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An analytical formulation for magnetic field penetration through a circular aperture in a thin perfect electric conductor (PEC) screen with finite-thickness is developed. Especially, we propose an analytical formula for the magnetic coupling between two circular loops separated by the screen and placed coaxially with the aperture. The formula is verified by finite element simulations and experimental data. The thickness effect is explained by the cut off attenuation of TE01 mode in the aperture. The influences of loop-screen-loop distance and loop radius on the coupling intensity are also investigated.

Currently, circuits for quantum informatics, communications and measuring equipment containing superconducting flux qubits in a planar design are being created by quantum engineering techniques. To function, such structures must be cooled in a refrigerator down to about 10 mK. The flux qubits have linear size of superconducting circuit of some tens of micrometers and are very sensitive to external magnetic fields and their variations. The qubit built in the gradiometer-like design has reduced sensitivity to external uniform magnetic fields, but remains quite sensitive to their variations. To protect the qubit from unwanted external magnetic fields, which include the Earth's field, man-made fields, and residual magnetic fields of the cryostat parts, it is necessary to create efficient magnetic shields. Earlier, we proposed a scheme for a single-photon microwave counter, in which a planar flux qubit in a gradiometer version serves as the receiving element. To let it function properly, a 3-layer hybrid magnetic shield composed of two superconducting and one ferromagnetic cylinders, has been designed for installation in a dilution refrigerator at 10 mK temperature. The effectiveness of such a shield depends on the correct design of all three shells. This paper presents the results of calculation and magnetic measurements of a cylindrical ferromagnetic screen made of low-temperature permalloy Cryoperm 10 in dc and low-frequency alternating magnetic fields. Cryoperm 10 keeps high magnetic permeability at liquid helium temperatures and below. It is shown that this shield is able of reducing the absolute value of the magnetic field and its variations by 55-70 dB. Together with superconducting lead magnetic shields, this design will reduce the absolute value of the field by 70 dB, and the field variation by 200 dB, which will provide the necessary conditions for the operation of a single-photon counter based on a flux qubit.

The Bloch equation of the nuclear magnetization of spin-1/2 nuclei in molecules, which have permanent electric dipole moments μe that are placed simultaneously in a magnetic field B and an electric field E, is derived. It is shown that if the principal components of the nuclear magnetic shielding tensor σ and the dipole moment μe are known, then the measurement of the transverse component to the magnetic field B of the nuclear magnetization, which is induced by the application of the electric field oscillating at the half of the spin precession frequency, allows determining the orientation of the dipole moment μe with respect to the principal axis system of the symmetric part of the tensor σ. Four-component relativistic density functional theory computations, which have been performed for several molecules containing heavy nuclei, i.e., 207Pb, 205Tl, 199Hg, 195Pt, and 125Te, indicate that coefficients of the relaxation matrix perturbed by the electric field E are in favorable cases of the order of 1000 pm² V-2 T-2. Therefore, the spin dynamics is perturbed at experimentally observable levels for the strengths of electric and magnetic fields E = 5 kV/mm and B = 10 T, respectively. [ABSTRACT FROM AUTHOR]

According to the requirements of weak current measurement in power grid, a weak current sensor with anti-low frequency interference ability is developed. The sensor adopts the principle of fluxgate detection and adds a magnetic ring on the original basis. The structure of the magnetic ring is simulated using comsol to further improve detection sensitivity. In order to solve the problem that the electromagnetic current sensor is vulnerable to the interference of geomagnetic field and power frequency magnetic field in weak current measurement, a magnetic shielding method with low cost is selected, and the shielding shell structure is designed using a finite element analysis method. The experimental results show that the minimum measurable current is 1 mA, the measurement range is 1 mA–1 A, and the bandwidth is DC-16 kHz. The designed magnetic shielding shell can effectively reduce 97.3% of the DC magnetic field interference and 95.7% of the power frequency magnetic field interference. The sensor can realize accurate measurement of weak current in power grid. [ABSTRACT FROM AUTHOR]

With the widespread use of magneto-sensitive elements, magnetic shields are an important part of electronic equipment, ultra-sensitive atomic sensors, and in basic physics experiments. Particularly in Spin-exchange relaxation-free (SERF) co-magnetometers, the magnetic shield is an important component for maintaining the SERF state. However, the inherent noise of magnetic shield materials is an important factor limiting the measurement sensitivity and accuracy of SERF co-magnetometers. In this paper, both amorphous and nanocrystalline materials were designed and applied as the innermost magnetic shield of an SERF co-magnetometer. Magnetic noise characteristics of different amorphous and nanocrystalline materials used as the internal magnetic shielding layer of the magnetic shielding system were analyzed. In addition, the effects on magnetic noise due to adding aluminum to amorphous and nanocrystalline materials were studied. The experimental results show that compared with an amorphous material, a nanocrystalline material as the inner magnetic shield layer can effectively reduce the magnetic noise and improve the sensitivity and precision of the rotation measurement. Nanocrystalline material is very promising for inner shield composition in SERF co-magnetometers. Furthermore, its ultra-thin structure and low cost have significant application value in the miniaturization of SERF co-magnetometers. [ABSTRACT FROM AUTHOR]

Visualization of electron delocalization and aromaticity in some selected arynes, including nonplanar examples, and their Diels–Alder or dimerization reactions was achieved through multidimensional isotropic magnetic shielding contour maps. These maps showed that arynes are generally less aromatic than the corresponding arenes, and that aromaticity peaks during their reactions when approaching the transition state. [ABSTRACT FROM AUTHOR]

