Fiber optic magnetometer with sub-pico Tesla sensitivity for magneto-encephalography

This work reports a highly sensitive resonant Faraday force magnetometer with a minimum detectable rms magnetic field of 277 fT at 17.2 Hz suitable for magneto-encephalography and brain circuit imaging at room temperature. At this level of sensitivity, our sensor can favorably compete with superconducting quantum interference devices (SQUIDs) without requiring liquid helium cooling and with the possibility of monitoring brain activity in humans behaving in our natural environment. In addition to room temperature operation, our sensor is more compact (~4 mm² device area) compared to SQUIDs and has power dissipation comparable to MEMS devices. The light intensity coupled to the fiber optic waveguide varies exponentially with the displacement of the sensing cantilever and in contrast to electron tunneling detectors, the optical magnetometer has a large dynamic range and high sensitivity.