Single-turn Coil Research Articles

Predicting the Effect of Field Shaper in Electromagnetic Welding Using FEM

The research work presents a 3D numerical simulation to predict the distribution of magnetic field and pressure in the desired region of the tubular jobs using coils with and without field shapers in electromagnetic welding (EMW). For finite element (FE) simulation, single-turn (ST) and multi-turn (MT) (disk type) coils are considered to analyze the effects of field shapers with varying material combinations in ANSYS MAXWELL environment. The change in magnetic field distribution on the outer peripheral region of the flyer tube along axial direction with and without field shaper is graphically shown and compared. Also, variation of magnetic pressure on the flyer tube with respect to increasing voltage and time is compared individually for various material combinations of ST/MT coil and field shaper. Results show that in welding simulation (FE) using single-turn Cu and SS coils with field shapers of Be, Nb and Ta, the magnetic pressure increases by 34, 12 and 11% and 35, 12 and 11%, respectively, as compared to the coil with no field shaper. In case of multi-turn SS coil with Cu and Be field shapers, the magnetic pressure increases by 16 and 10%, respectively. The novelty of the work is the proper guideline to select the material combinations for ST/MT coils and field shapers and positioning of work pieces inside the coil in order to achieve maximum utilization of input energy in EMW system.

A High-Bandwidth Integrated Current Measurement for Detecting Switching Current of Fast GaN Devices

Gallium nitride (GaN) devices are suitable for high-frequency power converters due to their excellent switching performance. To maximize the performance of GaN devices, it is necessary to study the switching characteristics, which requires measuring the switching current. However, GaN devices have a fast switching speed and are sensitive to parasitic parameters, so the current measurement should have a high bandwidth and should not introduce excessive parasitic inductance into the power converters. Traditional current measurements are difficult to meet these requirements, especially for fast GaN devices. This paper presents a high-bandwidth integrated current measurement for detecting the switching current of fast GaN devices. By effectively utilizing the parasitic inductance in the circuit, a single-turn coil is embedded in the printed circuit board. This coil could pick up a sufficiently strong voltage signal, which is then processed to reconstruct the switching current. Moreover, corrections are carried out to further improve the accuracy. The current measurement has a small insertion impedance and a high bandwidth with a small influence on the parasitic inductance of the converter. The accuracy of the current measurement is experimentally verified by a 40 V GaN-based double pulse test circuit with a load current up to 25 A.

Gimbal-Less Two-Axis Electromagnetic Microscanner with Twist Mechanism.

We present an electromagnetically driven microscanner based on a gimbal-less twist mechanism. In contrast to conventional microscanners using a gimbal-less leverage mechanism, our device utilizes a gimbal-less twist mechanism to increase the scan angle in optical applications requiring a large scanning mirror. The proposed gimbal-less scanner with twist mechanism increases the scan angle by 1.55 and 1.97 times for the slow and fast axes, respectively, under the same force; 3.64 and 1.97 times for the slow and fast axes, respectively, under the same maximum stress, compared to the gimbal-less leverage mechanism. The scanner with a 3-mm-diameter mirror and a current path composed of a single-turn coil was fabricated, and it showed the maximum scan angle of 5° (quasi-static) and 22° (resonant) for the slow and fast axes, respectively. The experimentally estimated crosstalk was as small as 0.47% and 0.97% for the fast and slow axes affected by the other axes, respectively, which was determined using a newly employed methodology based on fast Fourier transform.

Analytical model of mutual coupling between rectangular spiral coils with lateral misalignment for wireless power applications

Rectangular spiral coils are easier to implement in wireless power transfer (WPT) applications than circular spirals. Despite this fact, research into mutual coupling between rectangular spiral coils is insufficient. In this study, a new analytical model of mutual coupling is proposed, which converts a complex multi-turn rectangular spiral coil into a single-turn rectangular coil, simplifying calculation of the self- and mutual inductances. The mutual coupling between two different arbitrarily sized rectangular spiral coils with lateral misalignment and the rectangular cross-sections can be described accurately using this model. A series of experiments is carried out, the results of which agree well with the results of calculations. Finally, the effect of the number of turns in a coil on the coupling coefficient is discussed in order to determine the recommended number of turns. This research provides an effective tool for the design of a WPT system.

