Design and Implementation of a Tuning-Matching Framework for a High-Sensitivity Broad Band Proton Precession Magnetometer Sensing Coil

The proton precession magnetometer (PPM) is always employed for geomagnetic observation, magnetic anomaly detection, etc., while the tuning performance of the PPM determines the signal-to-noise ratio (SNR) of the free induction decay (FID) signal output from the sensing coil. A tuned circuit was always used for the PPM sensing coil because of its narrow-band characteristic and high sensitivity. However, the FID signals might be distorted by the narrow bandwidth, which influences the PPM's measurement accuracy for the geomagnetic field. To address this problem, we propose a tuning-matching framework consisting of an adjustable tuning capacitor network (ATCN) in parallel with a π-type LC band-pass filter (LCBF), dubbed ATCN-LCBF. The equivalent circuit of the ATCN-LCBF are investigated and the corresponding electrical parameters are theoretically calculated. Consequently, the proposed ATCN-LCBF is conducted with a bandwidth of 3500 Hz, a pass-band gain of 5 dB, and an average noise floor of 1.67 nV/Hz
^1/2
. The field experimental results demonstrate that the ATCN-LCBF can not only enhance the strength of the FID signal but also suppress the external noises, improving the signal detection performance of the PPM in a scenario with strong interference.