Investigation of continuous scanning laser Doppler vibrometry for non-contact measurement of linear and angular surface deflections.

Abstract

Laser Doppler vibrometry (LDV) is a non-contact technique for sensing surface vibrations. Traditionally LDV uses one or several fixed beams to measure vibrational velocity of specific points and orientations. Measurement of angular velocity requires at least two beams. Instead, we develop a technique, continuous scanning laser Doppler vibrometry (CSLDV), using a single laser beam continuously sweeping the area of interest using a scanning mirror. Linear scans allow the measurement of normal and angular velocities while circular scans allow the measurement of normal and two angular velocities. We validated the CSLDV technique for measuring low frequency (less than 50 Hz) broadband vibrations of gel samples which mimics natural vibration of human body. Such system could potentially be used to monitor multiple DOF of the skin surface for haptic or remote control applications. There is a disadvantage of using CSLDV which is speckle noise that is generated when coherent light source is reflected back from an optically rough surface. We will discuss the effects of scan lengths, scanning frequency, target to sensor distance, and the excitation amplitude on the performance of CSLDV.