Active magnetic field compensation system using proton precession scalar magnetometer for SQUID based applications

Abstract

A sensitive proton precession scalar magnetometer has been implemented and used for the active compensation of magnetic fields. For establishing a silent environment for SQUID applications, two approaches might be considered, which consist of passive and active magnetic shielding [1]. Each of these two approaches has its own benefits. In active shielding approach, using vector sensors for the active shielding or calibration systems, has a main complication in precise alignment of the sensor and the coils. This is due to the fact that, the sensitivities and offsets of individual sensors, their mutual angular deviations, and the misalignment between the coil and the sensor reference system have to be exactly considered [2]. Because of these complications, scalar magnetometers have an advantage of more accuracy than vector magnetometers in calibration of active shielding. In scalar active compensation system, shielding is based on elimination (compensation) of external magnetic field by applying proper currents through different coils of the system. In this work a magnetic compensation system has been made based on proton precession magnetometer. Proton Precession scalar magnetometer is used for external magnetic field measurement and based on the measured signal, other processing and amplification circuits apply the compensation currents into the coils of the system [3]. The readout circuits of the sensor which is based on measuring of the precession frequency of Hydrogen atoms around the external magnetic field, has been designed with especial noise consideration for increasing SNR for maximum sensitivity. This system is to be used for different SQUID applications which require a very silent magnetic environment. It should be noted that the mentioned system could be also used for the calibration of the coil systems for vector magnetometer calibration.