solar cell. One of these was folded together to the final configuration of a robot. However, the entire system could not be tested under full autonomous operating conditions. On the other hand, using wires, the locomotion module could be operated and used to move the entire system from a peak-to-peak voltage of 3.0 V.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2009. , p. 77
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 672
Keywords [en]
Energy efficient, microsystem, resonating cantilevers, microactuators, P(VDF-TrFE), surface mounting assembly, multi layers, flexible printed circuit board, conveyer, three legged
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-108696ISBN: 978-91-554-7609-0 (print)OAI: oai:DiVA.org:uu-108696DiVA, id: diva2:240329
Public defence
2009-10-30, 2001, Ångström Laboratory, Uppsala, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2009-10-09 Created: 2009-09-28 Last updated: 2009-10-09Bibliographically approved
List of papers
1. Monolithic fabrication of multilayer P(VDF-TrFE) cantilevers
Open this publication in new window or tab >>Monolithic fabrication of multilayer P(VDF-TrFE) cantilevers
2008 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 144, no 2, p. 314-320Article in journal (Refereed) Published
Abstract [en]

When operating a piezoelectric actuator the use of multilayers has for a long time proven to be a good solution to maintain a high electric field at a reduced applied voltage. The piezoelectric copolymer polyvinylidene-trifluoroethylene P(VDF-TrFE) has rather low piezoelectric constant compared to piezoceramics but it can withstand much higher electric fields. As the copolymer can be spin coated the individual layer thickness of the multilayer can easily be reduced to a few m and rather large strains can be achieved at a moderate voltage. Here a monolithic fabrication technique for producing P(VDF-TrFE) actuators, without any lamination or adhesive layers, is presented. To fabricate the multilayer successive spin coating of the piezoelectric polymer polyvinylidene-trifluoroethylene P(VDF-TrFE) and electrode evaporation on a substrate was performed. Four different substrate materials were coated with a multilayer stack of 6 active P(VDF-TrFE) layers and 7 aluminum electrodes. The monolithic multilayer structures with patterned electrodes were diced by a cutting saw to produce unimorph cantilevers. No delamination or dissolution could be observed between adjacent copolymer layers. The cantilevers were evaluated in terms of static and resonant deflection and the Q-factor was estimated from the frequency spectra. A discussion regarding the influence of the Q-factor on the fabrication process tolerance is given. The different substrate materials used was stainless steel, flexible printed circuit board (FPC), polycarbonate and aluminum. The Q-factor varied from 30 for the polycarbonate to 83 for the stainless steel. These results provide guidelines for the material choices of a forthcoming locomotion module to be used in the 3 mm 3 mm 3 mm I-SWARM robots. The FPC substrate showed to have the best compatibility to the fabrication processes and the most suitable Q-value of 42. This together with the high deflections makes the FPC the preferred substrate materials the future actuators for the I-SWARM locomotion module. 2008 Elsevier B.V. All rights reserved.

Keywords
Piezoelectric actuators, Copolymers, Electric fields, Multilayers, Printed circuit boards, Spin coating
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-108492 (URN)10.1016/j.sna.2008.01.004 (DOI)000256896700010 ()09244247 (ISBN)
Available from: 2009-09-20 Created: 2009-09-20 Last updated: 2017-12-13Bibliographically approved
2. Gentle dry etching of P(VDF-TrFE) multilayer micro actuator structures by use of an inductive coupled plasma
Open this publication in new window or tab >>Gentle dry etching of P(VDF-TrFE) multilayer micro actuator structures by use of an inductive coupled plasma
2008 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 18, no 1, p. 015007-Article in journal (Refereed) Published
Abstract [en]

To fully utilize the actuator properties of poly(vinylidenefluoride) (P(VDF))-based polymers, the electric field has to be rather high and one way to accomplish this, in particular with low voltage drive signals, is to build multilayered structures. This paper focuses on how to structure poly(vinylidenefluoride-trifluoroethylene) P(VDF-TrFE) by presenting an etch method to create multilayered miniaturized actuators, with intermediate aluminium electrodes. To create inter-connect areas for the multilayer electrodes, a modified Bosch process in an inductive couple plasma (ICP) etcher is used to remove all P(VDF-TrFE) not covered by the electrodes. Since each electrode mask is slightly different from the others, the result is a staircase-like inter-electrode contact area that is connected from above using a conductive adhesive. The developed ICP etch results in high selective etching and a good agreement between theoretical and measured capacitance values. The manufactured cantilevers, consisting of a multilayer on top of a flexible printed circuit (FPC) board, were tested and the resonant stroke was confirmed to agree with expected values. The successful establishment of interlayer connections between the electrodes open up the possibility for batch fabrication of cheap low voltage micro actuators built on a standard substrate used in millions of commercial products. 2008 IOP Publishing Ltd.

