Profiling of Microcantilever Vibration Modes by Scanning Astigmatic System

Abstract

The measurement of vibration shape modes in micromechanical devices is a task restricted to expensive and complex equipment like scanning laser doppler vibrometers or white light interferometers. At this work we show that using an optical pick-up extracted from a commercial CD-ROM drive, is possible with off-the-shelf equipment, measure the vibration modes of microcantilevers in one dimension, taking advantage of the built-in movable lens present in CD-ROM laser pick-up assembly. The focus lens scans the device in one dimension, measuring the vibration at various point of the structure with velocities in the range of$150~\mu \text{m}$/s while the device is excited with a piezo driven by composed frequency signal. The first 3 shape modes flexural vibration of a cantilever with micrometer dimensions were measured and compared to the theoretical shape. We also measured the noise density of the pick-up, comparing with the theoretical Brownian motion resulting in 3 pm/Hz1/2 noise floor.