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 article. 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 ${B} _{y}$ and $B_{z}$ is suppressed near zero, and the magnetic noise of ${B} _{y}$ and Bz at 0.01 Hz is restrained from 59.3 to 0.06 ${pT/Hz}^{1/2}$ and 92.7–0.24 ${pT/Hz}^{1/2}$ with the inhibition rate of 29.95 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.

Structural color (SC) has enormous potential for improving the visualization and identification of functional micro/nano structures for information encryption and intelligent sensing. Nevertheless, achieving the direct writing of SCs at the micro/nano scale and the change of color in response to external stimuli simultaneously is rather challenging. To this end, we directly printed woodpile structures (WSs) utilizing femtosecond laser two-photon polymerization (fs-TPP), which demonstrated obvious SCs under an optical microscope. After that, we achieved the change of SCs by transferring WSs between different mediums. Furthermore, the influence of laser power, structural parameters, and mediums on the SCs was systematically investigated, and the mechanism of SCs using the finite-difference time-domain (FDTD) method was further explored. Finally, we realized the reversible encryption and decryption of certain information. This finding holds broad application prospects in smart sensing, anti-counterfeiting tags, and advanced photonic devices.

The MINI-magnetically shielded cabin (MINI-MSC) offers a near-zero magnetic environment for optically pumped atomic magnetometers (OPMs) to measure the magnetocardiography (MCG) and magnetoencephalography (MEG). However, the MINI-MSC’s confined interior and restricted uniform area make it challenging to capture high-quality bodily signals. Once the external interference surpasses the passive magnetic shielding capacity of the MINI-MSC, the volume and the homogeneity of the uniform region are reduced significantly, leading to the poor quality of the signal collected by OPMs. Therefore, an uniform active magnetic compensation system (UAMCS) composed of bi-planar coils (BCs) is introduced to suppress interference for enlarging the uniform region. The performance of the UAMCS depends on the BCs, but under finite-size ferromagnetic boundaries, approximate magnetic field values that deviate from reality are usually provided by the image method with the inaccurate calculation. To overcome these limitations, an analytical expression of the absorption current is derived to accurately characterize the coupling effect, thereby maintaining the high uniformity performance effectively. A forward analytical model is proposed to characterize magnetic fields, and the equivalent current could be analytically determined, which are put into the target field method (TFM) to express the superimposed the magnetic field. The inhomogeneity errors of BCs using the forward analytical model are 0.39 times of the image method. After the magnetic compensation, the signal-to-noise ratio at 0.1 Hz, 1 Hz and 10 Hz were improved by 39.5 dB, 34.3 dB, and 6.7 dB, respectively, verifying the magnetic noise can be well compensated in the whole target region. Note to Practitioners —The challenge of ensuring high signal quality in MINI-MSC for OPMs is critical in biomedical imaging applications. An forward analytical method is introduced to character the absorbed magnetic field of shielding layers, and an advanced UAMCS utilizing BCs is used for the precise magnetic field compensation to significantly enhance the signal-to-noise ratio. This approach addresses the limitations of traditional image methods, offering improved accuracy in magnetic compensation and enhance the reliability of MEG and MCG tests.

Magnetocardiogram (MCG) requires near-zero magnetic environment, which cannot be achieved by passive shielding structure, and needs to be combined with active compensation to reduce environmental magnetic field interference. However, the environmental magnetic field is multi-directional. In this study, a multiplex coil compensation system with a matrix-based expansion magnetic field model was constructed for near-zero magnetic field environments in MCG. First, a matrix-based expansion model was established to quantify magnetic field distribution that could be used as compensation. Second, by using the particle swarm optimization algorithm with adjustable weights, the best adjustive excitation vector of the proposed matrix was obtained, despite ill-posed problems, allowing the active compensation system to suppress residual magnetic fields. Simultaneously, the multiplex compensation system was employed to follow and reduce magnetic field fluctuations in the measurement signals. Finally, cardiac magnetic signals were measured and evaluated based on the effectiveness of creating a near-zero magnetic field environment and the improvement of the signal-to-noise ratio.

This paper presents a design method of biplanar coils to realize precise compensation for residual magnetic fields inside magnetic shielding rooms (MSR) based on an improved particle swarm optimization algorithm with the moore-penrose pseudoinverse. The mirror image method (IM) is introduced into the traditional target field method (TFM) to weaken the coupling effect between the magnetic shielding material and the magnetic field generated by the coil. An improved particle swarm optimization (IPSO) algorithm with the moore-penrose pseudoinverse is used to obtain the coils’ parameters, thus determining the shapes of the coils. The simulation results show that the maximum deviations of B_x and B_z coil designed by this method are improved by 74.7% and 59.5%, respectively.

To establish a near-zero magnetic environment for accurate magnetocardiography (MCG) measurements, a magnetically shielded cylinder (MSC) is commonly used in combination with active magnetic compensation coils. However, the coupling effect between the field from internal coils and the magnetic shielding layer can distort the distribution of ideal magnetic field and degrade the quality of cardiac magnetic signals. To address this issue, this article proposes a design approach for self-shielding coils featuring curved structures that integrate the target-field method with the pigeon-inspired optimization algorithm. The results indicate that the optimized coils maintain nonuniformity error below 1% in the internal region with a side length of 0.2 m and attain an attenuation error below 5% in the external area. This means that the coils are not easily affected by ferromagnetic materials and are suitable for MSCs of different sizes. An optically pumped magnetometer-based magnetocardiography (OPM-MCG) system, using two sets of single-axis curved coils, is used to compensate for the background field interference, resulting in an improved signal-to-noise ratio (SNR) for cardiac magnetic signals. Within the frequency range of 1–40 Hz, the average sensitivity of the OPM-MCG compensation system improves from 810.59 to 97.63 $\text{fT/Hz}^{1/2}$ , and it achieves 9.19 dB of noise suppression. Based on the enhanced MCG system, the collected MCG signals reveal significant SNR gains of 6.44 and 5.89 dB in the R-wave and T-wave segments, which lays a foundation for further exploration of cardiac electrophysiological information and assisted cardiac treatment.