Eddy Current Field Research Articles

Efficient circuit representation of eddy-current fields

PurposeThis paper aims to discuss the relationship between the continued fraction form of the analytical solution in the frequency domain, the orthogonal function expansion and their circuit realization to derive an efficient representation of the eddy-current field in the conducting sheet and wire/cylinder. Effective frequency ranges of representations are analytically derived.Design/methodology/approachThe Cauer circuit representation is derived from the continued fraction form of analytical solution and from the orthogonal polynomial expansion. Simple circuit calculations give the upper frequency bounds where the truncated circuit and orthogonal expansion are applicable.FindingsThe Cauer circuit representation and the orthogonal polynomial expansions for the magnetic sheet in the E-mode and for the wire in the axial H-mode are derived. The upper frequency bound for the Cauer circuit is roughly proportional to N4 with N inductive elements, whereas the frequency bound for the finite element eddy-current analysis with uniform N elements is roughly proportional to N2.Practical implicationsThe Cauer circuit representation is expected to provide an efficient homogenization method because it requires only several elements to describe the eddy-current field over a wide frequency range.Originality/valueThe applicable frequency ranges are analytically derived depending on the conductor geometry and on the truncation types.

Analysis of synchronous parasitic torque in dual skew cage rotor induction motors with equivalent slot number

The squirrel-cage induction motor with equivalent slot number may have starting problem due to synchronous locking torque. This study adopts dual skew rotor structure to solve that problem. First, the distribution of rotor slot harmonics is described. Second, the synchronous parasitic torque acting on the rotor is calculated. Eddy-current field simulation is implemented to calculate locking torque in three kinds of structure rotors squirrel-cage induction motor with equivalent slot. The induction motor with straight rotor hardly line starts in some rotor position, which illustrates that skew rotor can attenuate the synchronous parasitic torque, but cannot remove it. The dual skew rotor can remove the synchronous parasitic torque in which odd rotor slot harmonics interact with the unassociated stator harmonics, and also attenuate others. The validity of this rotor structure is verified by simulation study and also experiment.

Austenitic Biomaterial Cracks Evaluation by Advanced Nondestructive Techniques

The article deals with Non-Destructive Evaluation (NDE) of austenitic stainless steels. Eddy current, ultrasonic testing and non-contact magnetic field mapping methods are used for this purpose. ECA (Eddy Current Array) and TOFD (Time of Flight Diffraction) are methods that have become widely-used in the field of NDE and this is the reason for their utilization. Magnetic field mapping is nowadays an effective method of evaluation of surface-breaking defects mainly in ferromagnetic materials. The fluxgate sensor-based measurement is presented and discussed. The artificial fatigue and stress-corrosion material’s cracks are inspected. Experimental results are presented and discussed in this paper.

Composite magnetic flux leakage detection method for pipelines using alternating magnetic field excitation

Pipelines are an important transportation medium for petroleum and chemical products, but defects in the pipelines can present hidden dangers and affect the safe operation of the pipeline. The traditional pipeline magnetic flux leakage (MFL) scanning technique generally adopts the axial magnetization mode, which has increased the difficulty in detection and the possibility of missed detection of axial cracks. In this paper, a new composite MFL method using alternating magnetic field excitation is proposed for the detection of cracks in pipelines. The alternating magnetic field is first superimposed on the MFL magnetization field, which will form a parallel eddy current field perpendicular to the magnetization direction in the pipeline wall. The defects in the pipeline not only cause the flux leakage of the magnetization field, but also lead to the disturbance of the circumferential eddy current field. The disturbance signals can be picked up through a secondary induced magnetic field. Because the magnetic field and the eddy current field are orthogonal, the presented method can implement synchronous detection in two orthogonal directions to avoid missed detection caused by the crack orientation. A series of physical experiments are carried out in this paper. The results show that two orthogonal detection signals can be separated by a simple low pass filter. Therefore, with only one scan, the new detector can obtain the defect characteristics in the axial and circumferential directions to overcome the blind spot problem seen in traditional MFL detectors.

Investigation of Gyroscopic Stabilization for Single-Stage Saddle Sextupole Field Electromagnetic Launcher

This paper presents a novel single-stage saddle multipole field electromagnetic launching mode for the realization of projectile linear acceleration with gyroscopic stabilization. The hollow cylindrical projectile with three symmetrical vertical slots can change the eddy current and magnetic field density distribution on the projectile surface. When twisted an angle relative to saddle multipole coils along the circumference, the projectile will be linear accelerated with spinning motion under the action of pulse current. In this paper, analytical calculations and simulation methods were used to analysis this mode, the simulation results indicated that the axial acceleration force and circumferential torque acting on the projectile were generated simultaneously, and an optimal initial twisted angle was existed to make the muzzle rotation speed reach peak. To verify the conceptual feasibility, a single-stage saddle sextupole field electromagnetic launcher was built and tested. The experiment demonstrate that the mode is indeed possible to realize the projectile linear acceleration moving with the gyroscopic stabilization, launching performance can be adjusted by changing the initial voltage or twisted angle, and the experimental results are accordant with the simulation results.

