Characterization of hydrophone with hydrothermal PZT thick film vibrator and Ti front layer for measurement in high intensity therapeutic ultrasound

Acoustic characterization of high intensity therapeutic ultrasound (HITU) field is important for the accurate prediction of ultrasound induced bioeffects in tissue. In this paper, the robust designed needle type hydrophones were fabricated by the titanium front plate to withstand cavitation and by the deposition of a hydrothermally synthesized lead zirconate titanate (PZT) thick film vibrator on the opposite surface of titanium plate. Direct measurements of acoustic distribution profile at a focal region of the HITU probe driven continuous wave (CW) with input power to the sound source up to 50 W were performed. The tough hydrophone sensitivity responding to CW driven power range up to 50 W was measured in a tank of degassed water. The sensitivity was responding linearly up to about 8 MPa and not responding linearly acoustic pressure higher than 8 MPa, while the velocity of the vibration at the HITU probe was responding linearly up to driven power of 50 W. This 8 MPa was estimated in comparison with the standard hydrophone at driven power of 1 W to the sound source. We confirmed the linearity of responsivity of our hydrophone at high acoustic pressure. However, sensitivity of this hydrophone should be calibrated with higher acoustic pressure for higher acoustic power measurements. It is necessary to enable accurate characterization of HITU fields.