High-reflectivity electromagnetic two-axis microscanner using dielectric multi-layer reflective surface

A high-reflectivity electromagnetic two-axis microscanner is presented, which uses dielectric multi-layer coating on the aluminum film at the reflective surface. The microscanner is driven biaxially with the torque generated between the radially directed magnetic field and the current path through a single-turn copper coil patterned on the scanner. To enhance reflectivity, dielectric multi-layers of Al2O3 and TiO2 films are coated on the aluminum reflective surface of the mirror. A reflectance of 96.31% was obtained by using two pairs of dielectric films at a wavelength of 850 nm. Laser irradiation tests were performed to measure the operational reliability of the microscanner. The temporal drift of the optical scan angle for the mirror with two pairs of dielectric layers was measured to be 0.16° during a 6-h operation using a femtosecond pulsed laser irradiation with an average power of 2.3 W and a high repetition rate of 80 MHz. However, for the mirror where the reflection surface was coated with an aluminum layer only, a 1.74° degradation of the tilting angle was observed.

Determination of Inductance of Vehicle Electromagnet in Magnetic Levitation Transprort System

Objective. Of the work consists in receiving new analytic expressions for determination of inductance of vehicular electromagnets of transport levitation systems. Methods. The key feature of calculation model of onboard coils in accordance with their inductance on the example of squared electromagnets lies an assumption about a smallness of the size «heights» in comparison with its other geometrical sizes. There is also an assumption that thickness of a skin layer of the conductor significantly surpasses cross sectional size of the wire making the coil. The single-turn coil is considered, inductance of an actual electromagnet is accepted proportional to a square of the number of turns. When calculating inductance the dimensionless quantities are used. As an absolute, a quarter of perimeter of the coil on the centerline is chosen. The condition of obtaining the approximate formula for calculation of inductance of the flat rectangular coil is the small thickness of a winding in comparison with the geometrical sizes of the coil. Results. Accurate analytical expression for inductance of a «thin» source of squareshaped magnetic field as the algebraic sum of elementary functions has been received. Results of a numerical analysis show dependence of the relative inductance of the square-shaped flat coil on thickness relation to its minimum size. Influence of «elongation» of the coil (relation of length to width) is investigated. It is noted that inductance decreases with decrease of «elongation», and also with increase in the relation of thickness to the minimum size. Practical importance. The approximate formula for calculation of value of inductance has been obtained. Its uncertainty does not exceed 14 % in the areas of changes of all geometrical parameters of an electromagnet is output. Borders of practical application of the received analytic expressions at the accepted assumptions have been set. The received expressions are fairly simple structurally and are easily programmed

Experimental investigation of the weldability of tubular dissimilar materials using the electromagnetic welding process

This paper describes the magnetic pulse welding process (MPW) for tubes. Material combinations of aluminium to steel and copper to aluminium were experimentally evaluated. The first major goal of this work is to experimentally obtain the optimal input parameters like the discharge energy, the stand-off distance and the tool overlap for MPW of the material combinations. Welding windows with all possible input parameters are created for both material combinations. Furthermore, a comparison is done between three coil systems; a single turn coil with field shaper, a single turn coil with a field shaper and transformer and a multi-turn coil and field shaper. Metallographic investigation of the samples, hardness tests and leak tests were executed to determine the most suitable machine set-up and the optimal input parameters for each set-up. A second major goal is to determine the influence of the target tube wall thickness on the deformation of tube-tube welds when no internal support is used.

Design of a 150T pulsed magnetic field generator device

A 150T pulsed magnetic field generator device which can generate a 150T pulsed magnetic field by a single-turn coil with a 3mm diameter was designed to study the coupling of laser-produced plasma and strong magnetic fields is described. An 880 kA current pulse is discharged into the coil by a pulsed-power system composed of 20 capacitors of 5μF, electric-trigger switches, and low-impedance strip transmission lines. The structure of the generator was optimized based on the results of electromagnetic analysis. A set of small pulsed discharge system with a 50kV/5μF capacitor bank was built to research synchronous trigger and the current curve. The circuit verification experiment was proceeded and the result was revealed to be consistent with theoretical analysis.

Quasistationary magnetic field generation with a laser-driven capacitor-coil assembly.

Recent experiments are showing possibilities to generate strong magnetic fields on the excess of 500 T with high-energy nanosecond laser pulses in a compact setup of a capacitor connected to a single turn coil. Hot electrons ejected from the capacitor plate (cathode) are collected at the other plate (anode), thus providing the source of a current in the coil. However, the physical processes leading to generation of currents exceeding hundreds of kiloamperes in such a laser-driven diode are not sufficiently understood. Here we present a critical analysis ofprevious results and propose a self-consistent model for the high current generation in a laser-driven capacitor-coil assembly. It accounts for three major effects controlling the diode current: the space charge neutralization, the plasma magnetization between the capacitor plates, and the Ohmic heating of the external circuit-the coil-shaped connecting wire. The model provides the conditions necessary for transporting strongly super-Alfvenic currents through the diode on the time scale of a few nanoseconds. The model validity is confirmed by a comparison with the available experimental data.

