Eddy Current Effects Research Articles

Hierarchical nitrogen/cobalt co-doped carbonaceous materials with electromagnetic waves absorption promoting nanostructures

In order to solve the pollution of electromagnetic interference (EMI), hierarchical Co/N-co-doped carbonaceous compounds with absorption promoting nanostructures were prepared as absorbing materials via a seaweed-based hydrogel strategy. XRD, Raman, SEM, TEM, VSM and XPS were used to characterize the resultant samples. All the tests indicated that the absorber carbonized at 700 °C (SA/N-CoxOy-700, among, SA represents sodium alginate and 700 means that the carbonization temperature was 700 °C) has an excellent performance, which minimal RL can reach to −47.31 dB at 16.16 GHz and the effective absorption bandwidth (RL < -10 dB) is 4.56 GHz from 13.44 to 18 GHz. The relative superior performance is mainly attributed to the cooperative effect of nitrogen-doped carbon skeleton, expanded surface, multiple defects, various phase interface and hierarchal pore structures, thus leading to the improvement in multiple reflections and scattering, nature resonance, eddy-current effect, the consumption of thermal energy, dipoles and interfacial polarization.

Mechanism Analysis of Eddy-Current Effects on Switching Power Amplifier of a Nonlaminated Magnetic Bearing

For thrust magnetic bearings (TMB), the stators and thrust disks are commonly made of nonlaminated material. Therefore, eddy currents are inevitable in solid ferromagnetic cores. However, the mechanisms of eddy-current effects on switching power amplifiers have never been investigated. Firstly, the fractional-order model of effective reluctance of a nonlaminated TMB is built. And the time domain solution of current ripples of switching power amplifiers is calculated. Then we define the effective inductance and present the equivalent circuit of current drive mode. Through model reduction, the main impact factor of eddy currents is found, and the simplified model as well as simplified equivalent circuit is obtained. Furthermore, the effects of eddy currents on two current control modes and control parameter design are analyzed. Through finite element method (FEM) and experiments, the established models are verified, and the current tracking performance is compared between laminated and nonlaminated TMB with different control parameters, which demonstrates the theoretical results.

A pulsed high magnetic field facility for electric polarization measurements

&lt;sec&gt;Multiferroic materials, which exhibit the coexistence of ferromagnetic, ferroelectric, or ferroelastic orders, are of particular interest for not only fundamental physics but also potential applications. An important physical property of multiferroic materials, especially those with magnetically driven ferroelectricity, is known as a strong magnetoelectric coupling between the magnetic order and the ferroelectric order. The external magnetic fields can directly interact with spins or magnetic moments of the materials and lead the spontaneous ferroelectricity to be suppressed, and in some cases result in field-induced ferroelectricity in a higher field. Depending on the exchange interactions, these ferroelectric phase transitions may take place in a critical magnetic field as high as several tens of tesla. The standard electric-polarization measurement based on a commercial PPMS system is limited by the strength of the static field consequently. As an extremely experimental condition, pulsed magnetic fields can be used to reveal new physical phenomena in multiferroic materials. Due to the short pulse duration and the effect of eddy current, this measurement technique under pulsed high magnetic fields is still a challenge to date although a few laboratories have developed it in recent years.&lt;/sec&gt;&lt;sec&gt;Wuhan National High Magnetic Field Center (WHMFC) of China is a newly built pulsed-field laboratory. This experimental station is equipped with the many measuring instruments such as for measuring electric transport, magnetization, electron spin resonance, magneto-optics, and high pressure, which were established after the national assessment at the end of 2014. Recently, using a pyroelectric technique we successfully constructed an electric-polarization measurement system based on the large-scaled facility at the WHMFC. The nondestructive magnet driven by discharging a 1.25 MJ capacitor bank can generate a pulsed field up to 60 T. By tuning the charging energy and voltages, the pulse duration time can be modulated from 4.3 ms to 10.8 ms. A helium-3 cryogenic system equipped on this facility can achieve a lowest temperature down to 0.5 K. A high-precision rotation probe is designed and fabricated with angle varying from –5° to 185° for an angular-dependent study. The pyroelectric current is detected by a shunt resistor of 10 kΩ and the electric polarization is derived by integrating the pyroelectric current over the time. The resulting data have a good accuracy and quality which are helpful in detecting weak ferroelectric phase transitions induced by pulsed fields with a fast field sweep rate. In this paper, we introduce this measurement system in detail including the method, principle and its advantages in comparison with those in static fields. Recent study and progress of magnetoelectric multiferroic materials under high magnetic fields are also reported.&lt;/sec&gt;

