압전배면체를 이용한 초음파 트랜스듀서의 대역폭 제어

Abstract

A study on the broadband characteristics of ultrasonic transducers has been reported by many researchers. Many of these studies have used the sound absorption and scattering effects by the backing layer attached to the back surface of the piezoelectric vibrator. These methods, which control the impedance and scattering effect of the backing layer with mixing the thermosetting resin and the metal particles, are required to be thick enough for the sound absorption effect. However, these methods are not suitable for the transducers needing thin thickness, such as insertion type ultrasonic diagnosis probes for human body. In this study, we propose a transducer with thin thickness and broadband characteristics using piezoelectric backing layer. The mechanical energy generated from the driving piezoelectric vibrator can be converted into the electrical energy by the direct piezoelectric effect in the piezoelectric backing layer and consumed and controlled by the electrical impedance connected to the electrical terminals of the piezoelectric backing layer. In order to obtain the theoretical analysis method, a calculation method with the equivalent circuit was derived for the analysis of the input admittance and the transfer function of the transducer. As a result of the theoretical analysis of the effect of the electrical impedance connected to the electrical terminals of the piezoelectric backing layer, it was confirmed that the range of the mechanical characteristic change was the largest when the electrical impedance was inductance. The ultrasonic transducer fabricated on the basis of the theoretical analysis results has the thickness about three times as large as the driving piezoelectric vibrator. From the results of the input admittance characteristics, the frequency of the fundamental resonance mode was changed in range of 59%. In order to determine the optimum external impedance to be connected to the electrical terminals of piezoelectric backing layer, the optimum impedance range was obtained based on the optimization by the theoretical analysis. It was confirmed that the –6 dB bandwidth of the fabricated transducer could be widened to about 55% by applying the optimized impedance. The suggested ultrasonic transducer with piezoelectric backing layer in this study could be expected to be applicable not only in the field of medical diagnosis but also in many ultrasonic industries such as nondestructive testing and underwater wireless communication system.