Numerical study of Single-turn and Multi-turn coil effect in the induction heating process

Induction heating has an important role in the industrial applications. Atypical induction heating system has three main parts where they are electricalsource, the RF-coil and work piece. The RF-coil is one of the importantparameters in setup of induction heating system. In this paper, we have beenstudied two kinds of coil (Single-turn and Multi-turn) using Finite ElementMethod (FEM) and by COMSOL MULTIPHYICS package. The results showthat considering of each of this coil has significant effect on theelectromagnetic fields, eddy currents and generated heat in the coil and workpiece.

Effect of magnetothermal force on heat and fluid flow of paramagnetic liquid flow inside a pipe

Three-dimensional numerical simulations are carried out for a pressure-driven laminar pipe flow of paramagnetic liquid heated from the pipe wall at a constant heat flux. In the presence of an external magnetic field by a single-turn electric coil, the fluid flow is directed to the center axis and the thermal boundary layer becomes thick ahead the coil. Behind the coil, the flow is reattached and the thermal boundary layer becomes thin. The local heat transfer is correspondingly suppressed and enhanced near the coil. These become remarkable in case of coil placed at downstream. The magnetothermal force also contributes to the flow rate corresponding to the coil location. It is concluded that the force by a single coil works like a rib at inner perimeter. The magnetothermal force is further examined for a solenoid coil. It is found that when both solenoid ends are covered by the heating region, the solenoid blocks the heat and fluid flow at the upstream solenoid end. A stagnant flow region is induced in the solenoid-overlapping area. The heat transfer enhancement can be expected when the solenoid is long enough so that the upstream solenoid end is ahead of the heating region. These suggest the heat transfer is enhanced behind the magnet, which is validated by an experiment. To confirm the effect in the gravity field, corresponding numerical simulations are carried out considering buoyancy.

A Unified Approach to the Calculation of Self- and Mutual-Inductance for Coaxial Coils in Air

This paper extends a previous formula for the mutual inductance between single-turn coils to include all coils in air with rectangular cross sections, without any restrictions on the dimensions (including overlapping coils). The formula is compared with a wide spectrum of examples from the literature and agreement is excellent in every case. Experimental results are presented to validate the formula for both solenoid and disk coils. The formula is relevant to coreless transformers, inductive coupling, wireless power transfer, and leakage inductance in resonant converters.

Prediction of Phase Transformation and Hardness Distribution of AISI 1045 Steel After Spot Continual Induction Hardening

An numerical and experimental study of spot continual induction hardening (SCIH) for AISI 1045 steel was carried out to gain a better understanding of this non-stationary and transverse flux induction hardening treatment. The SCIH device was set up by assembling the single-turn coil inductor to a five-axis cooperating computer numerical control system. The influence of inductor velocity, input current, and quenching medium on temperature field was estimated via the SCIH model, and the simulated micro-hardness and microstructure were validated by experimental verification. The heating delay phenomenon appearing in the SCIH process had been analyzed.

A 7 T Pulsed Magnetic Field Generator for Magnetized Laser Plasma Experiments

A pulsed magnetic field generator was developed to study the effect of a magnetic field on the evolution of a laser-generated plasma. A 40 kV pulsed power system delivered a fast (∼230 ns), 55 kA current pulse into a single-turn coil surrounding the laser target, using a capacitor bank of 200 nF, a laser-triggered switch and a low-impedance strip transmission line. A one-dimensional uniform 7 T pulsed magnetic field was created using a Helmholtz coil pair with a 6 mm diameter. The pulsed magnetic field was controlled to take effect synchronously with a nanosecond heating laser beam, a femtosecond probing laser beam and an optical Intensified Charge Coupled Device (ICCD) detector. The preliminary experiments demonstrate bifurcation and focusing of plasma expansion in a transverse magnetic field.

Acceleration of Miniature Targets by Kilo-Tesla Magnetic Field

The first demonstration of target acceleration by a strong magnetic field is conducted. Two miniature targets, a gold ball and a neodymium permanent magnet, are accelerated by a magnetic field. A magnetic-field strength as high as 1 kT is produced using a capacitor-coil in which two copper disks are connected by a single-turn coil, and the capacitor was driven by two beams from the GEKKO-XII high-power laser. The targets are accelerated by the interaction force between two magnetic moments: the target and the capacitor-coil. The velocity of the accelerated gold ball was estimated as 10 m/s from shadowgraphy images. In the case of the magnet, although the image could not be observed clearly due to the plasma generated around the magnet, it was confirmed that the magnet interacts with the magnetic field of the capacitor-coil.

