Study On Piezoelectric Coefficient Measurement Of Piezoelectric Materials By Laser Interferometer Method

Piezoelectric material is a kind of functional materials that have piezoelectric effect, which can realize transformation between mechanical energy and electrical energy, and is widely used in nondestructive testing, communications technology, biomedical, military technology and other fields. The performance of energy conversion is directly determined by the quality of piezoelectric material. The quality evaluation of the piezoelectric material characteristic parameters includes the piezoelectric coefficient, dielectric constants and electromechanical coupling coefficient, mechanical quality factor, etc. Among them the piezoelectric coefficient is one of the key indicators, which not only describes the efficiency of energy conversion, but also reflects the coupling relationship between elastic properties and dielectric properties of piezoelectric material.Measurement methods of piezoelectric coefficient d33 includes contact measurement and non-contact measurement. The contact measurement might damage the surface of material, the accuracy of measurement is not very high. Laser interferometry as a kind of non-contact measurement, is widely used in small dynamic displacement measurement with its unique advantages of traceable, non-contact, and high resolution.In this paper, Based on the condition of d33 measurement with instruments by contact method with low accuracy, the influence factors of piezoelectric coefficient measured by laser interferometry for piezoelectric material was studied, and the feasibility of establishing the measurement standard for piezoelectric coefficient of piezoelectric material was explored. With the development the laser interferometer measurement system, the influence factors of piezoelectric coefficient d33, the measurement uncertainty, consistency of different methods were carried out. The main work includes:1. By setting up the laser interference optical path, acquiring the orthogonal signal, demodulating the Doppler signal, establishing the laser heterodyne interferometer measurement system of piezoelectric coefficient d33 of piezoelectric material, the influence factors of piezoelectric coefficient are analyzed in detail, including excitation field, frequency, temperature. And evaluates the uncertainty laser interferometer measurement system.2. Comparison of the measured results by laser interferometer and quasi-static method are carried out. From the definition of the piezoelectric coefficient d33, analysis and discussion the consistency of piezoelectric coefficient d33 under the direct and inverse piezoelectric effect, as well as the reason for their differences.3. Results show that at the frequency far below the resonant frequency, the piezoelectric coefficient d33 remains unchanged with the increase of frequency; when the excitation field is less than the polarization field, the d33 of hard piezoelectric ceramic does not change with the excitation field strength, and there is a linear relationship between the d33 of soft piezoelectric ceramic and the excitation field; Because of the uniformity of material, the difference of polarization degree and different degree of material homogeneity and polarization, as well as the restricting of constraint conditions during the measuring, the d33 of piezoelectric material measured at different point on the sample surface are not the same at all the time, the value at center usually presents minimum, and maximum at the edge. The laser heterodyne interferometer uncertainty evaluation results show that the measurement of d33 is less than 2.3% within the displacement of 10 nm to 150 nm; Studying on consistency of different methods indicate that the result measured by laser interferometer method is slightly larger than that of quasi static method and closer to the real d33 of material under direct and inverse piezoelectric effect. Laser interferometer method can be used as an absolute calibration method, and assign values to the piezoelectric coefficient of piezoelectric material, as well as to be used to calibrate the quasi static instrument.