Circular Coil Research Articles

Fast evaluation of the critical current of high-temperature superconducting coils based on the integral method

The need for energy is growing as civilization develops. Superconductors have various benefits over regular conductors, including a high current-carrying density and nearly no resistance. Therefore, the objective that scientists continue to seek is the use of superconductors to replace traditional conductors in order to satisfy the demand for energy. As a key part of the superconducting electrical system, the critical current is one of the key properties of high-temperature superconducting (HTS) coils. Scholars have created a variety of numerical simulation models to estimate the performance of HTS coils. However, the extremely nonlinear E–J power law relationship that characterizes the voltage–current relationship in superconducting materials necessitates numerous iterative refinements during the coil design stage, which is time-consuming from the perspective of computing efficiency. Consequently, it is essential to increase computational efficiency. In this study, the critical current of HTS coils was calculated using the J model (integral method with the current density J as the state solution variable), and it was proved to be an efficient research method. The accuracy of the method is verified by comparing with the H model and the experimental measurement results of the critical current of the HTS coil. Moreover, compared with the reference finite element simulation model, this model has a speed advantage of at least four times, which is a good choice, especially, for HTS circular coils with large turns.

Электродинамические силы между соосными плоскими катушками круговой формы

Object and purpose of research. Non-contact power transfer to various marine facilities. Subject matter and methods. The study relied on the methods of theoretical electric engineering. Main results. This paper gives analytical estimates for electrodynamic forces acting on inductively-coupled coaxial flat coils of circular shape. Conclusion. The study yielded the expressions for the electrodynamic forces in inductively coupled circular coils interfaced so as to perform non-contact power transfer.

Study on the Effect of Non-Symmetrical Current Distribution Controlled by Capacitor Placement in Radio-Frequency Coils for 7T MRI.

In this paper, we present a study on the effects of varying the position of a single tuning capacitor in a circular loop coil as a mechanism to control and produce non-symmetric current distribution, such that could be used for magnetic resonance imaging (MRI) operating at ultra-high frequency (UHF). This study aims to demonstrate that the position of the tuning capacitor of a circular loop could improve the coupling between adjacent coils, used to optimize transmission field uniformity or intensity, improve signal-to-noise ratio (SNR) or specific absorption rate (SAR). A typical loop coil used in MRI consists of symmetrically distributed capacitors along the coil; this design is able to produce uniform current distributions inside the coil. However, in UHF conditions, the magnetic flux density (|B1+|) field produced by this setup may exhibit field distortion, requiring a method of controlling the field distribution and improving the field intensity of the circular loop coil. The control mechanism investigated in this study is based on the position of the tuning capacitor in the circular coil, the capacitor position was varied from 15° to 345°, in steps of 15°. We performed electromagnetic (EM) simulations, fabricated the coils, and performed MRI experiments at 7T, with each of the coils with capacitor position from 15° to 345° to determine the effects on field intensity, coupling between adjacent coils, SAR, and applications for field uniformity optimization. For the case of free space, a coil with capacitor position at 15° showed higher field intensity compared to the reference coil; while an improved decoupling was achieved when a coil had the capacitor placed at 180° and the other coil at 90°; in a similar matter, we discuss the results for SAR, field uniformity and an application with an array coil for the spinal cord.

Effect of winding methods: transport AC losses in CORC coils

AC losses undoubtedly increase the burden on the cooling system and affect the overall performance of high-temperature superconducting (HTS) cables. Therefore, AC losses in HTS cables are important design factors for large-scale HTS equipments. Extensive research has been conducted on straight, densely wound conductors. However, AC losses of bending/circular HTS cable conductors have not been sufficiently studied. In this article, the transport AC losses in a circular HTS conductor coil bended by a conductor on round core (CORC) type cable were investigated using experiments and numerical simulations. The effect of different winding methods was also studied. First, the modeling method of the three-dimensional simulation and the experimental procedures were presented. The simulation results of the straight densely wound conductor (SDWC) and circular densely wound coil (CDWC) were compared with the corresponding experimental results. Finally, the winding method for the CDWC was optimized using both the simulation and experimental approaches. Both the experiments and simulations showed that reducing the tape-to-tape frontal area was able to decrease the transport AC loss, and the results show that the optimum winding angle of the HTS CORC coil was 24.15°. Overall, the modeling and experiments provide useful optimization strategies for designing winding structures of high-performance CORC coils/magnets.

