Inertial Gyroscopic Systems: FLEMS Technology

A floating microelectromechanical system at its core is composed of a charged mass electrostatically suspended within a similarly charged suspension. The mass can be at rest, spinning, or vibrating depending upon the design. Sense and actuation can be achieved through either electrical (non-contact) or optical means. An attractive feature of such a system is that the mass is not structurally linked to the suspension thus avoiding the losses associated with anchor loss and material damping.
- This leads to low power requirements as one obvious benefit.
- A second clear benefit is a large improvement in sensor drift level due to the elimination of suspension torques.
- A third interesting benefit is that elimination of the mechanical suspension avoids residual stress effects on the system dynamics.
Additionally, the electrostatic suspension provides, in principle, for a high fidelity self-centering system due to centering forces that are inversely proportional to the square of the gaps between the proof mass and the suspension. Thus, in principle, it is possible to operate at high dynamic range without worrying about mechanical stops interfering with operation. For application at high dynamic ranges a number of issues arise and need to be studied. In particular, the precisedynamics of a floating mass are not well understood across large ranges. There are competing effects that need to be quantified and for which governing design level formulae need to be developed. In this study we propose to theoretically examine the dynamics of a floating MEMS mass across a wide dynamic range to understand effects from air gaps, surface charge rearrangement, EM-field interactions, and thermo-elastic waves in the floating mass -- with particular emphasis on system time constants. Relative rankings of the governing phenomena will be determined along with design level formulae giving net system dynamics in terms of controllable parameters such as geometric dimensions, surface modifications, charge levels, etc. These points will allow us to determine the effective range of operation of such devices; they will also allow us to understand the implication on sensor and actuator drift sensitivity of such systems and uncover ways for which even minor drift can be eliminated or compensated for. These estimates will be placed in relation to those for conventional MEMS devices.
The theory part of the study is to begin immediately so as to quickly develop a handful of possible designs for floating masses. Starting about 6 months later, assuming successful theoretical computations, will be an effort to fabricate a proof of concept floating mass MEMS.
Initial efforts will be focused upon the fabrication of a single axis vibrating and/or spinning mass. Major technical hurdles to be overcome include the design of representative geometric layouts along with control methodologies, the initial charging and levitation of the mass. The initial designs and control efforts will be tackled through the use of finite element computations of the EM-fields in the device. The fabrication efforts will center about the creation of a structure only system within a tightly controlled process.