Coil Design Research Articles

Design, Fabrication, and Assembly of the SPARC Toroidal Field Model Coil

Design, Fabrication, and Assembly of the SPARC Toroidal Field Model Coil

Magnetic Shielding Design and Performance Improvement of HTS Coil for Single HTS-Excitation Claw-Pole Field-Modulation Machine

Magnetic Shielding Design and Performance Improvement of HTS Coil for Single HTS-Excitation Claw-Pole Field-Modulation Machine

Design, construction and test of a prototype coil with demountable CuBe joints for pulsed table-top tokamaks

In a classic small tokamak, the magnetic confinement is achieved by toroidal coils that fit into a donut-shape mechanical structure. To facilitate their handling and maintenance as well as the access to various auxiliaries components, their design has evolved toward a modular configuration. For such demountable design, it is important to guarantee the electrical continuity of the winding of the coil across the modular parts through electrical contacts. The resulting joints rely on pressure and specific materials to transfer high current densities at a good mechanical stability and manageable losses. In the present work, a prototype of a circular demountable toroidal field coil (CDTFC) was designed and built to test some technical choices to be used in the final coils of a table-top tokamak referred to as TPM-1U. For this small tokamak, the magnet wires to wind the toroidal coils should be able to handle large pulsed currents in the tens of thousands of Amperes whereas the coil joints should handle a peak current density of at least 75 kA/cm2. The case study here is the TPM-U1 table-top tokamak. Its conceptual design is recalled and mechanical and magnetic details of the demountable coil prototype are provided. For the experimental test, the contacts were slightly pressed using a custom-made contact assembly and current pulses between 4 kA and 8 kA were fedto the coil prototype. The degradation of the joint was visually estimated by assessing the amount of micro-melting, plastic deformation and oxidation appearing at the interface between the materials in contact. It is shown that the selected AWG-04 magnet wire is appropriate for carrying kiloAmpere range pulsed currents and that the CuBe contacts are able to withstand current densities larger than the specification, up to 263 kA/cm2, under low contact pressures of a few mega-Pascal simplifying their handling. Some technical choices have been probed on a prototype coil yielding a generic sequence of tasks to build and test mechanically and electromagnetically demountable coils and their joints.

Design of continuous repeater power transmission coil for wireless power transfer system for EVs with consideration of vehicle deviation

In recent years, EVs have become increasingly popular around the world, and research on wireless power supply technology for EV driving has progressed accordingly. In order to realize this wireless power transfer system for EVs on a real scale, it is necessary to lengthen the power transfer section per power transfer unit and to secure a sufficient power transfer section with a small number of power transfer units as a whole. To solve this problem, the single coil method, in which one coil is lengthened, has been proposed. However, as the coil length increases, resistance loss increases and efficiency decreases. Therefore, a repeater coil system has been proposed. In this in-transit power-feeding system, it is necessary to consider transient phenomena when the EV to be fed deviates from the feeding lane. Therefore, we propose a new repeater coil configuration on the transmission side that assumes a no-load condition. In this study, a new repeater coil system combining rectangular coils and orthogonal coils is proposed, which enables stable feeding of power to EVs by rectangular coils and response to transient phenomena. A comparison was also made with the single coil method that has been studied previously.

Superconducting Shim Coils Design for the 9.4 T Whole-Body MRI Magnet

Superconducting Shim Coils Design for the 9.4 T Whole-Body MRI Magnet

Impact of MRI RF coil design on the RF-induced heating of medical implants: fixed B 1 + rms exposure versus normal operating mode

