What is the working principle of ultrasonic piezoelectric ceramics?
The principle of piezoelectric ceramic sheet: When pressure or tension is applied to the ceramic sheet, charges of opposite polarities are generated at both ends of the ceramic sheet, and current is generated through the circuit. This effect is called the piezoelectric effect. If a transducer made of this piezoelectric ceramic is put into water, under the action of sound waves, charges will be induced at both ends of the transducer, which are sound wave receivers. Furthermore, the piezoelectric effect is reversible. If an alternating electric field is applied to the piezoelectric ceramic sheet, the ceramic sheet becomes thinner and thicker from time to time, vibrating and emitting sound waves. Therefore, the problem of the ultrasonic transmitter is solved.
There are two materials for piezoelectric ceramic transducers: magnetostrictive metals and piezoelectric ceramics. The purpose of this article is to design transducers for high power mechanical ultrasonic machining, so only piezoelectric ceramic transducers will be discussed. As an energy transmission network, piezoelectric ceramic transducer has the problem of energy conversion efficiency. The conversion efficiency is related to the selection of the transducer material, vibration form, structure of the mechanical vibration system (including the support mechanism), and operating frequency. Therefore, in the design of ultrasonic transducers, various factors should be considered, such as acoustic impedance, frequency response, impedance matching, acoustic structure, vibration modes and conversion materials, and how to design and coordinate these factors so that the electro-acoustic conversion can reach best value.
Piezoelectric ceramic transducer is an electronic ceramic material with piezoelectric properties. The main difference from a typical piezoelectric quartz crystal without ferroelectric components is that the crystal phases that make up its main components are all ferroelectric crystal grains. Because ceramics are polycrystalline aggregates with randomly oriented grains, the spontaneous polarization vector of each ferroelectric grain is also disoriented. In order for the ceramic to exhibit macroscopic piezoelectric properties, the piezoelectric ceramic must be polarized in a strong DC electric field after firing, and the end face is subjected to multiple electrodes, so that the polarization vector of the original disorderly orientation is preferentially oriented in the direction of the electric field, and after the electric field is eliminated , the piezoelectric ceramics after polarization treatment will maintain a certain macroscopic residual polarization, so that the ceramics have a certain pressure.
