A HIGH-SENSITIVITY MAGNETORESISTIVE MAGNETOMETER

A high-sensitivity, small-size, low-power-consumption, broad-bandwidth magnetometer has been built in which a magnetoresistive element is located adjacent to a gap between two thin-film flux concentrators. The concentrators magnify the sensed component of magnetic field 20-fold while simultaneously shielding orthogonal fields by more than a factor of 10. The sensor plus bias coil fit inside a 6-mm-diam probe. The intrinsic sensitivity is approximately 50 mV/(VOe), and is flat from dc out to 50 MHz. With a sensitivity of 300 mV/Oe at 100 mW power, a 2-Hz slot signal-to-noise ratio (SNR) of 30 dB at dc, and a 200-Hz slot SNR of 40 dB at 1 MHz, has been measured when detecting a 1 gamma (10(-5) Oe or 1 nT) signal field. With design enhancements and ac detection techniques to eliminate thermal drift and 1/f-type noise, detection of low-frequency magnetic fields of the order 1 mgamma could be achievable.