Inertial Sensor
Coriolis vibratory gyroscopes measure angular rotation by tracking the acoustic wave patterns that arise in a vibrating mechanical structure. A hemispherical resonator gyroscope utilizes a ground quartz glass shell to sustain a standing wave that shifts when the housing rotates. This high precision design is widely selected for spacecraft and marine navigation where long term reliability is essential.
Resonance Pattern
Operation begins by electrostatically exciting a flexural mode in the hemispherical shell, which creates a symmetrical standing wave with four nodes and four antinodes. When the gyroscope rotates about its axis, the Coriolis force causes the standing wave to precess relative to the housing. Pickoff electrodes measure this angular displacement directly or feed it into a closed loop that forces the wave back to its null position, with the required force indicating the rate of rotation.
Structural Material
Ultra high purity fused silica forms the vibrating element to minimize energy dissipation through internal friction. This choice of material yields an exceptionally high quality factor, allowing the resonator to vibrate with minimal driving power. The structural assembly is sealed in a high vacuum to eliminate gas damping.
Operational Limit
Manufacturing tolerance limits dictate the bias stability and drift rates of the completed instrument. Minute mass asymmetries on the quartz rim cause the standing wave to lock to a preferred axis, causing drift. Chemical etching and laser tuning are applied during production to balance the shell to sub micron tolerances.
