Study of coupling fluids for the microacoustic characterization of high velocity materials

摘要

Mechanical characterization of materials using acoustic microscopy requires acquisition of acoustic signatures. These signatures or V(z) are not only characteristic of the investigated materials but are also influenced by the use of appropriate coupling fluids. The aim of this work is to demonstrate the modifications of the acoustic signatures recorded at 570 MHz and the deduced FFT curves versus the concentration of a series of coupling liquids. These liquids, chosen according to their acoustic properties, are aqueous solutions of potassium hydroxide KOH. Acoustic microechography and acoustic microscopy were used to determine absorption and velocity of these electrolyte solutions as a function of their concentration in a large range (0-19M). The theoretical approach of the electrolyte/sample system enlightens on the part of the density of the coupling fluid. The experimental study was carried out on three materials chosen according to their acoustic waves velocities: steel, glass and silicon. The peaks appearing in the curves deduced by FFT treatment from the experimental acoustic signatures are assigned by comparison with theoretical models. The longitudinal mode velocity of steel and the Rayleigh mode velocity of silicon which lie in the range 5500-7500 mis can be measured using high concentrated solutions. The evolution of the shape of the curves as a function of the solutions concentration confirms that the increase in density of the coupling fluids improves the radiation of the surface waves in the liquid. [References: 14]