Research On Electromechanical Coupling Model Of Piezoelectric Ultrasonic Transducer Working At Bending Vibration Mode

The piezoelectric ultrasonic transducer is a new device that developed in thelast century. It could achieve the energy conversion and the motion transmission.By virtue of its unique characteristics, it has caused widespread concern all overthe world. It has been widely used in modern industrial production, aerospace,and people’s daily lives. However, the effective electromechanical couplingfactor of piezoelectric ultrasonic transducer is so low that it is subjected to manyconstraints in practical applications. In other words, there is a large part ofenergy existing in the piezoelectric ceramics in the form of electrical energy. Itcauses that the transducer only uses a small part of energy to be an actuator. So,it greatly restricts the development and application of the piezoelectric ultrasonictransducer. So far, there isn’t detailed study on the effective electromechanicalcoupling factor of piezoelectric ultrasonic transducer home and abroad, and theenergy efficiency and the structural optimization design and of piezoelectricultrasonic transducer can’t be effectively solved. Therefore, a sandwich typepiezoelectric ultrasonic transducer with an exponential variable cross sectionworking in the form of bending vibration mode is chosen to study the effectiveelectromechanical coupling factor in this paper. The structure of piezoelectricultrasonic transducer is optimized on the basis of the study, and then theutilization of energy is fundamentally improved.Firstly, based on knowledge of vibration curriculum and piezoelectriccurriculum, the piezoelectric ultrasonic transducer is simplified as an exponentialvariable cross section piezoelectric-metal composite beam with free-freeboundary condition. The bending vibration model of piezoelectric ultrasonictransducer is solved by means of the Timoshenko beam theory. Then, accurateresonant frequency and vibration curves are obtained. The analytical structure issimulated by the method of finite element modal analysis to verify the bendingvibration model. Secondly, for the bending vibration model of the piezoelectricultrasonic transducer with an exponential variable cross section has been solved,the electromechanical equivalent diagram can be established according topiezoelectric equations and the theory of energy method. Then anelectromechanical coupling model of piezoelectric ultrasonic transducer isproposed in this paper. The effective electromechanical coupling factor could besolved. The harmonic response analysis is adopted to validate theelectromechanical coupling model of piezoelectric ultrasonic transducer. Basedon the above results, when the overall size of the transducer and the dimension of piezoelectric ceramics remain unchanged, the influence of the piezoelectricceramics to effective electromechanical coupling factor is studied by changingthe position of piezoelectric ceramics. The quadratic interpolation method istaken to optimize the structure of the piezoelectric ultrasonic transducer in thisstudy. The more reasonable position of piezoelectric ceramics is obtained, andthen the more reasonable structure of the piezoelectric ultrasonic transducer isfound.According to the analytical model and finite element simulation, therepresentative piezoelectric ultrasonic transducers are fabricated, and vibrationcharacteristics and impedance characteristics are measured with laser Dopplervibrometer and Agilent Precision Impedance Analyzer. The bending vibrationmodel and electromechanical coupling model of piezoelectric ultrasonictransducer, whose structure is the sandwich structure with an exponentialvariable cross section, are verified by comparing the results of experiments withthe results of analytical model and finite element simulation.