Study of the efficiency of coupling fluids for acoustic microscopy

The aim of this study is to increase the efficiency of the acoustic microscopes by using coupling liquids with properties suitable for the characteristics of the samples. The investigated properties are the velocity of the longitudinal mode, the density and the attenuation of the acoustic waves. The acoustic properties of the aqueous solutions of electrolytes can be adapted as a function of the nature and the concentration of the cation and the anion. The aqueous solutions of potassium hydroxide KOH present velocities up to 2300 m/s and an attenuation lower than the one of water, which make them suitable for the characterization of fast materials. The peaks present in the curves deduced from the experimental acoustic signatures by fast Fourier transform are assigned through the modelling of the coupling/sample system. The velocity of the longitudinal mode of a fast material, steel, and the velocity of the surface mode (Rayleigh velocity) of a very fast material, sapphire, can be measured. The part of the density of the coupling liquid in the shape of the acoustic signature is studied. The reactivity against the samples and the lens is taken into consideration.