Application Cases

Experiment Name: Basic Principles of Piezoelectric Coefficient Measurement by Interferometry

Research Direction: The principle of light interference is now widely applied in various fields, particularly in spectroscopy, precision measurement, and detection. When two (or more) waves with the same vibration direction meet at a certain point in space, the amplitude at each point of intersection equals the superposition of the amplitudes of all waves at that point (for scalar waves, the wave function at the intersection equals the scalar sum of all wave functions; for vector waves, the wave function at the intersection equals the vector sum of all wave functions). At some positions, the amplitude is consistently enhanced, while at others it is consistently weakened, ultimately forming a stable distribution of light intensity.

Test Equipment: High-voltage amplifier, Signal generator, Oscilloscope, Lock-in amplifier, He-Ne laser, Photodetector, etc.

Experimental Process:

Figure 1: Experimental setup for measuring crystal piezoelectric coefficient by interferometry

The experimental setup for measuring the crystal piezoelectric coefficient by interferometry is shown in Figure 1, primarily consisting of a Michelson interferometer, signal generator, high-voltage amplifier, lock-in amplifier, photoelectric conversion element, and oscilloscope.

The interferometric measurement mainly utilizes the phase sensitivity of the Michelson interferometer. Two total reflection mirrors in the interferometer structure are bonded to the reference crystal and the test crystal, respectively. Two in-phase sine waves from the signal source are amplified by the high-voltage amplifier and applied to the reference crystal and the test crystal. The optical interference signal is converted into a voltage signal by a silicon detector and amplified by the lock-in amplifier. The signal source outputs a square wave signal with the same frequency as the sine signal as the reference signal for the lock-in amplifier. The lock-in amplifier only amplifies signals with the same frequency as the reference signal, thereby avoiding interference to some extent.

Experimental Results:

The interferometric method for testing the material's piezoelectric coefficient observes the relative phase change of the two beams of light based on the light intensity changes reflected by the photoelectric conversion element. Without an applied electric field, the two beams of light exhibit stable interference, and the interference light intensity at this time is defined as the initial value I₀. The light intensity after the reference crystal and the test crystal deform under the electric field is I'. The deformation caused by the inverse piezoelectric effect of the crystal is generally within 10 nm, much smaller than the laser wavelength. If I₀ = I', and there is no case where the deformation difference between the two crystals is an integer multiple of the wavelength, it can be considered that the net deformation of the reference crystal and the test crystal is the same. Using the change in light intensity before and after, the relative phase of the two beams of light can be obtained. When the interference light intensity I' is the same as the initial state I₀, the piezoelectric coefficient of the test sample can be calculated according to Formula .

High-Voltage Amplifier Recommendation: ATA-7010

Figure: ATA-7010 High-Voltage Amplifier Specifications

This document has been compiled and released by Aigtek. For more application cases and detailed product information, please follow us continuously. Xi'an Aigtek has become an instrument and equipment supplier with a wide range of product lines and considerable scale in the industry. Demo units are available for free trial.