Accurate estimation of scattering strength distribution by simultaneous reception of ultrasonic echoes with multichannel transducer array

Recently, there have been several studies on ultrasonic cross-sectional imaging based on simultaneous reception of echo signals with an array transducer without scanning ultrasonic beams during transmission. In those studies, parallel processing was applied to create an image from a data set simultaneously received by the array. However, the lateral resolution of the parallel processing is not high. In this study, in order to improve the spatial resolution of parallel processing, the least-squares estimation and the truncated singular value decomposition (tSVD) are applied to the echo signals from two wire targets simultaneously received with a multichannel transducer array. We introduced a weighting for correcting the effect of the directivity of the elements of the array. The experimental results show a higher lateral resolution of the tSVD method with weighting than that of conventional parallel processing. The axial resolution is also improved by considering the finite duration of the transmitted ultrasonic pulse. A typical application of this method is nondestructive evaluation, that is, the detection of cavities and cracks in welded metal structures.