Introduction. There are three main means of supression of electromagnetic interference that can reveal at the operation of SQUID magnetometers – spatial and frequency signal selection and digital processing. The spatial signal selection is the most effective means that allows to significantly improve the signal/interference ratio directly in the receiving superconducting antenna. To optimize the design of the balancing system of the receiving gradiometric antenna is an important task in the conditions of existence of high electromagnetic interference in the contemporary city.
The purpose of the work is to justify and develop a new design of the balancing mechanism of superconducting gradiometric antenna of the SQUID magnetometer for operation in conditions of a high level electromagnetic interference. To develop an algorithm for balancing the antenna of such a SQUID magnetometer.
Results. The paper considers the main implementations of gradiometric antennas and their balancing methods. As the main factor affecting the normal operation of the balancing system of the gradiometric antenna of the SQUID magnetometer over a long period of time (the time between refueling the cryostat with liquid helium), the decrease in the level of liquid helium in the cryostat was emphasized. Such a decrease in level leads to the deformation of individual elements of the balancing system. As an counteraction to this, it is proposed to place the mechanism for moving the gradiometer balancing elements directly in the antenna housing. In it the all parts of the mechanism are located below the level of liquid helium during the entire time the magnetometer is operating. The analysis of the resistance to temperature and mechanical effects of individual elements of the balancing system was carried out. The approach to choosing the optimal size of the balancing element is substantiated, this size influences at the degree of the balance of antenna.
The output of the magnetometer on the field of Helmholtz coils during the movement of balancing elements of different sizes along the axis of the axial gradiometer was obtained experimentally. Experimental results were obtained for a superconducting antenna – the second-order gradiometer, with a diameter of 20 mm and base of 60 mm.
Conclusions. The approach proposed by the authors to increase the efficiency of electromagnetic interference filtering with the help of superconducting gradiometric antennas made it possible to develop a new design of their balancing mechanism. Its advantage is the resistance to mechanical stresses of individual elements of the system, which arises as a result of the existence of significant temperature gradients during the evaporation of liquid helium.
The proposed algorithm for balancing of the superconducting gradiometer can be applied to balance superconducting gradiometric antennas of any configuration and size. Keywords: superconductivity, SQUID-magnetometer, antenna balance, optimization.
