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Engholm, Marcus
Publications (10 of 16) Show all publications
Engholm, M. & Stepinski, T. (2011). Direction of Arrival Estimation of Lamb Waves Using Circular Arrays. Structural Health Monitoring, 10(5), 467-480
Open this publication in new window or tab >>Direction of Arrival Estimation of Lamb Waves Using Circular Arrays
2011 (English)In: Structural Health Monitoring, ISSN 1475-9217, E-ISSN 1741-3168, Vol. 10, no 5, p. 467-480Article in journal (Refereed) Published
Abstract [en]

 Uniform circular arrays (UCAs) with 360 degrees azimuthal coverage are very useful for structural health monitoring (SHM) of large planar structures. Difficulties encountered when working with Lamb waves include their dispersive and multi-modal nature. In this paper three different methods for estimating the direction-of-arrival (DOA) of incoming Lamb waves are compared and verified using simulated and experimental data. The previously proposed phase-mode excitation based beamformer is compared with two high-resolution spectral estimation techniques, the Capon method and the multiple signal classification method (MUSIC). Design consideration and guidelines for UCAs are presented. To experimentally evaluate the performance of the considered DOA methods a prototype array consisting of 16 separate pinducers arranged in a ring was constructed. The array was provided with an analog multiplexer that enabled recording signals received by the individual elements using a digital oscilloscope. The array was used for the reception of ultrasonic pulses sent by broadband piezoelectric transmitters and propagating in an aluminum plate. A selection of simulation and experimental results is presented showing the superior performance of the Capon beamformer.

Keywords
array signal processing, adaptive beamforming, guided waves, dispersive waves, multi-modal waves
National Category
Engineering and Technology
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
urn:nbn:se:uu:diva-122107 (URN)10.1177/1475921710379512 (DOI)000294287000002 ()
Available from: 2010-04-07 Created: 2010-04-06 Last updated: 2017-12-12Bibliographically approved
Engholm, M., Stepinski, T. & Olofsson, T. (2011). Imaging and suppression of Lamb modes using adaptive beamforming. Smart materials and structures (Print), 20(8), 1-13
Open this publication in new window or tab >>Imaging and suppression of Lamb modes using adaptive beamforming
2011 (English)In: Smart materials and structures (Print), ISSN 0964-1726, E-ISSN 1361-665X, Vol. 20, no 8, p. 1-13Article in journal (Refereed) Published
Abstract [en]

Lamb waves have proven to be very useful for plate inspection because large areas of a plate can be covered from a fixed position. This capability makes them suitable for both inspection and structural health monitoring (SHM) applications. During the last decade, research on the use of active arrays in combination with beamforming techniques has shown that a fixed array can be used to perform omni-directional monitoring of a plate structure. The dispersion and multiple propagating modes are issues that need to be addressed when working with Lamb waves. Previous work has mainly focused on conventional, delay-and-sum (DAS) beamforming, while reducing the effects of multiple modes through frequency selectivity and transducer design. The paper describes an adaptive beamforming technique using a minimum variance distortionless response beamforming (MVBF) approach for spatial Lamb wave filtering with multiple-transmitter-multiple-receiver arrays. Dispersion is compensated for by using theoretically calculated dispersion curves. Simulations are used for evaluating the performance of the technique for suppression of interfering Lamb modes, both with and without the presence of mode conversion using different array configurations. A simple simulation model of the plate is used to compare the performance of different sizes of active arrays. An aluminum plate with artificial defects is used for the experimental evaluation. The results show that the MVBF approach performs a lot better in terms of resolution and suppression of interfering modes than the widely used standard beamformer.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-159262 (URN)10.1088/0964-1726/20/8/085024 (DOI)000294765600028 ()
Available from: 2011-09-26 Created: 2011-09-26 Last updated: 2018-06-08Bibliographically approved
Engholm, M. & Stepinski, T. (2010). Adaptive Beamforming for Array Imaging of Plate Structures Using Lamb Waves. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 57(12), 2712-2724
Open this publication in new window or tab >>Adaptive Beamforming for Array Imaging of Plate Structures Using Lamb Waves
2010 (English)In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 57, no 12, p. 2712-2724Article in journal (Refereed) Published
Abstract [en]

Lamb waves are considered a promising tool for the monitoring of plate structures. Active arrays employing beamforming techniques enables monitoring large areas of plate structures. Dispersion and multiple propagating modes are issues that need to be addressed when working with Lamb waves. Previous work has mainly focused on standard beamforming while reducing the effects of dispersion and multiple modes through frequency selectivity and transducer design. This paper presents a minimum variance distortionless response (MVDR) approach for Lamb waves using a uniform rectangular array (URA) and a single transmitter. Theoretically calculated dispersion curves are used to compensate for dispersion. The combination of the MVDR approach and the two dimensional array improves the suppression of interfering Lamb modes. The proposed approach is evaluated on simulated and experimental data and compared to the standard delay-and-sum (DAS) beamformer. It is shown that the MVDR algorithm performs better in terms of higher resolution and better sidelobe and mode suppression capabilities. Known issues of the MVDR approach, such as, signal cancellation in highly correlated environments, and poor robustness, are addressed using methods that have proven effective for the purpose in other fields of active imaging.

