Shield Room Research Articles

A user-friendly visual brain-computer interface based on high-frequency steady-state visual evoked fields recorded by OPM-MEG

Objective. Magnetoencephalography (MEG) shares a comparable time resolution with electroencephalography. However, MEG excels in spatial resolution, enabling it to capture even the subtlest and weakest brain signals for brain-computer interfaces (BCIs). Leveraging MEG’s capabilities, specifically with optically pumped magnetometers (OPM-MEG), proves to be a promising avenue for advancing MEG-BCIs, owing to its exceptional sensitivity and portability. This study harnesses the power of high-frequency steady-state visual evoked fields (SSVEFs) to build an MEG-BCI system that is flickering-imperceptible, user-friendly, and highly accurate. Approach. We have constructed a nine-command BCI that operates on high-frequency SSVEF (58–62 Hz with a 0.5 Hz interval) stimulation. We achieved this by placing the light source inside and outside the magnetic shielding room, ensuring compliance with non-magnetic and visual stimulus presentation requirements. Five participants took part in offline experiments, during which we collected six-channel multi-dimensional MEG signals along both the vertical (Z-axis) and tangential (Y-axis) components. Our approach leveraged the ensemble task-related component analysis algorithm for SSVEF identification and system performance evaluation. Main Results. The offline average accuracy of our proposed system reached an impressive 92.98% when considering multi-dimensional conjoint analysis using data from both the Z and Y axes. Our method achieved a theoretical average information transfer rate (ITR) of 58.36 bits min−1 with a data length of 0.7 s, and the highest individual ITR reached an impressive 63.75 bits min−1. Significance. This study marks the first exploration of high-frequency SSVEF-BCI based on OPM-MEG. These results underscore the potential and feasibility of MEG in detecting subtle brain signals, offering both theoretical insights and practical value in advancing the development and application of MEG in BCI systems.

Study on the magnetic shielding properties of nanocrystalline strips under bending stress

The study of the magnetic properties of nanocrystalline materials under stress is of great significance for the construction of small and lightweight magnetic shielding rooms. Therefore, this paper investigates the effect of stress on the magnetic properties of nanocrystalline materials under the action of external bending stress. By comparing the test results of the soft magnetic measuring device with and without bending stress, it is found that the magnetic permeability (μ i) decreases by about 51.41% when the introduced bending stress σ is increased by about 5.96 × 107 pa, whereas the KuFe−Si (induced magnetic anisotropy constant) and Hk (field of magnetic anisotropy) increase by 5.30 × 102 J m–3 and 1.08 × 102 A m−1, respectively. The Jiles-Atherton (J-A) model considering the bending stress and radius of change correlation is established, and the typical parameters of the J-A model are fitted using the Gazelle Optimization Algorithm (GOA), and the RMSE (root mean square error) of all of them are less than 0.056 T. The magnetic domain density increased with the increase of bending stress, which verified the correlation between the J-A model parameters and the bending stress. Our results reveal that the nanocrystalline macroscopic and micromechanical magnetic properties can be effectively combined with the J-A model, which will provide a theoretical basis for the simulation study of the nanocrystalline magnetic shielding device in the actual stress situation.

Low-Field, Low-Cost, Point-of-Care Magnetic Resonance Imaging.

Low-field magnetic resonance imaging (MRI) has recently experienced a renaissance that is largely attributable to the numerous technological advancements made in MRI, including optimized pulse sequences, parallel receive and compressed sensing, improved calibrations and reconstruction algorithms, and the adoption of machine learning for image postprocessing. This new attention on low-field MRI originates from a lack of accessibility to traditional MRI and the need for affordable imaging. Low-field MRI provides a viable option due to its lack of reliance on radio-frequency shielding rooms, expensive liquid helium, and cryogen quench pipes. Moreover, its relatively small size and weight allow for easy and affordable installation in most settings. Rather than replacing conventional MRI, low-field MRI will provide new opportunities for imaging both in developing and developed countries. This article discusses the history of low-field MRI, low-field MRI hardware and software, current devices on the market, advantages and disadvantages, and low-field MRI's global potential.

