Research on an omnidirectional proton precession magnetometer sensor based on solenoidal coils

The performance of the sensor determines one of the important factors in the measurement accuracy or uncertainty of the Proton Precession Magnetometer (PPM). Especially in mobile measurement application, the sensor’s orientation insensitivity and portability requirements are more stringent. In fact, sensors made of toroidal or cylindrical coils have many problems such as large volume and difficulty in winding, and thus the solenoidal coils are commonly used as PPM sensor coils and have excellent performance. However, when the aixs of solenoidal coil is the same as the direction of the magnetic field, the sensor cannot induce the NMR signal. Aiming at this problem, this paper proposes a simple omnidirectional PPM sensor with three solenoidal coils connected in series. The axial directions of the three solenoids intersect each other so that the sensor can induce signals in the direction of any geomagnetic field. This structure does not affect the polarization process and magnetization of the proton, but due to the axial crossing, the maximum induced signal amplitude is reduced compared to the sensor in which the coil axes are parallel to each other. Therefore, the relationship between the angle between the sensor coils and the sensitivity of the magnetic field orientation is analyzed. In order to improve the actual measurement accuracy, the design method of improving the SNR and anti-interference of the sensor is further studied. How to improve the coil structure, solve the signal loss problem, and improve the anti-interference ability of the sensor is one of the future research work. This paper aims to analyze the orientation sensitivity characteristics of an omnidirectional PPM sensor based on three solenoidal coils, which provides a new idea for sensor design in manual mobile measurement applications.