Keywords
imaging, array processing, adaptive beamforming, Lamb waves, guided waves, structural health monitoring, dispersive waves, multi-modal waves, mode suppression, 2d arrays
National Category
Signal Processing
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
urn:nbn:se:uu:diva-122187 (URN)10.1109/TUFFC.2010.1745 (DOI)000285359100012 ()
Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2018-06-08Bibliographically approved
Stepinski, T. & Engholm, M. (2010). Advanced beamforming of 2D arrays for structural health monitoring using Lamb waves. In: 5th European Workshop on Structural Health Monitoring 2010, Sorrento, Italien: . Paper presented at 5th European Workshop on Structural Health Monitoring 2010, Sorrento, Italien.
Open this publication in new window or tab >>Advanced beamforming of 2D arrays for structural health monitoring using Lamb waves
2010 (English)In: 5th European Workshop on Structural Health Monitoring 2010, Sorrento, Italien, 2010Conference paper, Published paper (Refereed)
National Category
Signal Processing
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
urn:nbn:se:uu:diva-133935 (URN)
Conference
5th European Workshop on Structural Health Monitoring 2010, Sorrento, Italien
Available from: 2010-11-18 Created: 2010-11-18 Last updated: 2018-06-08Bibliographically approved
Engholm, M. (2010). Ultrasonic Arrays for Sensing and Beamforming of Lamb Waves. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Ultrasonic Arrays for Sensing and Beamforming of Lamb Waves
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Non-destructive testing (NDT) techniques are critical to ensure integrity and safety of engineered structures. Structural health monitoring (SHM) is considered as the next step in the field enabling continuous monitoring of structures.

The first part of the thesis concerns NDT and SHM using guided waves in plates, or Lamb waves, to perform imaging of plate structures. The imaging is performed using a fixed active array setup covering a larger area of a plate. Current methods are based on conventional beamforming techniques that do not efficiently exploit the available data from the small arrays used for the purpose. In this thesis an adaptive signal processing approach based on the minimum variance distortionless response (MVDR) method is proposed to mitigate issues related to guided waves, such as dispersion and the presence of multiple propagating modes. Other benefits of the method include a significant increase in resolution. Simulation and experimental results show that the method outperforms current standard processing techniques.

The second part of the thesis addresses transducer design issues for resonant ultrasound inspections. Resonant ultrasound methods utilize the shape and frequency of the object's natural modes of vibration to detect anomalies. The method considered in the thesis uses transducers that are acoustically coupled to the inspected structures. Changes in the transducer's electrical impedance are used to detect defects. The sensitivity that can be expected from such a setup is shown to highly depend on the transducer resonance frequency, as well as the working frequency of the instrument. Through simulations and a theoretical argumentation, optimal conditions to achieve high sensitivity are given.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. p. 83
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 732
Keywords
imaging, array processing, guided waves, Lamb waves, dispersive waves, multi-modal waves, spatial filtering, mode suppression, resonant ultrasound, transducer design, direction of arrival estimation, adaptive beamforming
National Category
Signal Processing Control Engineering
Identifiers
urn:nbn:se:uu:diva-122189 (URN)978-91-554-7785-1 (ISBN)
Public defence
2010-05-21, Siegbahnsalen, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2010-04-28 Created: 2010-04-07 Last updated: 2018-05-28Bibliographically approved
Engholm, M. & Stepinski, T. (2010). Using 2-D Arrays for Sensing Multimodal Lamb Waves. In: Shull PJ, Diaz AA, Wu AF (Ed.), Conference on Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2010 San Diego, CA, MAR 08-11, 2010: . Paper presented at Conference on Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2010 San Diego, CA, MAR 08-11, 2010. , 7649
Open this publication in new window or tab >>Using 2-D Arrays for Sensing Multimodal Lamb Waves
2010 (English)In: Conference on Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2010 San Diego, CA, MAR 08-11, 2010 / [ed] Shull PJ, Diaz AA, Wu AF, 2010, Vol. 7649Conference paper, Published paper (Refereed)
Abstract [en]

Monitoring structural integrity of large planar structures requires normally a relatively dense network of uniformly distributed ultrasonic sensors. A 2-D ultrasonic phased array with all azimuth angle coverage would be extremely useful for the structural health monitoring (SHM) of such structures. Known techniques for estimating direction of arriving (DOA) waves cannot efficiently cope with dispersive and multimodal Lamb waves (LWs). In the paper we propose an adaptive spectral estimation technique capable of handling broadband LWs sensed by 2-D arrays, the modified Capon method. Performance of the technique is evaluated using simulated multiple-mode LWs, and verified using experimental data.