Simulation Model of a Direct-Current Electric Locomotive with Commutator Traction Motors

A dc electric locomotive simulation model is considered that makes it possible to study transient and steady processes and may serve as a basis for the notion of a “digital locomotive” being implemented within the “Digital Railway” project. One of the most popular electric locomotives is selected, which is designed for pulling freight trains along long-distance railways electrified with direct current with a voltage of 3000 V. The electric locomotive model is based on a mathematical model of a collector traction engine. The model takes into account the nonlinearity of the main pole’s magnetic characteristic, as well as the effect of eddy currents in solid magnetic circuit sections on the magnetic flux variation. The model provides a mechanism for regulating motors in the course of investigations in accordance with operating conditions. The processes of resistor starting and voltage regulation by connection to resistors by means of transposition, as well as motor regulation by changing the magnetic flux, are taken into account. The possibility of using the developed model to study the traction substation–traction network–electric rolling stock system, which is determined by different operating modes of the traction network in the process of converting electrical energy into mechanical, is shown. Calculations of various locomotive operating modes in the event of failure in the contact network are carried out.

Impurity transport and halo current effects on tungsten divertor system

This paper presents the development of theoretical model for the purpose to calculate and analyze halo and eddy current effects in the tungsten divertor of Tokamak (Fusion) reactor. In the first st...

Metal Object Detection in a Wireless Power Transfer System Based on Double-Layer Symmetric Sensing Coils

The intrusion of a metal object into a wireless charging system could cause safety issues, such as temperature rise and even combustion. This paper proposes a double-layer symmetric sensing coil design for metal object detection (MOD) of wireless electric vehicle charging to prevent the detection blind area. First, the magnetic effect and the eddy current effect of a metal object in high-frequency magnetic fields are analyzed. Second, the principle of the proposed double-layer symmetric sensing coils is detailed. Finally, the finite element simulation is implemented in order to test the performance of the proposed sensing coil design. The simulation results show that the proposed double-layer symmetric sensing coils can effectively detect the presence and position of the metal object simultaneously.

The FEM Calculation Considering Vector Magnetic Properties of Electrical Steel Sheet Under DC-Biased Field

This article proposes an enhanced dynamic vector magnetic hysteresis model for describing the effect of dc-biased field and eddy current on vector magnetic quantities. A governing equation combining the proposed model is derived for finite-element analysis of magnetic characteristics distribution of transformer core under dc-biased excitation. The numerical results of the transformer core by using the enhanced model with consideration of dc-biased excitation and eddy current are compared with the numerical results obtained by using the magnetizing curve. It proves that the proposed model can consider vector magnetic properties and iron loss of electrical steel sheet under both dc-biased and rotating magnetic fields during numerical analysis.

Simulation of the pulsating current traction motor

Design and improvement of traction electric engines ensuring reduction of the railway transportation power consumption is a current long-term objective. The objective is to develop technical requirements to the new electric engines, including implementation of the set haulage performance of locomotive, providing for constant power in the certain range of the running speed, as well as required properties in case of the supply network parameters change, selection of the weight and dimensions parameters ensuring fitting of the traction electric engines in the locomotive underframe, and other important tasks. The new technology is proposed for forecasting the engine properties using simulation modeling of the hauling features and electrical characteristics of engine in order to resolve the above mentioned objectives. The proposed pulsating current traction motor model takes into account the eddy currents effect on the processes of magnetic flux changes in the engine steel and the nature of electromagnetic processes in the engine. Electric component of the engine simulation model is added with the torque mechanical balance equation that allows assessing its operating properties to the full extent. Results of calculations are presented in the form of the engine electromotive force attenuation curve calculated for specific mode of operation at the armature current of 780 A and the initial value of electromotive force amounting to 525 V. Obtained parameter of attenuation correlates with the experimental data presented in the other information source. Value of determination factor between the specified curves certifies adequacy of the developed simulation model. Proposed model of engine and methodology of its design allows modeling its operation in transition and in static modes of operation. Engine properties obtained by means of the proposed simulation model n = f(iа) and M = f(iа) are almost similar to the properties of traction engine NB-514 in the entire range of the armature current change iа. Proposed simulation model allows designing pulsating current traction motor with the set operating properties, as well as studying the engine parameters effect on its energy indicators.

