Multiwave Total Focusing Method for Full-Matrix Imaging Using Ultrasonic Phased Array

Abstract

The imaging range of the traditional total focusing method (TFM) is usually limited by the directivity of excitation of a single wave pattern. In this paper, a multiwave TFM technique is proposed, which uses both compression and shear vertical (SV) waves for detection and imaging simultaneously. Based on this technique, a special ultrasonic transducer for multiwave detection is designed that can balance the excitation amplitude of compression and SV waves. Multiwave TFM uses the compression and SV wave fields generated by the same excitation, and the signals reflected by the two sound fields passing through the discontinuity are received. The signals are respectively processed by TFM according to the compression and SV wave velocities. The two processed signals are shifted and aligned according to the time difference between the compression wave with SV wave propagation, and then added together. Finally, the detection image of the block is obtained. Through simulation and experiments, it is shown that the special transducer can optimize the imaging range and effect of multiwave TFM, and multiwave TFM can effectively detect discontinuities and reduce the rate of missed detection at higher steering angles. The detection results show that the maximum amplitude gain of multiwave TFM relative to TFM can be increased about 6 dB.