Keywords
Multilayers, Actuators, Aluminum, Electric field effects, Electrochemical electrodes, Etching, Inductively coupled plasma, Microfabrication
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-108491 (URN)10.1088/0960-1317/18/1/015007 (DOI)000252965900009 ()09601317 (ISBN)
Available from: 2009-09-20 Created: 2009-09-20 Last updated: 2017-12-13
3. Quasi-static and dynamic electromechanical response of piezoelectric multilayer cantilever beams
Open this publication in new window or tab >>Quasi-static and dynamic electromechanical response of piezoelectric multilayer cantilever beams
2010 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 157, no 2, p. 198-209Article in journal (Refereed) Published
Abstract [en]

Piezoelectric multilayer cantilever beams were considered with the aim to establish a simple but general theoretical model, fabricate such beams by a procedure suitable for devices on millimetre scale such as actuators, and study their quasi-static and dynamic electro-mechanical responses. In addition to Euler-Bernoulli assumptions, the beams were assumed to be lossless and have linear piezoelectric response. Four types of beams of nominal length 10 mm, width 2 mm and thickness either 55 or 86 µm, and with two asymmetric configurations of 14 or 15 layers, were fabricated. From top to bottom, each beam consisted of six aluminium electrode layers alternating with five active P(VDF-TrFE) layers, of one passive such layer, and of one polyimide and one copper layer, or vice versa. The thicknesses of the layers and of the beam were determined by use of focused ion beam, scanning electron microscope, light microscope, and Heidenhain probe. Both theoretical and experimental results for resonance frequencies and transverse tip displacement per unit driving voltage showed fair overall agreement from quasi-static conditions to frequencies above the second resonance frequency. Deviations observed are mainly due to variations resulting from the manufacturing process, to nonlinear piezoelectricity and to the presence of losses.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2010
Keywords
Cantilever, multilayer, piezoelectric, quasi-static, dynamic, tip deflection, PVDF-TrFE.
National Category
Applied Mechanics
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-108496 (URN)10.1016/j.sna.2009.11.013 (DOI)000274979300004 ()
Available from: 2009-09-20 Created: 2009-09-20 Last updated: 2017-12-13Bibliographically approved
4. Design and manufacturing considerations of low voltage multilayer P(VDF-TrFE) actuators
Open this publication in new window or tab >>Design and manufacturing considerations of low voltage multilayer P(VDF-TrFE) actuators
2009 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 19, no 11, p. 115019-Article in journal (Refereed) Published
Abstract [en]

An actuator unit consisting of three multilayered cantilevers with poly(vinylidene fluoride-trifluoroethylene) on top of a flexible printed circuit board substrate is presented. The multilayer structure has five active polymer layers and six electrodes with an alternating ground and phase configuration. Different aspects regarding processing and deflection advantages, depending on which side of the substrate the multilayer structure is manufactured, are discussed.  One of the cantilever configurations is dynamically modelled using a finite element software and the results are compared to measured values. Because of the combination of a multilayer design and the resonant driving mode, the actuators could be powered by solar cells or used in portable electronics. A 2 V sine wave signal resulted in a tip deflection of 56 μm. To test the unit as a conveyer, speed measurements were conducted. With a 2.5 V square wave signal the speed was 29 µm/s whereas a 8 V signal resulted in 732 µm/s. Motion in all four directions could be confirmed by tuning the frequency of a 10 V square wave signal from 640 Hz to 740 Hz.

Place, publisher, year, edition, pages
Institute of Physics Publishing, 2009
Keywords
Multilayer, actuator, cantilever, PVDF-TrFE, low voltage, resonating structure
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-108484 (URN)10.1088/0960-1317/19/11/115019 (DOI)000270967800020 ()
Available from: 2009-09-20 Created: 2009-09-20 Last updated: 2017-12-13Bibliographically approved
5. Resonating low voltage P(VDF-TrFE) multilayered microactuator built on flexible printed circuit board
Open this publication in new window or tab >>Resonating low voltage P(VDF-TrFE) multilayered microactuator built on flexible printed circuit board
(English)In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158Article in journal (Refereed) Submitted
Abstract [en]

A resonating low voltage microactuator module is presented and evaluated as conveyer. The characterized module has four cantilevers, of which three are used as legs and one as a sensor. A lithographically patterned flexible printed circuit board acts as the passive part of the cantilever whereas the active part consist of 14 layers of spin coated poly(vinylidenefluoride-trifluoroethylene) with alternating evaporated aluminum electrodes. Among the process steps developed are: a batchwise contacting of the multilayer stack, a batchwise polarization method, and an extended polarization procedure. In the final manufacturing step, the legs are bent 60° out of the plane using a folding equipment. The locomotion module is characterized by connecting it with four copper wires and tested with the legs downwards and upside down against a glass plate. Different weights are added to the module and different driving voltage levels and frequencies are tested. The module was found to operate already at 3.0 V peak-to-peak and capable of forward, backward, right and left movement. With wires attached to it, and using a 80 V peak-to-peak square wave signal at 18020 Hz, it could move 150 mg, which is more than 37 times it own weight.