A Novel Coulomb-Gauged Magnetic Vector Potential Formulation for 3-D Eddy-Current Field Analysis Using Edge Elements

Magnetic vector potential (MVP) formulation combined with finite edge elements has gained substantial application in 3-D eddy-current field computation. Compared with its magnetic scalar potential counterpart, the MVP formulation is much easier to treat multiply-connected conductors. With the availability of advanced direct linear solvers with high performance on parallel or multi-core platforms, it becomes more and more important to develop gauged MVP formulations. To this end, the gauging technique is essential to ensure that the MVP formulation is uniquely solvable by direct solvers. In this paper, a novel method for imposing Coulomb gauge to transient eddy-current problems using edge elements for approximating the MVP is proposed. The resultant linear matrix equation is symmetric and uniquely solvable. Current excitations and voltage excitations for stranded conductors and solid conductors are formulated, respectively. Field-circuit coupled scheme for solid conductors is also presented. Extensive numerical examples are computed using the proposed formulation, which has proved to be promising in further engineering applications.

Flaw inspection of welded joints in titanium alloys by the eddy current method

The eddy current transducer (ECT) of the transformer type is used to construct a sensor for investigating titanium sheets joined by a welded joint. The characteristics of the ECT are presented. The measurement method for controlling the occurrence of defects in the welded joints in titanium alloys is described. The experimental results obtained by the ECT on two welded titanium sheets are presented. The depth of penetration of the field of eddy currents into the investigated object is determined and the dependences describing the response of the ECT at different depths of the defect are outlined. The relationships can be used for evaluating the quality of welded joints and determining the reliability of welding.

Equilibrium reconstruction with 3D eddy currents in the Lithium Tokamak eXperiment

Axisymmetric free-boundary equilibrium reconstructions of tokamak plasmas in the Lithium Tokamak eXperiment (LTX) are performed using the PSI-Tri equilibrium code. Reconstructions in LTX are complicated by the presence of long-lived non-axisymmetric eddy currents generated by a vacuum vessel and first wall structures. To account for this effect, reconstructions are performed with additional toroidal current sources in these conducting regions. The eddy current sources are fixed in their poloidal distributions, but their magnitude is adjusted as part of the full reconstruction. Eddy distributions are computed by toroidally averaging currents, generated by coupling to vacuum field coils, from a simplified 3D filament model of important conducting structures. The full 3D eddy current fields are also used to enable the inclusion of local magnetic field measurements, which have strong 3D eddy current pick-up, as reconstruction constraints. Using this method, equilibrium reconstruction yields good agreement with all available diagnostic signals. An accompanying field perturbation produced by 3D eddy currents on the plasma surface with a primarily n = 2, m = 1 character is also predicted for these equilibria.

Investigating a Process of Accelerating Macroscopic Objects in an Eddy-Current Inductance Coil Magnetic Field

The subject of this paper is an analysis of the process of applying kinetic energy to a projectile made of non-magnetic electrically conductive material and located inside an induction coil live with alternating current. An experimental verification was carried out of the analytical conclusions that were pertinent to the design and technology of an inductance coil gun, which is a ranged weapon type.

Spiral MRI on a 9.4T Vertical-bore Superconducting Magnet Using Unshielded and Self-shielded Gradient Coils.

Spiral MRI sequences were developed for a 9.4T vertical standard bore (54 mm) superconducting magnet using unshielded and self-shielded gradient coils. Clear spiral images with 64-shot scan were obtained with the self-shielded gradient coil, but severe shading artifacts were observed for the spiral-scan images acquired with the unshielded gradient coil. This shading artifact was successfully corrected with a phase-correction technique using reference scans that we developed based on eddy current field measurements. We therefore concluded that spiral imaging sequences can be installed even for unshielded gradient coils if phase corrections are performed using the reference scans.

Simulation Research on Temperature Rise of Meter Cabinet Using ANSYS

Meter cabinet was the abbreviation of electric energy meter cabinet, and it was a kind of device for measuring electric energy. In the long-term use of the metering cabinet often occurs the problem of excessive temperature. In order to improve the temperature rise of the meter cabinet, the temperature field was simulated and analyzed. Using the simulation software ANSYS Workbench can simulate the temperature field of the conductor of the meter cabinet. By changing different conductor materials and temperature simulation of the contact position of the conductor, the distribution of temperature was analyzed. According to the maximum of the distribution of the Joule heat and the highest temperature distribution, the best scheme was choose. In addition, the simulation of the eddy current field was carried out on the panel of the meter cabinet, after comparing and analyzing the simulation results and selecting the best panel material.

