Differentiating between longitudinal and shear wave echoes using arrival time differences across a phased array

Conventional phased array imagers use a parabolic approximation for focusing and assume a constant velocity of sound. If both longitudinal and shear modes of propagation can be supported in the sample then the possibility exists to see two echoes from a single target. By examining the signals received on different elements of an array, the authors are able to differentiate between longitudinal and shear wave echoes scattered from a side drilled hole in an aluminum test block. Although the results presented were obtained off-line using a-lines digitized from repeated transmitted pulses, hardware to perform these calculations in real time is achievable using current technology