Multi-turn Coil Research Articles

Radiofrequency-transparent local B0 shimming coils using float traps.

Static field (B0) inhomogeneities present a major challenge in high-field MRI. Multicoil shimming using independent, local, direct-current (DC) shim coils has emerged as a powerful and flexible technique to address this issue. However, many-turn DC coils can lead to significant mutual coupling with radiofrequency (RF) coils, causing transmit field (B1 +) distortions and signal-to-noise ratio degradation. We introduce an innovative RF-transparent DC coil that performs B0 shimming while minimizing RF performance impact. The design incorporates float traps to maintain high RF impedance, allowing flexible placement relative to the RF coil without compromising signal-to-noise ratio or affecting B1 +. We fabricated square-shaped DC coils with float traps for 3T MRI and compared them with conventional DC coils. To demonstrate high ΔB0/Amp efficiency, we conducted a B0 shimming experiment around a metal hip implant. Bench tests and MRI experimental results demonstrated that the RF-transparent DC coil effectively minimized RF interference, preserved signal-to-noise ratio, and maintained B1 +, even when placed near the RF receive coil. Additionally, the DC coil significantly improved B0 homogeneity near metal implants and substantially reduced image distortion. The RF-transparent DC coil offers a flexible, effective solution for managing B0 inhomogeneities, paving the way for integrating multiturn DC coils in clinical MRI settings without extensive hardware modifications.

Homogenized Finite Element Analysis for Multi-Turn Coils Considering Parasitic Capacitances

Homogenized Finite Element Analysis for Multi-Turn Coils Considering Parasitic Capacitances

Model of an E-cored probe over layered conductor containing corrosion for eddy current testing

PurposeIn eddy current nondestructive testing, ferrite-cored probes are usually used to detect and locate defects such as cracks and corrosion in conductive materials. However, the generic analytical model for evaluating corrosion in layered conductor using ferrite-cored probe has not yet been developed. The purpose of this paper is to propose and verify the analytical model of an E-cored probe for evaluating corrosion in layered conductive materials.Design/methodology/approachA cylindrical coordinate system is adopted and the solution domain is truncated in the radial direction. The magnetic vector potential of each region excited by a filamentary coil is derived first, and then the expansion coefficients of the solution are obtained by matching the boundary and interface conditions between the regions and the subregions. Finally the closed-form expression of the impedance of the multi-turn coil is derived by using the truncated region eigenfunction expansion (TREE) method, and the impedance calculation is carried out in Mathematica. In the frequency range of 100 Hz to 10 kHz, the impedance changes of the E-cored coil and air-cored coil due to the layered conductor containing corrosion are calculated, respectively, and the influences of corrosion on the coil impedance change are investigated.FindingsAn analytical model for the detection and evaluating of corrosion in layered conductive materials using E-cored probe is proposed. The model can quickly and accurately calculate the impedance change of E-cored coil due to corrosion in layered conductor. The correctness of the analytical model is verified by finite element method and experiments.Originality/valueAn accurate theoretical model of E-cored probe for evaluating corrosion of multilayer conductor is presented. The analytical model can be used to detect the inhomogeneity of layered conductor, design ferrite-cored probe or directly evaluate the corrosion defects of layered conductors.

Design of field shaper suitable for plate and experimental research on welding of dissimilar materials

Magnetic pulse welding realizes solid-state connection through a high-speed collision of materials, which can effectively overcome the welding difficulties of light metal materials. In the magnetic pulse welding system, in order to improve the welding efficiency, a field shaper is usually applied between the multi-turn coil and the workpiece to concentrate the magnetic field in the welding area, thereby improving the electromagnetic force. However, a large number of researchers are currently on the tube-welded field shaper, and very few researchers have studied the structure of the plate-welded field shaper. Therefore, this paper proposed a new field shaper for plate welding. The effect of the structure parameter of the field shaper on the magnetic field and electromagnetic force on the aluminum plate was analyzed in the COMSOL multiphysics software. The optimal structure parameters of the field shaper were selected. The plastic deformation and the generation of jets under different voltages and the welding of the same/dissimilar metal materials at different standoff distances were studied experimentally, which verifies the feasibility of the new field shaper.

