Improved ultrasonic interferometer technique for propagation velocity and attenuation measurement in liquids

Propagation velocity and attenuation are the two basic parameters used for the ultrasonic investigations of liquids. An ultrasonic interferometer is a widely used tool as a cost effective solution for propagation velocity measurement. The ultrasonic attenuation measurements are not possible using the existing interferometers commercially available in the market. Ultrasonic attenuation can be measured using the pulse echo method, which is relatively complex and expensive. Generally, in interferometers, a radio frequency voltage of more than 100 V is used to excite the piezoelectric transducer. In this article, an improved design of the ultrasonic interferometer with low (5 V) rf voltage excitation is discussed. The proposed design has several advantages over existing systems. The low voltage excitation reduces heating of the sample under study. Detection of the received signal is done directly at the transducer. The critical effects of a coaxial cable in rf detection are minimized by dc detection at the transducer node. The impedance response of the transducer is used for the detection of nodes and antinodes for attenuation and velocity measurements. The use of an instrumentation amplifier enables one to amplify the extremely small voltage changes across the transducer due to interference. The developed method has the capability to measure attenuation due to high receiver sensitivity. The technique has been validated for the propagation velocity and attenuation measurement in standard samples of water and other liquids. The results thus obtained have been compared with the literature and the conventional pulse echo technique which shows close agreement.