Research on an Improved Resonant Cavity for Overhauser Geomagnetic Sensor

Resonant cavity is an important component of Overhauser magnetometer sensor. Its function is to make the working substance generate dynamic nuclear polarization effect in the sensor. An alternative design of resonant cavity based on the birdcage coil structure is proposed to make the resonant frequency in accordance with the polarization frequency of the working substance. The structure and equivalent circuit of resonant cavity are analyzed. The model of resonant cavity is established, and S-parameter is calculated. The simulating results show that resonant frequency of the resonant cavity is about 60 MHz, which is consistent with the polarization frequency of the working substance in the sensor, and Q-factor of the resonant cavity is about 90. A dual-coil structure for pick-up coil and series resonant circuit are designed for reducing interference. In addition, output signal experiment and simultaneous comparison testing of sensor prototype are conducted. Overall, this design has the advantages of high performance and strong anti-interference. The resolution, uncertainty, and range of the sensor reach to 0.005 nT, 0.2 nT, and 20 000–100 000 nT, respectively.