Infants with esophageal atresia and/or tracheoesophageal fistula (EA/TEF) undergo screening for tethered cord syndrome (TCS) via ultrasound and magnetic resonance imaging. Existing literature lacks data to guide optimal timing of screening and magnetic resonance imaging (MRI) is often delayed until 3-6 mo of age, when it is frequently forgotten. Detethering surgery has a high rate of success in patients with TCS and is often performed prophylactically due to potential irreversible deficits. This study aims to improve screening procedure for infants with EA/TEF. A retrospective chart review was done of all EA/TEF patients treated over 6 y (n = 79). The study examined how often each imaging modality was performed and identified a TCS lesion, as well as age of screening/surgical intervention. Screening for TCS was done with MRI 58% of the time and US 15% of the time. However, 38% of patients did not undergo any screening. Out of the patients with TCS on MRI (n = 19, 41.3%), 73.7% had neurosurgery. Of patients who underwent ultrasound (US) (n = 12), nine patients also had MRI later: two reported TCS lesions and subsequently had neurosurgery. Surgical infection rates and complications were 0/14. MRI demonstrated a higher rate of detecting TCS lesions than US, and patients with TCS frequently had detethering. Patients with ≥3 VACTERL or vertebral anomalies had a higher incidence of TCS on MRI. Patients with vertebral anomalies reported false negative ultrasounds in two cases, suggesting the potential superiority of MRI screening in this subgroup. A third of children did not undergo any imaging and this will require a process improvement. [ABSTRACT FROM AUTHOR]

This article presents a design method of cylindrical uniform field coil based on quasi-elliptic function fitting (EFF) method with multiple optimizations. The EFF method is a type of discrete wire techniques aiming at simplifying the coil structure. Combing with particle swarm optimization (PSO) algorithm, the optimized parameters of EFF coil are obtained for highly uniform magnetic field. To further improve the uniformity of magnetic field in the central space, a new regional points selection optimization method is proposed. The calculation results show that after PSO optimization, the absolute maximum relative error in the target region is optimized to 0.098% by EFF coil comparing with modified single saddle coil (3.08%), nest coil (2.4%), and target field method (TFM) coil (0.11%). After regional points selection optimization, the volume proportion of absolute magnetic field relative error less than $1\times 10^{-4}$ increases from 35.24% to 54.38% by EFF coil comparing with TFM coil. In addition, the simple EFF coil structure is verified to be easy to process and keep high performance through experiments. As the EFF coil’s high uniformity and simple structure, the new method has important significance for the miniaturization of atomic sensors. [ABSTRACT FROM AUTHOR]

This article presents a new interior permanent magnet (IPM) rotor structure/ assembly, which inherits from the Halbach magnet configuration and spoke-type IPM rotor to achieve a high saliency ratio and high torque/ power density. With this rotor structure, the torque density and power density are improved obviously, while the rotor inner diameter can be maximized to reduce core material and increases internal space in the rotor. Accordingly, the electromagnetic performance of three motors consists of a unified stator but different rotors, namely flux-concentrating rotor, Halbach array permanent magnet (PM) rotor and spoke-type IPM rotor is compared by finite element analysis. Nevertheless, due to the segmented structure of flux-concentrating PM rotor without magnetic bridges, the mechanical challenges are analyzed in detail for electric vehicle application to hold the pole pieces validate the structural feasibility at 7200 r/min. Finally, a 72-slot/ 16-pole fractional-slot PM motor with new flux-concentrating rotor is manufactured and tested to verify its performance and feasibility. It can be concluded that the new rotor is superior to the spoke-type IPM and Halbach array PM rotor in terms of torque density and PM utilization. [ABSTRACT FROM AUTHOR]

Aiming at slippage and belt breakage of large mechanical conveyor belts, a new type of water-cooled permanent magnet brake (WPMB) is proposed. In order to determine the braking performance of WPMB, a multi-physics coupling model and analysis method of magneto-thermal-structure are built. The braking torque and temperature characteristics of WPMB under different working conditions are obtained. Based on the magnetic vector potential equation, an electromagnetic eddy current model is established, and the variation trend of braking torque with speed is predicted. The temperature field model is built based on the equivalent thermal network method. Using multi-field coupling analysis method and 3-D FEM, the influence factors of WPMB braking torque are analyzed. Two test prototypes with rated speed of 78 rpm, braking torque of 3000 N⋅m are designed and developed. Braking torque characteristic tests and magnetic shielding characteristic tests at different speeds and continuous braking characteristic test are carried out. Experiments show that the proposed method provides very practical results to ensure the continuous and stable operation of WPMB. [ABSTRACT FROM AUTHOR]

The Simons Observatory (SO) includes four telescopes that will measure the temperature and polarization of the cosmic microwave background using over 60,000 highly sensitive transition-edge bolometers (TES). These multichroic TES bolometers are read out by a microwave RF SQUID multiplexing system with a multiplexing factor of 910. Given that both TESes and SQUIDs are susceptible to magnetic field pickup and that it is hard to predict how they will respond to such fields, it is important to characterize the magnetic response of these systems empirically. This information can then be used to limit spurious signals by informing magnetic shielding designs for the detectors and readout. This paper focuses on measurements of magnetic pickup with different magnetic shielding configurations for the SO universal multiplexing module (UMM), which contains the SQUIDs, associated resonators, and TES bias circuit. The magnetic pickup of a prototype UMM was tested under three shielding configurations: no shielding (copper packaging), aluminum packaging for the UMM, and a tin/lead-plated shield surrounding the entire dilution refrigerator 100 mK cold stage. We also present measurements of the pickup in the UMM when aluminum feedhorns are installed. The measurements show that the aluminum packaging outperforms the copper packaging by a shielding factor of 8-10, and adding the tin/lead-plated 1K shield further increases the relative shielding factor in the aluminum configuration by 1-2 orders of magnitude. The addition of feedhorns provides a factor of 30 improvement when the tin/lead shield is not installed and a factor of 5 improvement when it is. [ABSTRACT FROM AUTHOR]