A direct comparison of the impact of RF coil design under specific absorption rate and B1+rms limitations are investigated and quantified using RF coils of different geometries and topologies at 64 MHz and 128 MHz. The RF-induced in vivo electric field and power deposition of a 50 cm long pacemaker and 55 cm long deep brain stimulator (DBS) are evaluated within two anatomical models exposed with these RF coils. The associated uncertainty is quantified and analyzed under a fixed B1+rms incident and normal operating mode. For a fixed B1+rms incident, the in vivo incident field shows a much higher uncertainty (>5.6 dB) to the RF coil diameter compared to other design parameters (e.g. <2.2 dB for coil length and topology), while the associated uncertainty reduced greatly (e.g. <1.5 dB) under normal operating mode exposure. Similar uncertainties are observed in the power deposition near the pacemaker and DBS electrode. Compared to the normal operating mode, applying a fixed B1+rms field to the untested implant will lead to a large variation in the induced incident and power deposition of the implant, as a result, a larger safe margin when different coil designs (e.g. coil diameter) are considered.

A high-performance electromagnetic code to simulate high-temperature superconductors

Superconductivity is a physical phenomenon of some materials that allow them to conduct electrical current without resistance. This property has a wide range of applications. In particular, type-II high-temperature superconductors appear promising for building strong electromagnets carrying large amounts of current in the extreme conditions foreseen for future fusion reactors. However, their fabrication and related experiments are highly expensive and complex. Therefore, there is an increasing need for numerical models to guide the design optimization of superconducting cables and to predict their performance. In this work, we present a new code to simulate high-temperature superconductors (HTS) based on the edge finite element discretization of Maxwell’s equations in the time domain using the widely adopted H-formulation in the superconductor analysis community. This code is integrated in the High-Performance Computing (HPC) Alya suite and obtain an excellent performance up to 1024 processors in MareNostrum 4 supercomputer. This capacity allows to us to solve a wide variate of problems in big domains in relatively reduce amount of computer time, being a promising tool to aboard HTS coils design problems. Furthermore, validations against experimental data are presented and code results for superconducting tapes with different magnetic properties are analyzed.

Helical coil design with controlled dispersion for bunching enhancement of protons generated by the target normal sheath acceleration.

The quality of the proton beam produced by target normal sheath acceleration (TNSA) with high-power lasers can be significantly improved with the use of helical coils. While they showed promising results in terms of focusing, their performances in terms of the of cut-off energy and bunching stay limited due to the dispersive nature of helical coils. A new scheme of helical coil with a tube surrounding the helix is introduced, and the first numerical simulations and an analytical model show a possibility of a drastic reduction of the current pulse dispersion for the parameters of high-power-laser facilities. The helical coils with tube strongly increase bunching, creating two collimated narrow-band proton beams from a broad and divergent TNSA distribution. The analytical model provides scaling of proton parameters as a function of laser facility features.

Developing an AI-empowered head-only ultra-high-performance gradient MRI system for high spatiotemporal neuroimaging

Recent advances in neuroscience requires high-resolution MRI to decipher the structural and functional details of the brain. Developing a high-performance gradient system is an ongoing effort in the field to facilitate high spatial and temporal encoding. Here, we proposed a head-only gradient system NeuroFrontier, dedicated for neuroimaging with an ultra-high gradient strength of 650 mT/m and 600 T/m/s. The proposed system features in 1) ultra-high power of 7MW achieved by running two gradient power amplifiers using a novel paralleling method; 2) a force/torque balanced gradient coil design with a two-step mechanical structure that allows high-efficiency and flexible optimization of the peripheral nerve stimulation; 3) a high-density integrated RF system that is miniaturized and customized for the head-only system; 4) an AI-empowered compressed sensing technique that enables ultra-fast acquisition of high-resolution images and AI-based acceleration in q-t space for diffusion MRI (dMRI); and 5) a prospective head motion correction technique that effectively corrects motion artifacts in real-time with 3D optical tracking. We demonstrated the potential advantages of the proposed system in imaging resolution, speed, and signal-to-noise ratio for 3D structural MRI (sMRI), functional MRI (fMRI) and dMRI in neuroscience applications of submillimeter layer-specific fMRI and dMRI. We also illustrated the unique strength of this system for dMRI-based microstructural mapping, e.g., enhanced lesion contrast at short diffusion-times or high b-values, and improved estimation accuracy for cellular microstructures using diffusion-time-dependent dMRI or for neurite microstructures using q-space approaches.

