Wavelet-based 2D fusing of ultrasonic pulse-echo traces measured from two arrays radiating orthogonal beams

Abstract

Ultrasonic measurements using orthogonal collimated beams provide both complementary and redundant information about internal parts of pieces or structures being tested, which must be fused. In this paper, a new wavelet-based digital-processing technique which fuses ultrasonic pulse-echo traces obtained from several transducers located in two perpendicularly coupled arrays is proposed. This is applied to accurately visualize the location of a small internal reflector by means of two-dimensional (2D) displays. A-scans are processed in a wavelet domain and fused in a common 2D pattern. A mathematical expression of the resulting 2D signal-to-noise ratio (SNR) is derived, and its accuracy is confirmed using benchmark tests performed with simulated registers and real measurements acquired using a multi-channel laboratory prototype. The measurement system consists of two properly coupled perpendicular arrays comprising four square pulsed transducers and electronic driving circuitry. This technique improves the 2D-SNR by a factor of twice the number of bands. In addition, good reflector location is obtained, since submillimeter 2D resolution is achieved, despite only requiring eight ultrasonic channels. This good performance is confirmed by comparing the new wavelet fusing method with the two previously described techniques. © 2011 IOP Publishing Ltd.