We present magnetic field sensitivity measurements of microwave SQUID multiplexers designed for bolometric applications. These devices are often used in environments with changing external magnetic fields, due to either motion through Earth's field or radiation from other pieces of instrumentation. To minimize the pickup of magnetic fields, these multiplexers utilize gradiometric SQUIDs, but residual pickup remains and must be characterized in order to design adequate magnetic shielding for a given application. To study the perpendicular field response, we utilize a single-axis cryogenic Helmholtz coil mounted to the mixing chamber of a dilution refrigerator, calibrated with a cryogenic fluxgate magnetometer. Measurements were made on multiplexer devices across varying microwave readout frequencies for AC magnetic fields from 0.01 to 100 Hz. We measure the magnetic field sensitivity of the multiplexer devices to be 0.1–0.3 ϕ 0 /Gauss, equivalent to an effective area of gradiometric failure of 2–6 μm 2 .Please check if the corresponding author affiliation is correctly identified.This looks correct to me. [ABSTRACT FROM AUTHOR]

To resolve the contradiction between the shielding performance and the magnetic noise in the design of magnetically shielded cylinder (MSC), an MSC optimization design method based on particle swarm optimization with multistage inertia weights algorithm (MW-PSO) is proposed. Using the segmented magnetic noise and material volume as constraints and taking the axial shielding factor as the target, the structure of a four-layer MSC is optimized to achieve the expected results. According to the previous optimization results, the relationship curve between the change rate of the axial shielding factor and that of the magnetic noise is obtained, and the structure parameters of the optimal four-layer MSC are determined by the extreme points of the curve. The simulation analyses are conducted to verify the effectiveness of the method. The results show that compared with the initial MSC designed by the conventional method, the axial and radial shielding factors of the optimized MSC are increased by 17.95 times and 15.3 times, respectively; meanwhile, the magnetic noise is decreased by 15%. [ABSTRACT FROM AUTHOR]

In this brief, a novel ultrawideband multi-component differential magnetic probe is proposed. Two pairs of differential loops and connecting vias were used to simultaneously sense two orthogonal magnetic-field components (Hx and Hy). Two rows of via fences next to the loops were used to prevent unwanted electromagnetic modes. The operating frequency band of the proposed probe ranges from the 1 MHz to 20 GHz. The accuracy of the proposed probe is verified by comparing its measurement and simulation results. This significantly improves the near-field scanning efficiency compared with the conventional single-component probe. [ABSTRACT FROM AUTHOR]

An innovative method to improve the efficiency of a single-phase electric-grid 125 kVA, 50 Hz shell type and distribution transformer is presented. The diamagnetism characteristic of a bulk high-temperature superconductor (HTS), designed in a specific dimension, is used to construct a magnetic shield around the air gaps that form between the core joints and among the coils of the transformer. Consequently, the shielded flux engages the core area and increases the flux density in the core, resulting in an increase in the output power, and hence an improved transformer efficiency. The transformer was designed and simulated using advanced electromagnetic software. Simulation results indicate that the width and thickness of the HTS material, as its precise location placed on the air gaps around the core and the coils, can be a substantial factor in generating a magnetic shield that results in an efficiency improvement, superior compared to conventional transformers. The most enhanced performance was received for HTS thickness of 2.6 mm, around 2.4% output power improvement compared with a conventional transformer model. In a transformer of this type that efficiency improvement can lead to great energy savings, around 10,000 kWh for half a year of working under load. [ABSTRACT FROM AUTHOR]

The ferrite magnetic shield is widely used in ultra-high-sensitivity atomic sensors because of its low noise characteristics. However, its noise level varies with temperature and affects the performance of the spin-exchange relaxation-free (SERF) co-magnetometer. Therefore, it is necessary to analyze and suppress the thermal magnetic noise. In this paper, the thermal magnetic noise model of a ferrite magnetic shield is established, and the thermal magnetic noise of ferrite is calculated more accurately by testing the low-frequency complex permeability at different temperatures. A temperature suppression method based on the improved heat dissipation efficiency of the ferrite magnetic shield is also proposed. The magnetic noise of the ferrite is reduced by 46.7%. The experiment is basically consistent with the theory. The sensitivity of the co-magnetometer is decreased significantly, from 1.21 × 10 − 5 ° /s/Hz 1 / 2 to 7.02 × 10 − 6 ° /s/Hz 1 / 2 at 1 Hz. The experimental results demonstrate the effectiveness of the proposed method. In addition, the study is also helpful for evaluating the thermal magnetic noise of other materials. [ABSTRACT FROM AUTHOR]

This study proposes a high-performance magnetic shielding structure composed of MnZn ferrite and mu-metal film. The use of the mu-metal film with a high magnetic permeability restrains the decrease in the magnetic shielding coefficient caused by the magnetic leakage between the gap of magnetic annuli. The 0.1–0.5 mm thickness of mu-metal film prevents the increase of magnetic noise of composite structure. The finite element simulation results show that the magnetic shielding coefficient and magnetic noise are almost unchanged with the increase in the gap width. Compared with conventional ferrite magnetic shields with multiple annuli structures under the gap width of 0.5 mm, the radial shielding coefficient increases by 13.2%, and the magnetic noise decreases by 21%. The axial shielding coefficient increases by 22.3 times. Experiments verify the simulation results of the shielding coefficient of the combined magnetic shield. The shielding coefficient of the combined magnetic shield is 16.5%. It is 91.3% higher than the conventional ferrite magnetic shield. The main difference is observed between the actual and simulated relative permeability of mu-metal films. The combined magnetic shielding proposed in this study is of great significance to further promote the performance of atomic sensors sensitive to magnetic field. [ABSTRACT FROM AUTHOR]

In this article, the shielding properties of wire mesh enclosures are studied, with emphasis on the importance of electrical contact between crossing wires. Experimental results are combined with numerical three-dimensional simulations to provide conclusions about the shielding effectiveness in a wide frequency range and how it depends on the contact conditions between crossing wires and between the wire mesh and a possible enclosure frame. [ABSTRACT FROM AUTHOR]