Numerical and experimental analysis of 3D spot induction hardening of AISI 1045 steel

In order to analyze and predict the material property of AISI 1045 steel during spot induction hardening (SIH), a 3D electro-magnetic model coupled temperature fields with time-dependent boundary conditions was developed using finite element simulation software ANSYS. A magnetizer mounted at single-turn copper coil inductor, the calculation of the material hardness and the prediction of phase transformation were taken into account in this model via defined material laws. The phenomenology model in this work presented a novel and simplified way to predict the temperature, the hardness and phase transformation in SIH process. In situ temperature and current measurement as well as hardness and microstructure analyses were carried out to verify this model.

The Physical Entity of Vector Potential in Electromagnetism

The scalar and vector potentials were introduced into electromagnetic physics in the second half of the nineteenth century. The chief aim was to use them as auxiliary mathematical quantities in order to solve certain practical problems.Nevertheless the discovery of the Aharonov-Bohm effect (1959) in quantum mechanics has suggested that vector potential rather than magnetic field is the causal agent in such an effect. Recent research on the Maxwell-Lodge paradox--induction of voltage in the loop circling a long solenoid carrying alternating current--has confirmed that induction occurs in a region of space effectively free from magnetic field. This again reinforces the idea of vector potential as a physical entity rather than the auxiliary artificial quantity of classical electrodynamics. The present investigation is intended to provide some degree of corroboration of the previous result.The experimental arrangement consists of a ‘special’ transformer containing movable, single turn coils wound onto rectangular frames. The primary coil is powered from a signal generator providing alternating current over a variable frequency range while the secondary output voltage is connected across a C.R.O./precision voltmeter. Measurements of transformer e.m.f. were carried out at several frequencies in the range 100 Hz–20 kHz and with various conditions of shielding around the primary and secondary coils.Certain additional experiments were carried out with a long solenoid and torus solenoid supplied with different core materials. Experimental results for induced e.m.f’s are presented and in special cases correlated with the calculated values of mutual inductance. Overall the results tend to confirm the primacy of vector potential over magnetic field as an explanation of the phenomenon.

Combined 3D and 2.5D modeling of the floating zone process with Comsol Multiphysics

The floating zone (FZ) technique is an industrially used method to crystallize silicon and make use of induction heating. The shape of the single-turn coil can be optimised with the help of numerical simulation of the electric current. The next step in process design is to discern the consequences on the temperature field, for what our axisymmetric model includes all important features like movement of silicon parts, temperature-dependent heat conductivity, view factor approximation for radiation heat transport, latent heat production and consumption along the phase boundaries as well as interface tracking. The simulations are conducted in Comsol Multiphysics and Matlab, assuming steady-state conditions. To verify the results, the calculated deflection of the crystallization interface is compared to results obtained from other numerical calculation software as well as to measurements, both showing a good agreement.The calculated temperature field is used as input to other physical models in Comsol. We calculated the thermal stress field of the crystal and the melt flow under the influence of a static magnetic field in axial direction. Model for other physical quantities like the doping distribution could be added with relatively low development effort.

Applied magnetic field design for the field reversed configuration compression heating experiment

Detailed calculations of the formation, guide, and mirror applied magnetic fields in the FRC compression-heating experiment (FRCHX) were conducted using a commercially available generalized finite element solver, COMSOL Multiphysics(®). In FRCHX, an applied magnetic field forms, translates, and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils generate the fast magnetic fields necessary for FRC formation. Solenoidal coils produce the magnetic field for translation and capture of the FRC prior to liner implosion. Due to the limited FRC lifetime, liner implosion is initiated before the FRC is injected, and the magnetic flux that diffuses into the liner is compressed. Two-dimensional axisymmetric magnetohydrodynamic simulations using MACH2 were used to specify optimal magnetic field characteristics, and this paper describes the simulations conducted to design magnetic field coils and compression hardware for FRCHX. This paper presents the vacuum solution for the magnetic field.

(Invited) Developments in Integrated On-Chip Inductors with Magnetic Yokes

Thin-film ferromagnetic inductors show great potential as the energy storage element for integrated circuits containing on-chip power management. In order to achieve the high energy storage required for power management, on-chip inductors require relatively thick magnetic yoke materials ({greater than or equal to} a micron). The first part of this paper includes a review of on-chip inductors with magnetic materials from earlier studies. The second part describes the fabrication and characterization of a magnetic inductor on a silicon interposer at IBM. These inductors contained a variety of yoke geometries, included single-turn and multi-turn coils, and were fabricated on 200mm silicon wafers in a CMOS back-end-of-line (BEOL) facility. Each inductor consisted of electroplated copper coils enclosed by electroplated Ni45Fe55 yokes. Aspects of the fabrication of the inductors are described, along with the magnetic properties of the electroplated yoke material and inductor performance.