Scanning tomographic acoustic microscopy using shear waves

摘要

We propose to use shear waves instead of longitudinal waves in annovel scanning tomographic acoustic microscope (STAM) in which thenspecimens are solid. When a specimen with a shear modulus is immersed innthe microscope's water bath, mode conversion takes place at thenwater-solid interface. The shear wave energy is detectable and can benused for image reconstruction. Although wave transmission in most solidnspecimens is limited to about 20° for longitudinal waves, it isnabout twice that for shear waves. Also, velocities of shear waves arenlower than those of longitudinal waves and hence the wavelengths at thensame frequency are smaller. For these and other reasons we can expectnthat for many specimens the resolution of a shear-wave STAM to bensubstantially better than that of a longitudinal-wave STAM. We usencomputer simulation in order to compare the operation of a shear-wavenSTAM with that of the conventional longitudinal-wave STAM. We havensimulated tomographic reconstruction for each. The correspondingncritical angles of incidence are computed and tomographicnreconstructions of a particular solid specimen is obtained by using thenback-and-forth propagation algorithm (BFP). Our simulation results shownthat shear-wave STAM has better resolution than longitudinal-wave STAM