Borehole transient electromagnetic response calculation and experimental study in coal mine tunnels

Water damage seriously threatens the safe production of coal mines, so it is necessary to carry out advanced detection to determine the hydrogeological situation, and the preliminary survey often involves the drilling of on-site drill holes in the tunnel. The use of directional drill holes, combined with advanced geophysical prospecting technology, enables advanced water disaster detection with long distance and high precision and is independent of the tunnel environment influence. The transient electromagnetic method (TEM) is highly sensitive to low-resistivity anomalies and plays a crucial role in water damage detection. To address the size limitation of borehole detection, in this study, a small rectangular multi-turn loop borehole advanced detection method was developed (borehole TEM, BTEM) to detect low-resistivity anomalies within 10 m of the borehole in the radial direction. To satisfy the size requirements for borehole detection and the detection distance, a small rectangular multi-turn loop device with a width of 6 cm and a length of 50 cm was designed. To resolve the issue of self-inductance and mutual inductance enhancement caused by multi-turn coils, a uniform full-space low-resistivity abnormal body model was established using the Ansys Maxwell software, and we analyzed the vertical magnetic field component of the rectangular multi-turn small loop at different time points and the transient electromagnetic response of the different turns. Then, we determined the appropriate parameters for the transmitting and receiving device. The developed method was applied to several different experimental scenarios to obtain the electrical distribution of the anomalous body in front of the device, and the measured data were inverted and interpreted to obtain the apparent resistivity-depth profile. The results demonstrate that the inversion results align well with the actual situation, confirming the effectiveness of the BTEM. This research offers a potential solution for borehole advance detection and provides a solid theoretical foundation for further studies.

Parallel Resonant Magnetic Field Generator for Biomedical Applications.

In recent years, pulsed magnetic field (PMF) have attracted significant attention as a non-invasive electroporation method in the biomedical field. To further explore the biomedical effects generated by oscillating PMF, we designed a novel PMF generator for biomedical research. Based on resonance principles, the designed generator outputs sinusoidal oscillating PMF. To validate the feasibility and application value of the designed topology, a miniaturized platform was constructed using a selected multi-turn solenoid coil. The output performance of the generator was tested under different discharge voltage levels. The results revealed that the current multiplication factor remained consistently around 2 times, with the energy efficiency and circuit quality factor maintained at 82% and above 4.5, respectively. In addition, the generator's ability to flexibly modulate the number of pulse oscillations was demonstrated. The compatibility of the designed coil parameters and generator circuit parameters was analyzed, with tests on the effects of coil resistance and switch action time on the generator's output performance. Based on the magnetic field action platform, a simulation model of the actual scale coil was established. The spatial and temporal distribution of the magnetic field, induced electric field, and power transmission in the target area were described from multiple angles. Finally, biological experiments conducted using the constructed generator revealed the synergistic effect of sinusoidal oscillating PMF combined with drugs in tumor cell killing.

Efficiency Assessment of Air Channel Cooling of a Multi-Turn Coil for Magnetic Pulse Processing of Metals

Efficiency Assessment of Air Channel Cooling of a Multi-Turn Coil for Magnetic Pulse Processing of Metals

Numerical signal calculation and detection capability of magnetic resonance antenna with high rectangular coefficient

Magnetic resonance technology is widely used for groundwater detection due to its direct and quantitative advantages, typically employing square antennas. However, in narrow environments such as mine roadways, canyons, and dams, rectangular antennas with varying dimensions are more practical than square ones. The existing literature lacks comprehensive discussion about the response characteristics of magnetic resonance signals of rectangular antennas, particularly those with high rectangular coefficients. This paper addresses the challenges encountered in a particular application scenario by computing the magnetic resonance excitation magnetic field generated by a rectangular antenna. In addition, it determines the response characteristics of the magnetic resonance signal of rectangular multi-turn coils. We propose coefficient indices of magnetic resonance antennas with different rectangular coefficients, in conjunction with the receiving antenna's matching system to evaluate the actual detection capabilities of various rectangular antennas. Field testing validates the proposed method's effectiveness, providing a robust foundation for assessing the actual detection capability of magnetic resonance antennas and selecting appropriate antennas for specific scenarios.

Магнитное поле многовитковой цилиндрической катушки с ферромагнитным сердечником в непосредственной близости от металлических конструкций в задаче поиска людей под завалами в шахтах

Some aspects of the low-frequency magnetic field propagation in heterogeneous medium in mines are discussed in the paper. The theoretical model for calculation of magnetic field distribution in case of the parallel axis of transmitting antenna and bulk metal is developed. Metal structures are rail tracks, magnetic antenna is multiturn cylindrical coil with ferromagnetic core. Magnetic field according to proposed models principle in several stages using the method of integral equations was numerical calculated. This method of calculation of magnetic field in considered inhomogeneous space is based. The calculations of magnetic field strength of the multiturn cylindrical coil with ferromagnetic core in nearby proximity and at various distances from bulk metal were carried out. The possibility of use of low-frequency magnetic field attenuation for people search under avalanches was proved.

