A Novel Magnetic Suppression Technique for Asymmetric-Distributed Magnetic Disturbance in CMS for MCG Test

The cylindrical magnetic shield (CMS) with the advantages of easy-process, low-cost and portable-mobility is widely utilized in magnetocardiography (MCG) for recording the weak biomagnetic field of cardiac. The one-side-open structure of CMS leads to excessive flux leakage and uneven-distributed magnetic field, which cause extra degradation of sensitivity and signal noise ratio of MCG test. Therefore, an enhanced magnetic suppression technique for reducing the asymmetric-distributed remanence and magnetic noise inside CMS is proposed in this paper. This method introduces the Fourier series with half-angle component for asymmetric compensation field generation and combines the analytic method to model and weaken coupling effect impact. The feedback control is employed in the compensation system for static and dynamic magnetic interference containment. The asymmetric-distributed remanence <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_y</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_z</i> is suppressed near zero, and the magnetic noise of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_y</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B_z</i> at 0.01 Hz is restrained from 59.3 to 0.06 pT/Hz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> and 92.7 to 0.24 pT/Hz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> with the inhibition rate of 29.95 dB and 25.87 dB respectively. The MCG test with high signal-to-noise ratio is then realized inside the MCS with the asymmetric compensation system.