Optimisation of data acquisition and processing for laser induced ultrasonic phased arrays

Lukacs, Peter and Stratoudaki, Theodosia and Wilcox, Paul and Clark, Matt and Gachagan, Anthony (2019) Optimisation of data acquisition and processing for laser induced ultrasonic phased arrays. Proceedings of Meetings on Acoustics, 38 (1). 030015. ISSN 1939-800X (https://doi.org/10.1121/2.0001170)

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A laser induced phased array (LIPA) synthesizes an ultrasonic array, performing beamforming in post processing and using lasers for ultrasonic generation and detection. It is a non-contact technique, with a small footprint and no need for couplant, offering remote ultrasonic imaging. In a previous work, the Full Matrix Capture (FMC) and the Total Focusing Method (TFM) have been adapted to LIPAs, providing superior imaging quality, overcoming the poor signal-to-noise ratio of conventional laser ultrasonics. However, long scanning times compromise industrial applications. Our aim is to optimise FMC for LIPAs, to achieve faster data acquisition, while ensuring that ultrasonic imaging is not undermined. In the work presented, optimisation of the data acquisition and signal processing is achieved by considering the directivity and sensitivity patterns of laser ultrasound. The array characteristics, such as the number of elements, pitch and distribution were optimised according to the location of defects, receiving input through post-processing performed performed in parallel. The potential of this method is demonstrated using previously experimentally acquired data. These simulated results are compared to the scanning times and image quality of conventional FMC. Results confirm that scanning time can be significantly reduced, leading to almost 10 times faster data acquisition for LIPAs.