Complex Piezoelectric Coefficients of PZT Ceramics: Method for Direct Measurement of d 33
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ABSTRACT A fiber-optic device is used to determine the magnitude and phase of the strain in the poling direction of lead zirconate titanate (PZT) ceramic wafers. This information yields the real and imaginary components of the piezoelectric strain coefficient d-;3. The measurement hardware and software are described and results from the measurements of (133for PZT 4 and 5 H wafers are presented. This method has the advantages of being direct, inexpensive and relatively simple to use. Verification of the results is provided through the use of the resonance method. INTRODUCTION Active control of structural vibrations and acoustic fields has received a great deal of attention in the last several years. Significant advancements have been made in various supporting areas, but current sensor and actuator technology limits further progress [1]. Practical limitations such as acceptable excitation voltages, mechanical durability, and control system complexity and stability are driving research for sensor and actuator improvement. Development of performance measurement techniques for piezoelectric devices is a key component of this research as recent
capabilities have been relatively inaccurate and incomplete. Impedance techniques are effective at high frequencies (resonance of the piezoelectric device), but measurement of performance characteristics at low frequencies (1Hz - 3 kHz) is needed for noise and vibration control applications. Furthermore, effects of dispersion at the low frequencies as well as nonlinearity at the high fields make it necessary to develop a method to measure the strain as a function of electric fields for a broad frequency and electric field range. Direct measurements of piezoelectric coefficients have been widely reported using strain gages, interference methods and capacitance techniques [2,3]. These methods are generally used to yield the magnitude of the response only, and no information on phase is reported. Pan et al. [4] used laser interferometry to calculate the real and imaginary parts of the piezoelectric coefficients from the measured strain amplitude and phase delay of the strain with respect to the applied electric field for PZT ceramics. To ensure stability and precision in the phase detection, evaporating or affixing mirrors to the samples was necessary. All of the above techniques tend to be complex and require tedious sample preparation and considerable effort to maintain accuracy. We saw a need in our laboratories to develop a simple, inexpensive and more direct method to characterize PZT wafers at low frequencies and both low and high fields. This paper presents a direct method for the measurement of the real and imaginary piezoelectric strain coefficient d33 using the converse effect.
231 Mat. Res. Soc. Symp. Proc. Vol. 459 01997 Materials Research Society
METHOD The measurement system consists of a fiber-optic displacement sensor, a computer (Toshiba T4700CT) running LabVIEW, a function generator, an amplifier and signal conditioning hardware as shown in figure 1. The PC is
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