Research On Radial Sandwich Piezoelectric Ultrasonic Transducer

Ultrasonic transducer can radiate high-intensity acoustic energy into medium in many applications, such as ultrasonic cleaning, ultrasonic treatment etc al. Sandwich piezoelectric ceramic transducer of longitudinal vibration is widely used in power ultrasound field for having some characteristics, such as simple structure, high electromechanical coupling factor, high thermoelectric conversion efficiency and optimal design. Meanwhile, this kind of transducer has three shortcomings. Its radiation surface is limited for its transversal size being smaller than the one-fourth wavelength of radiating acoustic wave.It can’t radiate acoustic energy to three-dimension space for its radiating energy propagating only along the longitudinal axis of transducer. It can’t satisfy the requirement of some specific application for it just resonating on its own unique natural frequency.A new kind of transducer is introduced in this paper in order to conquer shortcomings of traditional transducer. The new transducer is composed of circular caramics tube of radial polarization, inner circular metallic tube, and outer circular metallic tube. The new transducer has the advantages of simple structure. Meanwhile, it presents many new charateristics in some new power ultrsound fields. The appearing of this transducer has important theoretical significance and practical application value for the development of new ultrasonic technique and application field.In this paper, the main work includes as follows:(1) Metallic tube is one of the important components of the transducer. The radial vibration of metallic tude is researched. Based on the relationship of lenghth of metallic tube and its radius, three cases are considered:thin metallic disk or ring whose longitudinal length is far smaller than its radius, long metallic tube whose longitudinal length is far larger than its radius, and metallic circular cylinder or circular tube whose ratio of longitudinal length and its radius is close to 1.The electro-mechanical equivalent circuit of the metallic thin disk or ring is researched according to the theory of plane stress, and the frequency equation of radial vibration is obtained. Based on the frequency equation, the effects of the radial size of the disc or ring and Poisson ratio on the resonant frequency are explored. At the same time, the radial vibration is simulated by ANSYS software. The simulation results are matched with the theoretical ones.The electro-mechanical equivalent circuit of the metallic long tube is researched according to the theory of plane strain, and the frequency equation of radial vibration is obtained. Furthermore, the relationship of the tube size and resonance frequency is presented. The radial vibration of long tube is simulated by ANSYS software. The two results match each other, and the results of simulation show that the long metallic tube of thin wall can radiate high-intensity ultrasound along the radial direction of transducer.Using the apparent elastic theory, the large solid (and hollow) metallic cylinder which has the equivalent lateral size and the ones of longitudinal is analyzed through adopting equivalent method, in which its coupled motion can be equivalent to two one-dimension vibrations which interact each other by electro-mechanical coefficient. The results show that the electro-mechanical equivalent circuit of coupled vibrations for large metallic cylinder can be considered as two vibrating equivalent circuit, which are longitudinal vibration circuit of slim rod and the radial vibration circuit of thin disc (or ring). The frequency equations of two vibrating equivalent circuit are obtained respectively. Meanwhile, the conditions of generating high-intensity coupled vibration are obtained. The comparable analysis by ANSYS gives the similar conclusion.(2)The circular ceramic tube of radial polarization is the driving unit for the radial sandwich ultrasonic transducer, whose radial vibration is researched. According to the relationship of longitudinal and radial sizes, three kinds of piezoelectric tube are analyzed respectively. They are the short piezoelectric tube, long piezoelectric tube, and piezoelectric tube circular tube whose ratio of longitudinal length and its radius is close to 1.The electro-mechanical equivalent circuit of the short radial polarized tube is deduced according to the theory of plane stress, and the resonance and anti-resonance frequency equations are obtained. Based on the frequency equations, the effects of geometry size on resonance frequency, anti-resonance frequency and effective electromechanical coupling coefficient are presented. Compared to the simulation of ANSYS, the conclusions match theoretically and numerically, which proves that the theory related to the motion of the radial polarized tube is correct.Similarly, the radial vibration of long piezoelectric ceramic tube is deduced based on the theory of plane strain, and the electro-mechanical equivalent circuit, resonance and anti-resonance frequency equations are obtained. The expressions of resonance (anti-resonance) frequency and effective electro-mechanical coupling coefficient are given as functions of geometry size of the tube. The simulation by use of ANSYS gives the same prediction of results as that of our theory.Using the apparent elastic theory, the large piezoelectric tube which has the equivalent lateral size and the ones of longitudinal is analyzed through adopting equivalent method, and the equivalent circuit and frequency equation are obtained. The vibration properties are simulated by finite element method. The numerical results are in agreement with the experimental results.(3)In this paper a new type of transducer, radial sandwich transducer, is proposed. Based on the relationship of the longitudinal and lateral tube sizes, we designed three different radial sandwich transducers, such as short tube, long tube, and radial coupled vibrations tube.After the all components of the transducer are connected along their radial direction, the electro-mechanical equivalent circuits are obtained. Furthermore, the resonance and anti-resonance frequency equations are deduced, and the effects of geometry size of transducers on the resonance frequency, anti-resonance frequency and effective electro-mechanical coupling coefficient are analyzed. Based on our design, three kinds of radial sandwich transducers are manufactured. The experimental results are in agreement with theoretical and numerical results for these transducers. The ultrasound fields radiated by these transducers are simulated in water. The results show that the short and long tube transducers can radiate acoustic wave along the radial direction, and the radiating acoustic energy can focus in the inner region of the transducer. The transducer which has the equivalent lateral size and the ones of longitudinal can radiate acoustic waves along the radial direction and longitudinal direction. Moreover, this transducer has widely frequency bandwidth. So these kinds of transducer can be used in many fields, such as ultrasonic treating, sonochemistry, and ultrasonic extraction etc al.