Calibration of ultrasonic hydrophone probes in the frequency range from 250 kHz to 1 MHz

Calibration of ultrasonic hydrophone probes in the frequency range from 250 kHz to 1 MHz is required to sufficiently assess the peak rarefactional pressure (pr) and the Mechanical Index (MI) of medical ultrasound imaging devices. However, the ultrasonic hydrophone calibration in this low frequency is barely conducted. Therefore, the objective of this research was to develop a calibration technique for ultrasonic hydrophone probes in the frequency range from 250 kHz to 1 MHz. Two ultrasonic hydrophone probes, one membrane hydrophone and one needle hydrophone, were calibrated using a substitution method combined with time-delay spectrometry (TDS). The calibration results are presented in term of end-of-cable voltage sensitivity as a function of frequency. The calibration data show that the membrane hydrophone exhibit a very flat frequency response, to within ±1 dB for the entire investigated frequency range, whereas the needle hydrophone demonstrates a relative large variations in sensitivity of about 5 dB. These results are in good agreement with the limited data previously reported. Therefore, the substitution calibration technique with Time Delay Spectrometry (TDS) is capable of calibrating the ultrasonic hydrophone probes in the frequency range from 250 kHz to 1 MHz.