This paper describes the operation of two types of thermoacoustic sensors suitable for determining the absolute ultrasonic power in the MHz frequency range. The most essential component of both types, the single-layer and two-layer sensor, is an ultrasound-absorbing plate which transforms the incident ultrasonic energy into heat. In order to be able to estimate the uncertainty of measurement, the experimental results were compared with reciprocity measurements. The good agreement obtained confirms the suitability of the thermoacoustic procedure for determining the absolute value of ultrasonic power and calibrating ultrasonic transducers.
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