Low noise magnetic field compensation based on differential biplanar coils with small coil constant

Magnetic field noise is a key factor limiting the resolution of quantum precise measurement. In active magnetic field compensation systems, the large coil constant and fixed noise of the coil and current source, respectively, cause excessive noise. This study proposes a differential biplanar coils (DBCs) design method by comprehensively optimizing two sets of biplanar coils with differential evolution (DE) algorithm, which can reduce the coil constant by two magnitude orders while ensuring high uniformity. The peak-to-peak magnetic field at the center point is reduced to 0.8 pT, and the magnetic field noise is reduced to 8 fT/Hz, which is a reduction of 94.4%. The low noise active magnetic compensation system based on the differential biplanar coils can improve the accuracy of the magnetic shielding room (MSR) internal magnetic field control and reduce magnetic field noise effectively. The proposed method contributes to generating a near-zero magnetic field environment with low magnetic field noise, which is critical to promoting magnetoencephalography (MEG) measurements.

A Design Method of Biplanar Uniform Field Coils Based on Magnetic Shielding Rooms

A Design Method of Biplanar Uniform Field Coils Based on Magnetic Shielding Rooms

Analysis and Design of Biplanar Coils Within Magnetic Shielding Room Considering Actual Ferromagnetic Boundaries

Analysis and Design of Biplanar Coils Within Magnetic Shielding Room Considering Actual Ferromagnetic Boundaries

Radiation shielding and CuCr1Zr/Pb/PE and Fe/Pb/PE beam dump design for 220-MeV electron linear accelerator

This paper addresses the radiation issues, in particular the photon and neutron shielding, associated with the radiation shielding room and beam dump design for the 220-MeV electron linear accelerator. The energy deposition of a 220 MeV electron dump was investigated to determine the radius and length of the core of the dump with different materials. The angle of the primary shield relative to the beam direction was studied to design the perpendicular and lateral shield wall for the linear accelerator shielding room. In addition, the labyrinth design had been considered in this case. FLUKA Monte Carlo code has been computed to perform attenuation studies of photon and neutron radiation which were produced by the electromagnetic shower and photon interactions of materials. The prompt radiation fields which are photons and neutrons distributions in this design were observed. Two types of beam dump have been investigated. The first one is composed of CuCr1Zr, lead, and polyethylene. Another one is similar, but the first layer material was changed from CuCr1Zr to iron. The simulation results revealed that the beam dump and radiation shielding wall exhibit excellent performance in attenuating both photon and neutron radiation. The capability of beam dumps to absorb electron energy is well-designed. The dose distributions around the shielding room are below the design criteria, which can be applied to use for the 220-MeV electron linear accelerator.

Hybrid Method for Reducing the Residual Field in the Magnetic Shielding Room

This study proposes a hybrid method for improving the magnetic shielding performance of a magnetic shielding room (MSR) with few permalloy layers. In this method, two types of compensating coils are combined, one placed outside the MSR and the other placed inside. The coupling effect between the outside coil and the permalloy layer is used to adjust the residual field distribution characteristics of the MSR, and the inside coil is used to compensate for the adjusted residual field. This method has been verified with an MSR with two permalloy layers and an inner space of 1.3 m × 1.3 m × 2.2 m. According to the result, the residual field was reduced to less than 2.5 nT in a cube with a 0.4-m side length, which is seven times lower than that without compensation, and the inner space utilization rate was also improved by two times compared with existing MSRs with a comparable space size. The proposed method is of great significance in the development of magnetic shielding technology.

Analysis of the calculation method and evaluation of the magnetic acceleration noise of space inertial sensor

Accurately calculating the magnetic acceleration noise is essential to designing the space inertial sensor and constructing its evaluation system. In view of the shortcomings of the magnetic acceleration noise calculation model, which considers the test mass (TM) as an ideal magnetic dipole rather than an entity, the Maxwell stress tensor method (MSTM) and virtual work principle method (VWPM), which consider the influence of the shape and size of the TM into account are adopted in this study. Through comparison, it is concluded that the non-uniformities of the internal magnetic field and magnetization intensity of the TM are the reasons for the calculation error of the model, and when the magnetic susceptibility is <1 × 10−2, the model can satisfy the requirement of the calculation accuracy. Finally, two specific signals of the near-interplanetary magnetic field and the magnetic field of a circuit board were measured in a magnetic shielding room (MSR), and the magnetic acceleration noises induced by the two magnetic environments were calculated. These can act as significant reference values for magnetic acceleration noise experiments in orbit and the layout of electronic devices in satellite engineering.