Investigation of the eddy current effect on the high frequency response of the Mirnov probe on J-TEXT.

This paper investigates the high frequency response of the Mirnov probe based on a test platform, which is capable of generating a uniform AC magnetic field within the frequency range of 1-300 kHz. The eddy current effect is quantitatively reflected by the phase shift ϕc and normalized amplitude δ of the measured magnetic field between cases with and without a conducting plate located near the Mirnov probe. This method compensates the resonant effect in the Mirnov probe circuit and hence reflects purely the eddy current effect. The eddy current effect increases with the decrease in the distance between the probe and the conducting plate. With the increase in frequency, the magnitude of δ decreases to a saturated value at 10 kHz but increases significantly above 100 kHz for 304-stainless steel, while the eddy current effect with graphite appears at around 10 kHz and the magnitude of δ decreases to the minimum at 125 kHz, followed by a significant increase above 125 kHz. With the increase in f, the magnitude of ϕc increased until 2.5 kHz and 40 kHz for steel and graphite, respectively, then decreased with a further increase in f. The phasor expression is introduced to describe the AC magnetic field and allows an easy expression of the eddy current field. The phase of the eddy current field decreases toward -180° with f. The amplitude of the eddy current field increases with f and reaches its maximum when the skin depth reduces to a critical value. The eddy current field decreases with a further increase in the frequency.

An Application of Eddy Current Effect on the Active Detumble of Uncontrolled Satellite With Tilt Air Gap

The active removal of expired satellites on orbit is essential to ensure the safety of functional spacecrafts on orbit. The high tumbling rates of the uncontrolled satellites hinder the direct removal operation. Consequently, a non-contact method based on the eddy current effect is applied to despin and detumble the uncooperative satellite. A magnetic vector-based 3-D field model under the mean radius assumption is established to calculate the eddy current forces and torques. The honeycomb structure of the target surface and tilt air gap during detumbling are considered in the theoretical model. An underactuated detumble control model is applied to stabilize the nutation angle and attitude of the target. The simulation results show that the control strategy can stabilize the target’s attitude in a reasonable time. Controlling the tilt angle will generate despin and detumble torques simultaneously. The linear relationship between the despin torque and rotational velocity at several hundreds of rpm is verified by experiments. This article provides a new solution for detumbling an uncooperative satellite with a rotational magnetic field.

Improved Analysis and Modeling of Leakage Inductance for Planar Transformers

Planar transformers have often been mistaken to essentially have lower leakage inductances. The “radial effect” is a natural characteristic for planar windings due to a higher aspect ratio of conductor width to conductor thickness, which gives a reduction in leakage inductance. Traditional formulas for leakage inductance in traditional transformers, where the winding width is much smaller than the winding height, are not suitable for planar transformers. This paper specifically tailors the traditional 1-D solution of leakage inductance by decomposing the leakage flux into longitudinal and transversal fluxes. In this manner, the “eddy current effect” and the “radial effect” in leakage inductance can be analyzed individually. The proposed new formula including both ac (high-frequency eddy current effect) and dc effects (radial effect) offers an accurate prediction of leakage inductance in planar transformers. Finite element analysis and measurements are carried out to validate the proposed formula.

Analytical Optimization of Nonsaturated Thermally Limited High-Frequency Transformer/Inductor Design Considering Discreteness of Design Variables

This article proposes an analytical design methodology for nonsaturated thermally limited high-frequency transformers/inductors with the objective of minimum core size and minimum power loss. The major challenge of analytical design methodologies is to simultaneously retain the optimality of design results, simplicity/ease of use, and generality of design methodologies. Most of the reported analytical methodologies have a limitation on optimality due to neglect of discreteness of design variables and have limitations on simplicity and generality because of a complicated winding loss model with the consideration of eddy current effects. To address these limitations, a further optimization process considering discreteness of design variables is proposed to improve the optimality of the design results. A concept of an effective ac resistance factor in terms of all windings is proposed to model the winding loss in a simple and general way so that simplicity and generality of the design methodology are ensured. To illustrate the methodology and its improvement on optimality, the methodology is used to design a 150-W 100-kHz forward transformer and is compared with the methodology without further optimization. Theoretical calculations and experiments both indicate a decrease of about 5 °C of the methodology in this article compared with the methodology without further optimization.

