bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic field analysis of a magnetron composed of axisymmetric and rectangular structures
Authors: Kim Tae Heoung , Choi Seung-Kil , Lee Ju
Published: December 2018

In this paper, we deal with the magnetic field analysis of a magnetron composed of axisymmetric and rectangular structures using hybrid type finite element method. The magnetron used in microwave oven has cylindrical permanent magnet and rectangular iron plate to generate magnetic field. By comparing with the experimental results, we show that the proposed computational method is suitable to analyze a magnetron composed of axisymmetric and rectangular structures.
Improvement of the noisy signal pattern recognition using wavelet transform and weighting coefficients for each subblock
Authors: Midorikawa Yoichi , Akita Masanori
Published: December 2018

This paper shows the method for improving of the noisy signal pattern recognition. We have proposed the method for recognition of signal polluted with noise using spectral modification method by rule and smoothing method by wavelet transform. However, the modified spectral envelopes are flattened and added valleys become ambiguous. We applied emphasis method by weighting coefficient for each subblock. As a result, spectral shapes and performance of the pattern recognition are improved.
High sensitivity differential eddy current transducer
Authors: Chady Tomasz , Łopato Przemysław , Sikora Ryszard , Komorowski Mieczysław
Published: December 2018

In this paper a new version of eddy current differential transducer is proposed for evaluation of INCONEL thin plates in order to detect shallow hidden flaws. A 3D-finite element software package was used to analyse various configurations of the excitation coils and select optimal design. A set of experiments was carried out in order to prove usability of the transducer.
The optimal design method of permanent magnet assemblies with completely open architecture for MRI
Authors: Yao Yingying , Xie Junpeng , Ni Guangzheng , Hu Guanzhong
Published: December 2018

This paper presents a flexible design method to facilitate the construction of permanent magnet assemblies with completely open architectures for the Magnetic Resonance Imaging (MRI). The initial design is based on the ideally analytical assumptions. Then the dimensions and directions of the magnetization of each permanent element are optimized by using a modified genetic algorithm. Numerical implementations show that the proposed method provides a main magnetic field with modified homogeneity and strength at the imaging region, which is defined outside of the magnet structure, and minimizes the cost of the MRI equipment.
Electrical behaviour of a single crack in a conductor and exponential laws for conductivity in micro cracked solids
Authors: Giordano Stefano
Published: December 2018

In this paper we analyse the electrical effects of the presence of cracks in solid conductors. We have studied such problematic from different points of view. Firstly, we have analytically evaluated the behaviour of the electrical field near a crack in an isotropic solid where a uniform current density is flowing, drawing a comparison with the behaviour of the well known stress and strain tensor fields in the analogue elastic problem. This computation has been made with a slit-crack (two-dimensional field analysis) and with a circular crack (three-dimensional field analysis). So, in order to quantify the spatial fluctuations of the local electric field around the crack we have numerically found the density of states for the field showing that it exhibit sharp peaks and abrupt changes in the slope at certain critical points which are analogous to van Hove singularities in the density of states for phonons and electrons in solids. Finally, we have performed a theoretical analysis of the conductivity of a microcracked solid. The distribution of cracks in the solid follows a given orientational distribution, which modify the conduction properties of the overall material. In particular, we have shown that the conductivity depends exponentially on the cracks density and on the size of each crack embedded in the medium.
A generalized screw dislocation in a piezoelectric trimaterial body
Authors: Zhou Zhi-Dong , Nishioka Toshihisa , Kuang Zhen-Bang
Published: December 2018

A generalized screw dislocation in the piezoelectric trimaterial with two parallel plane interfaces is studied. The Burgers vector of the generalized screw dislocation normal to the isotropic base plane and a discontinuous electric potential locates in the isotropic plane, simultaneously a line force and a line charge are acted at the core. The singular solution of a generalized screw dislocation in a homogeneous piezoelectric ceramic is used as the basis for solving the piezoelectric trimaterial body. A Schwarz-Neumann's alternating technique [1] is applied to construct this trimaterial solution. Further, the generalized Peach Koehler forces acting on the generalized screw dislocation are considered. Numerical illustrations for the interaction are given and some discussions on the effects of the material mismatches are given. It is shown that the present solutions are available and useful.
The effect of magnetic anomaly detection technique in eddy current non-destructive testing
Authors: Kosmas Konstantinos , Hristoforou Evangelos
Published: December 2018

