ULTRASONIC COUPLANTS FOR ACOUSTIC MICROSCOPY OF LOW-SPEED MATERIALS

A method is presented for estimating the compression wave velocities o f organic fluids, based only on their density and molecular properties . The method is applied to a search for very low-speed ultrasonic coup lants, suitable for 250 MHz acoustic microscopy studies of epoxy mater ials. Experimental measurements confirmed that acoustic velocity could be predicted within 3% for simple fluorine-containing organic compoun ds, and within 10% for those with a more complex molecular structure. The compound 2-dichloropentafluoropropane (C3HCl2F5), with a compressi on wave velocity of C-L = 638 m/s and acceptably low attenuation coeff icient, was identified as a good coupling agent for acoustic microscop y studies of low speed materials.