Eddy Current Effects Research Articles

A Mass-Transfer Model of Nitric Oxide Removal In a Rotating Drum Biofilter Coupled with FeII(EDTA) Absorption

The biological nitric oxide (NO) reduction rate in a rotating drum biofilter (RDB) mainly depends on the mass transfer between the gas and liquid phase because of the poor solubility of NO. This work, aimed to facilitate the gas–liquid (GL) mass transfer of NO in RDB, the FeII(EDTA) was used to capture NO and porous drum was employed to increase the eddy current effect of the system. The denitrification rate of GL-RDB was stabilized at about 95% during the long-term operation. A dynamic model of GL-RDB was established to optimize the denitrification performance of this innovative RDB. Experimental results revealed that the developed model well described NO removal in GL-RDB. Model analysis also showed that the rotational speed and inlet NO concentration were the critical parameters in determining of the RBD performance. This work may provide fundamental theory for the further study of GL-RDB.

Multi-Input–Multi-Output Control of a Utility-Scale, Shaftless Energy Storage Flywheel With a Five-Degrees-of-Freedom Combination Magnetic Bearing

The modeling and control of a recently developed utility-scale, shaftless, hubless, high strength steel energy storage flywheel system (SHFES) are presented. The novel flywheel is designed with an energy/power capability of 100 kWh/100 kW and has the potential of a doubled energy density when compared to conventional technologies. In addition, it includes a unique combination magnetic bearing (CAMB) capable of providing five-degrees-of-freedom (5DOF) magnetic levitation. Initial test results show that the CAMB, which weighs 544 kg, can provide a stable lift-up and levitation control for the 5543 kg flywheel. The object of this paper is to formulate and synthesize a detailed model as well as to design and simulate a closed-loop control system for the proposed flywheel system. To this end, the CAMB supporting structures are considered flexible and modeled by finite element modeling. The magnetic bearing is characterized experimentally by static and frequency-dependent coefficients, the latter of which are caused by eddy current effects and presents a challenge to the levitation control. Sensor-runout disturbances are also measured and included. System nonlinearities in power amplifiers and the controller are considered as well. Even though the flywheel has a large ratio of the primary-to-transversal moment of inertias, multi-input–multi-output (MIMO) feedback control demonstrates its effectiveness in canceling gyroscopic toques at the designed operational spinning speed. Various stages of proportional and derivative (PD) controllers, lead/lag compensators, and notch filters are implemented to suppress the high-frequency sensor disturbances, structural vibrations, and rotor imbalance effects.

Moving magnets in a micromagnetic finite-difference framework.

We present a method and an implementation for smooth linear motion in a finite-difference-based micromagnetic simulation code, to be used in simulating magnetic friction and other phenomena involving moving microscale magnets. Our aim is to accurately simulate the magnetization dynamics and relative motion of magnets while retaining high computational speed. To this end, we combine techniques for fast scalar potential calculation and cubic b-spline interpolation, parallelizing them on a graphics processing unit (GPU). The implementation also includes the possibility of explicitly simulating eddy currents in the case of conducting magnets. We test our implementation by providing numerical examples of stick-slip motion of thin films pulled by a spring and the effect of eddy currents on the switching time of magnetic nanocubes.

Numerical simulations on active shielding methods comparison and wrapped angle optimization for gradient coil design in MRI with enhanced shielding effect.

The switching of a gradient coil current in magnetic resonance imaging will induce an eddy current in the surrounding conducting structures while the secondary magnetic field produced by the eddy current is harmful for the imaging. To minimize the eddy current effects, the stray field shielding in the gradient coil design is usually realized by minimizing the magnetic fields on the cryostat surface or the secondary magnetic fields over the imaging region. In this work, we explicitly compared these two active shielding design methods. Both the stray field and eddy current on the cryostat inner surface were quantitatively discussed by setting the stray field constraint with an ultra-low maximum intensity of 2 G and setting the secondary field constraint with an extreme small shielding ratio of 0.000 001. The investigation revealed that the secondary magnetic field control strategy can produce coils with a better performance. However, the former (minimizing the magnetic fields) is preferable when designing a gradient coil with an ultra-low eddy current that can also strictly control the stray field leakage at the edge of the cryostat inner surface. A wrapped-edge gradient coil design scheme was then optimized for a more effective control of the stray fields. The numerical simulation on the wrapped-edge coil design shows that the optimized wrapping angles for the x and z coils in terms of our coil dimensions are 40° and 90°, respectively.