In this paper, we demonstrate a first approach of a non destructive testing method that is being oriented in detecting mainly near subsurface defects in ferromagnetic materials. This new technique is related to the parametric control and combination of the classic magnetic anomaly detection and the eddy current techniques that can be potentially used in common geometries giving the possibility not only to reveal the presence of defects, but also lead to their reconstruction when being parallel or perpendicular to the under inspection surface. This method is limited in depths of few mm due to the barrier of the penetration of eddy currents but its contribution in non destructive testing is coplementary to that of ultrasonic testing.
Flow characteristics of ER fluid in the model damper
Authors: Yamaguchi Hiroshi , Shimada Kunio , Zhang Xinrong , Inoue Daisuke
Published: December 2018

A basic study of a gap flow in a closed piston – cylinder system of ER fluid was carried out. The purpose of this study is to elucidate flow behavior of ER fluid in the piston – cylinder system. The electric field is applied between inner wall of the cylinder and outer wall of the piston, and the pressure difference between upper and lower chamber of the cylinder is measured. Theoretical formula of pressure difference is obtained by the one-dimensional assumption of the flow in the gap of cylinder. Furthermore, simulation code is developed in the present study based on the finite volume method(FVM). In comparison with the theoretical and experimental results, it is revealed that a larger difference occurs for a smaller aspect ratio of the piston. The numerical results showed a good agreement with the experimental data.
Magnetic field distribution in and around thin ferromagnetic structures
Authors: Leiss Elisabeth , Schönhuber Peter
Published: December 2018

Approaches to determine the magnetic field distribution in and around thin ferromagnetic structures have been compared. Taking a strip as example, the field distribution has been evaluated from small magnetization up to saturation. These experimental results were compared with the results of analytical and numerical mathematical approaches.
Convergence of geometric multigrid method for electromagnetic field analysis
Authors: Watanabe Kota , Igarashi Hajime
Published: December 2018

The multigrid method has been applied to electromagnetic field problems to show that it can reduce computational time in comparison with conventional linear solvers. However the convergence of the multigrid method depends on the iteration number of smoothing. Thus it is important to estimate the optimum iteration number of smoothing. This paper discusses the convergence of the geometric multigrid method against the iteration number of smoothing in edge-based finite element analysis. Numerical results show that the optimum number of smoothing can be estimated using the aspect ratio of elements.
Relationship between minor hysteresis loops and copper precipitation in Fe-Cu alloys
Authors: Takahashi Seiki , Kubota Ayako , Kobayashi Satoru , Kamada Yasuhiro , Kikuchi Hiroaki , Ara Katsuyuki
Published: December 2018

We have analyzed minor hysteresis loops of Fe-Cu alloys with 0.3 wt.% Cu in isothermal aging at 773 K. We found that magnetic coefficients of minor loops show a maximum around the same aging time that Vickers hardness becomes maximum. Both magnetic and mechanical properties are correlated with the microstructure of copper precipitates. These magnetic properties are very useful for nondestructive evaluation of degradation due to neutron irradiation in the nuclear reactor pressure vessels. The minor-loop properties have three advantages compared with coercive force of the major loop in view of their high sensitivity, amount of information, and a small magnetic field to be required for magnetic measurements.
Ultrasonic imaging in the liquid metals
Authors: Kažys Rymantas , Mažeika Liudas , Voleišis Algirdas , Šliteris Reimondas , Jasiuniene Elena , Aït Abderrahim Hamid , Dierckx Marc
Published: December 2018

