STUDY OF THE EFFICIENCY OF COUPLING FLUIDS FOR ACOUSTIC MICROSCOPY

The aim of this study is to increase the efficiency of the acoustic mi croscopes by using coupling liquids with properties suitable for the c haracteristics of the samples. The investigated properties are the vel ocity of the longitudinal mode, the density and the attenuation of the acoustic waves. The acoustic properties of the aqueous solutions of e lectrolytes can be adapted as a function of the nature and the concent ration of the cation and the anion. The aqueous solutions of potassium hydroxide KOH present velocities up to 2300 m/s and an attenuation lo wer than the one of water, which make them suitable for the characteri zation of fast materials. The peaks present in the curves deduced from the experimental acoustic signatures by fast Fourier transform are as signed through the modelling of the coupling/sample system. The veloci ty of the longitudinal mode of a fast material, steel, and the velocit y of the surface mode (Rayleigh velocity) of a very fast material, sap phire, can be measured. The part of the density of the coupling liquid in the shape of the acoustic signature is studied. The reactivity aga inst the samples and the lens is taken into consideration. (C) 1997 El sevier Science B.V.