Torsion cantilever as magnetic torque sensor

Abstract

A macroscopic cantilever for capacitive torque magnetometry has been developed and tested. It is based on torsion arms in order to obtain better damping against external vibrations than with ordinary cantilevers of similar size but anchored on one side. Microfabricated out of silicon-on-insulator wafers by deep reactive ion etching, the sensor consists of a long (14 mm) and thin (40 μm) cantilever with two capacitive plates, anchored at its center to a rigid frame by two torsion bars having a rectangular cross section (80×40 μm2). By comparing the theoretical and experimental resonance frequencies in three different oscillation modes, we show that the elastic properties of the torque sensor can be evaluated with good accuracy. Calibrations performed with a piece of Fe2O3 audiotape and a cylindrical NdFeB magnet yield a torque sensitivity better than 5×10−13 N m under optimized conditions. This device can also be used as a sensitive Gauss meter to detect magnetic fields down to 10 nT.