Design and Parameter Optimization of Double-Mosquito Combination Coils for Enhanced Anti-Misalignment Capability in Inductive Wireless Power Transfer Systems

This paper proposes a novel double-mosquito combination (DMC) coil for inductive wireless power transfer (IPT) systems to improve their anti-misalignment capability. The DMC coil consists of a mosquito coil with single-turn spacing and a tightly wound close-wound coil. By superimposing the magnetic fields generated by both coils, a relatively uniform magnetic field distribution is achieved on the receiving coil plane. This approach addresses the challenges of significant output voltage fluctuations and reduced transmission efficiencies caused by coupling coil misalignments in conventional IPT systems. To further optimize the DMC coil, an interaction law between its parameters and the mutual inductance is established, setting the coil mutual inductance fluctuation rate as the optimization objective, and using the coil turn spacing, number of turns, and outer diameter as constraint conditions. The beetle antennae search algorithm (BAS) is employed to enhance the whale optimization algorithm (WOA), facilitating the adaptive optimization of the coil parameters. An experimental IPT system platform with a 50 mm transmission distance is developed to validate the robust anti-misalignment capability of the proposed coil. The results demonstrate that within a horizontal misalignment range of 50 mm, the system’s output voltage fluctuation rate stays below 7.4%, and the transmission efficiency remains above 83%.

Effect of DH-shaped coil symmetry coefficient on EMPW process

ABSTRACT The coil is used for electrical connection and energy conversion in the electromagnetic pulse welding (EMPW) process, so its structure affects the welding effect. In this work, for the dual H-shaped (DH) coil, the influence of the symmetry coefficient on the Cu-Al sheets EMPW was studied through the simulation and experiment. When the voltage was 7 kV and the symmetry coefficient g was 0.75, 1, and 1.33, the V c-β trajectory curve contained by the simulation combined with the welding window curve (WWC) to analyze the dynamic process and welding effect. The relative impact speed was the fastest and the corresponding weld seam length was the longest when g was 1.33. The welding experiment results were consisted with the simulation results, it was beneficial to weld the Cu-Al sheets when g was 133. The symmetry coefficient could change the impact speed and angle to affect the welding effect. This work is of great significance for DH coil design.

Advancements in MR hardware systems and magnetic field control: B0 shimming, RF coils, and gradient techniques for enhancing magnetic resonance imaging and spectroscopy.

High magnetic field homogeneity is critical for magnetic resonance imaging (MRI), functional MRI, and magnetic resonance spectroscopy (MRS) applications. B0 inhomogeneity during MR scans is a long-standing problem resulting from magnet imperfections and site conditions, with the main issue being the inhomogeneity across the human body caused by differences in magnetic susceptibilities between tissues, resulting in signal loss, image distortion, and poor spectral resolution. Through a combination of passive and active shim techniques, as well as technological advances employing multi-coil techniques, optimal coil design, motion tracking, and real-time modifications, improved field homogeneity and image quality have been achieved in MRI/MRS. The integration of RF and shim coils brings a high shim efficiency due to the proximity of participants. This technique will potentially be applied to high-density RF coils with a high-density shim array for improved B0 homogeneity. Simultaneous shimming and image encoding can be achieved using multi-coil array, which also enables the development of novel encoding methods using advanced magnetic field control. Field monitoring enables the capture and real-time compensation for dynamic field perturbance beyond the static background inhomogeneity. These advancements have the potential to better use the scanner performance to enhance diagnostic capabilities and broaden applications of MRI/MRS in a variety of clinical and research settings. The purpose of this paper is to provide an overview of the latest advances in B0 magnetic field shimming and magnetic field control techniques as well as MR hardware, and to emphasize their significance and potential impact on improving the data quality of MRI/MRS.

The Minimum Admissible Detuning Efficiency of MRI Receive-Only Surface Coils.

