Study Of The Coupling Vibration Characteristics On Piezoelectric Composites Transducer

The piezoelectric compound transducer which has the piezoelectric composite materials as the energy conversion materials is a device that can achieve energy conversion between sound energy and electricity energy. It has been an core part of the ultrasonic non-detective system. The ultrasonic non-destructive testing system need transducer with wide frequency band, high efficiency, high sensitivity, etc. characteristics in order to improve its performance of sensitivity,accuracy and reliability. The piezoelectric composite transducer can produce two kinds of vibration that are the longitudinal vibration of the transducer itself and flexural vibration caused by front cover in the process of practical work. Utilizing coupling between the two kinds of vibration modes mentioned previously to expand the working frequency band of transducer, by changing structure geometry size and material type of the transducer.In this article, the comprehensive review on piezoelectric composite, piezoelectric transducer and the theory of expanding the working band of frequency of transducer were firstly introduced. Then, the finite element method(FEM) for investigation of transducer was introduced. Finally, the finite element model of 1-3 piezoelectric compound transducer was established, and the relationships between the coupling vibration characteristics and its structure geometry size and material type were analyzed. The main contents and results are as following:(1) The effect of volume fraction on the coupling vibration characteristics of transducer were studied. The FEM model of 1-3 piezoelectric compound transducer was established and analyzed, through the FEM analysis, the results showed that the first two vibrating modes are longitudinal vibrating and flexural vibrating. In X, Y, Z three polarization direction, the resonance frequencies of the transducer is minimal when the piezoelectric are 60%, 40% and 30% the resonance frequencies of the transducer of the minimum value difference, and the minimum is the smallest under Z polarization direction.With the increases, the resonant frequencies become smaller, the resonance frequency is falling rapidly when volume fraction of piezoelectric ceramic is large.(2) The effect of the longitudinal size of piezoelectric composites and polymer type on the coupling vibration characteristics of transducer were studied. The model of transducer on the longitudinal size of piezoelectric composites and polymer type was established and analyzed, the results showed that the vibration modal of transducer with different sizes of piezoelectric composite materials and polymer type is different,with the Young's modulus increases, the difference of resonant frequencies become larger,The difference of resonant frequencies become smaller when the Poisson's ratio increases.But,with the longitudinal size of piezoelectric composites increases, the difference of resonant frequencies become larger.(3) The effect of the structure geometry size and material type of electrode slice on the coupling vibration characteristics of transducer were studied. The model of transducer on electrode slice was established and analyzed, the results showed that the vibration modal of transducer with different material type of electrode slice is different,with the Poisson's ratio and the thickness of electrode slice increases, the difference of resonant frequencies become larger,When the thickness and radius of electrodes were 0.2 mm and 5 mm,the difference of resonant frequencies is minimum, the value of 1.5 KHz.All in all, through the above research, the relationships between the coupling vibration characteristics of piezoelectric compound transducer and the structure and the material type of transducer are obtained. The results offer useful guidelines to the design and application of wideband piezoelectric compound transducer used in ultrasonic nondestructive fields.