Research On Effective Electro-mechanical Couple Fator Of Sandwich Type Piezoelectric Transducer Using Bending Vibration Mode

The piezoelectric driving device owns advantages like simple and compact instructure, flexible in configuration, response rapidly, high power density,anti-electromagnetic interference and high kinematic accuracy. However, becauseof reasons like the irrationality of piezoelectric transducer structure design andunreasonable placement of PZT, electro-mechanical coupling efficiency iscomparatively low at present. That means a quite part of energy is not transformedinto the vibration energy of the piezoelectric transducer, instead this part of energyact as an inner energy which circulates in the transducer, and eventually turn intothermal losses. Effective electro-mechanical couple factor acts as the representationof electro-mechanical coupling efficiency of a piezoelectric transducer, which is ofhigh value to research on. However, there isn’t yet a theory system which canimprove the effective electro-mechanical couple factor effectively. So it is quitenecessary to research on the analytical model of effective electro-mechanical couplefactor which can improve the electro-mechanical coupling efficiency effectively.Based on the researching background mentioned above, s andwich type piezoelectrictransducer using bending vibration mode is chosen as the research interest.Analytical model of effective electro-mechanical couple factor is studied in thiswork.The sandwich type piezoelectric transducer is simplified as apiezoelectric-metal composite beam. The Timoshenko beam theory and the free-freeboundary condition are used to build the bending vibration model. Resonantfrequencies and bending vibration curves of the piezoelectric-metal compositebeam in first three order bending vibration mode are obtained. FEM model of thetransducer is built, the result of modal analysis is obtaine d in comparison with theresult of the analytical model.Mechanical energy, electric energy and energy of electromechanical couplingare obtained based on the bending vibration model. In corresponding with theenergies obtained in equivalent circuit, the model of effective electro-mechanicalcouple factor can be built. The analytical model is optimized by using simplexreflection technique. The optimized ratio of axial structure parameters of thetransducer in first and second order bending vibration mode is obtained.Owing to the simplification of the analytical model, Two groups of FEMmodels marked as A and B are built. A and B are compared to analytical model andexperimental model respectively. The analytical model is indirectly validated bycomparing with the results of A and B. Experimental model of sandwich type piezoelectric transducer in typicalstructure parameters are made. By testing the bending vibration mode andimpedance characteristics of the piezoelectric transducer, resonant frequencies andrelative impedance parameters are obtained, then effective electro-mechanicalcouple factor can be calculated. In this way, the analytical model is validated.