Numerical study for the impact of current sharing effect upon dynamic behaviour of DC-carrying HTS coils under alternating magnetic fields

Numerical characterization for the dynamic behaviour of DC-carrying HTS coils subjected to alternating magnetic fields is crucial for its design and protection. In conventional approaches, only superconducting layers are modeled. The missing current sharing effect in those models results in the overestimation of dynamic voltage/resistance. In reality, the transport current will migrate into the metal layers, and therefore the dynamic voltage/resistance is limited. In this paper, we present an equivalent modeling approach (EPM) instead of modeling the real geometry which will cost massive computation resources. The effectiveness of the approach is validated against a full-scale model containing all the layers. Then, this approach is applied to estimate the dynamic behaviour of a multiturn racetrack HTS coil. It is found that the current sharing effect mainly happens at the outer layers of the coil due to the shielding effect, and is enhanced with the increase of external field amplitude then gradually spreads to the inner layers. Moreover, the competition between the transport current and the induced current in the metal layers is observed.

Image Analysis Capabilities and Methodologies of Nb3Sn Rutherford Cables

The unique Rutherford cabling facility at the Berkeley Center for Magnet Technology, LBNL, has been leading the production of a range of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn cables for a variety of magnet projects domestically and internationally. Cable fabrication is a critical step in accelerator magnet production: to ensure tight dimensional control of the multi-turn coils, fine tolerances must be kept on the cable width, thickness, keystone angle [1] with minimal degradation to the conductor. In addition to these dimensional measurements, we implemented an in-line image acquisition system that can monitor for critical defects such as cross-overs, as well as track the extent of strand deformation at the cable edges. At LBNL, we have collected a large dataset to establish the association between the cable edge facet dimension and the cross-sectional subelement damages. We thus can use image analysis on the facet as an integral and critical quick turn-around-time quality control monitor. Although such measurements are not direct and require a baseline for a given conductor and cable geometry combination, they are non-destructive. They can be measured across the entire length of the cable, which contrasts with critical current or residual resistance ratio measurements, which are only made at the point and tail of the cable and require a lengthy heat-treatment. Moreover, the high frequency of image acquisition coupled with Fast Fourier Transform analysis can give us insights into the key components of the cabling machine as they tend to produce periodic variations within the cable. Such analysis can help find potential faults and inform maintenance planning. This work describes our setup of in-line imaging of Rutherford cables during manufacture, the subsequent image analysis, and data processing. Several case studies illustrate typical usage of the system and lessons learned.

Static magnetic field amplification in high-T c superconducting flux transformer equipped with multi-turn coil prepared using REBCO tape conductor

In this study, a high critical temperature (high-T c) superconducting flux transformer is prepared using a commercially available REBa2Cu3O y (REBCO) high-T c superconducting (HTS) tape conductor. The device configuration includes a 10 cm diameter pickup coil and a 3 cm diameter multi-turn input coil, which are formed by the “cut-and wind” method. The static magnetic field transfer efficiency between both coils has been estimated using inductance calculation of the multi-turn coils. The transfer efficiency measured is close to the calculation, and the field amplification of the transferred magnetic field compared to the applied field to the pickup coil is confirmed in the device which equipped with the multi-turn input coil. The magnitude of this magnetic field amplification has achieved to 125% of the applied field. This result suggests that the HTS flux transformer proposed in this study is effective in the sensitivity enhancement of the magnetometer for static magnetic fields.

Time-Domain Homogenized Finite Eddy Current Analysis Using Recursive Convolution Method

This paper presents a novel method for effectively and accurately performing time-domain homogenized finite element analysis of multi-turn coil windings. In this method, the macroscopic complex permeability is represented by a partial fraction form, and then inverse Laplace transformation is performed using the recursive convolution method. The proposed method is approximately 100 times faster than conventional finite element analysis, with good agreement between the obtained results. Moreover, the results obtained by the proposed method were also in good agreement with those obtained by measurement.