Nanoparticle dispersionizer by ultrasonic cavitation and streaming

An ultrasonic dispersion method using ultrasonic cavitation and streaming effects is suggested for the effective dispersion of nanoparticle suspensions. To generate ultrasonic cavitation efficiently, a high-intensity ultrasonic field is formed with arrayed piezoelectric transducers in the inner surface of a cylinder. To use the eddy current effect caused by ultrasonic streaming in the suspension, the arrayed piezoelectric transducers are tilted by a regular degree from the inner surface of the cylinder. Titanium dioxide (TiO2) and carbon nanotube (CNT) suspensions that were dispersed by the suggested dispersion method showed excellent dispersion characteristics compared with those dispersed by the conventional method.

The effect of inductive sintering to iron based powder metal parts

Sintering is carried out by heating the graphite mold during pressing rather than direct heating of samples by eddy currents in many sintering applications. The effect of the induction on the powder metal samples is not fully visible due to graphite mold. The aim of this study is to observe the direct effect of eddy currents to powder metal parts. For this purpose, sintering was performed in a copper coil after pressing without a mold. Pure iron powder and two different iron based powder mixtures were used. Copper was added to the iron powder for liquid phase formation, and carbon was added for the formation of alloy. Effect of sintering method, sintering duration, pre-sintering and sintering temperature were investigated. In addition, conventional sintering has also been applied for comparison. As the result of the studies it was observed that, direct heating of powder metal samples with induction generates completely different sintering kinetics. It provides better mechanical properties in shorter sintering durations only in some instances and electrical resistivity values play an important role about this. Also resistivity values can give a preliminary idea about the mechanical strength after sintering.

Magnetization Time Lag Caused by Eddy Currents and Its Influence on High-Speed Magnetic Flux Leakage Testing

ABSTRACTIn high-speed magnetic flux leakage (MFL) testing, the tested workpieces pass rapidly through magnetizers. Thus, the magnetization time for workpieces is short. Because of the eddy current effect, the magnetic field inside the workpieces cannot instantly reach equilibrium, and if the magnetizing time is insufficient for the field to reach equilibrium, the MFL signals will be changed because of incomplete magnetization. In this article, the magnetization time lag caused by eddy currents and the influence of this lag on high-speed MFL testing is investigated. The time required for magnetic field to reach equilibrium in specimens, including steel bars and pipes, is obtained by theoretical calculations, finite element simulations, and experiments. The results indicate that the time required for a magnetic field inside a specimen to reach equilibrium is in the range of 50–100 ms. Using conventional magnetizers, the defect signals at testing speed of 10 m/s change because the workpiece reaches the detection zone before the magnetic field inside reaches the stable state. A simple solution is to increase the axial length of the magnetizing coil. After this procedure, signals obtained at 0.1 m/s and 10 m/s are almost identical.

Simulation of an Octupole Scanning Magnet for Spot Scanning in Proton Therapy

Current proton therapy scanning systems always use two independent dipole magnets for spot scanning in proton therapy. However, the space occupied by these two dipole magnets located after the final gantry bending magnets is very large and increases the overall size of the gantry. In order to construct a compact nozzle and decrease the size of the gantry, we decide to design an octupole scanning magnet to replace these two separate dipole magnets. The octupole scanning magnet, which is completely different from traditional octupole magnet, can generate rotating dipole magnetic field with the change of the loaded sinusoidal current phases. In this paper, we have finished the static optimization of an octupole scanning magnet model, including the length and shape of the poles, the diameter of the gap, and the shims on the pole edges, both in Opera two-dimensional (2-D) and 3-D. The corresponding relationship between the size of the gap and the good field region was also studied. The effect of eddy currents on magnetic field stability was also simulated in Opera 3-D. All the simulation results are presented in this paper.

Dynamic Behavior of Laminated Magnets With Solid Tension Bars

An important criterion for the design of fast-ramping accelerator magnets is their field distribution in the time-transient regime. Eddy current effects in different components of the magnet become more or less significant depending on the field level, the ramp rate, the magnet geometry, and the materials used. In this paper, we focus on eddy currents in solid tension bars of laminated magnets and quantify their effects based on finite-element simulations of a dipole model magnet. Several configurations are studied to derive empirical laws for the dynamic behavior of the magnets. The simulation results are validated with magnetic measurements.

Status of AC Magnets for CSNS RCS

China spallation neutron source accelerators include a 80-MeV Linac, 1.6-GeV rapid cycling synchrotron (RCS), and two beam transport lines. There are 24 direct current (dc)-biased 25-Hz alternating current (ac) dipole magnets, 48 dc-biased 25-Hz ac quadrupole magnets, 16 dc sextupole magnets, 34 ac correcting magnets, and 23 injection and extraction magnets for the RCS. In this paper, the status of RCS ac magnets will be presented and the key technical issues for the ac magnet performance, such as eddy current effect, high voltage, vibration, field nonlinearity, and fringe field interference will be thoroughly discussed.