The article investigates the shielding effectiveness (SE) of a metallic enclosure with a multilayer composite cover over a wide frequency range, from near-field magnetic shielding (1 Hz–1 MHz) to far-field electromagnetic shielding (4–14 GHz). Two enclosures are considered: a conductive enclosure made of aluminum and a magnetic enclosure made of steel. The multilayer composite is a trilayer combining a thin conductive layer of graphene and a thin magnetic layer of a Fe-Ni alloy on either side of a fiberglass plate. To determine the SE of these enclosures in both low-frequency and high-frequency approaches, two experimental setups and two numerical models are developed. The use of the composite cover, instead of the metallic one, gives a similar level of SE in the far-field and a higher specific SE (i.e., SE divided by the material density) in the near-field from 1 Hz to 2 kHz. Such quantitative analysis is the first step to designing practical enclosures entirely covered with composite panels to face electromagnetic compatibility (EMC) constraints in embedded systems. [ABSTRACT FROM AUTHOR]

This article describes a method to reduce electromagnetic interference (EMI) components at odd harmonic frequencies of a wireless power transfer (WPT) system. In a WPT system, a leakage magnetic field is generated, which may adversely affect the human body or other electronic devices. The previous reactive shielding method could reduce the magnetic field, but it has the disadvantage of reducing the power transfer efficiency (PTE). By using frequency split phenomena, the reactive shielding method can reduce the EMI components with increasing PTE. In this article, a reactive shielding method that can reduce the magnetic field while increasing PTE is proposed. Specifically, the method for designing resonant system of transmitting, receiving, and shielding for the WPT system is proposed. In addition, a method for obtaining a coupling coefficient between a shielding coil and a transmitting coil for designing structure in which magnetic field reduction can be maximized is also proposed. The theoretical analysis based on the impedance of each part is strongly correlated with the simulation and measurement result. As a result of the experiment, the PTE is increased by about 2.7%, and EMI components at odd harmonic frequency can be reduced by up to 6.81 dB in a 50 W-WPT system. [ABSTRACT FROM AUTHOR]

The magnetic shielding effectiveness of a single planar screen of infinite extent against a parallel current loop source is evaluated through an analytic closed-form expression which is valid for arbitrarily thick screens and for any source-observation distance. The only assumption in the formulation consists in considering small loops having a constant current. The resulting formula can be expressed in terms of only elementary functions and is believed to represent the most general closed-form expression for the magnetic shielding effectiveness of a planar screen in the presence of a parallel loop. Numerical results are provided to show the generality and the validity of the proposed formula. [ABSTRACT FROM AUTHOR]

This article analyzes a near-field shielding performance of conformal shielding materials for integrated-circuits (ICs) by experiments. Two test boards with loop-type and patch-type patterns are designed to generate magnetic-field and electric-field, respectively. These sources mimic typical electromagnetic radiations from actual ICs. For shielding analysis, single-layered conductive materials, multilayered conductive and magnetic materials, hybrid materials with a mixture of conductive and magnetic pastes are considered as conformal shielding materials, which are coated on the test boards for measurements. Magnetic-field and electric-field shielding effectiveness (SE) of the materials evaluate by measurements using loop-probe, strip-line, and gigahertz transverse electromagnetic cell at the frequency range from 300 kHz to 3 GHz. Near-field SEs measured by three methods correspond generally well with each other at the frequency range up to a few hundred MHz. At the higher frequency, the ambient EM environment can affect the accuracy of the near-field measurements by the loop-probe and strip-line. For validation, numerical simulation is fulfilled and compared with measured results. Theoretical interpretation based on the Schelkunoff's SE decomposition is also addressed. [ABSTRACT FROM AUTHOR]

A high-frequency electromagnetic plane wave arises owing to a high-altitude electromagnetic pulse (HEMP), which may cause overvoltages in distribution lines and insulation failure. To protect distribution lines from such overvoltages properly, it is necessary to evaluate the effectiveness of countermeasures. Nowadays, the finite-difference time-domain (FDTD) method, which is one of the full-wave numerical approaches, has become a powerful tool for analyzing electromagnetic transient phenomena. In this article, first, we propose a simplified approach to modeling an impinging plane wave by taking into account homogeneous soil parameters in the three-dimensional FDTD method on the basis of a total field/scattered field technique for the analysis of HEMP-based plane-wave coupling. Second, using the proposed technique, we carry out the statistical analysis of overvoltages in a three-phase distribution line and evaluate the effectiveness of a multipoint grounded overhead shield wire and surge arresters, which are commonly used as lightning protection measures, while modeling the reinforcing bars of concrete utility poles, earth electrodes, and vertical grounding wires to simulate a realistic condition. [ABSTRACT FROM AUTHOR]

We study the Kondo screening of a spin-1/2 magnetic impurity coupled to a superconductor, which is fabricated by combination of an s-wave superconductor, a ferromagnet and a semiconductor with Rashba spinâ€"orbit coupling (RSOC). The proximity induced superconducting states include the s-wave and p-wave pairing components with the aids of RSOC, and the ferromagnet induces a Zeeman field which removes the spin degeneracy of the quasiparticles in the triplet states. Thus, the Kondo screening of magnetic impurity involves the orbital degrees of freedom, and is also affected by the Zeeman field. Using the variational method, we calculate the binding energy and the spinâ€"spin correlation between the magnetic impurity and the electrons in the coexisting s-wave and p-wave pairing states. We find that Kondo singlet forms more easily with stronger RSOC, but Zeeman field in general decreases the binding energy. The spinâ€"spin correlation decays fast in the vicinity of the magnetic impurity. Due to the RSOC, the spatial spinâ€"spin correlation becomes highly anisotropic, and the Zeeman field can induce extra asymmetry to the off-diagonal components of the spinâ€"spin correlation. Our study can offer some insights into the studies of extrinsic topological superconductors fabricated from the hybrid structures containing chains of magnetic impurities. [ABSTRACT FROM AUTHOR]

