Two-degree of freedom capacitive MEMS velocity sensor with two coupled electrically isolated mass-spring-damper systems

This paper presents initial experimental results obtained with a novel two degree of freedom (2-DOF) capacitive MEMS sensor intended for vibration control applications. The sensor comprises a principal spring-mass system mechanically in series with a secondary spring-mass system for the implementation of an internal feedback loop. The control loop produces a sky-hook damping force on the principal system, so that the output of the sensor becomes proportional to the base velocity rather than the base acceleration. The design proposed in this work enables direct capacitive displacement sensing of the secondary proof mass with respect to the principal sensor. The sensor closed loop response function is characterized by a low frequency (400-1000 Hz) flat spectrum proportional to the base velocity and a smooth resonance peak around 1000 Hz with a -90° phase lag.