Keywords
PVDF-TrFE, conveyer, microrobot, batch polarisation, three legs, resonating operation
National Category
Other Materials Engineering Other Materials Engineering
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-108485 (URN)
Available from: 2009-09-20 Created: 2009-09-20 Last updated: 2017-12-13Bibliographically approved
6. Evaluation of building technology for mass producible millimetre-sized robots using flexible printed circuit boards
Open this publication in new window or tab >>Evaluation of building technology for mass producible millimetre-sized robots using flexible printed circuit boards
Show others...
2009 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 19, no 7, p. 11pp-Article in journal (Refereed) Published
Abstract [en]

Initial tests of a building technology for a compact three-dimensional mass produciblemicrorobot are presented. The 3.9 × 3.9 × 3.3 mm3 sized prototype robot represents amicrosystem with actuators, sensors, energy management and integrated electronics. Theweight of a folded robot is 65 mg and the total volume is less than 23 mm3. The design of theinterfaces of the different modules in the robot, as well as the building technology, isdescribed. The modules are assembled using conductive adhesive with industrial surfacemounting technology on a thin double-sided flexible printed circuit board. The final shape ofthe microrobots is achieved by folding the flexible printed circuit board twice. Electrical andmechanical studies are performed to evaluate the assembly and it is concluded that thetechnology can be used for this type of microsystem. Several issues using the presentedassembly technique are identified and addressed.

Place, publisher, year, edition, pages
Institute of Physics Publishing, 2009
Keywords
microrobot surface mounting technologies microsystem autonomous flexible printed circuit boards
National Category
Manufacturing, Surface and Joining Technology
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-108482 (URN)10.1088/0960-1317/19/7/075011 (DOI)000267516800034 ()
Projects
I-SWARM
Available from: 2009-09-20 Created: 2009-09-20 Last updated: 2017-12-13Bibliographically approved
7. A vibrating microcantilever sensor for microrobotic applications
Open this publication in new window or tab >>A vibrating microcantilever sensor for microrobotic applications
(English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439Article in journal (Refereed) Submitted
Abstract [en]

In order to actively interact with the environment and to perform advanced tasks, microrobots need to be equipped with sensing tools to detect object and obstacles, and eventually manipulate and transport micro-parts. The concept, design, simulations and first characterization of a simple multifunctional microsystem, a vibrating microcantilever, capable of working as touch sensor and potentially as manipulation tool with feedback sensing is presented. The presented microcantilever was designed to be integrated onboard a microrobot of about 3 × 3 × 3 mm3. The microcantilever is applied as a sensing antenna on the microrobot in order to recognize objects or obstacles through direct contact, causing a voltage drop in a feedback layer. The microcantilever produced is 2.85×0.45×0.098 mm, and the experiments verified that it could be used as a contact sensor featuring high sensitivity with extremely low power consumption and good mass-manufacturability.

Identifiers
urn:nbn:se:uu:diva-108495 (URN)
Available from: 2009-09-20 Created: 2009-09-20 Last updated: 2017-12-13Bibliographically approved
8. Design and validation of the control circuits for a micro-cantilever tool for a micro-robot
Open this publication in new window or tab >>Design and validation of the control circuits for a micro-cantilever tool for a micro-robot
Show others...
2009 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 153, no 1, p. 76-83Article in journal (Refereed) Published
Abstract [en]

The objective of this paper is to present the design and validation of a cantilever-based contact sensing system for a micro-robot. Key elements of the fabrication process of the sensor and the electrical model extraction used to design the control electronics are described. The architecture used for the sensor corresponds to a micro-cantilever fabricated of piezoelectric-polyvinylidene fluoride-trifluoroethylene stacked in a multilayer structure with the possibility of both actuating and sensing. A lumped electro mechanical equivalent model of the micro-cantilever was used to design the control electronics for the cantilever. A driving signal from, the control system is used to vibrate the cantilever at its first mechanical resonance frequency. The control system contains an analog front-end to measure the sensor output signal and a digital control unit designed to track and keep the resonance frequency of the cantilever. By integrating the cantilever control system is integrated in the application specified integrated circuit used to control of the circuit is simplyfied and very compact. Experimental results show a similar behavior between the electrical model and the fabricated system, and the deviations between the model and the measured structure are analyzed. The results also show that the designed control system is capable to detect the resonance frequency of the system and to actuate despite small deviations in process parameters of different batches of cantilevers. The whole system was designed to be integrated into an autonomous micro-robot, although it can be used in other applications.

Place, publisher, year, edition, pages
P.O. Box 211, Amsterdam, 1000 AE, Netherlands: Elsevier, 2009
Keywords
Vibrating cantilever, Multilayer PVDF-TrFE sensor, Control electronics, Interface circuits
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-108493 (URN)10.1016/j.sna.2009.04.030 (DOI)000267646600012 ()09244247 (ISBN)
Note

Compilation and indexing terms, Copyright 2009 Elsevier Inc. 20092412122278 Analog front-end Contact sensing Control circuits Control electronics Digital control units Driving signal Electrical models Electro-mechanical Equivalent model Fabricated system Fabrication process In-process parameters Interface circuits Key elements Mechanical resonance frequency Micro robots Micro-cantilever Multilayer structures Other applications Polyvinylidene fluorides Resonance frequencies Sensor output Trifluoroethylene Vibrating cantilever Whole systems

Available from: 2009-09-20 Created: 2009-09-20 Last updated: 2017-12-13Bibliographically approved

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