1Toin University of Yokohama·Research Fellow of Japan Society for the Promotion of Science, 2Honda Electronics Company Limited, 3National Institute of Advanced Industrial Science and Technology, 4Tokyo Institute of Technology, 5Toin University of Yokohama
hydrophone, hydrothermally synthesized lead zirconate titanate (PZT) polycrystalline film, Ti front plate, backing material, high-intensity ultrasound
Recently, a number of diagnosis and treatment methods employing high-intensity ultrasound have been developed and used clinically. However, it is important from the standpoint of protecting human tissue and the standpoint of effective utilization of high-intensity ultrasound to accurately measure sound field, sound pressure, and acoustic intensity. Thus, we have been developing an anti-cavitation hydrophone that can withstand measurement in a high-intensity ultrasound field with inertial acoustic cavitation by deposition of a hydrothermally synthesized lead zirconate titanate (PZT) poly-crystalline film on the reverse side of the titanium front plate. However, our conventional anti-cavitation hydrophone with low specific acoustic impedance backing had limitations, i.e., the receiving sensitivity decreased with an increase in frequency, and it could not describe the actual ultrasound waveform with high fidelity. Therefore, we considered improving the frequency characteristics of the receiving sensitivity by performing numerical simulations based on the Mason’s equivalent circuit model and one-dimensional acoustic transmission line model. It was found that flat frequency characteristics of the receiving sensitivity could be obtained by using a backing with about 20 MRayl specific acoustic impedance. We then developed a new anti-cavitation hydrophone using a backing with about 20 MRayl specific acoustic impedance based on the simulated results. The decrease in receiving sensitivity in the high-frequency range could be suppressed in our newly fabricated anti-cavitation hydrophone. Furthermore, durability tests of each hydrophone under ultrasound exposure were performed in a water tank containing ultrasound cleaner with generation of inertial acoustic cavitation. It was found that our new anti-cavitation hydrophone had a 10-fold longer lifetime as compared with a commercial needle-type hydrophone.