Hemispherical resonator gyroscope  The Hemispherical Resonator Gyroscope (HRG), also called "wine-glass gyroscope" or "mushroom gyro", is a compact, low noise, high performance angular rate or rotation sensor. An HRG is made using a thin solid-state hemispherical shell, anchored by a thick stem. This shell is driven to a flexural resonance by electrostatic forces generated by electrodes which are deposited directly onto separate fused-quartz structures that surround the shell. The gyroscopic effect is obtained from the inertial property of the flexural standing waves. Although the HRG is a mechanical system, it has no moving parts, and can be very compact. The HRG makes use of a small thin solid-state hemispherical shell, anchored by a thick stem. This shell is driven to a flexural resonance by dedicated electrostatic forces generated by electrodes which are deposited directly onto separate fused quartz structures that surround the shell. For a single-piece design (i.e., the hemispherical shell and stem form a monolithic part) made from high-purity fused quartz, it is possible to reach a Q-factor of over 30-50 million in vacuum, thus the corresponding random walks are extremely low. The Q-factor is limited by the coating (extremely thin film of gold or platinum) and by fixture losses. Such resonators have to be fine-tuned by ion-beam micro-erosion of the glass or by laser ablation in order to be perfectly dynamically balanced. When coated, tuned and assembled within the housing, the Q-factor remains over 10 million. In application to the HRG shell, Coriolis forces cause a precession of vibration patterns around the axis of rotation. It causes a slow precession of a standing wave around this axis, with an angular rate that differs from input one. This is the wave inertia effect, discovered in 1890 by British scientist George Hartley Bryan (1864–1928). Therefore, when subject to rotation around the shell symmetry axis, the standing wave does not rotate exactly with the shell, but the difference between both rotations is nevertheless perfectly proportional to the input rotation. The device is then able to sense rotation. The electronics which sense the standing waves are also able to drive them. Therefore, the gyros can operate in either a “whole angle mode” that sense the standing waves' position or a “force rebalance mode” that holds the standing wave in a fixed orientation with respect to the gyro.