Series
Proceedings of SPIE-The International Society for Optical Engineering, ISSN 0277-786X ; 7649
Keywords
structural health monitoring, phased arrays, beamforming
National Category
Signal Processing
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
urn:nbn:se:uu:diva-148148 (URN)10.1117/12.847607 (DOI)000285543200025 ()978-0-8194-8064-4 (ISBN)
Conference
Conference on Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2010 San Diego, CA, MAR 08-11, 2010
Available from: 2011-03-02 Created: 2011-03-02 Last updated: 2018-06-08Bibliographically approved
Stepinski, T., Engholm, M. & Olofsson, T. (2009). Inspection of copper canisters for spent nuclear fuel by means of ultrasound, copper characterization, FSW monitoring with acoustic emission and ultrasonic imaging..
Open this publication in new window or tab >>Inspection of copper canisters for spent nuclear fuel by means of ultrasound, copper characterization, FSW monitoring with acoustic emission and ultrasonic imaging.
2009 (English)Report (Other academic)
Series
Technical Report, Swedish Nuclear Fuel and Waste Management Co, Stockholm ; TR-09-28
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:uu:diva-117775 (URN)
Available from: 2010-02-22 Created: 2010-02-22 Last updated: 2018-06-08Bibliographically approved
Stepinski, T. & Engholm, M. (2009). Piezoelectric circular array for structural health monitoring using plate waves. In: 7th International Workshop on Structural Health Monitoring, Stanford, CA: . Paper presented at 7th International Workshop on Structural Health Monitoring, Stanford, CA.
Open this publication in new window or tab >>Piezoelectric circular array for structural health monitoring using plate waves
2009 (English)In: 7th International Workshop on Structural Health Monitoring, Stanford, CA, 2009Conference paper, Published paper (Refereed)
National Category
Signal Processing
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
urn:nbn:se:uu:diva-111855 (URN)
Conference
7th International Workshop on Structural Health Monitoring, Stanford, CA
Available from: 2009-12-28 Created: 2009-12-28 Last updated: 2018-06-08Bibliographically approved
Stepinski, T. & Engholm, M. (2008). On the development and testing of a uniform circular array for structural health monitoring of planar structures. In: Proceedings of the 4th European Workshop on Structural Health Monitoring: . Paper presented at 4th European Workshop on Structural Health Monitoring. Krakow, Polen
Open this publication in new window or tab >>On the development and testing of a uniform circular array for structural health monitoring of planar structures
2008 (English)In: Proceedings of the 4th European Workshop on Structural Health Monitoring, Krakow, Polen, 2008Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Krakow, Polen: , 2008
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:uu:diva-111048 (URN)
Conference
4th European Workshop on Structural Health Monitoring
Available from: 2009-12-02 Created: 2009-12-02 Last updated: 2018-06-08Bibliographically approved
Stepinski, T. & Engholm, M. (2008). Uniform circular array for structural health monitoring of composite structures. In: Kundu, T (Ed.), HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS 2008: . Paper presented at Conference on Health Monitoring of Structural and Biological Systems San Diego, CA, MAR 10-13, 2008 (pp. A9352-A9352).
Open this publication in new window or tab >>Uniform circular array for structural health monitoring of composite structures
2008 (English)In: HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS 2008 / [ed] Kundu, T, 2008, p. A9352-A9352Conference paper, Published paper (Refereed)
Abstract [en]

Phased array with all-azimuth angle coverage would be extremely useful in structural health monitoring (SHM) of planar structures. One method to achieve the 360 degrees coverage is to use uniform circular arrays (UCAs). In this paper we present the concept of UCA adapted for SHM applications. We start from a brief presentation of UCA beamformers based on the principle of phase mode excitation. UCA performance is illustrated by the results of beamformer simulations performed for the narrowband and wideband ultrasonic signals. Preliminary experimental results obtained with UCA used for the reception of ultrasonic signals propagating in an aluminum plate are also presented.

Series
PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS (SPIE), ISSN 0277-786X ; 6935
Keywords
structural health monitoring, phased arrays, beamforming
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:uu:diva-111051 (URN)000257136900067 ()978-0-8194-7121-5 (ISBN)
Conference
Conference on Health Monitoring of Structural and Biological Systems San Diego, CA, MAR 10-13, 2008
Available from: 2009-12-02 Created: 2009-12-02 Last updated: 2018-06-08Bibliographically approved
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