Experimental verification of the performance of the self-tunable loop-current array shielding module

An active shielding module consisting of a self-tunable loop-current array is verified experimentally. Loop currents in the array are independently controlled by the magnetometer dedicated to each of them. Since magnetic field decays as 1 z3 along the distance z from the loop, the magnetic noise should be overcompensated at the location of the loop-current array to provide a good cancellation in the shielded area. In order to enable overcompensation in a stable feedback system, a small additional loop is combined to the magnetometer that reduces the magnetic direct coupling from the main loop current to the magnetometer. A feedback electronic circuit with a proportional-integral (PI) controller is combined with each of the array element to establish a stable canceling operation. An orthogonal fluxgate magnetometer is used to monitor incident magnetic noise. Shielding performance of an array consisting of nine loop currents arranged in a 3×3 grid was evaluated numerically and confirmed by experiments. Evaluation and measurements are done over the 1.5×1.5 m2 area 2 m in front of the array. The magnetic dipole disturbance source is placed 2 m further beyond the array. Attenuation of the magnetic field is calculated as 115. Experimental data show 110 attenuation.