Based On The Finite Element Method Coupled Vibration Sandwich Transducer Characteristics And Design Research

Sandwich piezoelectric ultrasonic transducers are widely used in underwater acoustics, ultrasonics and non-destructive inspection. According to traditional design theory of this type of transducer, the vibration of the sandwich transducer is considered as one dimensional with the Poisson effect and the radial vibration being ignored. Therefore, it is required that the lateral dimensions of the transducer must be less than the longitudinal dimension. However, along with the development of ultrasonic technology, ultrasonic transducers are used in more and more new applications, such as high frequency ultrasonic metal and plastic welding and some practical applications concerning very large ultrasonic power. In these cases, the radical dimensions are usually larger than a quarter of a longitudinal wavelength, and the vibration model of this kind of transducer in practice will couple with longitudinal vibration and horizontal vibration, thus the vibration becomes quite complicated, and the influence of horizontal coupled vibration can't be ignored. Therefore, one-dimensional design theory of the sandwich transducers is no longer applicable. Therefore, in the application of large power, the research on the coupled vibration of sandwich transducer with high power has great significance theoretically and practically. Based on the apparent elasticity method, finite element method and experiment validation, this paper will discuss the vibration characteristic and function parameter change of sandwich transducer in different couplings, the main content and conclusion as follow.1. The basic theory of the finite method to model the transducers is studied. As the analyzed transducer configuration was axially symmetric, a 3D analysis was performed by using 2D quadratic elements. The advantage of using 2D model is that it can greatly reduce the amount and time calculated by computer. Meanwhile, it can also filtrate the modes of the flexural vibration and torsional vibration, so we can easily find the longitudinal vibration model from all the computed models. This provides convenience for the analysis.2. By using two methods--increasing the radical dimension of the transducer while itslongitudinal dimension remains constant and decreasing the longitudinal dimension of the transducer while its radical dimension remains constant, we can gradually change the coupling vibration of the transducer and characterize the coupling vibration behaviors, and some conclusions are as follows:1). Increasing the radical dimension of the transducer while its longitudinal dimension remains constant:a. The first three resonance frequencies of the transducer decrease with it's radial dimension increasing.b. With the transducer's radial dimension increasing, the effective electromechanical coupling factor(K_eff1) increased in the beginning and decreased in the last, and reached its maximum while the radial dimension was close to the longitudinal dimension.c. With the transducer's radial dimension increasing, the coupled vibration between the longitudinal and radical intensified, and for the dimensions of the transducer is constant, the coupled vibration intensifies with the resonance frequency increasing.d. With the transducer's radial dimension increasing, while the transducer vibrated in its second or third resonance frequency, the axial displacement of the transducer presents a node at the end surface.2). Decreasing the longitudinal dimension of the transducer while its radical dimension remains constant:a. The first three resonance frequencies of the transducer increase with it's longitudinal dimension decreasing.b. With the transducer's longitudinal dimension increasing, the displacement amplitude of the transducer at its end surface is not identical, the radical displacement amplitude increases and the coupled vibration between the longitudinal and radical increases.c. The effective electromechanical coupling factor( K_eff1 ) increased in the beginning and decreased in the last, and reached its maximum while the radial dimension was close to the longitudinal dimension.d. The dynamic capacitance (C₁) increased in the beginning and decreased in the last, and reached its maximum while the radial dimension was close to the longitudinal dimension. The dynamic inductance (L₁) decreased in all the variable range of the longitudinal dimension.3). The trait that position of the piezoceramic disks influences the performance parameters of the transducer is investigated, When the lateral dimension of the transducer is more than a quarter of the wavelength, and some conclusions are obtained.a. While the design frequency remains constant, the resonance frequency of transducer has no relation with the change of position of piezoceramic disks, the anti-resonance frequency of the transducer decreases while the piezoceramic disks are far away from the displacement node of the transducer.b. As the piezoceramic disks are far from the displacement node of the transducer, the effective electromechanical coupling factor (K_eff) decreases gradually, and when the piezoceramic disks are in the middle of the transducer, the value of K_eff is the most.c. With the distance between the piezoceramic disks and the displacement node of the transducer increasing, the static capacitance (C₀) has a little increase; the dynamic resistance(R₁) and the dynamic inductance (L₁) increase; but the dynamic capacitance (C₁) decreases gradually.By using the finite element software ANSYS, this paper systematically research the traits of the coupling vibration in different coupling cases, applying ANSYS's powerful general postprocession to obtain the change rule of parameter function under different coupling cases, using the displaying function of ANSYS's vivid animation to observe the vibration performance in different coupling cases, thus we can profoundly study and know the vibration features on different occasions. All the results would be useful and helpful for the transducer's design and its matching electro circuit's design.