Exploiting the non-uniform characteristics of Silicon photodiode in vibration monitoring

A reliable measurement of vibration is needed in many civil and industrial engineering fields. The work presented in this paper is a direct non-contact type measurement of displacement and vibration technique using a photodiode.The work involves designing of experimental methods for measuring vibration of objects with special emphasis on out-of-plane vibration. A laser beam illuminates the surface of interest and the reflected light is collected on the photodiode which is placed normally to the direction of reflected beam. Spatial uniformity is considered to be the most significant feature of an ideal photodiode when it is used as a light intensity sensor in optical systems. A photodiode is said to have spatial uniformity if the detector output is independent of the incident position of light in the active area. But some spatial nonuniformity are observed in real time applications.These nonlinear characteristics were studied to explore the possibility of using the nonlinear region for vibration monitoring and analysis which involves measurement of both amplitude and frequency.