  A modified conventional three-transducer reciprocity calibration method is
used to measure the magnitude and phase responses of the transmitting voltage
response and the free-field open-circuit receiving voltage sensitivity of
ultrasonic piezoelectric transducers radiating in air at 1 atm. The transducers
used in this work are 20 x 2 mm circular piezoelectric ceramic disks with their
first and second radial modes at approximately 100 and 250 kHz, respectively.
The transducer characterization is supported and aided by finite element
simulations of the measurement system and the measured frequency responses.
Preliminary results indicate that the magnitude and phase responses of the
transmitting voltage response and the free-field open-circuit receiving voltage
sensitivity can be measured with fair accuracy in a limited frequency band
around the first radial mode of the piezoelectric ceramic disk. Further work is
needed to demonstrate and quantify the accuracy actually obtained using the
three-transducer reciprocity calibration method, to achieve transducer
characterization at a calibration accuracy level, and to achieve calibration
above the calibrated frequency range of the B&K 4138 microphone.
