Effects of couplant mass loading on the acoustic signature V(z)

Abstract

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.

Theoretical and experimental investigations of acoustic signatures of materials using scanning microscopes with variable lens illumination

“…The suppression of the constant unwanted signal with a filter in the time domain rather than a stop in the space domain is always possible since the SAM is a linear system, but it has many disadvantages (Smith and Sinclair 1982) and the lens-stop system remains the best solution, for example, in dark-field imaging. It is worth noting that the choice of specific surface-mode generation could also be achieved via an appropriate use of coupling liquids, as has been reported recently (Doghmane et al 1992, Hadjoub et al 1994.…”

Scanning Acoustic Microscopy of Annealing Effects for Aluminium Thin Film Deposited on Silicon Substrate

“…Mercury also ensures a good signal transmission at the lens-liquid and liquid-solid interfaces [16][17][18].…”

“…The Rayleigh wave is the surface acoustic wave that contributes most to the V(z) interference curve. It results from the superposition of longitudinal and shear waves, which travel along the surface with a same phase velocity V R ; this V R is, however, smaller than the velocity for the other wave kinds that may be present in the bulk [16][17][18][19][20][21]. In the particular case of isotropic solids, this wave consists of two components: the longitudinal and the shear components.…”