Simulation And Experimentation Research On The Transient Characteristic Of Longitudinal Wave Piezoelectric Sensor

Piezoelectric sensor is based on the piezoelectric effect of piezoelectric materials, and it can achieve the conversion between sound energy and electricity energy. Because of ultrasonic piezoelectric sensor works in the transient state, the transient performance of piezoelectric sensor is an important part in the ultrasonic testing.In this paper, the comprehensive review on the research status and the basic transient performances theory of piezoelectric sensor were firstly presented. Then, through finite element method, many configurations were simulated by changing the damping structure size and acoustic impedance of the piezoelectric sensor. Finally, the simulation results were validated, and the experiment results showed that the trend of the resolution and sensitivity curve has good agreement with the simulation results. The main contents and results as follows:(1) From the electromechanical coupling finite element simulation method, the influencers of various thickness and diameter of backing on the resolution and sensitivity of sensor were studied. It was found that the resolution increases with the thickness of backing in the early part, followed by a region reducing down ultimately to a steady value. The resolution increases with the backing diameter, and then decreased. The larger the diameter, the smaller influence of backing thickness on the resolution of sensor. The sensitivity decreases when the backing becomes thick. For the same thickness, the sensitivity is higher at smaller backing diameter. The results show that with the increase of the thickness and diameter of backing, the detection resolution can be improves, but the sensitivity will be reduced.(2) By using the electromechanical coupling finite element simulation, the resolution and sensitivity of sensor under different acoustic impedance of backing parameter was studied. The result indicated that the resolution increases with the acoustic impedance, and the optimum resolution of sensor was obtained when the acoustic impedance ranges from 30 to 35MRayl. The sensitivity of sensor decreases with the increasing acoustic impedance. It can be seen that we should choose the low acoustic impedance of backing materials in order to ensure the good sensitivity when the resolution of the sensor is guaranteed(3) Through the electromechanical coupling finite element simulation, the influencers of various thickness and diameter of filled epoxy resin on the resolution and sensitivity of sensor were studied. The results showed that the filled epoxy resin can improve the resolution of sensor further. The resolution increases with the thickness and diameter of epoxy resin in the early part, followed by a region reducing down ultimately to a steady value. The larger epoxy resin diameter used, the higher resolution obtained. The sensitivity of sensor decreases with the increasing thickness of filled epoxy resin. For the same thickness, the sensitivity is higher at smaller backing diameter. It is apparent that choosing proper geometry size of epoxy resin can improve the performance of the transducer.(4) According the geometry size in the stimulation, we manufactured the components and assembled the piezoelectric sensor. The resolution and sensitivity of sensor were validated by DB16 ultrasonic testing device. The experiment results showed that the trend of the resolution and sensitivity curve has the good agreement with the simulation results.In a word, through the above research, the relation curves about the size and material property of the sensor damping structure versus the sensitivity and resolution were obtained. The results may offer useful guidelines to design the high-performance piezoelectric sensor used in ultrasonic non-destructive fields.