A magnetic shield is widely used in the end region of a synchronous condenser (SC) to decrease the flux densities and losses of the end structural components. In order to investigate the influence of different magnetic shield thicknesses on the distributions of the flux density and loss in the end region, a 300-Mvar SC is selected as the investigation reference in this article. A three-dimensional (3-D) mathematical model used for the calculation of electromagnetic field and loss in the end region of the SC is established. The flux densities and losses of the end structural components are calculated and compared under the different thicknesses of the magnetic shield. From the detailed performance evaluations by the 3-D finite-element analysis, the variation of the flux densities and loss densities in the end region of the SC along with the thickness of the magnetic shield is revealed. The loss distributions of the main end structural components are studied and the end zones where the loss is most significantly affected by the magnetic shield thickness are obtained. The results provide the theoretical basis for the improvement of the loss distribution in the end region of the SC. [ABSTRACT FROM AUTHOR]

We present magnetic, mechanical and thermal modeling results for a 3 Tesla actively shielded whole body MRI (Magnetic Resonance Imaging) magnet consisting of coils with a square cross section of their windings. The magnet design was a segmented coil type optimized to minimize conductor length while hitting the standard field quality and DSV (Diameter of Spherical Volume) specifications as well as a standard, compact size 3 T system. It had an overall magnet length and conductor length which can lead to conduction cooled designs comparable to NbTi helium bath cooled 3 T MRI magnets. The design had a magnetic field homogeneity better than 10 ppm (part-per-million) within a DSV (Diameter of Spherical Volume) of 48 cm and the total magnet winding length of 1.37 m. A new class of MgB2 strand especially designed for MRI applications was considered as a possible candidate for winding such magnets. This work represents the first magnetic, mechanical and thermal design for a whole-body 3 T MgB2 short (1.37 m length) MRI magnet based on the performance parameters of existing MgB2 wire. 3 Tesla MRI magnet can operate at 20 K at 67% of its critical current. [ABSTRACT FROM AUTHOR]

Lightweight carbon foams with high-performance electromagnetic interference (EMI) shielding have attracted extensive attentions. However, it is challenging for researchers to effectively regulate the EMI shielding of carbon foams independent on shield's thickness. Herein, we proposed a macroscopic magnetic carbon foams through a chemical engineering strategy under the synergies of nickel ion reduction and in-situ growth of carbon nanotubes on carbon frameworks derived from carbonized woods. The macroscopic magnetic carbon foams present high-performance EMI shielding with absorption-dominant mechanism, and the removal of oil pollutants for water purification. Magnetic properties favor the manipulation of oil absorption without direct mechanic contact. After burning, the magnetic carbon foams can be re-used in EMI shielding and oil absorbency. Furthermore, we used a novel electric voltage-driven strategy to upgrade EMI shielding performances of magnetic carbon foams. By the increase in applied voltages, the enhanced absorption-dominant EMI shielding and fast oil absorbency due to the decrease viscosity of crude oil could be simultaneously obtained. The strategy developed here may lead a new avenue toward the design of porous magnetic carbon foams with the enhanced voltage-driven multifunctionalities for practical applications. The magnetic carbon foams exhibit voltage-driven EMI shielding performance with absorption-dominant mechanism, Joule heating and recyclable removal of oil contaminant for water purification. [Display omitted] • Macroscopic multi-functional magnetic carbon foams were fabricated. • The magnetic carbon foams present superior EMI shielding performance with absorption-dominant mechanism. • We used a novel electrical voltage-driven strategy to upgrade EMI shielding of magnetic carbon foam. • By increasing applied voltages, the enhanced absorption-dominant EMI shielding and fast oil absorbency can be achieved. • The magnetic carbon foams can be re-used in electromagnetic shielding and oil absorbency. [ABSTRACT FROM AUTHOR]

Superconducting linear synchronous motor (LSM) with superconducting magnets as its secondary is a promising candidate for driving high-speed transportations. The superconducting secondary operates at an ultra-low temperature environment generally supplied by a complex cryogenic system that contains numerous metal components, in which the eddy current losses are produced due to the magnetic fields from the primary. The ensuing temperature rise will inevitably lead to a reduction in the current-carrying capacity of superconducting secondary and threaten the operation safety of LSM. It is crucial to clarify the eddy current losses. To this end, we established a three-dimensional numerical model based on the A-formulation of Maxwell's equations. In this model, a kind of virtual primary was introduced to efficiently simulate the movement of the secondary instead of through a moving mesh technique since that is no longer suitable for this calculation. Afterwards, a testing setup of the superconducting LSM was constructed and the eddy current losses in the superconducting secondary were measured to validate the model. With the valid model, the eddy current losses in the secondary were systematically studied in consideration of different operating conditions of the LSM, followed by a discussion regarding the influence of cryogenic system on the losses. [ABSTRACT FROM AUTHOR]

The compact structure restrains the application of magnetic shielding in low-power Hall thrusters (LpHTs), leading to an asymmetric magnetic field or partial magnetic shielding of the channel wall. This study employs a trim coil to implement an asymmetric magnetic configuration in a 100Â W laboratory Hall thruster. The locations of the maximum curvature of magnetic lines are deflected toward the inner and outer channel wall corresponding to the inward and outward deflected magnetic field configurations. Effects of the magnetic field deflection on the position of the ionization zone, efficiency of the thruster, discharge oscillations, and wall erosion are studied. Optical imaging and electrostatic probes are employed to monitor and scan the plasma beam. Experimental results show that the outward deflection induces a change in the magnetic mirror effect and alters the location of the ionization zone. The radial movement of the ionization zone away from the inner channel wall decreases the near-wall conductivity, reducing the electron current by 13.5% and promoting the current efficiency. Discharge oscillations are suppressed, and the propellant utilization efficiency is improved by 8.2%. Erosion of the channel wall shows an improvement of 40%. Generally, an outward deflected magnetic configuration can significantly improve the performance of LpHTs. [ABSTRACT FROM AUTHOR]

