Hemispherical resonator gyroscope
The Hemispherical Resonator Gyroscope (HRG), also called wine-glass gyroscope or mushroom gyro, 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. Gyroscopic effect is obtained from the inertial property of the flexural standing waves. HRG has no moving parts, is very compact, is extremely reliable and very accurate.
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 Q-factor over 30-50 million in vacuum, so, the corresponding random walks are extremely low. The Q-factor is limited by 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 totally rotate with the shell. 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.
Originally used is space applications (Attitude and Orbit Control Systems for spacecrafts), HRG is now used in advanced Inertial navigation system, in Attitude and Heading Reference System and gyrocompass.
The HRG is extremely reliable because of its extremely simple hardware. It has no moving parts; its core is made of a monolithic part which includes the hemispherical shell and its stem. They demonstrated outstanding reliability since their initial use in 1996.
The HRG is extremely accurate and is not sensitive to external environmental perturbations. The resonating shell weighs only a few grams and it is perfectly balanced which makes it insensitive to vibrations, accelerations and shocks.
The HRG doesn't generate any acoustic nor radiated noise because the resonating shell is perfectly balanced and operates under vacuum.
The material of the resonator, the fused quartz, is naturally radiation hard in any space environment. This confers intrinsic immunity to deleterious space radiation effects to the HRG resonator.
Thanks to the extremely high Q factor of the resonating shell, the HRG has an extremely low angular random walk and extremely low power dissipation.
HRG, unlike optical gyros (FOG and RLG), has inertial memory: if the power is lost for a short period of time (typically few seconds), the sentitive element integrates the input motion (angular rate) so that when the power returns, the HRG signals the angle turned in the interval of power loss.
HRG is a very high-tech device which requires sophisticated manufacturing tools. The control electronics required to sense and drive the standing waves, is somewhat sophisticated. This high level of sophistication strongly limits the dissemination of this technology and only few companies were able to develop it. Up to now, only two companies are manufacturing HRG in series: Northrop Grumman Corporation and Safran.
HRG is relatively expensive due to the cost of the precision ground and polished hollow quartz hemispheres. This issue is now overcame thanks to an innovative design. Rather than depositing electrodes on an internal hemisphere that must perfectly match the shape of the outer resonating hemisphere, electrodes are deposited on a flat plate that matches the equatorial plan of the resonating hemisphere.
- HRG are used in space applications (satellites and spacecraft)
- HRG are used in Space launchers 
- HRG are used for marine maintenance-free gyrocompasses as well as Attitude and Heading Reference Systems
- HRG are used in Target locators and land navigation systems 
- HRG are poised to be used in Commercial Air Transport navigation systems 
- Ring laser gyroscope
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- Sarapuloff S.A., Rhee H.-N., and Park S.-J. Avoidance of Internal Resonances in Hemispherical Resonator Assembly from Fused Quartz Connected by Indium Solder //Proceedings of the 23rd KSNVE (Korean Society for Noise & Vibration Engineering) Annual Spring Conference. Yeosu-city, 24–26 April 2013. – P.835-841.
- Bryan G.H. On the Beats in the Vibrations of a Revolving Cylinder or Bell //Proc. of Cambridge Phil. Soc. 1890, Nov. 24. Vol.VII. Pt.III. - P.101-111.
- The Hemispherical Resonator Gyro: From Wineglass to the Planets, David M. Rozelle
- Hemispherical Resonator Gyro
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- Lynch D.D. HRG Development at Delco, Litton, and Northrop Grumman //Proceedings of Anniversary
- Workshop on Solid-State Gyroscopy (19–21 May 2008. Yalta, Ukraine). - Kyiv-Kharkiv. ATS of Ukraine. 2009.
- 7th International ESA Conference on Guidance, Navigation & Control Systems. 2–5 June 2008, Tralee, County Kerry, Ireland
- REGYS 20: A promising HRG-based IMU for space application L.Rosellini, JM Caron. SAGEM Defense and Security, Paris, France
- D. Roberfroid, Y. Folope, G. Remillieux Sagem Défense Sécurité, Paris, FRANCE)) HRG and Inertial Navigation
- Inertial Sensors and Systems – Symposium Gyro Technology 2012
- A Carre, L Rosellini, O Prat (Sagem Défense Sécurité, Paris,France) HRG and North Finding
- 17th Saint Petersburg International Conference on Integrated Navigation Systems 31 May – 2 June 2010, Russia
- HRG by Sagem from laboratory to mass production - Alain Jeanroy; Gilles Grosset; Jean-Claude Goudon; Fabrice Delhaye - 2016 IEEE International Symposium on Inertial Sensors and Systems