Electrostatic-Capacitive MEMS Stiffness Sensor with Position-Feedback Mechanism

A Micro Electro-Mechanical System (MEMS) stiffness sensor based on position-feedback mechanism which integrates a capacitive position sensor and a variable-area electrostatic actuator mechanically connected to a movable probe tip is presented. A closed-loop mechanism allows to electrically set the working position of the probe tip and to measure the electrostatic force required to impose the working position, ensuring an ideally infinite output mechanical impedance. The proposed sensor is intended for the estimation of the mechanical stiffness of microsamples, such as tissues or cells, placed in contact with the probe tip from their force-displacement characteristic. To verify the effectiveness of the proposed MEMS sensor, the mechanical stiffness of the internal spring of the device itself has been estimated as 3.71 N/m, imposing the working position of the probe tip ranging from 0.56 to 1.42 µm.