A New Correction Method of Distributed Magnetic Sensor System Based on Magnetic Shielding Room

Distributed Magnetic Sensor System (DMSS) can measure vector magnetic field and magnetic gradient tensor (MGT) and is widely used in magnetoencephalography, geological exploration, magnetic navigation, magnetic positioning, and other fields. The posture and position of the magnetic sensor are the key factors that affect measurement accuracy. For the first time, using a magnetic shielding room (MSR) and a composite coil that can switch between uniform and gradient fields in situ, a new correction method for various errors is proposed to reduce vector measurement errors. In addition, sensor position deviation can also lead to MGT calculation errors. This paper establishes a compensation model by using the magnetic field gradient formula. The simulation results show that the average calibration errors of the posture and position of the magnetic sensor are 0.08% and 0.53%, respectively, and the measurement error of the MGT is reduced by four times. Experimental results in the MSR show that the measurement error of the vector magnetic field is reduced by two orders of magnitude and that of the MGT by one order of magnitude. Therefore, the new calibration method can effectively enhance the measurement accuracy of the DMSS.

Graphene and Fe2O3 filled composites for mitigation of electromagnetic pollution and protection of electronic appliances

With extensive advancement and abundant availability of telecommunication and electronic devices, electromagnetic pollution has become a serious concern not only for human health but also for much sensitive electronic equipment which may fail or malfunction due to electromagnetic interference. Therefore, effective and lightweight electromagnetic interference (EMI) shielding structures are of vital importance for human protection as well as for safeguarding sensitive electronic equipment from interference. In this regard, carbon fiber reinforced composite structures (CFRCS) have proven as one of the best options due to their light weight, extraordinary mechanical properties, and excellent durability. This study explored the synergistic incorporation of graphene and ferric oxide nanoparticles in the CFRCS at various loading concentrations to enhance their electromagnetic shielding effectiveness (EMI SE). According to the results, maximum EMI shielding effectiveness of 95.57 dB was attained at a 4% loading concentration of graphene and a 6% loading concentration of ferric oxide, over a broader frequency range of 0.1 GHz–13.6 GHz. In light of these results, different EMI shielding structures can be developed, including EMI shielding rooms for better protection of humans as well as any sensitive electronic equipment from the harmful effect of electromagnetic radiation. The obtained results are outstanding and may be employed commercially for the protection of electronic equipment and human individuals.

Fast Error Calibration for Three-Axis SQUID Magnetometers Based on Full-Space Rotational and Frequency-Controllable Magnetic Field

In order to overcome the limitations of the traditional error calibration method for three-axis superconducting quantum interference device (SQUID) magnetometers, this article presents a fast error calibration method for three-axis SQUID magnetometers. In the proposed method, a full-space rotational and frequency-controllable magnetic field with constant total field intensity can be generated by a triaxial Helmholtz coil. Meanwhile, the nonorthogonal error, zero offset error, and proportional coefficient error of the three-axis SQUID magnetometers, which measure the relative value rather than the absolute value, can be accurately solved by an error modeling and ellipsoid fitting theory. Compared with the traditional scalar calibration method, this method replaces the rotation of Dewar and three-axis SQUID magnetometers with a rotating magnetic field, thus avoiding the interference and influence of motion. Compared with the traditional vector calibration method, this method does not need to ensure the alignment between the three-axis SQUID magnetometers and triaxial Helmholtz coil. Moreover, the interference of low-frequency magnetic field can be suppressed by shortening the period of rotating magnetic field. Simulation and experiments prove the effectiveness of this method. After calibration by the proposed method, the root-mean-square error is reduced to 0.414 from 138.411 nT in the electromagnetic shielding room. Repetitive and comparative experiments with the traditional method in field also prove the superiority and stability of the proposed method.

Iterative Optimization Algorithm to Design Biplanar Coils for Dynamic Magnetoencephalography

In this article, an iterative optimization algorithm is proposed to design biplanar coils, which is used for dynamic magnetoencephalography to compensate for residual fields in the magnetic shielding room. The effects of magnetic shielding layers and plane’s side length on the uniformity are both considered for designing coils. The iterative calculation is used to minimize the side length of the coil plane. The biplanar coils with 1.3-m side length are designed, which consist of three homogeneous-field coils ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B_{x}, B_{y},\; { \rm and }\; B_{z}\; { \rm coils }$</tex-math></inline-formula> ) and five gradient-field coils ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dB_{x}/dy, dB_{x}/dz, dB_{y}/dy, dB_{y}/dz,\; { \rm and }\; dB_{z}/dz\; { \rm coils }$</tex-math></inline-formula> ). The coil system can produce homogeneous and gradient fields within 1% error over the volume of 40 cm × 40 cm × 40 cm. Through active magnetic shielding, the central field inside the magnetic room is reduced from 7.56 to 0.17 nT, and standard deviation from the mean value in the target area falls from 1.366 to 0.177 nT. The dynamic auditory stimulation experiment proves that the biplanar coil system will improve the quality of the evoked signals.

