Design and Fabrication of a MEMS AC Electric Current Sensor

Abstract

The need for energy efficiency combined with advances in compact sensor network technologies present an opportunity for a new type of sensor to monitor electricity usage in residential and commercial environments. A novel design for a self-powered, proximity based AC electric current sensor has been developed. This sensor device is constructed of a piezoelectric cantilever with a permanent magnet mounted to the cantilever's free end. When the sensor is placed in proximity to a wire carrying AC electric current, the permanent magnet couples to the wire's alternating magnetic field, deflecting the piezoelectric cantilever and thus producing a sinusoidal voltage proportional to the current being measured. Analytical models were developed to predict the magnetic forces and piezoelectric voltage output pertaining to this design. MEMS-scale cantilevers are currently under development using a three-mask process and aluminum nitride as the active piezoelectric material. Very small (300 μm) permanent magnets have been dispenser-printed using magnetic powders in a polymer matrix. Previously presented meso-scale (2-3 cm3) prototype devices exhibited sensitivities of 74 mV/A, while simulations suggest MEMS device sensitivity of 2-4 mV/A.