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Adaptive Beamforming for Array Imaging of Plate Structures Using Lamb Waves
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. (NDT)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. (NDT)
2010 (English)In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 57, no 12, 2712-2724 p.Article 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.

Place, publisher, year, edition, pages
2010. Vol. 57, no 12, 2712-2724 p.
Keyword [en]
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
URN: urn:nbn:se:uu:diva-122187DOI: 10.1109/TUFFC.2010.1745ISI: 000285359100012OAI: oai:DiVA.org:uu-122187DiVA: diva2:309416
Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2016-04-19Bibliographically approved
In thesis
1. Ultrasonic Arrays for Sensing and Beamforming of Lamb Waves
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. 83 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 732
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
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)
Available from: 2010-04-28 Created: 2010-04-07 Last updated: 2010-04-28Bibliographically approved

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Engholm, MarcusStepinski, Tadeusz
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