The sensitivity of the Overhauser magnetometer is closely related to the polarization degree of the free radical solution in the sensor, and the polarization degree of the solution depends on the matching degree between the radio frequency excitation frequency and the electron paramagnetic resonance frequency in the free radical solution. To study the electron paramagnetic resonance frequency characteristics of the free radical solution in the Overhauser effect sensor, an electron paramagnetic resonance instrument for measuring the free radical electron paramagnetic resonance frequency is designed. The host of the electron paramagnetic resonance instrument uses DDS(Direct Digital Synthesizer) chip as a continuously adjustable radio frequency signal source of 30 MHz ~ 70 MHz, and adopts a high-bandwidth birdcage coil as the sensor radio frequency resonant cavity. The experiment results shows that under the condition of radio frequency power of 1. 5 W and polarization time of 10 s, the signal-to-noise ratio of the resonator output signal is 38, and the electron paramagnetic resonance frequency of the unknown free radical solution can be successfully calibrated.

Overhauser magnetometer, birdcage coil, electron spin resonance, Larmor precession