Eddy current pressure sensor based on planar coil

The traditional pressure sensors are mostly based on piezoresistive, piezoelectric effect, and strain gauge, which are easily affected by ambient temperature. The structure of some sensors is rather complex to effectively acquire the signal or measure distribution force. Therefore, a pressure sensor based on the planar coil and elastic element was designed to solve this problem. The newly designed sensor has a spiral planar coil made by a printed circuit board and a polydimethylsiloxane (PDMS) thin film as the elastic element. The conductive layer is attached on the upper surface of PDMS to realise the eddy current effect. Meanwhile, a simulation model was established to find the relationship between deformation displacement and the pressure of the elastic element. By generating the experimental curves of the deformation displacement of the elastic element and the output frequency of the eddy current sensor, the pressure measurement on the surface of the elastic element can be identified. The preliminary experimental results showed that the eddy current pressure sensor based on the plane coil has good linearity and repeatability, and it can realise large area distributed pressure measurement, which is also suitable for accurate measurement of distribution force.

Distributed current source modeling method for 3D eddy current problem in magnetic conductor with discrete state-space J-φ formulation

This paper presents a distributed-current-source (DCS) modeling method to analyze the eddy-current (EC) induced in an electrically conductive material with a weak magnetic permeability. Formulated in state space to solve for an unknown EC density J and electric potential φ, the method decomposes the conductor into elemental volume/surface current sources to model the eddy-current and magnetization effects. The closed-form solutions to a three-dimension (3D) EC problem with geometrical boundary effects are derived and verified by comparing with finite-element methods and published data, both numerically and experimentally. An element-refinement method, which accounts for the skin-depth effects and non-uniform boundary EC, is proposed and validated. The DCS modeling method has been applied to a field-reconstruction application for parametric analysis demonstrating its effectiveness and efficiency.

Machine Perception Based on Eddy Current for Physical Field Reconstruction of Conductivity and Hidden Geometrical Features

This paper presents a new machine perception method based on eddy-current (EC) effects to reconstruct physical fields (EC field, electrical-conductivity field, and hidden geometrical features) of a nonferrous material commonly encountered in intelligent manufacturing using one-time finite magnetic flux density (MFD) measurements. An analytical model for EC testing system with conductor discretization is established and expressed in state-space representation. Two improvements (physical constraints and adaptive element refinement) are developed and integrated into the system model. The measurement models of physical fields using discrete MFD measurements are linearly established, reducing the physical field reconstruction to a linear inverse problem for solving using the Tikhonov regularization method. The EC-based machine perception is numerically illustrated by reconstructing the EC density field, conductivity field, and hidden geometrical features of aluminum plates. Additionally, the effects of element refinement, physical constraints, and sensor configurations on the reconstruction results are analyzed numerically. Using an experimental prototype consisting of an air-cored electromagnet and a two-dimensional (2-D) array of magnetic sensors with associated electronics, the effectiveness of the machine perception method and the accuracy of the reconstructed physical field are demonstrated experimentally.

New Discoveries on Electromagnetic Action and Signal Presentation in Magnetic Flux Leakage Testing

Based on the authors’ previous work of magnetic flux leakage (MFL) quantitative description and the research plan especially for the magnetic component of eddy current effect factor $$ B_{other} $$, further explorations for electromagnetic actions, magnetic and signal presentations in the defect in electromagnetic nondestructive testing (ENDT, such as direct current field measurement (DCFM), MFL and eddy current testing (ECT)) are continued here. Primarily, new discoveries indicate that the magnetic component of $$ B_{other} $$ is actually composed of the secondary magnetic field component of $$ \Delta B_{mfl} $$ which manifests as raised signal waves and volume current perturbation component of $$ \Delta B_{\Delta I} $$ which features as double peaked signals due to the departure or bypassing of the “volume current” in the defect. What’s more, the concrete expressions of magnetic components are deduced and given through Ampere’s (or the Ampere–Maxwell) law. Afterwards, the theory is well demonstrated and verified by means of finite element analysis for current density and magnetic flux density or MFL signals in typical quasi-static testing by DC magnetization for different specimens with defects. Additionally, suggestions for installation site of sensor elements in ENDT are also given. Finally, a unified evaluation standard for magnetic flux density is formed, which provides the basic theory or analysis principles for the ENDT techniques as well as research directions for precision defect detection and related applications.

