In a practical multichannel magnetocardiography (MCG) system based on superconducting quantum interference device (SQUID) magnetometers, the Tesla/Volt coefficient must be precisely calibrated for accurate analysis of heart diseases. In this article, we utilize the biplanar coil to calibrate the SQUID magnetometers in an MCG system for the first time. The coil design theory is discussed in detail, including the target-field theory and the Tikhonov regularization method. Also, the coil winding patterns can be obtained after discretization of the stream function, which is related to the current density. By defining the parameter of calibration uncertainty, the performance of the biplanar coil is analyzed and compared with a rectangular Helmholtz coil based on the COMSOL simulation method and experimental measurement. The measurement results are well in coincidence with the simulation ones, indicating that the biplanar coil has remarkable advantages over the Helmholtz coil. Also, Tesla/Volt coefficient calibrations of four SQUID magnetometers in an MCG system are conducted inside a magnetically shielded room (MSR) depending on these two coils. The final results show the superiority of the biplanar coil method in MCG system calibration.

Traditional active magnetic compensation systems applied to magnetocardiography (MCG) suffer from low compensation accuracy and high structural complexity. To further suppress the residual magnetic field and improve the integration degree of the compensation system, an active magnetic compensation system based on a digital signal processor (DSP) and an active disturbance rejection controller (ADRC) is proposed in this paper. In this system, a cylindrical coil driven by the DSP is utilized to generate a compensation field. After introducing the ADRC, the cylindrical coil receives a dynamic compensation current, and the residual magnetic field monitored by a reference optically pumped magnetometer (OPM) changes significantly, which is manifested as a magnetic compensation signal of high precision generated in the predetermined target area. The experimental results show that the system suppresses the DC component and fluctuation of the residual magnetic field to 0 pT and 4 pT. It improves the noise suppression ratio (NSR) to more than 6.5 times in the low frequency range from 1Hz to 50 Hz, which indicates that the compensation system has great suppression performance.

In this article, a modified design method is proposed for a kind of highly uniform magnetic field (UMF) coil, whose target region is off-center defined. Combining the traditional target field method (TFM) with the slime mold algorithm (SMA), a new intelligent algorithm with excellent searching ability, optimal parameters can be obtained to determine the structure of the designed coil. To further improve the uniformity performance in the target region, a distance factor is introduced to optimize the distribution of target points. According to the simulation results from the finite element analysis (FEA), the absolute maximum uniformity error can be optimized from 0.098% to 0.060% if the SMA is utilized, and after the optimization of target points, the volume proportion of absolute uniformity error less than $10^{-4}$ can be increased to 64.60%. An upscaled coil of 10 times is fabricated via the flexible printed circuit technology, and test results of the magnetic field generated by this coil show a good agreement with the simulation ones. It indicates that the actual uniformity error in the range of ±0.35 R reaches to 0.11%, which is acceptable when taking manufacture and measurement errors into consideration.

Magnetically shielded cylinder (MSC) is an efficient way to construct a proper working environment for spin-exchange relaxation-free (SERF) magnetometers. In this paper, we propose a modified hybrid method combining analytical solutions with finite element analysis (FEA) to improve the design efficiency and validity of an MSC. Focusing on the radial and axial shielding factors, the number of Permalloy-shell can be fast determined as 4 via analytical solutions. Then based on a carefully built FEA model in COMSOL, shielding factors together with uniformity factors extracted from magnetic distribution maps, are employed to optimize the distance of air gaps and the size and shape of access holes. The shielding performance is well tested after the realization of MSC with optimal structural parameters. It shows that the static residual field can reach as low as 0.50 nT and 1.39 nT in radial and axial directions, and the field uniformity are superior to 5% in most of the target region. The measurement results are well in coincidence with the simulation ones, indicating the validity of this hybrid design method.

Dielectric-metal nanostructures have lately emerged as one of the most promising approaches to modulating light at the optical frequency. Their remarkable electric and magnetic resonances give them a one-of-a-kind ability to augment local field enhancements with negligible absorption losses. Here, we propose a hybrid metal-dielectric-metal (MDM) nanoantenna that contains a dimer of three-layers of shell nanoparticles. In addition, we only theoretically and numerically show the optical properties of the hybrid dimer nanoantenna. We found that the nanoantenna sustained unidirectional forward scattering with narrow beamwidth (30.9 deg) and strong scattering intensity (up to 5 times larger than the single MDM particle). Furthermore, when the hybrid asymmetric dimer was excited by the plane wave with different electric polarization directions, our findings revealed that the hybrid nanoantenna boosted the gap’s electric near-field while also supporting unidirectional forward scattering. Finally, we analyzed the hybrid dimer with substrates of different materials. It supported strong electric high-order moments along the z-axis and x-axis in gaps between MDM nanoparticles and between MDM nanoparticles and the Ge substrate, owing to the intense displacement currents inside of the dielectric layer. We found that the local electric field of this MDM hybrid dimer nanoantenna with Ge substrate was well improved and attained 3325 v/m.

Synthetic gradiometers constructed by Superconducting QUantum Interference Device (SQUID) magnetometers are effective ways to suppress the magnetic disturbance while keeping the useful signals unaffected. In this paper, in order to obtain the optimal baseline for a first-order synthetic gradiometer (FOSG) inside a thin magnetically shielding room (MSR), a modeling method based on the magnetic flux distributions in the sensing and reference magnetometers is proposed. Then the model is built in the Ansys platform, and the baseline can be determined as 6 cm under a certain signal source depth of 4 cm after conducting the finite element calculation. Two kinds of magnetometers with different pickup coils contribute to the realization of the testing system. The testing results have a good agreement with the simulation ones. And depending on this optimized configuration of the FOSG, the residual field of a real thin MSR can be restrained from 2.0 nT to 4.0 pT. Moreover, a clear magnetocardiography (MCG) signal with an amplitude of 48 pT and stable zero-line can be observed when applying a subject for test, which further verifies the effectiveness of this modeling method.