Development and experimental study of the low-temperature SQUID magnetometers

The goal of the study is to create and test the 4/9-channel magnetometers based on Superconductive Quantum Interference Device (SQUID) with high magnetic field resolution, dynamic range, and long-term noise-immunity (stability), which enables working at a lab or clinic location under the presence of high-level industrial magnetic interferences, but without a Magnetic Shielded Room and Reference Vector Magnetometer. Results of experimental studies on the signal and noise parameters of SQUID magnetometers based on direct current (dc) and relaxation oscillation (RO) designs were presented. It was demonstrated that the RO SQUID magnetometer exhibits better resolution and a higher transfer factor compared to the dc one in an urban environment and in the presence of high industrial magnetic disturbances, without the need for magnetic shielding. On the contrary, dc magnetometer has better noise-immunity against pulse disturbances, thus dc SQUIDs are more appropriate for an unshielded environment. The frame of the input antenna, i.e., magnetic flux gradiometer of the 2nd order, was made from carbon-filled composite, which has a lower magnetic susceptibility than graphite and better hardness during many cycles from helium to room temperature. Designed dc SQUID magnetometers have a resolution of 0.3 pT, a transfer factor of 4 mV/рТ, and a dynamic range of 84 dB. Developed SQUID magnetometers are used in magnetocardiographic scanners intended for medical diagnostics of cardiology diseases in clinical location, and in low-frequency susceptibility system intended for lab studies of the magnetic susceptibility of biological and technical samples, including live animals (mice, rat, rabbit) and magneto-sensitive nanocomposites for biomedical applications.