A Free-Rotation Asymmetric Magnetic Coupling Structure of UAV Wireless Charging Platform With Conformal Pickup

This article proposes an asymmetric magnetic coupler using the horizontal magnetic field to realize the conformal and lightweight unmanned aerial vehicle (UAV) side pickup mechanism and solve the problems of rotation misalignment and horizontal offset of UAVs. The novel structure uses multiple groups of series circular coils as the transmitting coil to construct a uniform near harness horizontal magnetic field. The solenoid structure covered with flexible magnetic material is used as the receiver, which is attached to the UAV landing gear. A 200-W prototype is produced to validate the proposed structure. The system can maintain smooth mutual inductance with a dc–dc efficiency of 90% under a ±20 mm offset and free-rotation.

Design and Analysis of Omnidirectional Receiver with Multi-Coil for Wireless Power Transmission

In order to solve the misalignment problem of wireless power transmission, this paper designed and analyzed the omnidirectional receiver with multi-coil. The circuit models and transmission characteristics of the wireless power transfer system (WPTS) containing multi-coil were established. Besides, an accurate mutual inductance modelling method of the circular coil under different horizontal offset and angular deflection was presented. Based on the circuit models and the mutual inductance model, the relationship between transmission characteristics and the coil parameters were studied. Simultaneously, the design method which can synthetically and quantificationally consider the radius of the coil and the number of turns was proposed. Finally, an omnidirectional receiver with multi-coil using the quantificational model and transmission characteristics in different horizontal offset and angular deflection was designed.The transmission efficiency of three-coils-receiver system was up 12.3% higher than that of one-coil-receiver system and 4% higher than that of two-coils-receiver system when horizontal offset was between 0 cm and 30 cm. Similarly, when angular deflection was between 0 and π/2, the efficiency of three-coils-receiver system was up 73.25% higher than that of one-coil-receiver system and 1.6% higher than that of two-coils-receiver system.

Numerical Evaluation on Mechanical Behavior of No-Insulation REBCO Pancake Coils in Small-Scale Model of Skeleton Cyclotron

We are developing a high-temperature superconducting (HTS) air-core compact cyclotron, named Skeleton Cyclotron (Ueda <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> 2013), (Ueda <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> 2019), that can accelerate various particles and variable energy for radioisotope (RI) production. The coil system of Skeleton Cyclotron consists of circular main coils and noncircular sector coils which are wound by REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+δ</sub> (REBCO) tape applied no-insulation (NI) winding technique for both high current densities and thermal stabilities. The electromagnetic and thermal behaviors in NI coil differs from those in conventional insulated coils during charging, discharging, and quenching. Therefore, it is necessary to investigate the mechanical behavior and reinforcement structure of multiple NI coils in Skeleton Cyclotron. In this study, we report on the numerical evaluation of mechanical properties of NI REBCO coils in Skeleton Cyclotron at charging and quenching considering the current distributions and electromagnetic stresses unique to NI coils. In the quenching process, the radial current in a quenching pancake of the sector coil became dominant, resulting in generating the rotating force and non-symmetric deformation. YOROI-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure is effective for the additional magnetic stress.

Exploring Beyond the Helmholtz Coils for Uniform Magnetic Field Generation With Topology Optimization

Uniform magnetic fields are desired in a wide range of applications. The most known device achieving such a purpose is the pair of Helmholtz coils. It consists of two identical circular coils, with their main axis aligned and placed at a distance equal to their common radius from each other. The goal of this research is to find another arrangement of the coils in space so as to achieve the largest region possible with a uniform magnetic field. A topology optimization framework is developed for this purpose. It investigates the ideal distribution of current densities in an axisymmetric 2-D domain. The designed topology provides a significant improvement of the volume with a uniform field, which is 6.37 times larger than the reference one obtained with Helmholtz coils.

The influence of interlaminar microstructure on the induction heating patterns of CFRP laminates

The impact of interlaminar microstructure on the induction heating patterns of CFRP laminates is investigated using thermography technique. Different consolidation methods were used to obtain the varying interlaminar distances. When excited by a circular induction coil, the induction heating pattern of laminates shifted from a circular to a rectangular shape as the interlaminar distance increased. The shift in the heating patterns is caused by the increase in fiber separations at the interface, which leads to fewer electrical contacts. The effect of varying interlaminar distance was modeled as an effective through-thickness electrical conductivity in the numerical model. When the separation between the fibers increased from 8 ± 3.6 µm to 15.3 ± 3.8 µm, the ratio of junction heating to fiber heating increased from 60% to 135%.

