Thermal Methods For Low Level Ultrasonic Energy Measurement

Bruce A. Herman; Harold F. Stewart; Ronald A. Robinson; George Zieniuk

doi:10.1117/12.965441

23 December 1976 Thermal Methods for Low Level Ultrasonic Energy Measurement

Bruce A. Herman, Harold F. Stewart, Ronald A. Robinson, George Zieniuk

Proceedings Volume 0096, Application of Optical Instrumentation in Medicine V; (1976) https://doi.org/10.1117/12.965441
Event: Application of Optical Instrumentation in Medicine V, 1976, Washington, D.C., United States

Abstract

Two thermal methods capable of determining time averaged, total radiated ultrasonic power at diagnostic levels are described. The first, a portable instrument, utilizes a parabolic reflector to focus the ultrasonic beam onto a thin film thermistor sensing element mounted on sound absorbing rubber. The sensor's temperature rise alters its resistance, which is monitored with a simple bridge circuit. Maximum sensitivity of the device is 0.1 mW and beams up to 19 mm diameter can be accomodated. Calibration was performed using 1 MHz, 2.25 MHz, 3.5 MHz, 5 MHz and 10 MHz resonant transducers. The second device, a twin, series flow, ultrasonic comparator, is a primary measurement laboratory system. Ultrasound is absorbed by a series of rubber wafers within a vessel and is compared with measured dc electrical power dissipated in a second, identical vessel. The heat produced within the vessels is carried to twin, resistance thermometer temperature sensors by an inert perfluorinated liquid, within a closed circuit. In automatic mode the bridge is coupled to a feedback circuit which applies electrical power to regain bridge balance. Unwanted heat produced within the transducer being tested is carried away by a flow of water between the transducer and absorbing vessel. This instrument can measure power from 0.2 MW to 10 W and can accomodate transducers resonant at 1 to 15 MHz and up to 26 mm in diameter.

Citation Download Citation

Bruce A. Herman, Harold F. Stewart, Ronald A. Robinson, and George Zieniuk "Thermal Methods for Low Level Ultrasonic Energy Measurement", Proc. SPIE 0096, Application of Optical Instrumentation in Medicine V, (23 December 1976); https://doi.org/10.1117/12.965441

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