The minimum admissible detuning efficiency (DE) of a receive coil is an essential parameter for coil designers. A receive coil with inefficient detuning leads to inhomogeneous B1 during excitation. Previously proposed criteria for quantifying the DE rely on indirect measurements and are difficult to implement. To present an alternative method to quantify the DE of receive-only surface coils. Theoretical study supported by simulations and phantom experiments. Uniform spherical (100 mm diameter) and cylindrical (66 mm diameter) phantoms. Dual repetition time B1 mapping sequence at 1.5T, and Bloch-Siegert shift B1 mapping sequence at 3.0T. One non-planar (80 × 43 mm2) and two planar (40 and 57 mm diameter) surface coils were built. Theoretical analysis was performed to determine the minimum DE required to avoid B1 distortions. Experimental B1 maps were acquired for the non-planar and planar surface coils at both 1.5T and 3.0T and visually compared with simulated B1 maps to assess the validity of the theoretical analysis. None. Based on the theoretical analysis, the proposed minimum admissible DE, defined as DEthr = 20 Log (Q) + 13 dB, depended only on the quality factor (Q) of the coil and was independent of coil area and field strength. Simulations and phantom experiments showed that when the DE was higher than this minimum threshold level, the B1 field generated by the transmission coil was not modified by the receive coil. The proposed criterion for assessing the DE is simple to measure, and does not depend on the area of the coil or on the magnetic field strength, up to 3T. Experimental and simulated B1 maps confirmed that detuning efficiencies above the theoretically derived minimal admissible DE resulted in a non-distorted B1 field. 2 TECHNICAL EFFICACY: Stage 1.

Design and construction of gradient coils for an MRI-guided small animal radiation platform

Small animal radiation experiments use a dedicated hardware platform to deliver radiation to small animals to support pre-clinical radiobiological studies. Image guidance is critical to achieve experiment accuracy. MR-based image guidance became recently available in human radiation therapy by integrating an MR scanner with a medical linear accelerator. Our group is developing a small animal MR-guidance system for pre-clinical radiation studies using a unique low-field unilateral magnet design. In this paper, we reported our design, construction, and characterization of split gradient coils for the MRI scanner. The coils were designed to have a 4 cm gap to allow the radiation beam to pass through for radiation experiments. We designed the coil patterns by solving an optimization problem. We constructed the coils by printing molds for the designed coil patterns using 3D printing technology and wiring the coils following the pattern. We measured parameters of the coils to characterize their performance. The coils achieved a linear magnetic field throughout a 4 cm spherical region of interest. The slew rates were 8640 and 1970 T/m⋅s, and the efficiencies were 1.2 and 0.21 mT/m⋅A for the Y-coil and X-coil, respectively. Preliminary imaging with the coils on our proposed system validates spatial encoding functions of the developed coils.

A proton birdcage coil integrated with interchangeable single loops for multi-nuclear MRI/MRS.

Energy metabolism is fundamental for life. It encompasses the utilization of carbohydrates, lipids, and proteins for internal processes, while aberrant energy metabolism is implicated in many diseases. In the present study, using three-dimensional (3D) printing from polycarbonate via fused deposition modeling, we propose a multi-nuclear radiofrequency (RF) coil design with integrated 1H birdcage and interchangeable X-nuclei (2H, 13C, 23Na, and 31P) single-loop coils for magnetic resonance imaging (MRI)/magnetic resonance spectroscopy (MRS). The single-loop coil for each nucleus attaches to an arc bracket that slides unrestrictedly along the birdcage coil inner surface, enabling convenient switching among various nuclei and animal handling. Compared to a commercial 1H birdcage coil, the proposed 1H birdcage coil exhibited superior signal-excitation homogeneity and imaging signal-to-noise ratio (SNR). For X-nuclei study, prominent peaks in spectroscopy for phantom solutions showed excellent SNR, and the static and dynamic peaks of in vivo spectroscopy validated the efficacy of the coil design in structural imaging and energy metabolism detection simultaneously.