This article presents an investigation of the optimal positioning of tank-wall magnetic shunts in power transformers. Magnetic shunts are made of grain-oriented magnetic silicon steel laminations and are used to avoid hot spots in metallic regions inside the power transformer. The magnetodynamic equations are solved in terms of the electric vector potential and the magnetic scalar potential. Thermal effects are calculated using heat transfer coefficients. This article proposes and solves an optimization problem where the objective is to position several shunts near the tank wall. Several design variables, temperature, and geometrical constraints are considered. As the finite-element (FE) model to be solved is in 3-D, the computing resources must be efficiently used. A multi-threading method was developed and numerically tested where the 3-D FE model, temperature calculation, and the particle swarm optimizer (PSO) are executed in a multicore computer in a parallel scheme. [ABSTRACT FROM AUTHOR]

A low residual environmental magnetic field is required for the proper operation of most optically pumped magnetometers (OPMs). This is achieved using a combination of passive and active magnetic shielding. Passive magnetic shielding often uses multiple layers of highly permeable materials. A realistic two-layer magnetically shielded room (MSR) for biomagnetic measurements is numerically studied using the finite element method. A measured B-H characteristic of Mumetal is used, which is linearly extrapolated from the Rayleigh region (RR) into the low magnetic field range. This extension of the magnetization curve yields no significant differences compared to using a constant permeability value for the low magnetic field range. Furthermore, we model the MSR with only one shield and apply a simple analytical method of images (MOI). The MOI yields on average a 100-fold reduction in computation time. The relative difference of the magnetic flux density computed with MOI and finite element method (FEM) is smaller than < 1% at the center of a spherical region of interest (ROI) with a radius of 0.3 m desired from the point of magnetoencephalography (MEG) using OPMs. The achieved accuracy of the MOI makes it suitable for the optimization of active shielding coils. [ABSTRACT FROM AUTHOR]

Shielding involves much more than just putting a conductive screen in between an emitting source and a susceptible device. Starting from Maxwell's equations, the concept of electromagnetic shielding is formally explained. The physical working mechanisms behind the two basic forms of shielding, electric field and magnetic field shielding, are given, and the link between them at higher frequencies is clarified. Several aspects, like the effect of gridding or weaving a shield, the effect of the finite size of a shield, and the penetration through the metal of a shield, are discussed based on very simple canonical shielding topologies that can be solved analytically. Although the classical paradigm to explain shielding based on the notions of skin depth and eddy current is not followed, conceptual links with this classical paradigm are explained. [ABSTRACT FROM AUTHOR]

Non-ionizing dosimetry investigations of extremely low frequency (ELF) magnetic fields that are generated by underground power cables as well as the minimization of their health effects are significant topics handled by numerous researchers. In this study, ELF magnetic fields and current densities caused by three-phased underground transmission lines induced in the human model were examined utilizing both analytical and numerical methods. Analyses were carried out using a two-dimensional problem scenario for the comprehensive head and body model. The results of the finite element method (FEM)-based simulation studies and the analytical calculations are consistent with each other. Moreover, a magnetic field shielding method utilizing conductive material was presented in the study. The shielding technique performed with copper material was carried out to mitigate the magnetic field and possible dosimetry hazards in the ELF region. The proposed shield was a 4-mm reverse U-shaped copper material. [ABSTRACT FROM AUTHOR]

Prostate cancer is the second most common neoplasia and fifth-leading cause of cancer death in men worldwide. Electromagnetic and magnetic fields have been classified as possible human carcinogens, but current understanding of molecular and cellular pathways involved is very limited. Effects due to extremely low magnetic/hypomagnetic fields (LMF) are furthermore poorly understood. Extracellular vesicles (EVs) are crucial mediators of cellular communication with multifaceted roles in cancer progression, including via transport and uptake of various protein and microRNA (miRNA) EV-cargoes. miRNAs regulate gene expression and are implicated in cancer-related processes such as proliferation, metastasis, and chemoresistance. This study investigated the effects of LMF exposure (20 nT) by magnetic shielding on the prostate cancer cell line PC3 compared to the prostate epithelial cell line PNT2 under short-term (4 h) conditions. We examined EV profiles following a 4 h LMF exposure alongside associated functional enrichment KEGG and GO pathways for the EV proteomes. The 4 h LMF exposure significantly reduced cellular EV release and modified PC3 EV cargoes to a more inflammatory and metastatic profile, with 16 Disease Pathways and 95 Human Phenotypes associated specifically with the LMF-treated PC3 EV proteomes. These included cancerous, metabolic, blood, skin, cardiac and skeletal Disease Pathways, as well as pain and developmental disorders. In the normal PNT2 cells, less EV protein cargo was observed following LMF exposure compared with cells not exposed to LMF, and fewer associated functional enrichment pathways were identified. This pointed to some differences in various cellular functions, ageing, defence responses, oxidative stress, and disease phenotypes, including respiratory, digestive, immune, and developmental pathways. Furthermore, we analysed alterations in matrix metalloproteinases (MMPs) and miRNAs linked to metastasis, as this is crucial in cancer aggressiveness. The 4 h LMF exposure caused a significant increase in MMP2 and MMP9, as well as in onco-miRs miR-155, miR-210, miR-21, but a significant reduction in tumour-suppressor miRs (miR-200c and miR-126) in the metastatic PC3 cells, compared with normal PNT2 cells. In addition, 4 h LMF exposure significantly induced cellular invasion of PC3 cells. Overall, our findings suggest that changes in magnetic field exposures modulate EV-mediated and miR-regulatory processes in PCa metastasis, providing a basis for exploring novel therapeutic strategies.

