Visualization of variations in Rayleigh wave velocity along the surface of a specimen by the diaphragm acoustic lens method

We have investigated the diaphragm lens method for observing small variations in the elastic properties on the surface of a specimen. The method is based on the following phenomenon. variations in elastic properties appear as variations in the local values of the velocity of the Rayleigh wave. Since the leaky Rayleigh wave makes an important contribution to the output signal of the acoustic microscope, its formation will occur differently depending on whether or not the Rayleigh angle theta(R) falls within the angular aperture theta(m) of the lens.