A new MEMS sensor for AC electric current

Abstract

This paper presents new results in the testing and characterization of a MEMS sensor for AC electric current. The sensor is comprised of a piezoelectric MEMS cantilever with a microscale permanent magnet mounted to its free end. When placed near a wire carrying AC current the magnet couples to the oscillating magnetic field around the wire, deflecting the cantilever and generating a sinusoidal voltage proportional to the current. Unlike inductive sensors, this sensor does not need to encircle the conductor and it can measure current in a two-wire “zip-cord”. It is also self-powered, and is thus more suitable for wireless sensor node applications than a powered sensor device. The theoretical basis of this new sensor's operation is presented, as well as the fabrication of a MEMS sensor device, and the first test results of this new sensor measuring current in single-wire and two-wire conductors. Sensor response is linear (R2 > 0.99) with sensitivity in the range of 0.1–1.1 mV/A. An integrated self-powered sensor device is also presented, which employs a piezoelectric energy harvester to power the sensor's signal conditioning circuitry at a 2.6% duty cycle.