Scanning the welded seams of titanium alloys by using subminiature eddy current transducers

The eddy current transducer (ECT) of the transformer type is used to construct a sensor for investigating titanium sheets joined by a welded joint. The characteristics of the ECT are presented. The measurement method for controlling the occurrence of defects in the welded joints in titanium alloys is described. The experimental results obtained by the ECT on two welded titanium sheets are presented. The depth of penetration of the field of eddy currents into the investigated object is determined and the dependences describing the response of the ECT at different depths of the defect are outlined. The relationships can be used for evaluating the quality of welded joints and determining the reliability of welding.

Calculation of equivalent magnetic permeability of ferromagnetic materials for modeling of three-dimensional eddy current fields

The paper presents a method of calculating a constant value of magnetic permeability of ferromagnetic materials, equivalent to the basic magnetization curve by the criterion of real power. The proposed method makes it possible to use linear differential equations of the electromagnetic field in the analysis of three-dimensional fields of eddy currents in ferromagnetic materials, thus significantly reducing the calculation time. We propose a method of calculating the power of inductors using two-dimensional axisymmetric models. The scope of the proposed methods is limited to the case of placement of the inductor inside the ferromagnetic body.

電力・電気機器の高精度等価回路表現

1．はじめに

High Frequency Nonlinear Modeling of Magnetic Sheets using Polynomial Expansions for Eddy-current Field

High Frequency Nonlinear Modeling of Magnetic Sheets using Polynomial Expansions for Eddy-current Field

Sensitivity difference caused by eddy-current magnetic field in Hi-speed MFL testing and its elimination method

Sensitivity difference caused by eddy-current magnetic field in Hi-speed MFL testing and its elimination method

A novel approach to deal with periodic boundary conditions for 3D eddy current field problems

A novel approach to deal with periodic boundary conditions for 3D eddy current field problems

Nano- and micro-scale Bi-substituted iron garnet films for photonics and magneto-optic eddy current defectoscopy

Synthesis technology of nano-scale Bi-substituted iron garnets films with high magneto-optic activity for photonics and plasmonics applications were proposed. The micro-scale single-crystal garnet films with different types of magnetic anisotropy as a magneto-optic sensors were synthesized. It was shown that easy-axis anisotropy films demonstrated the best results for visualization of redistribution eddy current magnetic field near defects.

Research on an integrated electromagnetic auxiliary disc brake device for motor vehicle

In view of low chassis and limited space of small vehicles, this paper presents an integrated electromagnetic auxiliary disc brake device. The device is formed by an excitation winding and the main magnetic circuit, both of which are located on the structure of the conventional brake caliper. The excitation winding is powered synergistically with the antilock braking system. Based on the presented main magnetic circuit, we construct the physical model of the proposed system, analyze the working principle, electromagnetic braking power, and torque, and calculate electromagnetic braking torque with conventional algorithms. To calculate the eddy current and magnetic field distribution on the disc, using three‐dimensional finite element simulation method taking full account of the penetration depth and the marginal effect, we compare the electromagnetic braking torques obtained using the conventional algorithm and finite element simulation. Results show that the braking effect is effective and obvious, especially at medium and high speeds. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Structural health monitoring using torsional guided wave electromagnetic acoustic transducers

Torsional guided wave inspection is widely used for pipeline inspection. Piezoelectric and magnetostrictive transducers are most commonly used to generate torsional guided waves. These types of transducers require bonding or mechanical contact to the pipe which can result in changes over time which are undesirable for structural health monitoring. This article presents a non-contact Lorentz force–based electromagnetic acoustic transducer for torsional guided wave monitoring of pipelines. First, the excitation mechanism of the transducer is simulated by analyzing the eddy current and the static magnetic field using the finite element method. An electromagnetic acoustic transducer transformer model is presented which describes the eddy current generation transfer function and the ultrasound excitation. Independently simulated eddy current and magnetic fields are used to calculate the Lorentz force that an electromagnetic acoustic transducer array induces on the surface of a 3-in schedule 40 pipe, and an explicit finite element solver is then used to simulate the elastic wave propagation in the pipe. Then, the reception mechanism and the expected received signal levels are discussed. The construction of an experimental transducer is described, and measurement results from the transducer setup are presented. The measured and modeled performance agree well. Finally, a monitoring example is presented where an artificial defect with 3% reflection coefficient is introduced and successfully detected with the designed sensor.