Study On Sandwiched Piezoelectric Ultrasonic Transducers Of Radial And Radial-Torsional Compound Vibration Mode

The sandwiched piezoelectric ultrasonic transducers are widely used in the fields of high power ultrasonic applications, such as ultrasonic welding, ultrasonic cleaning, ultrasonic cutting and ultrasonic motor, etc. So the design of this kind of transducer is the kernel part of high power ultrasonics. The advantages of sandwiched transducers are high power and high energy conversion efficiency, and their resonance frequency can be varied by means of changing the dimensions of the back and front metal block of the transducers as well. At present, traditional sandwiched piezoelectric ultrasonic transducers mainly include longitudinal, torsional and flexural vibration mode sandwiched transducers as well as the composite vibration modes of them, such as longitudinal-torsional and longitudinal-flexural mode sandwiched transducers, etc. However, with the development of ultrasonic technologies, the applications of high power ultrasonics become wider and wider, various vibration mode ultrasonic transducers are needed, so as to satisfy the different fields of ultrasonic applications.Based on the principle of sandwiched piezoelectric ultrasonic transducers, a new type of radial vibration mode sandwiched piezoelectric ultrasonic transducer is first presented and studied systematically in this paper. The equivalent circuit of this kind of transducer is established and the frequency equation is derived. At the same time, the radial vibration mode shapes of the transducer are analyzed by using Finite Element Method (abbreviation: FEM) and verified by experiments. Furthermore, a new type of radial-torsional composite transducer is studied. Also, its equivalent circuit and frequency equation are derived. As a living application of this kind of piezoelectric ultrasonic transducer we presented, it was practiced in ultrasonic motor and then, a new kind of radial-torsional conversion mode ultrasonic motor is made.In detail, the context includes several parts:(1) The fundamental and the first overtone frequency of annular and solid piezoelectric ceramic disc are further studied, and the vibration mode shapes of them are analyzed by using FEM. The relationship between the ratio of inside and outside radius of annular piezoelectric ceramic disc and the ratio of the first radial overtone frequencyof the same size annular and solid piezoelectric ceramic disc is discussed. It is shown that if the ratio of inside and outside radius of an annular piezoelectric disc tends to one, the firstr radial overtone and the higher order frequency of it will tend to infinite. For this reason, it could explain why the thin piezoelectric ring has no higher order radial resonance frequency, and the conclusion is also suitable for non-piezoelectric annular disc.(2) The equivalent circuits of radial and tensional vibration modes of annular disc whose thickness varies along the radial direction uniformly, taperly and exponentially are established and the frequency equations are derived. The formulae of radial and angular displacement distribution along the radial direction and the ratio of amplitude of the annular disc are given. We also probed into, for different Poisson's ratio, the relationship between the first order roots of frequency equations of radial and torsional vibration modes of a circular resonator and the ratio of inside and outside radius of the annular disc. Therefore, it will be much more convenient for the engineering design of a ring resonator.(3) We also established the equivalent circuit of the radial vibration sandwiched piezoelectric ultrasonic transducer that is compounded of an annular metal block and piezoelectric ceramic disc that is polarized in the thickness direction. The nodal circular lines of radial displacement of the transducer are analyzed, and the radial displacement distribution diagrams of the first, the second and the third order radial vibration mode of the transducer which is compounded of steel and PZT-4 disc, aluminum and PZT-4 disc respectively are given. Furthermore, the equivalent electromechanical parameters and the effective electromechanical couple coefficient K_eff near the radial resonant frequency of the transducers are measured, and the radial fundamental vibration modes of the transducers are simulated by using FEM. It is shown that the theoretical values and the simulated values basically agree with the experimental results.(4) On the bases of radial vibration sandwiched ultrasonic piezoelectric transducer, a new type of radial-torsional composite transducer by slanting slots on its circular metal block is proposed. The equivalent circuit of this kind of transducer is set up and the frequency equation is also derived. At the same time, we probed into the effect of the oblique angle of slanting slots on resonance frequency of the transducer. Experiments show that the theoretical results basically agree with the experimental results. As an application and a verification of this kind of transducer that studied in this...