Damping characteristics of electromechanical coupling between piezo ceramics crystal and electric circuit

Views: 4 Author: Site Editor Publish Time: 2020-03-05 Origin: Site

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Piezoelectric ceramics, as a new functional ceramic material,which have been widely used in the many technical fields, including the application in the field of structural vibration control. Because of its ability to transform mechanical energy and electrical energy, it can be embedded into the system as a ultrasonic sensor or actuator for active control of structural vibration. When piezoelectric ceramic materials and external circuits form a closed circuit, due to the mechanical and electrical coupling, it will show some damping characteristics, which can be used for passive control of structures.

In 1979, Forward first proposed the possibility of using piezoelectric ceramics in parallel with circuit components for vibration control, and then hagood and von ,In this paper, the mechanical and electrical coupling characteristics of piezoelectric ceramics and external circuits are theoretically modeled, and the influence of PZT piezoceramic tube on cantilever vibration when they are connected in parallel with pure resistance circuit and series resistance inductance circuit respectively. The experimental results are in good agreement with the theoretical results, which systematically proves the feasibility of piezoelectric ceramics and external circuits in parallel for vibration control. Since then, many researchers have begun to invest in this field.

In order to better apply the damping characteristics of ultrasonic level transducer to vibration control, based on the research work in this paper, a theoretical model of the damping characteristics of parallel coupling of piezoelectric ceramics with resistance inductance and resistance capacitance circuits is established, and the theoretical model is verified based on the cantilever system, which provides a theoretical basis for the application of piezoelectric ceramics in the field of passive control foundation.

Damping characteristics of parallel piezoelectric ceramics

Piezoelectric ceramic materials have the property of converting mechanical energy into electrical energy. When piezoelectric ceramics are subjected to external force, the surface will produce electric charge. If the piezoelectric ceramic is in the circuit state, the charge will gather on the surface of the piezoelectric ceramic. When piezoelectric ceramics form a close circuit with the external circuit, part of the electric charge will be consumed in the form of heat energy by the impedance in the circuit, that is to say, part of the mechanical energy will be released in the form of heat energy. This is the mechanism that piezoelectric ceramics and external circuits are connected in parallel for passive vibration control.

1.2 theoretical model

From the electrical point of view, piezoelectric ceramics can be simplified as a series model of a voltage source and a capacitor. It is an equivalent electrical model of piezo ceramics in parallel with the external circuit. The electrical impedance of the system when the external circuit is closed or open. The mechanical impedance is equivalent to the mechanical stiffness of piezoelectric materials. Therefore, the damping characteristics of parallel piezoelectric ceramics, the energy dissipation factor ŋ and the stiffness ratio e can be defined respectively.When the external circuits are resistance inductance parallel circuit and resistance negative capacitance series circuit respectively,the material damping characteristics model of piezoelectric ceramics can be obtained: the damping characteristics of piezoelectric ceramics and the electromechanical coupling coefficient of piezoelectric ceramics, working frequency and vibration factor are all related. The damping characteristics of parallel piezoelectric ceramics are related to many factors, such as the characteristics of piezoelectric ceramics, the types of external circuits, and specific circuit parameters. With the change of these factors, piezoelectric ceramics show different damping characteristics.

Simulation Research Based on cantilever beam system

In order to verify the influence of circuit type and related parameters on the damping characteristics of parallel piezoelectric ceramics transducers, a set of simulation system based on cantilever beam is designed. PZT-5 piezoelectric ceramic sheet is pasted on the surface of cantilever beam, the surface of beam is grounded, and the polarization direction of piezoelectric ceramic sheet is shown. Among the four piezoelectric ceramic sheets, two are actuators, which are the driving sources of cantilever beam vibration; one is the sensor, which reflects the vibration intensity of corresponding position on the cantilever beam through the measured voltage value; the other is in parallel with the external circuit, the first pair of piezoelectric ceramic sheets is 60mm * 26.4mm * 0.25mm, and the second pair is 50mm * 26.4mm * 0.25mm. The distance between the left end of two pairs of piezo ceramic chips and the fixed end of cantilever beam is 18mm and 100mm respectively. There is a transfer function relationship between the input voltage of the actuator and the output voltage of the sensor. By comparing the transfer function of the external parallel circuit in open circuit and closed circuit, the influence of the parallel piezoelectric ceramics on the system vibration can be determined.

According to the above model, the influence of piezoelectric ceramics on the vibration of cantilever beam system is simulated in four cases.it is resistance, series resistance inductance, parallel resistance inductance and negative capacitance of parallel resistance. Negative capacitance is realized by negative impedance conversion circuit. The parameters of the cantilever and piezoelectric ceramics used in the simulation only involve the first mode of the cantilever, and the influence of the change of resistance on the damping characteristics of piezoelectric ceramics is considered.

In the different parallel circuits, piezoelectric ceramic has a great influence on the vibration of cantilever beam system. For the same circuit, the damping effect changes with the change of resistance value, and there is an optimal value from the change trend. This is consistent with the theoretical model in the previous part. It can be seen from the comparison that the damping effect is the smallest when connected in parallel with the resistance, and the strongest when is connected in parallel with the resistance negative capacitance series circuit. For two kinds of resistance inductance parallel circuits, the influence of piezoelectric ceramic on the system is similar, but the sensitivity of damping performance with the change of resistance is quite different. Moreover, when the resistance of the series resistance inductance circuit changes from large to small, and the resistance of the parallel resistance inductance circuit changes from small to large, the trend of their influence on the performance of the cantilever system is the same. Considering the damping characteristics of the piezoceramics in parallel and its influence on the system performance, a comprehensive comparison is made.