Research of a Tri-Axial Coil With Co-Surface Structure in Residual Field Suppression for Atomic Magnetometers

For atomic magnetometer applications, cylindrical magnetic coils providing high uniform field are essential for residual field compensation inside a magnetically shielded cylinder (MSC). In this paper, we present a tri-axial co-surface (TACS) coil aimed to simplify the compensation coil structure and save the inner MSC space. The design method of this new coil is based on a modified target field method (TFM). And the particle swarm optimization (PSO) algorithm, enhanced by an adaptive strategy, is developed to determine the optimal structure parameters of this coil. According to the simulation results from the finite element analysis (FEA), the maximum uniformity errors for B<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub>, B<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> and B<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sub> coils can be kept at 4.6×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup>, 5.1×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and 5.6×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup>, respectively. The coil performance is well confirmed as the test results from a real coil are consistent with the simulation ones. Moreover, an active compensation system is built based on this TACS coil and a traditional proportional-integral-derivative (PID) controller. It indicates that the DC component of the residual field inside an MSC can be successfully suppressed to 0 pT and the remained radial and axial fluctuations are respectively in percentage ranges of [-1.50%, 1.69%] and [-2.44%, 2.42%], which further verifies the usefulness of this coil.