A Concise Analytical Formula of Mutual Inductance for Circular Rogowski Coil Revealing Spatial Distribution Characteristics of Mutual Inductance Deviation

Mutual inductance between primary wire and circular Rogowski coil varies with the position of primary conductor, the deviation of mutual inductance referred to center of circle causes the measurement error. Usually, the mutual inductance of Rogowski coil can be calculated by the summation of each turn of coil, however the spatial distribution characteristics of mutual inductance deviation has not been revealed. A concise analytical formula of mutual inductance is derived based on the summation form and verified by experiment in this paper, which leads to three characteristics of mutual inductance deviation. The first is the mapping relation of mutual inductance deviation between inside and outside Rogowski coil which established connection between positional accuracy and anti-interference ability. The second is the zero deviation line of mutual inductance deviation given by simple equation, which describes the position of primary wire where the measurement error vanishes. The third is approximate function on turns number, inner and outer radius of Rogowski coil and measurement error, which is easy to calculate and simplifies the design progress of Rogowski coil. Furthermore the formula and characteristics of mutual inductance can be generalized from uniform Rogowski coil and perpendicular primary wire to discontinuous PCB RC, primary conductor with cross section, and inclined primary wire. The mapping relation, zero deviation line and improved formula of mutual inductance deviation are discussed.

A Differential Excitation Eddy Current Probe Based on Novel Annular Fractal Curve for Defects Inspection

A flexible eddy current probe can detect the defects in components with a complex structure due to its bendability and adaptation to the surface of the tested specimen for nondestructive testing. However, the traditional, flexible eddy current probe with circular and rectangular coils may neglect small cracks along certain special orientations. In this paper, the authors introduce the theory of fractal geometry to guide the design of flexible probes. An annular fractal curve is first proposed, and its system of iterative functions and geometric characteristics are then studied. Following this, six flexible differential excitation-based eddy current probes are designed based on the annular fractal curve. Simulations and experiments are used to compare the performance of the probes to identify the optimum one for inspecting defects. The results show that the M6K3 probe delivers the best performance in terms of the identification of cracks with lengths shorter than half the length of the coil of the probe.

An ergonomic evaluation of workers in the winding section of the pump manufacturing industry.

Work-related musculoskeletal disorders (WMSDs) are prevalent and have an impact across occupations. However, there are very few studies that document the prevalence of WMSDs in the pump industry. In manufacturing industries, the common issue for WMSDs and physiological stress among the workers is caused by poor working posture. To investigate the occupational risks at the winding station in the pump manufacturing industry. In addition, this study examined the influence of work-study on mitigating occupational risks. Workers who were involved in circular coil winding and insulation testing were considered for the study. Awkward postures adopted while performing these tasks cause fatigue, injuries and WMSDs. Tasks were evaluated as per the National Institute for Occupational Safety and Health (NIOSH) standards. A work-study was conducted to better understand the workflow. Virtual ergonomic postural evaluation (Rapid Upper Limb Assessment, RULA) was used to identify the occupational risks. Time taken for making circular windings and insulation testing (7.5 Hp submersible motor) was found to be 4.04 minutes and 0.95 minutes, respectively. A CAD model was used for ergonomic evaluation in the virtual environment. The RULA final score of 2 and 3 is attributed to coil winding and insulation testing. For further studies, the whole pump manufacturing process should be taken into account. The ergonomic tools used in this study will considerably reduce the occupation risks at the winding station in the pump manufacturing industry.

Safety of low-intensity repetitive transcranial magneTic brAin stimUlation foR people living with mUltiple Sclerosis (TAURUS): study protocol for a randomised controlled trial

