Magnetic field of rectangular current loop with sides parallel and perpendicular to the surface of high-permeability material

Juhas, Anamarija; Pekaric-Nadj, Neda; Toepfer, Hannes

doi:10.2298/sjee1404701j

Cited by 8 publications

(7 citation statements)

References 10 publications

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“…The proximity of the coil to the walls of the MSR means that the magnetic fields produced by the interaction of the coils with the MuMetal walls need to be accounted for when designing a high-performance active-shielding system. These interactions have been investigated previously and can be evaluated using a set of virtual mirror currents produced via reflection of the coil wirepaths in the walls of the MSR 19 , 26 , 27 . Recursive reflections of the reflected wirepaths are applied to ensure that the boundary conditions are correctly fulfilled, such that tangential field components are zero on the internal surface formed by the walls of the MSR.…”

Section: Methodsmentioning

confidence: 99%

A lightweight magnetically shielded room with active shielding

Holmes

Rea

Chalmers³

et al. 2022

Sci Rep

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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.

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Section: Methodsmentioning

confidence: 99%

A lightweight magnetically shielded room with active shielding

Holmes

Rea

Chalmers³

et al. 2022

Sci Rep

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“…In a vacuum space, the magnetic field generated by a current source could be calculated following Biot-Savart law. However, the effects of the magnetization current should be considered if there is a ferromagnetic medium nearby [15]. A whole resist-eddy current plate (thickness: d) can be divided into three regions, two boundaries are produced in the process, namely interface 1 and interface 2 (see the Fig.…”

Section: Mirror-image Theory Combined Finite-difference Methodsmentioning

confidence: 99%

A theoretical framework of gradient coil designed to mitigate eddy currents for a permanent magnet MRI system

Zhang

Wang

Yan

2022

THC

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BACKGROUND: High installation and operating cost have limited applications for many circumstances. In practice, primary and shielding coils cannot insert into the magnet pole simultaneously owing to deficient workspace for the planar permanent MRI systems OBJECTIVE: To minimize eddy currents induced in the resist-eddy current plates and pole piece when the gradient coil current switches on and off rapidly. METHODS: A theoretical framework that have minimum power dispassion and magnetic energy with eddy plate is proposed for a planar gradient coil. The mirror image of the magnetostatic model is substituted into the stream function for designing a minimum power dispassion planar gradient coil. A finite-difference is used to formulate the coil distribution that makes magnetic field similar to the required magnetic field for gradient coil design. RESULTS: A coil designed with actively shielded was simulated and compared with the designed gradient coils using mirror image theory and piece pole effect. According to the numerical evaluation of the x and z coils, the operating currents in the cases were reduced to 34.4% using magnetostatic mirror-image method to replay the active shielding. Moreover, there was a significant improvement on the shielding effect when added to resistive eddy current plate. CONCLUSIONS: Using the magnetostatic mirror image theory and mirror-image model, the current density function that could not only gives the minimum power dissipation and magnetic energy with the presence of the eddy plate and pole piece effect, but also provides excellent coil performance compared with active shielding solution.

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“…Furthermore, when ferrites are sandwiched between each other, image coils are continuously generated against the image coils. Equation ( 12) and ( 13) represent the position of the image coil [8]. Z ′ i,k represents the coordinates of successive image coils on its own ferrite side and Z ′′ i,k represents the coordinates of successive image coils on the side opposite its ferrite.…”

Section: Derivation Of Mutual Inductance L M When Ferrite Is Attached...mentioning

confidence: 99%

“…In references [7], [8], [9], [10], [11], and [12], the high permeability material such as ferrite attached in the coil is represented by a image coil, which exists in a plane symmetrical to the ferrite boundary plane. In reality, however, the ferrite shield is of finite size and thickness, which introduces errors in the design values.…”

Section: Introductionmentioning

confidence: 99%

Theorizing a Simple Ferrite Cored Coil Using Image Coils in Wireless Power Transfer

2023

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The technology of wireless power transfer, which wirelessly transmits power to any device, has been widely studied. Wireless power transfer using magnetic field resonance involves the use of coils and a material called ferrite, which improves the transmission characteristics. Until now, electromagnetic field analysis has been used to design ferrite cored coils, but electromagnetic field analysis requires a long analysis time and a computer with a large amount of memory. In this study, the ferrite shield and coil are represented as a image coil under the condition that the positional relationship between the ferrite shield and the coil does not change. This enabled the derivation of mutual inductance only by numerical analysis, which had been difficult up to now. In addition, experiments have shown that when the coil size does not change, mutual inductance can be derived only by numerical analysis using arbitrary coil parameters, regardless of the number of turns and pitch. The average error in deriving the design value was 5.2%. This facilitated the design of ferrite cored coils at 85 kHz and contributed greatly to the design of the system.INDEX TERMS Wireless power transfer, ferrite core, coil design, numerical analysis, inductive wireless power transfer, image method.

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Magnetic field of rectangular current loop with sides parallel and perpendicular to the surface of high-permeability material

Cited by 8 publications

References 10 publications

A lightweight magnetically shielded room with active shielding

A lightweight magnetically shielded room with active shielding

A theoretical framework of gradient coil designed to mitigate eddy currents for a permanent magnet MRI system

Theorizing a Simple Ferrite Cored Coil Using Image Coils in Wireless Power Transfer

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