Optically-Interrogated Zero-Power MEMS Magnetometer

• Published in: Journal of microelectromechanical systems 2007-04, Vol.16 (2), p.336-343
• Main Authors: Vasquez, D.J., Judy, J.W.
• Format: Article
• Language: English
• Subjects: Application specific integrated circuits; Arrays; Beams (radiation); Detection; Diode lasers; Exact sciences and technology; Ferromagnetic materials; Ferromagnetism; General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Integrated circuits; Laser beams; Magnetic field measurement; Magnetic fields; Magnetic sensors; Magnetometers; magnets; Mechanical instruments, equipment and techniques; microelectromechanical devices; Microelectromechanical systems; Micromechanical devices; Micromechanical devices and systems; microsensors; Mirrors; multisensor systems; Optical arrays; optical device fabrication; optical diffraction; Optical sensors; Physics; Torsion; Transducers
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2007.892795

A magnetic-field-sensing system that consists of a miniature zero-power magnetometer, an integrated micromachined corner-cube reflector (CCR), a commercially available diode laser, and a photodetector array, has been designed, fabricated, assembled, and tested. The zero-power-magnetometer design is based on a ferromagnetic MEMS magnetometer, which consists of a permanent magnet that is torsionally suspended to allow rotation about a single axis. A single mirror of the CCR is attached to the magnetometer torsion beam. When the magnet rotates in response to a change in magnetic field, the torsion beam will twist and cause the mirror to become misaligned. The non-ideality of the CCR can be interrogated with a laser and a photosensor array can be used to measure the reflected signal. This method of magnetic sensing completely eliminates sensor-node power consumed at the remote location. The sensor node developed for this paper occupies a volume of only 1.5 mm 3 and can detect a magnetic field between 820 A/m to 6 kA/m with an uncertainty of 90 A/m at a 1-m optical-interrogation range. The primary application of this technology is in wireless sensing systems that must operate continuously without providing or maintaining the sensor-node energy (e.g., replacing batteries or scavenging energy) or in extremely harsh environments where power supplies and integrated circuits (IC) are not an option