A high-sensitivity magnetoresistive magnetometer

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Abstract
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/(V Oe), 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.

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