Development of a MEMS Xylophone Bar Magnetometer Using Optical Interferometry for Detection

We report the results of an optical interferometric study, which was designed to measure the magnetic-field induced displacement of a resonating xylophone bar MEMS magnetometer. The MEMS magnetometer is a Lorentz-force sensor, which transduces an alternating current and an orthogonal directed magnetic field into an alternating displacement of the xylophone bar. The Michelson interferometer system includes optics and electronics for active stabilization of the optical path length difference between the reference and sample beams. The active stabilization results in the ability to control or detect pathlength differences as small as ∼ 0.6 ×10 −3 A. With this level of operational sensitivity, the presence of a one nano Tesla magnetic field was found to produce a detectable bar displacement on the order of ∼10 −3 A. In addition to the high sensitivity, the interferometer photodetector displayed linear behavior over six decades of optical path length differences, which corresponded to a magnetic field dynamic range that spanned nano- to milli-Tesla amplitudes.