Optimizing transcranial magnetic stimulator coils for minimal influence of individual variability in head geometry

In prior studies focused on transcranial magnetic stimulator (TMS) coils, optimization of coil windings typically occurred on generic curved surfaces, such as planes or cylindrical shapes. However, these surfaces do not consider the challenge of coil misalignment, which arises due to variations in individual head geometries. This misalignment can significantly diminish the coil's effectiveness. To address this issue, we propose a novel coil design approach that identifies the 'best-fit' curved surface, minimizing the likelihood of mismatch with diverse skull geometries. We further enhance the coil winding pattern using the stream function applied to this custom curved surface. Numerical simulations using a hemisphere brain model demonstrate that the coil designed on this 'best-fit' curved surface exhibits a remarkable 22% increase in efficiency and a 41% expansion in stimulation area compared to the conventional butterfly coil. These findings underscore the advantages of our method in crafting high-efficiency and wide-ranging therapeutic TMS coil.

Passive magnetic coil design for electromagnetic interference evaluation of axle counters

Measurement of magnetic fields near the railway tracks is crucial to ensure compatibility with the operation of axle counters. According to EN 50592 standard, the magnetic field is detected with a passive magnetic coil and an oscilloscope. From previous studies, in general, there has been no in-depth analysis of how the choice of coil winding parameters could affect the coil output voltage, which then affect the measurement sensitivity, in particular the coil design based on the standard and it is applicability for electromagnetic interference (EMI) evaluation of axle counters. Therefore, this paper will explore the design of a passive magnetic coil to obtain the optimum coil output voltage within the frequency range. Simulations showed that for 10-100 kHz and 100 kHz–1.3 MHz range, the optimum number of turns happened at 60-100 and 15-60 turns, respectively. Based on that, two example coils had been built. Simulations and measurements of their frequency response were in good agreement, with a deviation less than 1.0 dB.

Taguchi-Based Design of Planar Circular Coils Used in Wireless Charging of Mobile Phones

Taguchi-Based Design of Planar Circular Coils Used in Wireless Charging of Mobile Phones

Double-Layer Coils Design for 11 kW Wireless Power Transfer

The design of a wireless power transfer system with double rectangular coils for 11 kW power transfer is considered. System modeling and numerical calculation of the system parameters are described. Coils are made from available Litz wire, which has a smaller than necessary diameter for the required power. Thus, a setup with double layer coils was developed, which resulted in a modified design. Starting from a system consisting of coupled coils, as suggested by the standard for wireless power transfer Level 3 in class Z1, different coil and ferrite shield layouts were tested in numerical simulations, and their parameters were calculated. The prototype was constructed based on the simulated model with the best results and properties. Numerical results were verified by laboratory measurements, and a successful power transfer at 11 kW was achieved.

Design and Simulation of a High-Efficiency Micro-Transformer for Photovoltaic Application

This paper presents the design and analysis of a micro-transformer model aimed at achieving high efficiency in photovoltaic applications. The proposed micro-transformer structure consists of two circular planar coils made of copper mounted on PCB (FR4) and Si substrates. The Mohan formula is employed to calculate the micro-transformer’s geometric parameters, ensuring alignment with flyback converter specifications. Consequently, the inductance, quality factors, and coupling factor variation parameters versus frequency, and the impact of the gap between the coils (500, 750, and 1000 µm) on them were analyzed. The simulation findings unequivocally demonstrated that a judicious reduction in gap thickness to 500 µm resulted in a remarkable enhancement of the coupling factor by an impressive 91%. Moreover, finite element-based software was used to analyze the thermal, magnetic, and electric performance of the micro-transformer across varying gap sizes. The investigation led to the determination of the optimal gap thickness that achieves adequate temperature, current, and magnetic flux distribution in the micro-transformer. Finally, the simulation circuit of a photovoltaic system that incorporates a flyback converter including the proposed micro-transformer was performed. Overall, the results revealed that the proposed micro-transformer model with its circular planar coil design offers high efficiency in PV applications.