EFFECTS OF COUPLANT MASS LOADING ON THE ACOUSTIC SIGNATURE V(Z)

Nondestructive investigations of elastic properties of materials via acoustic material signature, using reflection acoustic microscopy systems, are becoming more and more attractive. The necessity of using coupling liquids in such systems leads to the generation of generalized surface leaky waves such as Rayleigh waves. The V(z) response and hence the postion of its Fourier transform peaks change according to the liquid impedance due to a fundamental phenomenon known as mass loading. This effect, neglected up till now, has been studied in details on several materials (tungsten, stainless steel, and SiO2) with water, mercury, and other coupling liquids having different densities assuming the same velocity. For example, it is found that skimming shear velocity can be determined with a better precision when heavy coupling liquids are used. However, skimming longitudinal velocity seems to be independent of the coupling liquid density, whereas its efficiency gets larger with higher liquid densities.