Machinability of nickel based alloys using electrical discharge machining process

The high temperature materials such as nickel based alloys and austenitic steel are frequently used for manufacturing critical aero engine turbine components. Literature on conventional and unconventional machining of steel materials is abundant over the past three decades. However the machining studies on superalloy is still a challenging task due to its inherent property and quality. Thus this material is difficult to be cut in conventional processes. Study on unconventional machining process for nickel alloys is focused in this proposed research. Inconel718 and Monel 400 are the two different candidate materials used for electrical discharge machining (EDM) process. Investigation is to prepare a blind hole using copper electrode of 6mm diameter. Electrical parameters are varied to produce plasma spark for diffusion process and machining time is made constant to calculate the experimental results of both the material. Influence of process parameters on tool wear mechanism and material removal are considered from the proposed experimental design. While machining the tool has prone to discharge more materials due to production of high energy plasma spark and eddy current effect. The surface morphology of the machined surface were observed with high resolution FE SEM. Fused electrode found to be a spherical structure over the machined surface as clumps. Surface roughness were also measured with surface profile using profilometer. It is confirmed that there is no deviation and precise roundness of drilling is maintained.

Electromagnetic Field Analysis Considering Reaction Field Caused by Eddy Currents and Hysteresis Phenomenon in Laminated Cores

An analysis method for characteristics calculation of electric machines is proposed in order to take the effects of eddy currents and hysteresis phenomenon in laminated cores into account. In the proposed method, both the effects of eddy currents and hysteresis phenomenon are expressed as reaction magnetic fields against the exciting field. These fields are determined by coupling the main electromagnetic field analysis that neglects the detailed structures of laminated cores, and 1-D time-stepping analysis along the thickness of electrical steel sheets. The validity of this coupling is confirmed by comparing the measured and calculated results of the core-material characteristics. The effects of the reaction field on the torque characteristics of rotating machines are also clarified.

A Simple Method for Performance Prediction of Permanent Magnet Eddy Current Couplings Using a New Magnetic Equivalent Circuit Model

A simple and practical magnetic equivalent circuit (MEC) based analytical technique for calculating the performance parameters of the permanent magnet (PM) eddy current coupling is presented. In the proposed MEC model built with the lumped parameters, the eddy current effects are inherently taken into account by introducing a branch magnetic circuit allowing for the magnetomotive force and the reaction magnetic flux. A complete formulation for the reaction flux which is treated as a kind of leakage flux is derived. A verification process is conducted and it is shown that in a considerably wide range of slip speeds, the torques predicted by the presented method match well with those obtained by both the three-dimensional finite element analysis and experimental measurement. The new MEC-based method also proves to be effective in the performance simulation of the PM eddy current coupling with different design parameters. In addition, the limitation of the proposed approach is also discussed and the reasons are fully investigated.

Wideband Electromagnetic Model and Analysis of Shielded-Pair Through-Silicon Vias

The 3-D multistrata integration puts forward high requirements for signal integrity. The shielded-pair through-silicon vias (SPTSVs) proposed in this paper feature superior transmission properties and high jamming immunity suitable for differential-mode and common-mode transmission. Based on the quasi-static field theory, a wideband impedance model of SPTSVs considering the proximity effect, the line-to-line crosstalk, and the eddy current effect is derived. The parasitic parameters calculated by the impedance model are further given. The finite-element analysis shows that the proposed model highly agrees with the 3-D full-wave simulation and the analytical calculation. In addition, the characteristics of the impedance and the transmission coefficient are deeply analyzed with different design parameters. Finally, the impacts of the substrate effect and the metal–oxide–semiconductor effect on electrical characteristics of SPTSVs are revealed.

Eddy-Current-Effect Homogenization of Windings in Harmonic-Balance Finite-Element Models Coupled to Nonlinear Circuits

This paper deals with the harmonic-balance (HB) finite-element (FE) analysis of a multi-turn winding device coupled to electrical circuits comprising nonlinear components. The eddy-current effects in the windings are accounted for via a frequency-dependent reluctivity and impedance determined with a homogenization technique. The proposed multi-frequency approach is validated through a single-phase four-diode rectifier with an axisymmetric FE model of an inductor. The system of nonlinear algebraic equations is solved by means of the Newton–Raphson method. The HB results are validated with classical time-stepping simulations. The computational cost is briefly discussed.

