Reciprocity calibration method for ultrasonic piezoelectric transducers in air
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The conventional three-transducer reciprocity calibration method for use in gas at ambient pressure and temperature is studied. Modifications are introduced, introducing correction factors for absorption in air, diffraction effects, and receiving and transmitting electronics. The use of voltage and impedance measurements instead of current measurements are also included in the modifications. The frequency range studied is 50 kHz to 300 kHz, with emphasis on the frequencies around 100 kHz. Measurements have been performed on piezoelectric ceramic disks of the material Pz27 and in-house constructed piezoelectric transducers, yielding the magnitude of the transmitting voltage responses and free-field open-circuit receiving voltage sensitivities. Results are compared to measurements conducted with calibrated condenser microphones from Brüel & Kjær and to FE simulations in FEMP 5.0. The effects of the correction factors are studied.