Advantages and disadvantages of piezoelectric sensor and its application

Brief Introduction of Piezoelectric Sensors

Piezoelectric sensor is a kind of sensor made of piezoelectric effect produced by some dielectrics. The so-called piezoelectric effect refers to the phenomenon that when some dielectrics are deformed by external forces in a certain direction (including bending and stretching deformation), due to the polarization of internal charges, they will generate charges on the surface of the dielectrics. Piezoelectric materials can be divided into piezoelectric single crystals, piezoelectric polycrystals and organic piezoelectric materials. The most widely used piezoelectric sensors are various piezoelectric ceramics 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, which are suitable for high temperature radiation environment.

Advantages and disadvantages of piezoelectric sensor and its application

Main parameters of piezoelectric sensor

(1) Piezoelectric constant is a parameter to measure the strength of piezoelectric effect of materials. It directly affects the sensitivity of piezoelectric output.

(2) The elastic constants and stiffness of piezoelectric materials determine the natural frequency and dynamic characteristics of piezoelectric devices.

(3) For piezoelectric components of certain shape and size, their inherent capacitance is related to dielectric constant, and the inherent capacitance affects the lower frequency limit of piezoelectric sensors.

(4) In piezoelectric effect, the mechanical coupling coefficient is equal to the square root of the ratio of the converted output energy (e.g. electrical energy) to the input energy (e.g. mechanical energy); it is an important parameter to measure the electromechanical energy conversion efficiency of piezoelectric materials.

(5) The insulation resistance of piezoelectric materials will reduce the charge leakage, thus improving the low frequency characteristics of piezoelectric sensors.

(6) The temperature at which the piezoelectric material begins to lose its piezoelectric properties is called Curie point temperature.

Advantages and disadvantages of piezoelectric sensor and its application

Advantages and Disadvantages of Piezoelectric Sensors

The advantages of piezoelectric sensors are wide frequency bandwidth, high sensitivity, high signal-to-noise ratio, simple structure, reliable operation and light weight. Piezoelectric crystals can work at temperatures over 400 C for a long time, impact temperatures over 4000K in an instant (10 milliseconds), withstand high surface pressure ("150N/mm2"), high stiffness, good linearity, small hysteresis, constant sensitivity in a wide temperature range, wide frequency response range, almost unlimited load cycles, and very high insulation impedance.

In addition, due to the high rigidity of quartz crystal, the corresponding material deformation is very small. Generally within a few microns, the high natural frequency of quartz sensor is especially suitable for the measurement of fast and dynamic process. They can be used not only in research and development, but also in industrial production and test process. Because the measurement process is almost invisible, the error of slow or quasi-static process measurement is very small. The disadvantage of piezoelectric sensors is that some piezoelectric materials need moistureproof measures, and the output DC response is poor. High input impedance circuit or charge amplifier are needed to overcome this disadvantage.

Advantages and disadvantages of piezoelectric sensor and its application

Application of Piezoelectric Sensors

1. For vibration reduction and restlessness reduction

The application of piezoelectric smart structures in vibration control is the earliest and the research results are abundant, mainly focusing on the vibration control of large space flexible structures. There are usually three methods for the design of control systems, namely active control, passive control and active-passive hybrid control. Passive control system has simple structure, easy realization and low cost, but it lacks flexibility in control and poor ability to respond to sudden environmental changes. Compared with passive control, active control, with modern control theory as its main tool, has greater flexibility and strong adaptability to the environment, is a research hotspot in current vibration engineering. Passive control is connected with active control. Hybrid control strategy is a new direction of vibration engineering. Another important application direction of piezoelectric smart structures is active noise control. It is mainly used to control the internal noise of submarines, aircraft and vehicles in three-dimensional enclosed space. The difference between active vibration control and wall panel vibration control is that vibration control is the mode of the control panel, while noise control is mainly the part of controlling the sound intensity.

2. Static Deformation Control of Structures

By controlling the deformation of piezoelectric smart structure, the geometric shape of the structure can be adjusted and the exact shape and position of the structure can be maintained. This has important application value in the control of space station, other space vehicles and flexible machinery. For example, in the space vehicle, the deformation of the precise structure can be controlled to ensure the normal operation of space antenna reflector, telescope and other precision instruments; in the robot, the motion accuracy of the flexible manipulator can be improved by controlling the motion of the flexible manipulator through piezoelectric elements.

3. Monitoring of Structural Damage

There are two main ways to use piezoelectric sensors to monitor structural damage. One is to use piezoelectric sensors to accurately perceive the changes of structural mechanical properties, and to predict structural damage by further calculation and analysis; the other is to predict structural damage by analyzing the vibration waves propagating in the structure. These two methods can provide reliable information for structural safety assessment and damage location, thus providing a new method for long-term and real-time health detection of civil engineering structures.

4. Monitoring of Processing Technology

Piezoelectric force, stress, vibration and acoustic emission sensors have become the ideal choice for condition monitoring in modern automatic control manufacturing industry because of their unique advantages. For grinding, drilling and tapping, a new type of quartz multi-component force and moment sensor is designed by using the latest telemetry technology, which is a new type of rotation.