Research on the Design Method of Gradient Magnetic Field Coil Based on the Magnetic Shielding Room

Research on the Design Method of Gradient Magnetic Field Coil Based on the Magnetic Shielding Room

Design of Biplanar Nested Square Uniform Coil in Lightweight Magnetically Shielded Room for Magnetocardiography System

Design of Biplanar Nested Square Uniform Coil in Lightweight Magnetically Shielded Room for Magnetocardiography System

Design of Biplane Coils Based on Funnel Algorithm for Generating a Near-Zero Magnetic Environment in MSR

The biplane coils (BCs) based on the inverse-design method are crucial for creating the near-zero magnetic environment in magnetic shielding room (MSR), but multi-parameters optimization remains a key factor that limits the performance of the BCs. This study proposes a funnel algorithm (FA) to solve the issue of multi-parameter optimization in the design. The upper and lower limits of the parameters are dynamically adjusted based on the previous calculating step. By gradually reducing the upper and lower limits, we achieve the BCs with optimal performance. This method has been verified by both the theoretical analysis and experimental test. Compared with other methods, the designed coils show a higher space utilization ratio (SUR) and smaller relative errors, with the SUR improved from 1.6% to 3.75% and the relative errors all less than 2%. Based on the designed BCs, the total residual magnetic field is stabilized below 40.4 pT at the central point of the MSR, with the noise reaching the intrinsic noise of the flux-gate magnetometer in the frequency range of interest. The proposed method can significantly improve the performance of the BCs, thus reducing the space and construct cost of the MSR and promoting the magnetoencephalogram (MEG) measurement based on the quantum technology.

Simulation of Large-scale Magnetic Shielding Room for High-precision Vector Magnetometer Ground Test and Calibration System

Simulation of Large-scale Magnetic Shielding Room for High-precision Vector Magnetometer Ground Test and Calibration System

Nested Magnetic Field Compensation With Regulated Coefficients for Bio-Magnetic Field Measurement

For a spin-exchange relaxation free (SERF) optically pumped magnetometer (OPM) that obtains its best performance in a zero magnetic field, an operation environment with approximately zero magnetic field is desired. This article proposes a nested magnetic field compensation system for a magnetic shielding room (MSR) to suppress the magnetic field. Two sets of coils, one set located outside of the MSR and the other one placed inside of the MSR, are combined in the system. The magnetic fields outside of the MSR are measured by tunneling magnetoresistance (TMR) sensors, while the fields inside the MSR are monitored by SERF OPMs. The two kinds of sensors complement each other in terms of measurement range and sensitivity. A nested two-stage proportional-integral (PI) closed-loop control strategy is employed to compensate for the magnetic field inside the MSR. The control parameters are regulated by the magnitude of the magnetic field to take advantage of the two kinds of sensors. The effect of the proposed system is experimentally tested. The three-axis field fluctuations are reduced by 97.52%, 98%, and 98.64% by the proposed method, respectively. The proposed method is compared with a conventional two-stage series PI control system. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -axis magnetic field fluctuations of the conventional PI control system and the proposed system are 75.81 and 11.71 pT, respectively. The magnetic fluctuation of the proposed system is about 15.5% of the fluctuation of the conventional PI system. To validate the feasibility of the proposed magnetic field compensation system for ultra-weak bio-magnetic field measurement, magnetocardiography (MCG) and magnetoencephalography (MEG) signals are measured.

Simulation of Large-scale Magnetic Shielding Room for High-precision Vector Magnetometer Ground Test and Calibration System

Simulation of Large-scale Magnetic Shielding Room for High-precision Vector Magnetometer Ground Test and Calibration System

Analysis of the operation of mechanical equipment during the operation of hydro engineering facilities of HPP

According to its technological purpose and location, the mechanical equipment of the hydrotechnical structures of the hydroelectric power station is divided into three groups: the equipment of the upstream shield room, the turbine room and the downstream shield room. The article discusses in detail the main features and problems that arise during the operation of the mechanical equipment of the upstream shield compartment. This mechanical equipment serves to protect the units from overclocking; overlapping of inlet openings of spillways in case of accidents with main gates; for fencing from the headwater side when access to the underwater parts of the structure and equipment is required. It is noted that a feature of the operation of mechanical equipment is a large number of metal structures that are under water or are wetted with water and thereby undergo biochemical corrosion, which causes intensive destruction of the metal. The ways of preventing the development of corrosion and methods that ensure the durability and effectiveness of protection against biological fouling, metal structures at hydroelectric power plants are presented.