Acquisition and correction for early surface nuclear magnetic resonance signal based on multi-turn small air-core coil sensors

Surface nuclear magnetic resonance (SNMR) with multi-turn small air-core coil sensor (ACS) has considerable potential for the detection of shallow soil water or oil. However, loss of the early free induced decay signal and the distortion of the recorded signal arising from the ACS, make it difficult to quantitatively evaluate hydrological information. To address this problem, we propose an early signal acquisition and correction method. A fast-switching unit is applied to acquire the early signal. And a correction method based on the mathematical model of the ACS is proposed. Finally, the performance of the proposed method is evaluated by simulation experiments. Results show that the proposed method overcomes the signal attenuation caused by the ACS, while the fitting error of key parameters decreases from about 15% to 2%. Comparative test results of the existing method in an electromagnetically shielded laboratory further demonstrate the effectiveness of the proposed method.

Lifetime extension of the high voltage asynchronous machine in relation to the voltage endurance test

The study aims to achieve a simple, reliable, and significant lifetime extension of the high-voltage asynchronous machine in relation to the voltage endurance test. To achieve this goal, the focus was on achieving longer-lasting and more stable insulation of the stator package of an asynchronous machine. Longer-lasting and more stable insulation of a stator is achieved by reinforcing the weak points on its prefabricated multiturn coils. These reinforcements were performed with standard insulating materials that are used for the production of the prefabricated multiturn coils (because there is no data regarding the long-term behavior of new materials that show some better properties in laboratories, but only during short-term tests). With such reinforced weak spots based on prefabricated models, they were made by the classical procedure with the use of standardized tools. To track the effects of the improvement of the insulation characteristics of a stator, an algorithm was developed based on the law of increasing probability and the determination of lifetime curves to the voltage endurance test. The lifetime curves were determined by the method of increasing voltage with the transformation of the obtained results to the corresponding results by the constant voltage method. The applied algorithm that was formed for this study, had been verified with statistical reliability of 95%. The combined measurement uncertainty of the measurement procedure was about 5%.

Modeling transcranial magnetic stimulation coil with magnetic cores

Objective. Accurate modeling of transcranial magnetic stimulation (TMS) coils with the magnetic core is largely an open problem since commercial (quasi) magnetostatic solvers do not output specific field characteristics (e.g. induced electric field) and have difficulties when incorporating realistic head models. Many open-source TMS softwares do not include magnetic cores into consideration. This present study reports an algorithm for modeling TMS coils with a (nonlinear) magnetic core and validates the algorithm through comparison with finite-element method simulations and experiments. Approach. The algorithm uses the boundary element fast multipole method applied to all facets of a tetrahedral core mesh for a single-state solution and the successive substitution method for nonlinear convergence of the subsequent core states. The algorithm also outputs coil inductances, with or without magnetic cores. The coil–core combination is solved only once i.e. before incorporating the head model. The resulting primary TMS electric field is proportional to the total vector potential in the quasistatic approximation; it therefore also employs the precomputed core magnetization. Main results. The solver demonstrates excellent convergence for typical TMS field strengths and for analytical B–H approximations of experimental magnetization curves such as Froelich’s equation or an arctangent equation. Typical execution times are 1–3 min on a common multicore workstation. For a simple test case of a cylindrical core within a one-turn coil, our solver computed the small-signal inductance nearly identical to that from ANSYS Maxwell. For a multiturn rodent TMS coil with a core, the modeled inductance matched the experimental measured value to within 5%. Significance. Incorporating magnetic core in TMS coil design has advantages of field shaping and energy efficiency. Our software package can facilitate model-informed design of more efficiency TMS systems and guide selection of core material. These models can also inform dosing with existing clinical TMS systems that use magnetic cores.

An electrometric method for the interface stress and contact resistance of pancake coil under winding force.

Interface stress and contact resistance play key roles in the safety and stability assessment of non-insulated superconducting pancake coils. An electrometric method for the interfacial stresses and contact resistance of multi-turn coils of different materials has been established, which is further applied to the measurement and analysis of contact stresses and resistances of the composite superconducting coils under the extremely low temperature environment. The mechanical and electrical behaviors are coupled through an extended electro-mechanical contact model, which also reveals the electro-mechanical interaction mechanism of the coil. The extended contact model was verified by comparison with experimental results, and the proposed electrometric method was verified by comparing the interface stresses calculated by two approaches. The contact stresses and resistances of superconducting coils with different turns are successfully obtained through the proposed electrometric method, which provides bases for the evaluation of the transport and mechanical performance of superconducting coils.