Numerical Model for Magnetic Fluid Hyperthermia in a Realistic Breast Phantom: Calorimetric Calibration and Treatment Planning.

This paper aims to apply a proposed, based on calorimetric measurements, a reliable numerical model for magnetic fluid hyperthermia (MFH) treatment planning of breast cancer. Furthermore, we perform a comparative analysis of magnetic nanoparticles (MNPs) and tumour tissue interactions by means of the magnetic-field-dependent Néel and Brownian relaxation times. The analysis was based on an anatomically correct breast model (developed in-house) and a modified linear response theory, which was applied to investigate the heat dissipation from the magnetic nanoparticles dispersed in the breast tumour. The calculations of the single-domain magnetic power losses were conducted for a case where the magnetic field value and the applied frequency were known, but also for the different concentrations of the MNPs in the tumour. Two scenarios were considered: The MNPs mobilised and immobilised in the tumour. In parallel, the eddy currents effect, together with the related temperature distributions, were considered in order to analyse safety issues. By changing the MNP concentration in the tumour, the corresponding temperature distributions were calculated. The eddy current effect, together with the related temperature distribution, were considered in order to analyse safety issues. Varying the MNP concentration in the tumour, the corresponding temperature distribution was calculated. Moreover, the cumulative equivalent minutes at were analysed. In the anatomically correct breast phantoms, the tissue location can lead to “hot spots” due to the eddy current effect and subsequently to the high gradients of the temperature. That is why the analysis of safety issues related to the overheating side effect should be taken into consideration during the treatment planning of magnetic fluid hyperthermia. The phenomenon of heat dissipation from MNPs is very sophisticated and depends on their concentration, the distribution and the relaxation mechanism in the tumour, together with magnetic field strength and frequency. Furthermore, we inferred that the phenomenon of heat dissipation from MNPs equally depends on MNP-tissue interactions, and it can lead to 30% differences in the power assessment. Nevertheless, the aforementioned factors should be considered in parallel using anatomical, volume-dependent models to enhance the efficiency of in vivo treatment.

Achieving excellent metallic magnet-based absorbents by regulating the eddy current effect

We present the results that a suitable eddy current effect could act as an effective microwave dissipative mechanism for metallic magnet-based electromagnetic wave absorbents. With no need to introduce low or nonconductive components, the strongest absorption of −43.2 dB at 14.7 GHz could be achieved with a thin absorbent layer of 1.1 mm and at the mass fraction of the nickel fibers filler in the composite of 40 wt. %. This work utilizes the intrinsic dependence of electromagnetic wave dissipation on the eddy current effect and opens a simple and feasible way for designing of microwave absorption materials and composites.

Continuum Modeling of Inductor Magnetic Hysteresis and Eddy Currents in Resonant Circuits

This paper presents a high-fidelity finite-element modeling technique for magnetic hysteresis and eddy current losses in toroid inductors. The method is based on the separation of ferromagnetic loss characteristics into two components: a quasi-static hysteresis component and a dynamic eddy current component. The Preisach model is used to describe the quasi-static magnetic hysteresis behavior of the core, providing strong guarantees on the reproducibility of the experimentally measured characteristics. This model is used to represent the magnetic field constitutive relationships within a finite-element framework combining the effects of hysteresis and eddy currents in a unified dynamic simulation. The finite-element model of the toroid is used as a high-order inductor model coupled to a resonant circuit simulation. The modeling technique is validated through experimental measurements on two different series RLC circuits. The first circuit is based on an M19 electrical steel toroid having resonant frequency near 200 Hz. The second circuit is based on a T38 ferrite toroid having a resonant frequency near 10 kHz. The models agree closely with the measured voltages, currents, and losses. The models also successfully predict discontinuities in the measured frequency responses due to the existence of bistable operating regimes.

A multi-objective optimal design methodology for solid core no-thrust-disk/thrust hybrid magnetic bearings considering eddy-current effects and leakage

A multi-objective optimal design methodology for solid core no-thrust-disk/thrust hybrid magnetic bearings considering eddy-current effects and leakage