Suspension stiffness of micromachined electrostatically suspended accelerometers

Electrostatically suspended accelerometers can offer extremely high resolution in micro-gravity space measurement with significantly reduced operating bandwidth and measurement range. In this paper, a tri-axis micromachined electrostatically suspended accelerometer (MESA) was designed with a free parallelepiped proof mass, and realized in a glass-silicon-glass sandwich structure by bulk silicon micromachining. The relationships between dynamic stiffness characteristics and control parameters in a typical suspension loop were derived and discussed. A DSP-based digital control scheme was realized to achieve stable levitation of the proof mass electrostatically in six degrees of freedom. The analytical and experimental results of the accelerometer operated in the atmospheric environment show that the suspension stiffness is mostly dominated by controller parameters and air damping within the closed-loop suspension bandwidth. It is also shown that the allowable input range and suspension stiffness of such accelerometers can be varied over a wide range by changing the preload voltage online.