An Active Homodyne Demodulation Optic-fiber Interferometer for the Dynamic Characterization of Microstructures

Student:  Chong Peng

Advisor:  Dr. Rajpal S. Sodhi

ABSTRACT

A relatively simple measuring system has been designed to evaluate the dynamic characteristics of micromechanical structures. The system is based on active homodyne demodulation M-Z optic-fiber interferometer. To characterizing structures in micron scale, a microscopy and a vibration excitation device are added into the interferometer. The system can measure out-of-plane movement with sensitivity of 0.1 nm.

To validate the system, vibration measurements have been carried on a typical MEMS structure—the sensitive elements of an uncooled IR imaging system, an array of micromachined bimaterial cantilevers. The first natural frequency of the structure and modal damping are determined from data obtained by vibrating the structures using a PZT exciting system. The natural frequency result agrees with that from FEM analysis. The mode shapes will be found out soon after a scanning system is completed.

This interferometer has low cost, high stability and high precision. A scanning system and signal analyzing module is to be completed for the commercial use.