Optomechanical calibration for absolute seismic acceleration references

Abstract:

Optomechanical accelerometers that can “self-calibrate” have been proposed for inertial sensing and gravity gradient detection and are being tested against primary acceleration calibration methods using a shaker table and laser interferometric reference. Demonstration of such calibration “equivalency” is a necessary step in the determination of a sensor’s utility as an alternative reference. Recently, we performed a test between 5 Hz and 50 Hz, where we mounted an optomechanical self-calibrating sensor (natural frequency is 573.25 Hz) to a shaker table and compared its self-calibrated output to the accelerations of the shaker table measured using a separate commercial laser interferometer. The optomechanical sensitivity maintained relative accuracy consistent with the shaker/interferometer value, demonstrating a convenient alternative path to primary acceleration calibration. The sensor, despite its comparatively high natural frequency, achieved a calibrated bandwidth and dynamic range compatible with many strong motion, seismic accelerometer applications. Such a sensor might evolve to become a useful part of networked seismic sensors, providing a continuous absolute reference point. We suggest that the sensor design and fabrication are quite flexible, and modifications to the design could enable extension to weak motion detection, and perhaps, ultimately, relative gravity measurements.