Study On Adaptive Matching System Of Piezoelectric Ultrasonic Transducer

With extensive use of high-power piezoelectric ultrasonic transducers in different fields,its driving efficiency has become a crucial aspect.Load changing or temperature rising of high power piezoelectric transducer,would lead to the change of impedance and drift of frequency of piezoelectric ultrasonic transducer,then reduce efficiency of static impedance matching or even make it failure totally.Although dynamic impedance matching can solve the problem that the parameters of piezoelectric ultrasonic transducer change in the working process,but it still has different problems such as low efficiency and poor accuracy of matching.According to the above problems,this paper has put forward the adaptive matching method for piezoelectric ultrasonic transducer by optimizing the existing dynamic matching scheme and pointing out that thermal power consumption of the piezoelectric transducer continues to affect its electrical properties and it needs reasonable heat dissipation for reducing the influence on the driving system caused by temperature rising of piezoelectric ultrasonic transducer.First of all,dynamic inductance capacitance matching circuit in which electronic components are switched by controling the relays has been chosen after analyzing different kinds of matching circuits according to the principle of impedance matching.The permissible error for values of components in the matching circuit is±10%and the resolution of frequency of excitation signal should be less than 10 Hz through analyzing the simulation on driving system of piezoelectric transducer with MATLAB,besides the experiment on each equivalent parameters of piezoelectric transducer influenced by temperature and load has been done respectively,the results showed that the driving efficiency of piezoelectric transducer would be decreased when its temperature is greater than 50℃or pressure is greater than 1.77×10~4 N/m~2.Then the static temperature field distribution of piezoelectric transducer was analyzed by ANSYS,and semiconductor refrigeration was selected as the method for heat dissipation after comparing with other methods.Finally an adaptive matching system based on FPGA is designed according to the previous analysis and experiments,which mainly includes DDS module,impedance detection,temperature control,dynamic matching circuit,upper monitor and so on.After testing the system,the results shows that the average error of frequency generated by DDS module is less than 10 Hz,when the transducer was driven in a large signal,the measurement errors for impedance modulus and impedance angle are within±10%,the result of dynamic matching is good,the temperature can be controlled at about 50℃,its error is less than 3℃.