The principle of piezoelectric ceramic sheet: When pressure or tension is applied to the ceramic sheet, charges of opposite polarity will be generated at the two ends of the ceramic sheet, and a 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, then under the action of sound waves, charges will be induced at both ends of the transducer, which is a sound wave receiver. In addition, the piezoelectric effect is reversible. If an alternating electric field is applied to a piezoelectric ceramic sheet, the ceramic sheet will become thinner and thicker from time to time, and it will vibrate and emit 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 are discussed. As a kind of 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, the form of vibration, the structure of the mechanical vibration system (including the support mechanism) and the 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 mode and conversion materials, and how to design and coordinate these factors to achieve electro-acoustic conversion. best value.
Piezoelectric ceramic transducer is an electronic ceramic material with piezoelectric characteristics. The main difference from a typical piezoelectric quartz crystal that does not contain ferroelectric components is that the main component of the crystal phase is 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 disordered orientation is preferentially oriented in the direction of the electric field. After the electric field is eliminated , The piezoelectric ceramic after polarization treatment will maintain a certain macroscopic residual polarization strength, so that the ceramic has a certain pressure.