Homogenization of the vertically stacked medium frequency magnetic metamaterials with multi-turn resonators

The paper presents a homogenization method of the magnetic metamaterials, made of perpendicularly oriented resonators consisting of multi-turn planar coils. A resulting composite, in the form of parallel stripes with metamaterial cells, exhibits extraordinary properties in the medium frequency magnetic field, such as zero permeability. To identify an effective permeability of this metamaterial, two models were presented, i.e., a three-dimensional numerical model with current sheet approximation as well as Lorentz oscillator model, where individual coefficients are based on the lumped circuit parameters and directly related with a geometry of the unit cell. The accuracy of the second approach is improved by taking into account mutual inductances in a metamaterial grid. Then, a comparison is made with numerical model results to show adequacy of the adopted analytical attempt, and properties of this type of metamaterial are discussed. It is shown that discussed metamaterial structure can achieve negative permeability as well as its values, at identical resonant frequency, are dependent on number of turns of the planar coil.

Performance analysis of induction heated-porous thermochemical energy storage for heat applications in power systems

Power flexibility with fast and long-duration heat storage systems is crucial in modern power systems to meet the increasing cooling and heating demand and reduce the gap between renewable intermittent power generation and power demand. The hereby study analyzes the thermal and electrical performances of induction heated-porous thermochemical energy storage for heat applications into microgrids. The induction heating model is built with Maxwell equations for fast induction heat generation and the Surface-to-Surface (S2S) model, P1 approximation and Brinkmann model are adopted for induced and diffused heat transfer in the fluid phase and porous heat storage medium. The effects of the conductive plates’ orientation and location and the coil’s location are investigated. Furthermore, the effect of operating and structural parameters in terms of the electrical power supplied to the coil and the heat transfer coefficient of the coil’s cooling system and reactor insulation are sufficiently examined. Finally, essential parameters for the thermochemical material selection are assessed. It is found that the model with the highest magnitude of the induced magnetic flux passing through the conductive plates has outperformed at 107.57 % the worst model among the developed reactors. Moreover, the temperature distribution of the reactor resulted from the supplied power to the homogenized multi-turn coil and the heating rate at the heat storage material significantly increases with the supplied power. However, increasing the power supplied to the coil leads to higher conductive and convective heat loss resulting in less efficient electrical to heat conversion performance. Thermochemical materials with low emissivity should be preferred as the emissivity could lead to a 13.7 % improvement in the energy efficiency of the reactor. Implementing the proposed model in a microgrid for cooling and heating load improved the energy cost and self-consumption by 31.7 and 8 %, respectively.

An accelerated analytical method for predicting workpiece velocity and displacement during electromagnetic forming

This paper presents complementary analytical analyses, experiments, and numerical simulations of the electromagnetic tube compression (EMTC) process using a multi-turn axisymmetric coil with a field shaper. In earlier contributions, we proposed an analytical model capable of predicting the magnetic pressure, radial velocity, and radial displacement for EMTC. In the present paper, our understanding of EMTC is expanded with the aid of a modified analytical model, a series of experimental tests with various materials, and 3D coupled electromagnetic-mechanical numerical simulations. First, the analytical model was improved by generating elements across the entire landing area of the field shaper. This modification provided a more accurate induced magnetic pressure in the analytical model. In addition, the experimentally measured coupling coefficients between the coil, field shaper, and workpiece tube were directly incorporated into the analytical model as opposed to utilizing them as correction factors during the magnetic pressure calculation in the previous studies. In the proposed analytical model, at each time increment, the magnetic field geometry is updated in response to the tube deformation. Second, to assess the proposed analytical model, experimental tests with Photon Doppler Velocimetry (PDV) were carried out for three different materials with different thermo-mechanical properties, i.e., Al6061-T6, Cu101, and Cu260 (Brass). Third, to compare the computational cost of the analytical model and to determine the accuracy of the proposed analytical model compared to the existing software packages in the market, a 3D coupled electromagnetic-mechanical finite element model was used. To investigate the influence of discharge energy on tube deformation, all three methods were examined at three different charging energies, i.e., 2.4, 3.6, and 4.8 kJ. Reasonably good agreement between all three approaches validates the ability of the analytical model to accurately capture the deformation velocity and displacement for this complex multi-physics manufacturing process in a computationally cost-effective manner. Such an analytical model can be used as a base model for predicting the impact velocity during electromagnetic pulse welding and crimping processes prior to performing expensive and time-consuming experimental tests or numerical simulations.