Working principle of piezoelectric ceramic transducer

Overview of piezoelectric ceramic transducers

Piezoelectric ceramic transducer is composed of piezoelectric ceramic crystal and light and heavy two metals. After polarization treatment at a certain temperature, it has piezoelectric effect. Piezoelectric ceramic ultrasonic transducers have entered the research field of people for a long time. It is easy to manufacture, has strong controllability, high sensitivity and good electromechanical coupling. Transducers are developed based on piezoelectric ceramics include power ultrasonic transducers and detection ultrasonic transducers.

Ultrasonic technology is a widely used nondestructive testing technology. It is based on acoustic theory and is continuously used in the fields of electronics, communications, medicine, biology and physics. In modern detection technology, transducers developed using ultrasound technology are gaining more and more attention because of their high sensitivity and high accuracy.

Commonly used transducers in the inspection process are piezo rings transducer, magnetostrictive transducers, electromagnetic acoustic transducers and laser transducers. The most commonly used is the piezoelectric transducer, its core component is the piezoelectric chip. The piezoelectric wafer can be deformed by the pressure, which leads to polarization of the wafer itself, and positive and negative bound charges appear on the surface of the wafer. This effect is a piezoelectric effect. Moreover, the piezoelectric effect is reversible, that is, it deforms when a voltage is applied to the wafer. In the detection process, the ultrasonic sensor can generate ultrasonic waves by using the inverse piezoelectric effect, and use the piezoelectric effect to achieve the purpose of receiving ultrasonic waves. Piezoelectric ceramic ultrasonic transducers have entered the research field of people for a long time. It is easy to manufacture, has strong controllability, high sensitivity and good electromechanical coupling. Transducers developed based on piezoelectric ceramics include power ultrasonic transducers and detection ultrasonic transducers.

Working principle of piezoelectric ceramic transducer

The principle of piezoelectric ceramic transducers is that when pressure or tension is applied to thepzt ceramics, charges of opposite polarities are generated at both ends of the ceramics, and current is generated through the circuit. This effect is called the piezoelectric effect. If a transducer made of this piezoelectric ceramic is placed in water, then under the action of sound waves, charges will be induced at both ends of the transducer, which is an acoustic wave receiver. In addition, the piezoelectric effect is reversible. If an alternating electric field is applied to the piezoelectric ceramic sheet, the piezo ceramic sheet will become thinner and thicker from time to time, and at the same time generate vibration and emit sound waves. Therefore, the problem of the ultrasonic transmitter is solved.

There are two types of piezoceramic ring componnets magnetostrictive metal 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 choice of transducer material, vibration form, structure of mechanical vibration system (including 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 mode, and conversion materials, as well as how to design and coordinate these factors in order 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 crystal phases that constitute its main components are ferroelectric crystal grains. Because piezo ceramics are polycrystalline aggregates with randomly oriented grains, the spontaneous polarization vector of each ferroelectric grain is also disorientated. In order for the piezo ceramics to exhibit macro 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 disorder orientation is preferentially oriented in the direction of the electric field. After the polarization treatment, the piezoelectric ceramic will maintain a certain macro residual polarization intensity, so that the ceramic has a certain pressure.

Application of piezoelectric ceramic transducer

Due to the non-contact advantages of ultrasonic technology, try to apply piezoelectric ceramic ultrasonic transducers to the liquid concentration detection system. The chip in the system uses Spartan 3E series FPGA. The piezoelectric ceramic transducer plays an important role in transmitting and receiving signals. The ultrasonic signal of a certain frequency and amplitude generated by the transducer is driven into the liquid through the transmitting circuit. After the signal is attenuated by the liquid, the signal with liquid concentration information can be received from the receiving transducer. Through the analysis of the sound attenuation method, the approximate concentration of the liquid is effectively obtained. The software design of the system includes the main program, ultrasonic measurement program, pulse control program, pulse transceiver program, ADC acquisition control program and clock and alarm program.

In the experiment, the static liquid can be measured first, the ultrasonic attenuation method is used to analyze the signal collected at the receiving end, the envelope is processed, and the concentration information is obtained by combining the signal propagation path (pipe diameter). Then, the dynamic measurement of the dynamic liquid is carried out, and the signal propagation path needs to consider the flow velocity of the liquid to calculate the approximate path.