degrees. One of the elliptical resonant modes is excited to a prescribed amplitude. When the device rotates about its sensitive axis (along its inner stem), the resulting Coriolis forces acting on the resonator's vibrating mass elements excite the second resonant mode. The angle between major axes of the two modes is also 45 degrees. A closed loop drives the second resonant mode to zero, and the force required to null this mode is proportional to the input rotation rate. This control loop is designated the force-rebalanced mode. Piezo-electric elements on the resonator produce forces and sense induced motions. This electromechanical system provides the low output noise and large dynamic range that demanding applications require, but suffers from intense acoustic noises and high overloads. Piezoelectric gyroscopes A piezoelectric material can be induced to vibrate, and lateral motion due to Coriolis force can be measured to produce a signal related to the rate of rotation. Tuning fork gyroscope This type of gyroscope uses a pair of test masses driven to resonance. Their displacement from the plane of oscillation is measured to produce a signal related to the system's rate of rotation. F.W. Meredith registered a patent for such a device in 1942 while working at the Royal Aircraft Establishment. Further development was carried out at the RAE in 1958 by G.H. Hunt and A.E.W. Hobbs, who demonstrated drift of less than 1°/h or (2.78)°/s. Modern variants of tactical gyros use doubled tuning forks such as those produced by American manufacturer Systron Donner in California and French manufacturer Safran Electronics & Defense / Safran Group. Wine-glass resonator Also called a hemispherical resonator gyroscope or HRG, a wine-glass resonator uses a thin solid-state hemisphere anchored by a thick stem. The hemisphere with its stem is driven to flexural resonance and the nodal points are measured to detect rotation. There are two basic variants of such a system: one based on a rate regime of operation ("force-to-rebalance mode") and another variant based on an integrating regime of operation ("whole-angle mode"). Usually, the latter one is used in combination with a controlled parametric excitation. It is possible to use both regimes with the same hardware, which is a feature unique to these gyroscopes. For a single-piece design (i.e., the hemispherical cup and stem(s) form a monolithic part) made from high-purity quartz glass, it is possible to reach a Q-factor greater than 30-50 million in vacuum, so