A torsion MEMS magnetic sensor with permanent magnet and fiber-optic detection

A novel microelectromechanical system (MEMS) magnetic sensor based on fiber-optic detection is presented in this paper. The magnetic field is detected by measuring the tilting motion of a mechanical suspension with permanent magnet attached. When the magnet is magnetized in different directions, the magnetic sensor can detect the in-plane or out-of-plane magnetic field. The MEMS structure was designed analytically, fabricated by using a bulk micromachining process, and assembled with the permanent magnet manually. Finally, the magnetic-sensing capability of an as-prepared sensor was tested by assembling it into the fiber-optic detection system. The testing result shows a sensitivity of 2.86 mV/μT for the in-plane magnetic field and 6.57 mV/μT for the out-of-plane. According to the mechanical-thermal noise theory, estimated resolutions are, respectively, close to 142 and 62 nT for the in-plane and out-of-plane magnetic field, which suggest the adequacy for measurement in earth magnetic field range. The reported magnetic sensor shows the capability to fulfill the high-resolution detection of low-frequency signals, benefitted from the utilization of permanent magnet and fiber-optic detection. Moreover, the sensitive direction of reported magnetic sensor can be easily switched by varying its magnetized direction, which, therefore, paves the way to the integrated tri-axis magnetic sensor.