MEMS Motion Measurements Based On Laser Doppler Technology

Micro-electro-mechanical system (MEMS) has been widely used in national defense, high-tech, life science, communication and intelligence technology. The measurements of MEMS have become the bottle neck factor in its development. In this project, a method for measuring dynamic parameters, such as velocity, acceleration, angular velocity, angular acceleration, of the MEMS resonator and the micro motor etc., based on laser Doppler technology is investigated.Based on the early work, the measurement system, including optical diagram, signal processing circuit and data analysis program has been improved. A phase-locked loop is applied to demodulate the signal and a circuit discriminating MEMS motion direction is introduced.A study on the method of laser Doppler signal processing is carried out. Wavelet filters are used and the time-frequency analysis method is applied. A distribution function which shows the signal energy or intensity in time domain and in frequency domain simultaneously is forwarded. The dynamic characteristics of MEMS are extracted from the output of the optical system. By taken care of the actual transformation functions, aberrations of the lenses and practical requirements to the laser spot an optical spot with tens of micrometers diameter is obtained by using aspheric lenses. The methods used here improve the resolution and accuracy of the whole system effectively.A laser Doppler system for measuring the in-plane transient motion and the out-of-plane vibration simultaneously is set up. The dynamic parameters of the MEMS, such as velocity, angular velocity, angular acceleration, displacement, etc., can be measured. High-order vibrations of the MEMS can be also measured by the system. A special modal experimentalion method is introuduced to obtain resonator modal parameters, such as natural frequency, vibration shape, etc.A position micro adjustment system with a CCD camera is designed to place the light spot accurately. In the mean time, a MEMS driving system is developed to drive Micro-electro-mechanical Systems with different parameters.Experiments on measuring the motion characteristics of the MEMS resonators have been conducted. Experimental results show that the system can be used to measure Micro-electro-mechanical System motion.