High frequency and high intensity ultrasonic transducers for medical applications using oriented piezoelectric thick films by hydrothermal method

Recently, high-frequency ultrasonic transducers are proposed for medical applications using piezoelectric crystal. In this case, it is known that the high piezoelectric constant and the higher limitation of vibration velocity are important for high power application. Normally, the piezoelectric ceramics has limitation due to maximum vibration velocity. Thus it is very difficult to radiate for high intensity ultrasound with nonlinear acoustics due to the limitation of maximum vibration velocity. Therefore, we tried to develop a very high intensity and high frequency ultrasonic transducer using hydrothermal KNbO3 thick film. The piezoelectric constant was over 80 pm/V and the vibration velocity of thickness mode of KNbO3 thick film was 2.5 m/s or over at 20 MHz. This maximum vibration velocity is twice of reported piezoelectric materials. Then, a radiation sound-pressure from the prototype ultrasonic transducer with KNbO3 thick film was measured. The result of radiation ultrasound was 4 MPa or over in a water. It is very high intensity at high frequency. Consequently the hydrothermal KNbO3 thick film is usefulness for medical applications. The reason for why it is able to radiate for high intensity ultrasound at high frequency will be discussed in this presentation.