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Reciprocity calibration of ultrasonic transducers

Reciprocity calibration of ultrasonic transducers

(OP)
Hi

I need to calibrate my ultrasonic microphones (used on bat detectors). I had the thought that the small, inexpensive ultrasonic ceramic transducers produced by Kobitone or Prowave might be a means to do this by reciprocity calibration. Then, once calibrated, the ceramic transducers could be used as calibrated microphones to compare with my bat detector microphones.

On the surface these transducers seem ideal, they are inexpensive and fairly sensitive (~ -56 dB in volt/microbar dyne/cm world) and can function as both receivers and transmitters. On the downside the bandwidth is very poor (only about 1-2 kHz).

When I did the reciprocity calibration I got sensitivities of about -48 to -49 dB for several transducers. The datasheets from Prowave indicate expected sensitivity of about -54 for these transducers. The difference in my results and theirs is too big for comfort. Part of the problem may be that I am using open circuit voltage (for reciprocity calibration) and Prowave may be using an impedance of 4 kohms (perhaps trying to be helpful for real world applications of hardware). That difference would narrow the gap between sensitivities.

So are the ultrasonic ceramic transducers good candidates for reciprocal calibration or not? Anybody with some experience in this area? Anybody every calibrate these mics by either reciprocity method or calibrated microphones?

Thanks
Clemen2

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