Optimization of a Coil System for Generating Uniform Magnetic Fields inside a Cubic Magnetic Shield

Cao, Qinjie; Pan, Donghua; Li, Ji; Jin, Y.; Sun, Zhiyin; Lin, Shengxin; Yang, Guangcan; Li, Liyi

doi:10.3390/en11030608

Cited by 34 publications

(11 citation statements)

References 21 publications

(27 reference statements)

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“…To ensure that the boundary conditions are properly fulfilled, reflections have to be calculated recursively so that the mirrored currents are themselves mirrored. Here, the effect that the mu-metal walls have on the form of the field produced by the balanced coils operating inside the MSR has been modelled via the addition of a truncated set of mirror currents 17,18 .…”

Section: Methodsmentioning

confidence: 99%

“…This was not considered in the process of coil design here, though similar interactions have been incorporated into gradient coil design methods for MRI 16 . It has been shown that this interaction can be modelled by a method of images approach 17,18 . This was utilised to simulate the effects of interactions on the efficiency and homogeneity of the designed coils when operated inside a MSR.…”

Section: Introductionmentioning

confidence: 99%

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Balanced, bi-planar magnetic field and field gradient coils for field compensation in wearable magnetoencephalography

Holmes

Tierney

Leggett

et al. 2019

Sci Rep

100

116

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To allow wearable magnetoencephalography (MEG) recordings to be made on unconstrained subjects the spatially inhomogeneous remnant magnetic field inside the magnetically shielded room (MSR) must be nulled. Previously, a large bi-planar coil system which produces uniform fields and field gradients was used for this purpose. Its construction presented a significant challenge, six distinct coils were wound on two 1.6 × 1.6 m2 planes. Here, we exploit shared coil symmetries to produce coils simultaneously optimised to generate homogenous fields and gradients. We show nulling performance comparable to that of a six-coil system is achieved with this three-coil system, decreasing the strongest field component Bx by a factor of 53, and the strongest gradient dBx/dz by a factor of 7. To allow the coils to be used in environments with temporally-varying magnetic interference a dynamic nulling system was developed with a shielding factor of 40 dB at 0.01 Hz. Reducing the number of coils required and incorporating dynamic nulling should allow for greater take-up of this technology. Interactions of the coils with the high-permeability walls of the MSR were investigated using a method of images approach. Simulations show a degrading of field uniformity which was broadly consistent with measured values. These effects should be incorporated into future designs.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Balanced, bi-planar magnetic field and field gradient coils for field compensation in wearable magnetoencephalography

Holmes

Tierney

Leggett

et al. 2019

Sci Rep

100

116

View full text Add to dashboard Cite

show abstract

“…There are some reasons for the errors between the simulation and the experiment results. (1) The actual MSR is made of pieces of a permalloy plate, and the air gap between these plates can cause magnetic flux leakage, which reduces the shielding factor of the MSR [14]. In addition, the actual MSR has a door in each layer, and several holes are distributed in each surface, edge, and corner, which will influence the shielding factor.…”

Section: The Shielding Factors When the External Fields Are Sine Wavesmentioning

confidence: 99%

A New Approach to Calculate the Shielding Factor of Magnetic Shields Comprising Nonlinear Ferromagnetic Materials under Arbitrary Disturbances

et al. 2019

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To enable the realization of ultra-low magnetic fields for scientific and technological research, magnetic shielding is required to create a space with low residual magnetic field and high shielding factors. The shielding factors of magnetic shields are due to nonlinear material properties, the geometry and structure of the shields, and the external magnetic fields. Magnetic shielding is used in environments full of random realistic disturbances, resulting in an arbitrary and random external magnetic field, and in this case, the shielding effect is hard to define simply by the shielding factors. A new method to simulate and predict a dynamic internal space magnetic field wave is proposed based on the Finite Element method (FEM) combined with the Jiles-Atherton (JA) model. By simulating the hysteresis behavior of the magnetic shields and establishing a dynamic model, the new method can simulate dynamic magnetic field changes inside magnetic shields as long as the external disturbances are known. The shielding factors under an AC external field with a sine wave and certain frequencies are calculated to validate the feasibility of the new method. A real-time wave of internal magnetic flux density under an AC triangular wave external field is simulated directly with the new method versus a method that splits the triangular wave into several sine waves by a Fourier transform, divides the shielding factors, and then adds the quotients together. Moreover, real-time internal waves under some arbitrary fields are measured. Experimental internal magnetic flux density waves of a 4-layer magnetically shielded room (MSR) at the Harbin Institute of Technology (HIT) fit the simulated results well, taking experimental errors into account.

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“…Planar high-permeability materials have been incorporated into optimization procedures using the method of mirror images [26,27] to determine the total magnetic field generated by a static current source inside a magnetically shielded room [28][29][30][31]. Similar work in magnetic resonance imaging has investigated the interaction of switched magnetic field gradients with high-conductivity materials used for passive shielding [32].…”

Section: Introductionmentioning

confidence: 99%

Planar Coil Optimization in a Magnetically Shielded Cylinder

et al. 2021

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Hybrid magnetic shields with both active field generating components and high-permeability magnetic shielding are increasingly needed for various technologies and experiments that require precisioncontrolled magnetic field environments. However, the fields generated by the active components interact with the passive magnetic shield, distorting the desired field profiles. Consequently, optimization of the active components needed to generate user-specified target fields must include coupling to the highpermeability passive components. Here, we consider the optimization of planar active systems, on which an arbitrary static current flows, coupled to a closed high-permeability cylindrical shield. We modify the Green's function for the magnetic vector potential to match boundary conditions on the shield's interior surface, enabling us to construct an inverse optimization problem to design planar coils that generate user-specified magnetic fields inside high-permeability shields. We validate our methodology by designing two biplanar hybrid active-passive systems, which generate a constant transverse field, B =x, and a linear field gradient, B = (−xx − yŷ + 2zẑ), respectively. For both systems, the inverse-optimized magnetic field profiles agree well with forward numerical simulations. Our design methodology is accurate and flexible, facilitating the miniaturization of high-performance hybrid magnetic field generating technologies with strict design constraints and spatial limitations.

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Optimization of a Coil System for Generating Uniform Magnetic Fields inside a Cubic Magnetic Shield

Cited by 34 publications

References 21 publications

Balanced, bi-planar magnetic field and field gradient coils for field compensation in wearable magnetoencephalography

Balanced, bi-planar magnetic field and field gradient coils for field compensation in wearable magnetoencephalography

A New Approach to Calculate the Shielding Factor of Magnetic Shields Comprising Nonlinear Ferromagnetic Materials under Arbitrary Disturbances

Planar Coil Optimization in a Magnetically Shielded Cylinder

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