A WIDE-RANGE LINEAR OPTICAL ACCELEROMETER

An optical accelerometer has been designed and fabricated using conven tional KOH etching of [100]-orientation silicon. The seismic mass acts as an optical shutter and consists of evenly spaced vertically etched slots. The shutter is suspended by two cantilever beams and controls the amount of light flux from a red light-emitting diode (LED) source reaching a PIN diode detector. The special structure of the device and the high aspect ratio; (7.5) of the cantilever beams permit freedom o f movement for the seismic mass (the shutter) along only one axis. The actual size of the device is 3 mm X 4 mm and its amplified output var ies linearly from -3.6 to +3.6 V for static accelerations from -84g to +84g. The dynamic response of the device shows a flat relative sensit ivity up to 700 Hz and increases to 21.9 dB at 3.2 kHz, which is the r esonance frequency. The second harmonic appears at 6.8 kHz with a rela tive sensitivity of 9.9 dB. A dual diode structure is chosen for the p hotodetector to compensate for temperature drift and the amplified out put voltage changes by less than 40 mV for a temperature variation fro m 25 to 50 degrees C when the applied acceleration is zero.