Views: 10 Author: Site Editor Publish Time: 2020-09-11 Origin: Site
Piezoelectric transducers are ultrasonic sensors made by using the piezoelectric effect produced by certain dielectrics. The so-called piezoelectric effect refers to the phenomenon that when certain dielectrics undergo deformation (including bending and stretching deformation) due to the polarization of internal charges, they will generate charges on their surface when they are deformed by external forces in a certain direction. Piezoelectric materials can be divided into piezoelectric single crystal, piezoelectric polycrystalline and organic piezoelectric materials. The most commonly used piezoelectric transducer are various types of piezoelectric ceramics tube belonging to piezoelectric polycrystals and quartz crystals in piezoelectric single crystals. Other piezoelectric single crystals include lithium niobate, lithium tantalate, lithium gallate, and bismuth germanate suitable for high-temperature radiation environments.
Introduction for the characteristics of piezoelectric ceramic sensors
Piezoelectric ceramics include barium titanate ceramics belonging to the binary system, lead zirconate titanate series ceramics, niobate series ceramics and lead magnesium niobate ceramics belonging to the ternary system. The advantages of custom piezoelectric hemispheres are convenient firing, easy shaping, humidity resistance and high temperature resistance. The disadvantage is that it has pyroelectricity, which will interfere with the measurement of mechanical quantities. Piezoelectric materials include more than ten kinds of polymer materials such as polyvinylidene fluoride, polyvinyl fluoride, and nylon. Piezoelectric materials can be mass-produced and made into larger areas. It has unique advantages in matching the acoustic resistance of air and is a new type of electro-acoustic material with great development potential. Since the 1960s, crystals with both semiconductor properties and piezoelectric properties, such as zinc sulfide, zinc oxide, and calcium sulfide, have been discovered. The use of PZT material can be made into a new type of piezoelectric sensor integrating sensitive components and electronic circuits, which is very promising.
The application of piezoelectric sensor: piezoelectric ceramics sensor has simple structure, small size, small mass, low power consumption, long life, especially it has good dynamic characteristics, so it is suitable for a wide band of periodic force and high-speed change of impact force.
dynamic measurement of piezoelectric ceramic sensor
Piezoelectric sensors can only be used for dynamic measurement
Because the charge generated by the external force acting on the piezoelectric element can only be stored without leakage, that is, the measurement needs to have an infinite input impedance, which is practically impossible, so the piezoelectric sensor cannot be used for static measurement .
Under the action of alternating force, the piezoelectric element can continuously supple the charge and can supply a certain current to the measurement circuit, so it is only suitable for dynamic measurement (generally it must be higher than 100Hz, but above 50kHz, the sensitivity decreases).
Measurement of Piezoelectric ceramic sensor:
(1) Force measurement Piezoelectric sensors mainly use the longitudinal and shear piezoelectric effects of piezo ceramic disc quartz crystals, because quartz crystals have large stiffness, low hysteresis, high sensitivity, good linearity, wide operating frequency, and low pyroelectricity. In addition to measuring the unidirectional force, the force sensor can also use multiple crystals with different cutting directions to measure multi-directional force depending on its different piezoelectric effects, such as the three-direction component force of the spatial force Fx, Fy, Fz
(2) Pressure measurement: Piezoelectric pressure sensors mainly use elastic elements (diaphragm, piston, etc.) to collect pressure and become a force acting on the crystal, because the properties of the PZT material used in the elastic element have a great influence on the characteristics of the sensor.
(3) Acceleration measurement: The piezoelectric acceleration sensor uses the mass to be pressed against the crystal by preloading force. When the measuring acceleration acts, the piezo crystal will be subjected to an inertial force, which produces a piezoelectric effect. Therefore, the quality of the mass determines the sensitivity of the sensor and also affects the high-frequency response of the sensor.