BackgroundMultiple sclerosis (MS) is an inflammatory and neurodegenerative disease, characterised by oligodendrocyte death and demyelination. Oligodendrocyte progenitor cells can differentiate into new replacement oligodendrocytes; however, remyelination is insufficient to protect neurons from degeneration in people with MS. We previously reported that 4 weeks of daily low-intensity repetitive transcranial magnetic stimulation (rTMS) in an intermittent theta-burst stimulation (iTBS) pattern increased the number of new myelinating oligodendrocytes in healthy adult mice. This study translates this rTMS protocol and aims to determine its safety and tolerability for people living with MS. We will also perform magnetic resonance imaging (MRI) and symptom assessments as preliminary indicators of myelin addition following rTMS.MethodsParticipants (N = 30, aged 18–65 years) will have a diagnosis of relapsing-remitting or secondary progressive MS. ≤2 weeks before the intervention, eligible, consenting participants will complete a physical exam, baseline brain MRI scan and participant-reported MS symptom assessments [questionnaires: Fatigue Severity Scale, Quality of Life (AQoL-8D), Hospital Anxiety and Depression Scale; and smartphone-based measures of cognition (electronic symbol digit modalities test), manual dexterity (pinching test, draw a shape test) and gait (U-Turn test)]. Participants will be pseudo-randomly allocated to rTMS (n=20) or sham (placebo; n=10), stratified by sex. rTMS or sham will be delivered 5 days per week for 4 consecutive weeks (20 sessions, 6 min per day). rTMS will be applied using a 90-mm circular coil at low-intensity (25% maximum stimulator output) in an iTBS pattern. For sham, the coil will be oriented 90° to the scalp, preventing the magnetic field from stimulating the brain. Adverse events will be recorded daily. We will evaluate participant blinding after the first, 10th and final session. After the final session, participants will repeat symptom assessments and brain MRI, for comparison with baseline. Participant-reported assessments will be repeated at 4-month post-allocation follow-up.DiscussionThis study will determine whether this rTMS protocol is safe and tolerable for people with MS. MRI and participant-reported symptom assessments will serve as preliminary indications of rTMS efficacy for myelin addition to inform further studies.Trial registrationAustralian New Zealand Clinical Trials Registry ACTRN12619001196134. Registered on 27 August 2019

Sensitivity Analysis of Circular and Helmet Coil Arrays in Magnetic Induction Tomography for Stroke Detection.

Magnetic induction tomography (MIT) is harmless and contactless technique for measuring the conductivity of the biological tissue. MIT could be used for initial diagnosis and continuous monitoring of stroke. Different kinds of coil arrays have been proposed for MIT systems. Previous research results using a circular 16-channel MIT model reported difficulties with detection and measurement of small bioelectric signals. For stroke imaging, a system with a higher sensitivity is required. We aim to improve the sensitivity by increasing the number of coils and placing them closer to the head. In this paper, a helmet type coil array with 31 coils is introduced. For simplicity, the head is modelled as a sphere with white matter as a material. The stroke is simulated as a single inclusion with blood and assigned different sizes and positions. Sensitivity distribution and target response of the stroke were evaluated for the helmet model and compared with the circular MIT system. The simulations and analysis were performed at 10 MHz frequency with different coil pairs. Results from comparison of the two MIT models show that the Helmet coil array provides better spatial sensitivity, which has been estimated to be more than 20 times higher than the circular model. Further, when all coils are taken in account, the recorded sensitivity improvement was in the range of 13-90-fold.

Analytical solutions for flexible circular spiral eddy current array coils inside a conductive tube under different operation modes

The eddy current induction of flexible eddy current array probe composed of thin curved circular spiral coils is studied using the second-order vector potential formalism. The analytical expressions of self-and mutual impedance change of coil array element inside a conductive tube under three standard eddy current array operation modes are derived. They are self-transmitting and receiving, absolute and differential transmit-receive, respectively. Further derivation shows that the coefficient matrices of characteristic equations in these modes are the same regardless of whether the element is placed inside or outside a tube, but the non-homogeneous terms are different. Therefore, the solution to another case can be obtained quickly through the transformation relationship. The experimental results show that the theoretical predictions are consistent with the experiment over the 5 kHz–1 MHz excitation frequency range. At the same time, the real and imaginary part errors of impedance change are analyzed, and the application of small inductance flexible coil in three operation modes is discussed. Finally, these expressions provide academic support for the eddy current testing of pipeline defects and their significance in the inversion of tube electromagnetic properties.

Field models for the electromagnetic compatibility of wireless power transfer systems for electric vehicles

PurposeThe paper presents the Finite Element (FE) evaluation of the magnetic field emitted by a Wireless Power Transfer Systems used to charge the battery of electrical vehicles. An original approach for reducing the mesh size of the 3D FE model is used.Design/methodology/approachA minicar equipped with a circular coil is considered, while the transmitting coil is coherent with the Society of Automotive Engineers (SAE) standard. The different shape of the coils and a possible misalignment are considered as possible sources of emitted magnetic field, which a person could be exposed to. To this end, a FE model is implemented. Because of the complexity of the mesh, a suitable 3D model is used. This model is previously validated and then used for evaluating the magnetic field around the Wireless Power Transfer Systems (WPTS).FindingsThe magnetic flux density around the WPTS is calculated and compared with the International Commission on Non-Ionizing Radiation Protection (ICNIRP) limits.Originality/valueThe proposed 3D model, whose validation is shown in the paper, is able to compute the magnetic field with high accuracy despite the presence of a conductive and ferromagnetic thin structure, the steel layer related to the car frame, which would need a very fine mesh with a large number of elements to solve Maxwell equations.

