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Imaging and Suppression of Lamb Modes Using Multiple Transmitter Adaptive Beamforming
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)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. (NDT)
(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.

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 Control Engineering
Identifiers
URN: urn:nbn:se:uu:diva-122188OAI: oai:DiVA.org:uu-122188DiVA: diva2:309418
Available from: 2010-04-07 Created: 2010-04-07 Last updated: 2010-04-12
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.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 732
Keyword
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: 2010-04-28Bibliographically approved

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