There is a need for ever more accurate gyroscopes. In the prior art, Reference [1] below, which is incorporated herein by reference, describes gyroscope trimming for frequency tuning of the resonant modes of a gyroscope. In particular Reference [1] describes trimming to frequency tune a hemispherical resonating gyroscope (HRG), which is a large macro-scale cup sized structure with tines at the top lip of the wineglass. Tuning may be carried out either by machining the tines or chemically etching the tines. On the micro mechanical electrical system (MEMS) scale, tuning of gyroscopes has been explored both theoretically, as described in Reference [2] below, which is incorporated herein by reference, and experimentally, as described in References [3], [4] and [5] below, which are incorporated herein by reference.
There are several disadvantages with the approaches of the prior art. In almost all cases materials, such as metals, are initially added to a micro-scale structure, for example the structure described in Reference [3], so that the added material may be later ablated to tune the resonant frequencies. However, the added materials inherently lead to a low Q and frequency splits, which are the differences in resonant frequencies between one mode of resonance and another mode of resonance.
Further, where the region to be ablated is very close to the vibrating regions, trimming and therefore tuning may be difficult and very risky, as the structure may be ruined. Also the material properties of the structure may be degraded. In the case where tuning is carried out further away from the vibrating regions, surfaces are often not flat and not amenable to trimming.
In the prior art, several gyroscope resonating structures with spokes are described in references [6], [7], [8], and [9], below, which are incorporated herein by reference. The spoke structures of these prior art references generally have thicknesses that are similar to the thickness of the resonant structure, and/or are made of different materials, which leads to the disadvantages referred to above.