Analytical model for calculation of the magnetic field of triaxial uniform coils in magnetically shielded cylinder

An analytical model to calculate the magnetic field of triaxial uniform coils inside magnetically shielded cylinders (MSCs) composed of high-permeability materials is proposed. The proposed model offers two major advantages over existing methods. First, the model is not limited to the research on coaxial circular coils, but also can be used to analyze the magnetic field characteristics of saddle coils inside MSCs. Second, based on Green’s function expansion and the ferromagnetic boundary conditions, the image method is introduced to consider the reflection effect of the MSC end cap on the coil, thus enabling the coupling effect between the coil and the MSC to be analyzed. To verify the model’s correctness, simulations and experiments are performed separately. With regard to the magnetic field distributions of the saddle coil and the Lee-Whiting coil within a range of 80 mm along their axes, the results show that the maximum relative error between the analytical method and the finite element method results is 0.08% and 0.06%, respectively; the maximum relative error between the experimental values and the analytical values is 0.29% and 0.13%, respectively, thus confirming the validity of the analytical model. The results of this research have far-reaching implications for the research of quantum precision measurement devices and triaxial uniform field coils.

Mutual inductance model of double printed circuit board‐based coplanar rectangular spiral coils for eddy‐current testing

AbstractIn the field of eddy‐current testing (ECT), most studies on detection probes are primarily based on circular solenoid coils; related research on rectangular spiral coils is rare. In this study, an analytical model of the mutual inductance (MI) between two coplanar rectangular spiral coils was developed in which the two coplanar rectangular spiral coils were placed above a conductive plate. The MI calculation does not need to consider the thickness of the coils, which is consistent with the actual situation of the printed circuit boards (PCB)‐based spiral coils, and simplifies the multi‐turn rectangular spiral coil into a set of concentric single‐turn coils. Two experimental setups were constructed to verify the analytical model and they were used to detect defects in the aluminium plate. The experimental results indicate that the analytical model can be used to evaluate the performance of ECT probes using PCB‐based spiral coils, through the geometrical dimensions of the coils, centre distance and lift‐off, and so forth. Compared with traditional methods, this method can still obtain satisfactory calculation accuracy after ignoring thickness parameters. The analytical model is also an effective tool to aid in the design of detection probes and optimisation of related parameters.

500W Circular Coil Parameters Mathematical Design for Wireless Power Transfer with Ferrite Core

The efficiency of wireless pad designs with ferrite cores has been established in several investigations. However, they seldom offered a viable solution to the problem of modifying the ferrite form's geometric shape. The use of a ferrite core in the primary and secondary coils has been suggested by several researchers. The ferrite core design, on the other hand, is still in the works. Using the wrong ferrite core design might result in unnecessary extra weight and higher production costs. The circular coil design in the primary and secondary for wireless power transfer (WPT) in electric vehicles is studied in this research. The suggested coil design is used to develop mathematical design utilizing numerical solutions. Later, using Multisims software, this coil design is produced in simulation. The suggested coil design's power efficiency is examined and contrasted between computed and simulated results. Finally, based on the results of the power efficiency, a definitive discussion is presented.

Spatial filtering of Zeeman sub-states in an atomic fountain.

In an atomic fountain, atoms in motion can be spatially separated into discrete Zeeman sub-states by magnetically induced Stern-Gerlach effect. With resonant light pulses acting as a shutter, specific states are selected for subsequent experiments. Such separation-selection process in atomic optics is the analogue of a spatial filter in physical optics which selects and purifies the modes of light. This technique is demonstrated by injecting a pulsed current in a circular coil around a vertical atomic fountain, separating the pre-cooled Rubidium atoms by a distance of centimeters in between, and filtering each single sub-state with block pulses. The filtered atoms after the process is highly purified in the desired sub-state. The apparatus of the atomic spatial filter is adaptable in atomic optics and can be integrated into the high-vacuum chamber of an atomic fountain.