Small vibration measurement using laser grating Doppler effect

In order to increase the accuracy and dynamic range of measuring small vibration, a measuring system using grating Doppler effect was proposed. By analyzing the frequency of the beat wave, the frequency of object to be measured was obtained, its amplitude was evaluated and the turning point of the beat wave was found out. The relationship between the small displacement around the turning point and the amplitude was deduced. Accordingly the displacement less than the equivalent value can be calculated by the amplitude ratio. This method can promote the survey accuracy, and dynamic range, and find out other vibration characteristics of the object to be measured with the simple instrument. When frequency range to measure vibration is in 0.5-500 Hz, and the amplitude is in 20 nm-10 mm, the experimental results show that the relative error is less than 1%, and the dynamic range is better than 100 dB.