Magnetoencephalography (MEG) systems are advanced neuroimaging tools used to measure the magnetic fields produced by neuronal activity in the human brain. However, they require significant amounts of liquid helium to keep the superconducting quantum interference device (SQUID) sensors in a stable superconducting state. Additionally, MEG systems must be installed in a magnetically shielded room to minimize interference from external magnetic fields. We have developed an advanced MEG system that incorporates a superconducting magnetic shield and a zero-boil-off system. This system overcomes the typical limitations of traditional MEG systems, such as the frequent need for liquid helium refills and the spatial constraints imposed by magnetically shielded rooms. To validate the system, we conducted an evaluation using signal source estimation. This involved a phantom with 50 current sources of known location and magnitude under active zero-boil-off conditions. Our evaluations focused on the precision of the magnetic field distribution and the quantification of estimation errors. We achieved a consistent magnetic field distribution that matched the source current, maintaining an estimation error margin within 3.5 mm, regardless of the frequency of the signal source current. These findings affirm the practicality and efficacy of the system.

In this article, we delve into the intricate behavior of electronic mechanisms underlying NMR magnetic shieldings σ in molecules containing heavy atoms, such as cadmium, platinum, and mercury. Specifically, we explore PtXn−2 (X = F, Cl, Br, I; n = 4, 6) and XCl2Te2Y2H6 (X = Cd, Hg; Y = N, P) molecular systems. It is known that the leading electronic mechanisms responsible for the relativistic effects on σ are well characterized by the linear response with elimination of small components model (LRESC). In this study, we present the results obtained from the innovative LRESC-Loc model, which offers the same outcomes as the LRESC model but employs localized molecular orbitals (LMOs) instead of canonical MOs. These LMOs provide a chemist’s representation of atomic core, lone pairs, and bonds. The whole set of electronic mechanisms responsible of the relativistic effects can be expressed in terms of both non-ligand-dependent and ligand-dependent contributions. We elucidate the electronic origins of trends and behaviors exhibited by these diverse mechanisms in the aforementioned molecular systems. In PtX4−2 molecules, the predominant relativistic mechanism is the well-established one-body spin–orbit (σSO(1)) mechanism, while the paramagnetic mass–velocity (σMv) and Darwin (σDw) contributing mechanisms also demand consideration. However, in PtX6−2 molecules, the σ(Mv/Dw) contribution surpasses that of the SO(1) mechanism, thus influencing the overall ligand-dependent contributions. As for complexes containing Cd and Hg, the ligand-dependent contributions exhibit similar magnitudes when nitrogen is substituted with phosphorus. The only discrepancy arises from the σSO(1) contribution, which changes sign between the two molecules due to the contribution of bond orbitals between the metal and tellurium atoms.

The evolution of human cognitive function is reliant on complex social interactions which form the behavioural foundation of who we are. These social capacities are subject to dramatic change in disease and injury; yet their supporting neural substrates remain poorly understood. Hyperscanning employs functional neuroimaging to simultaneously assess brain activity in two individuals and offers the best means to understand the neural basis of social interaction. However, present technologies are limited, either by poor performance (low spatial/temporal precision) or an unnatural scanning environment (claustrophobic scanners, with interactions via video). Here, we describe hyperscanning using wearable magnetoencephalography (MEG) based on optically pumped magnetometers (OPMs). We demonstrate our approach by simultaneously measuring brain activity in two subjects undertaking two separate tasks—an interactive touching task and a ball game. Despite large and unpredictable subject motion, sensorimotor brain activity was delineated clearly, and the correlation of the envelope of neuronal oscillations between the two subjects was demonstrated. Our results show that unlike existing modalities, OPM-MEG combines high-fidelity data acquisition and a naturalistic setting and thus presents significant potential to investigate neural correlates of social interaction.

An edge displacement sensor is one of the key technologies for building large segmented mirror astronomical optical telescopes. A digital interface is one novel approach for sensor technologies, digital transformation and the Internet of Things (IoT) in particular. Frequency output sensors and inductance-to-digital converter (LDC) demonstrated significant advantages in comparison with conventional sensors with analog-to-digital converter (ADC) interfaces. In order for the differential inductive frequency output displacement (DIFOD) sensor to meet the high-stability requirements of segmented mirror astronomical telescopes, it is important to understand the factors for time drift of the sensor. This paper focuses on the investigation of key factors of sensor structure and material, signal conditioning and interface, and fixtures for time drift to permanently installed applications. First, the measurement principle and probe structural characteristics of the sensor are analyzed. Then, two kinds of signal conditioning and digitalization methods using resonance circuits and LDC chips are implemented and compared. Finally, the time drift stability experiments are performed on the sensors with different signal conditioning methods and fixtures under controlled temperature. Experimental results show that the magnetic shield ring effectively improves the sensitivity and quality factor of the sensors, the time drift stability of the sensor using the signal conditioning based on resonance circuits is better than that of the sensors using LDC chips, and the root mean square (RMS) of the sensor time drift meets the requirement of 0.01 μm/24 h. This study will help further development of high-stability of frequency output sensors and IoT-based systems for scaled-up applications in the future. [ABSTRACT FROM AUTHOR]

