Measurement of elastic impedance with high spatial resolution using acoustic microscopy

The magnitude of the gray levels in an image obtained by an acoustic microscope can be exploited to measure the acoustic impedance of a sample with the spatial resolution of the instrument. Theoretical considerations show the functional dependence of the masimal amplitude of specular reflection from material constants, which is confirmed by experiments. It turns out that for these amplitude values the opening angle of the lens plays a minor role. For a quantitative evaluation of the impedance, calibration by a known object material is necessary.