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Ultrasonic Arrays for Sensing and Beamforming of Lamb Waves
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. (NDT)
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 [en]
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: urn:nbn:se:uu:diva-122189ISBN: 978-91-554-7785-1 (print)OAI: oai:DiVA.org:uu-122189DiVA, id: diva2:309420
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
List of papers
1. Direction of Arrival Estimation of Lamb Waves Using Circular Arrays
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
2. Adaptive Beamforming for Array Imaging of Plate Structures Using Lamb Waves
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
3. Imaging and Suppression of Lamb Modes Using Multiple Transmitter Adaptive Beamforming
Open this publication in new window or tab >>Imaging and Suppression of Lamb Modes Using Multiple Transmitter Adaptive Beamforming
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

Lamb waves have proven to be very useful for plate inspection since large areas of a plate can be covered from a fixed position. This ability 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 have shown that a fixed array can be used to perform omni-directional monitoring over a large area of a plate structure. The dispersion and multiple ropagating 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 dispersion and 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 transmitters-multiple receivers. Dispersion is compensated for 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. An aluminum plate with artificial defects is used for the experimental evaluation. A simple simulation model of the plate is used to compare the performance of different sizes of active arrays. The results show that the MVBF approach performs much better in terms of resolution and interfering mode suppression than the widely used standard beamformer.

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 Control Engineering
Identifiers
urn:nbn:se:uu:diva-122188 (URN)
Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2010-04-12
4. Narrowband ultrasonic spectroscopy for NDE of layered structures
Open this publication in new window or tab >>Narrowband ultrasonic spectroscopy for NDE of layered structures
2005 (English)In: INSIGHT, the Journal of The British Institute of Non-Destructive Testing, Vol. 47, p. 220-224Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-75944 (URN)
Available from: 2006-03-10 Created: 2006-03-10 Last updated: 2011-01-11
5. Designing and evaluating transducers for narrowband ultrasonic spectroscopy
Open this publication in new window or tab >>Designing and evaluating transducers for narrowband ultrasonic spectroscopy
2005 (English)In: 2005 IEEE Ultrasonics Symposium, 2005Conference paper, Published paper (Refereed)
Identifiers
urn:nbn:se:uu:diva-75987 (URN)
Available from: 2006-03-10 Created: 2006-03-10 Last updated: 2010-04-07
6. Designing and evaluating transducers for narrowband ultrasonic spectroscopy
Open this publication in new window or tab >>Designing and evaluating transducers for narrowband ultrasonic spectroscopy
2007 (English)In: NDT & E international, ISSN 0963-8695, E-ISSN 1879-1174, Vol. 40, no 1, p. 49-56Article in journal (Refereed) Published
Abstract [en]

Introduction of new composite materials in aerospace applications has created a demand for an efficient NDE technique. Ultrasonic resonance inspection is especially suitable for the inspection of multilayered structures. In our previous work we have described the principle of narrowband ultrasonic spectroscopy (NBUS), where the surface of an inspected structure is scanned with a resonant transducer whose frequency response is monitored in a narrow frequency band. This paper is concerned with optimizing the NBUS setup consisting of a piezoelectric transducer coupled to a multi-layered structure. Differences in the electrical impedance of a piezoelectric transducer caused by variations of parameters of the inspected structure are estimated using an equivalent circuit model and a finite element analysis. The theoretical analysis presented in the paper results in design guidelines for NBUS transducers.

Keywords
Narrowband ultrasonic spectroscopy, Transducer design, Layered materials
National Category
Computer and Information Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-13355 (URN)10.1016/j.ndteint.2006.07.006 (DOI)000242411700007 ()
Available from: 2008-01-22 Created: 2008-01-22 Last updated: 2018-01-12Bibliographically approved

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