Continuous Wave Ultrasonic Interferometers with Relatively Higher Excitation are Inappropriate for Liquid Characterization

Ultrasonic velocity is an important property for various physicochemical investigations in the liquids. The continuous wave ultrasonic interferometers are widely used as a cost-effective instrument for the estimation of ultrasonic propagation velocity. One of the critical aspects of this instrument is the level of radio frequency excitation supplied to piezoelectric transducer, which can cause heating of the sample. The error in the ultrasonic velocity measurement due to heating by the ultrasonic interferometer is described. In this article, the distilled water was used as experimental liquid to study the heating effect. Firstly, the ultrasonic transducer has been used to generate ultrasound in the sample and was calibrated for its radiation conductance by using primary radiation force balance facility of the laboratory. Primary calibration of the ultrasonic transducer in a commercially available system used in the liquid cell showed 68 mW power for excitation level. In a laboratory interferometer designed for low-power operation in the same test cell, the measured power was only 85 µW. In order to study the heating effect, the ultrasonic velocity was measured with both the systems without controlling the temperature of liquid cell. The measurements by commercial system showed significant deviation (5.6 ms −1 ) in ultrasonic velocity as compared to that measured under low power excitation, which remains almost undeviated. The Marczak equation was used to calculate the deviation in velocity due to ultrasound heating.