Mr. Matthew Brown Profile

Matthew Brown

at California State Univ. Northridge

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Publications (2)

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Proceedings Article | 1 April 2019 Paper

Experimental investigation of Lamb wave-based edge detection methods

Christoph Schaal, Matthew Brown, Katja Schulz

Proceedings Volume 10972, 1097223 (2019) https://doi.org/10.1117/12.2515452

KEYWORDS: Sensors, Transducers, Edge detection, Actuators, Waveguides, Wave propagation, Nondestructive evaluation, Aluminum

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In recent years, many researchers have explored the use of guided ultrasonic waves for nondestructive testing (NDT). When guided waves are transmitted into a structure, any geometric and material discontinuities in the waves’ path modify these waves. Using appropriate signal processing methods for the waves received at a sensor, information about these features can be extracted. However, little research has been conducted to locate the features and automatically generate maps without using a priori knowledge. For NDT of large-scale structures, such as the wings of an airplane, many (automated) measurements need to be conducted, and localization of identified features on a map is crucial for successful damage detection. Hence, in this work, methods to detect edges are investigated in an effort to generate a map of the structure using Lamb waves. Measurements are conducted with contact and air-coupled ultrasound transducers in laboratory experiments. While the used contact transducers do not exhibit any directional sensitivity, air-coupled transducers are only sensitive to incoming waves from one direction. Therefore, different data processing methods have to be applied, depending on the applied actuator or sensor technology. Even though the experiments are conducted for a pristine aluminum plate, an outlook for composite plates is given as well. In addition, it is explored whether guided-wave based methods also allow for the detection of other structural features, such as stiffeners. The accuracy of the applied identification methods is validated against the structures’ true dimensions. Even though substantial assumptions have to be made, the investigated methods show promise for successful application in real scenarios.

Proceedings Article | 27 March 2018 Presentation + Paper

Visualization of the scattering of focused ultrasonic waves at solid-fluid interfaces

Matthew Brown, Mehran Safisamghabadi, Christoph Schaal, Vibhav Durgesh

Proceedings Volume 10600, 106000V (2018) https://doi.org/10.1117/12.2296744

KEYWORDS: Bone, Visualization, Ultrasonics, Transducers, Scattering, Acoustics, Image visualization

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While high-intensity focused ultrasound (HIFU) is already being used for the ablation of tissue near the skin, such as in the case of prostate cancer, targeting tissue deeper inside the body remains challenging due to the increased obstruction and scattering of ultrasonic waves. In this work, the partial and complete obstruction of the ultrasonic beam path from a HIFU transducer operating at 670 kHz by bone phantom is imaged in laboratory experiments to visualize wave transmission and reflection at solid-fluid interfaces. Ultrasonic wave-scattering under such conditions has scarcely been the focus of previous ultrasound visualization studies. Thus, this work provides a qualitative visual reference for focused waves scattering at water-bone interfaces. A diffraction-based shadowgraph technique is used for the ultrasound visualization. The ultrasonic waves are imaged in water with no obstruction, with varying partial obstruction, and with complete obstruction by a thin fiber-filled epoxy plate mimicking bone tissue. Experimental findings are compared to those obtained through finite element simulations, showing good agreement. Furthermore, it is found that in certain partial obstruction cases, the waves scatter in such a way that the destructive interference between the transmitted waves lead to a significantly reduced maximum pressure at the focal point. Overall, the results of this study can provide a visual framework for future research in the field of therapeutic ultrasound.

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