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Magnetically shielded rooms (MSRs) use multiple layers of materials such as MuMetal to screen external magnetic fields that would otherwise interfere with high precision magnetic field measurements such as magnetoencephalography (MEG). Optically pumped magnetometers (OPMs) have enabled the development of wearable MEG systems which have the potential to provide a motion tolerant functional brain imaging system with high spatiotemporal resolution. Despite significant promise, OPMs impose stringent magnetic shielding requirements, operating around a zero magnetic field resonance within a dynamic range of ± 5 nT. MSRs developed for OPM-MEG must therefore effectively shield external sources and provide a low remnant magnetic field inside the enclosure. Existing MSRs optimised for OPM-MEG are expensive, heavy, and difficult to site. Electromagnetic coils are used to further cancel the remnant field inside the MSR enabling participant movements during OPM-MEG, but present coil systems are challenging to engineer and occupy space in the MSR limiting participant movements and negatively impacting patient experience. Here we present a lightweight MSR design (30% reduction in weight and 40–60% reduction in external dimensions compared to a standard OPM-optimised MSR) which takes significant steps towards addressing these barriers. We also designed a 'window coil' active shielding system, featuring a series of simple rectangular coils placed directly onto the walls of the MSR. By mapping the remnant magnetic field inside the MSR, and the magnetic field produced by the coils, we can identify optimal coil currents and cancel the remnant magnetic field over the central cubic metre to just |B|= 670 ± 160 pT. These advances reduce the cost, installation time and siting restrictions of MSRs which will be essential for the widespread deployment of OPM-MEG. [ABSTRACT FROM AUTHOR]

Rogowski current sensors play an important role in detecting the condition of electrical power substation equipment. An electromagnetic field shielding shell is necessary for some of these sensors to operate correctly, especially those with large diameters and small heights. These are used for frequency-response analysis in power transformers. In this study, the magnetic-shielding effectiveness of a normal C-type metal shell was tested and simulated. The distribution and direction of the magnetic field were analyzed using finite-element simulation calculations to reveal the reasons for its poor shielding effectiveness. It was found that the magnetic field induced by an interference current crosses the shell and enters its cavity through the gap in its inner wall. Shells with larger inner-diameter-to-height ratios have worse magnetic-shielding effectiveness. Therefore, a novel shell structure with a spiral gap is proposed here. The magnetic-shielding effectiveness of this new type of shell was analyzed by further simulations and verified in experimental tests. The results showed that a shell with a spiral gap has better shielding effectiveness when it has a long gap. In addition, the spiral gap was found not to inhibit the current-measurement function of the sensor. This provides a new approach to the design of electromagnetic shielding shells for Rogowski sensors. [ABSTRACT FROM AUTHOR]

Compared with a conventional propulsion system, an electromagnetic railgun is characterized by an in-bore pulsed high magnetic field. However, the dynamic distribution of the magnetic field in the projectile has rarely been experimentally studied. To this end, this paper discusses the possibility of utilizing magnetic field environment information. An equivalent model of an electromagnetic railgun is established by using the finite element method. Based on the magnetic diffusion equation and the Biot-Savart law, the in-bore magnetic induction is determined. The velocity skin effect and projectile shielding are considered in the model. Furthermore, the magnetic measurement method is presented to validate a simulation result. The results obtained from the simulation and experiment show that package shielding affects the pulse width and amplitude of the internal value. The peak magnetic induction of low carbon steel and copper is reduced by 33.6 %, and the pulse width lags by 2.7 ms. Moreover, projectile shielding has a substantial influence on the timing accuracy during launch, and the time error reaches approximately 18 %. Therefore, the in-bore magnetic field is a practical signal for the control module since it considers the influence of different projectile shields. [ABSTRACT FROM AUTHOR]

The bipolar pad is one of the most promising topologies in inductive power transfer (IPT) systems for electric vehicles. However, there is scant literature on the analytical model of the bipolar pad. In this article, a three-dimensional (3-D) analytical model of the IPT system including a bipolar transmitter and a square receiver is developed based on the superposition of two 2-D subdomain analytical models. Ferrite and the aluminum shields with finite dimension are taken into account on the transmitter and receiver sides. An analytical calculation of the mutual inductance is then carried out with respect to the main parameters of the IPT system, namely the dimension of the coils, the conductivity, and the permeability of the shield. Three study cases are demonstrated to highlight how the proposed method can accelerate speed up the pad design process. Calculation results of the proposed model are compared with both a finite-element analysis (FEA) model and experimental measurements, demonstrating that the proposed model is nine times faster than the FEA method. When comparing with the experimental results, computational error of the proposed model is less than 6% in most of the study cases. [ABSTRACT FROM AUTHOR]

This paper proposes using Finite Element Analysis (FEA) simulations to optimize the design structure for low-frequency Magnetically Shielded Rooms (MSRs). In constructing a multi-layer MSR, the different characteristics of the material and laminated structure will bring different levels of magnetic Shielding Effectiveness (SE). The theoretical SE of an MSR can be determined quickly. By using the method used in this paper, the ideal laminated material structure can be found without increasing the MSR construction cost. According to the simulation results and the actual MSR measurement results we built, the optimized MSR design structure can improve the SE by 13 dB. In the area where the external measurement magnetic field is 37 820 nT, the magnetic field in the MSR is as low as 28 nT, and the SE of the MSR is higher than 57.3 dB. The method proposed by this research can provide the theoretical basis for optimal design structure and the FEA simulation method for engineering practice, which can effectively improve the SE of shielded rooms and save the construction cost. The FEA simulations used in this paper can be obtained from the following URL: https://github.com/YuukiAsuna/-Finite-element-simulation-of-material-lamination-sequence. [ABSTRACT FROM AUTHOR]

The spin exchange relaxation free (SERF) atomic magnetometer plays an important role in ultrahigh sensitive magnetic measurements. With the improvement of signal response and the reduction of sensor noise, the sensitivity of the SERF atomic magnetometer is limited mainly by environmental magnetic noise. In order to improve the performance of magnetic shielding, the models of a magnetic shielding cylinder with triangular holes were established in this paper, and the effect of aperture angle (θ) on the efficiency of shielding by a permalloy cylinder was investigated by the finite element analysis. The results showed that the shielding effectiveness decreases first and then increases with the augment of θ. The cylinder showed that the worst shielding effect at θ equals 60°, resulting from the magnetoresistance of leakage flux in the air dielectric. This research focuses on providing theoretical support for the design of magnetic shields and improvement of the magnetic shielding ability. [ABSTRACT FROM AUTHOR]