A Magnetically Excited and Sensed MEMS-Based Resonant Compass

An all-magnetic micromachined resonant compass was designed, fabricated by a low-temperature CMOS-compatible microfabrication technique, and characterized. The microelectromechanical sensor consists of a silicon micromachined mechanically resonant disk structure bearing a small permanent magnet. The resonant structure is powered using an electromagnetic excitation coil, which requires very little operating voltage. The interaction between the external magnetic field surrounding the sensor (such as the Earth´s field) and the permanent magnet generates a rotating torque on the disc, changing the stiffness of the beam and therefore the resonant frequency of the sensor. By monitoring changes of the resonant frequency while changing the orientation of the sensor with respect to the external magnetic field, the direction of the external magnetic field can be determined. The fabricated device can measure the direction of the magnetic field of the Earth with a resolution of 15deg, for a 100-mV resonator excitation voltage