Formation of Maximum Eddy Current Force by Non Ferrous Materials

This project is concerned with the study of eddy current effects on various materials such as aluminum, copper and magnesium. Two types of magnets used in this study; magnetic ferrite (ZnFe+2O4) and magnetic neodymium (NdFeBN42). Eddy current force will be exerted to these materials due to current flows along the magnet. This force depends on the type of magnet, type of material and the gap between the magnet and the material or between the two magnets. The results show that at constant magnet to material gap, the eddy current force decreases as the magnet to magnet gap increases. Similarly, at constant magnet to magnet gap, the eddy current force decreases as the magnet to material gap increases. The minimum force was achieved when the gap of magnet to material is maximum, similarly to the gap of magnet to magnet. The weakest force was between Copper and Neodymium at a magnet to material gap of 20 mm and magnet to magnet gap of 40 mm; the eddy current force was 0.00048 N. The strongest force (maximum) was between Magnesium and Ferrite and 0.42273 N at a magnet to material gap of 3 mm and magnet to magnet gap of 5 mm.

Prospects of using a permanent magnetic end effector to despin and detumble an uncooperative target

Space debris, such as defunct satellites and upper stages of rockets, becomes an uncooperative target after losing its attitude control and communication ability. In addition, tumbling motion can occur due to environmental perturbations and residual angular momentum prior to the object’s end-of-mission. To minimize the collision risk during docking and capturing of the tumbling target, a non-contact method based on the eddy current effect is put forward to transmit the control torque to the tumbling target. The main idea is to induce a controllable torque on the conducting surface of the tumbling target using a rotational magnetic field generated by a Halbach rotor. The radial and axial Halbach rotors are used to damp the spinning and nutation motions of the target, respectively. The normal and tangential force are evaluated concerning the relative pose between the chaser and the target. A simplified dynamic model of the nutation damping and despinning processes is developed and the influences of the asymmetrical principal moments of inertia and transverse angular velocity are discussed. The numerical simulation results show that the designed Halbach rotor stabilized the target attitude within an acceptable time. The electromagnetic nutation damping and despinning method provides new solutions for the development of on-orbit capture technology.

Optimal Design of the PMSM Retaining Plate With 3-D Barrier Structure and Eddy-Current Loss-Reduction Effect

From the constant-speed variable-output motor driving test result of an interior permanent-magnet synchronous motor for a pump drive, we observed that there was an additional loss factor, which was not previously considered. Furthermore, a 3-D finite-element method analysis was performed to investigate the cause of the additional electromagnetic loss. Accordingly, it was confirmed that there was an additional eddy-current loss in the rotor retaining plate structure for the rotor assembly. Using the shape of the eddy-current path in the plate, it was determined that the eddy current was formed inside the plate itself by the bypassing magnetic flux from the permanent magnet and the slot harmonics. It was confirmed that the eddy-current path can be changed according to the structure of the plate, and the optimal retaining plate design that satisfies the design constraints was derived via the topology optimization method. Finally, the retaining plate design with the 3-D barrier structure was derived by arranging the void shape considering the total eddy-current path. Using the actual model test results, it was verified that the new retaining plate design was effective for loss reduction compared to the conventional structure.

A New Pulse Magnet for the RCS Injection Shift Bump Magnet at J-PARC

The 3-GeV rapid-cycling synchrotron at the Japan Proton Accelerator Research Complex has achieved the high-power beam operation equivalent to 1 MW. As a next step, a study of an upgrade is in progress to mitigate the dose exposure of the maintenance workers in a high residual dose environment and realize the further high intensity beam power. Regarding the upgrade plan's provisions for radiation protection, a new injection scheme has been proposed to make space available for radiation shielding. The total length of the two shift bump magnets of the four magnets is reduced for this purpose, while the other two magnets in the injection straight section remain unchanged. As a result, the two types of pulse magnets are connected separately in series and are excited by two independent power supplies, which are made possible by splitting the presently installed power supply. A structural analysis of the new shift bump magnet is in progress, including simulations of the effects of eddy currents and the coil temperatures by OPERA-3D. This paper describes preliminary results of this analysis and the outlines the modified power supply design.

Three-Dimensional Numerical Analysis and Optimization of Electromagnetic Suspension System for 200 km/h Maglev Train Considering Eddy Current Effect

Electromagnetic suspension (EMS) is an important type of maglev train systems. With commercial success in the low-speed maglev train, developing a medium-speed maglev type with a top speed of 200 km/h based on the current low-speed maglev technology has been attracting great research interest and engineering effort. This new maglev system will nicely meet the requirement of inter-city transportation. However, at a higher speed, the eddy current effect in the EMS system of the leading end of a maglev train becomes an unnegligible factor, as the induced eddy current in the non-laminated steel rails will tremendously reduce the levitation force. This paper comprehensively investigates the mechanism of eddy current effect in the EMS system and uses a 3-D finite-element method to fully analyze the impacts of eddy current on levitation force adopting an accurate simulation model. Compared with the experimental data, the simulation results show good agreement. With this accurate simulation model, an optimized design of an electromagnetic levitation system is proposed as well as its corresponding control scheme. The proposed design at 200 km/h effectively mitigates the eddy current effect while still maintaining the required levitation force at the leading end of maglev train.