Interferometric Measurement Method of Ultrasonic Attenuation in Small Liquid Samples

Abstract

A description and validation of a system to measure ultra- sound attenuation in small samples of biological liquids using a contin- uous wave method is presented. It has been coupled to an existing velocity measurement apparatus. A two-transducer interferometric method is used. The specimen under study is placed in a triangular shaped prismatic sample holder immersed in a reference liquid. The sample holder is moved perpendicular to the ultrasonic beam in order that the acoustic path length m the sample varies. The transmitted and received signals are cross-correlated using an analog correlator com- posed of a mixer followed by a low-pass filter. The output of the correlator is plotted on an X- Y recorder while the sample holder moves across the acoustic beam. A modeling of the system has been achieved so that the attenuation coefficient can be computed numeri- cally from the data read on the recorded curves. In order to validate the method, experiments have been made with two test-liquids: Dow Corning no. 7 10 silicone oil and castor oil. The results are in good agreement with the literature. The reproducibility of the method (about 10 percent) is good in view of the small dimensions of the sample (8 cm3) and the limitations in the performance of the mixer in the high-frequency range.