In some nuclear reactors the core is intended to be cooled by means of liquid metal, for example, lead-bismuth eutectic alloy. For safety and licensing reasons, an imaging method of the interior of reactor has thus to be developed. The paper is devoted to development of ultrasonic imaging and measurement technique suitable for performance in the liquid Pb/Bi alloy.
The design method of voltage-controlled and current-controlled observer in sensorless magnetic levitation system of steel plate
Authors: Tada Kiyokazu , Torii Susumu
Published: December 2018

The magnetic levitation system does not hurt thin steel plate. The system for conveyance is constructed by a lot of electromagnets and gap sensors. Because of these many sensors, expense and space are required. Therefore, the introduction of sensorless control with observer is significant. The sensorless system is not always stable when the coil resistance changes slightly by room temperature change. This study examines the design method of voltage-controlled and current-controlled observer for constructing a robust sensorless system. This paper describes the experiment with the model of voltage-controlled observer. Then, the availability of the model is evaluated by the experiment.
Tomographic imaging for border security applications
Authors: Arunachalam Kavitha , Udpa Satish S. , Udpa Lalita
Published: December 2018

Efficient Non-Intrusive Inspection(NII) systems with high throughput are required for screening cargo containers at sea, air and land ports. Of all the available NII techniques, systems employing high energy X-rays have become very popular. Though well established, the probability of detecting contraband goods in the radiographic image obtained using conventional high energy X-ray systems is a function of operator skill and the orientation of the contraband material inside the container. In this paper, we present a limited-view tomography technique capable of reconstructing 2D tomograms of 3D objects. Such a system can be used in border security applications for screening cargo.
Vibration suppression for high temperature superconducting levitation flywheel system using coil dampers
Authors: Nagaya Kosuke , Saito Masato , Kobayashi Kazuya , Murakami Iwanori
Published: December 2018

A simple and stable flywheel system with high temperature superconducting levitation is presented that needs no control for levitation. The drive system consists of eight-poles cylindrical permanent magnet and eight cylindrical coils, in which magnetic forces in the direction perpendicular to the shaft axis are cancelled. Hence, vibration force due to the driving is zero in this system. A coil-type electromagnetic damper is also presented which works in the magnetic field of levitation permanent magnet. The dampers lie at both ends of the shaft. Using this system, a control like the sensorless control can be performed by using coils only. The control method has been presented and analytical expressions are also obtained for vibrations of the shaft. To validate the analysis, experimental tests have been carried out.
Layered soft ferromagnetic materials with moving interfacial crack in uniform magnetic field
Authors: Zhao She-Xu , Lee Kang Yong
Published: December 2018

Within the framework of linear magnetoelasticity, the plane strain problem of a layered medium composed of three dissimilar soft ferromagnetic materials with a Yoffe-type moving crack at the interface is considered. The medium is subjected to a uniform in-plane magnetic field and the crack is opened by internal normal and shearing tractions. By using the Fourier integral transform technique, the current mixed boundary problem is reduced to a pair of integral equations of the second kind with Cauchy-type singularities. To determine the dynamic magnetoelastic stress intensity factors, the singular integral equations are solved numerically by means of the Jacobi polynomial expansion method. Results are presented graphically to show the dependence of the DSIFs on the velocity of the moving crack, the magnetic field, the magnetic properties of the materials and the geometric parameter of the problem.
Microwave imaging of piecewise constant objects in a 2D-TE configuration
Authors: Féron O. , Duchêne B. , Mohammad-Djafari A.
Published: December 2018

In this paper we propose a stochastic algorithm applied to an electromagnetic inverse scattering problem. The objective is to characterise an unknown object from measurements of the scattered fields at different frequencies and for several illuminations.

This inverse problem is known to be nonlinear and ill-posed. It then needs to be regularized by introducing prior information. The particular prior information we account for is that the object is composed of a known finite number of different materials distributed in compact regions. The algorithm is applied to the inversion of experimental data collected at the Institut Fresnel (Marseille) and has already provided satisfactory results in a 2D-TM configuration. Herein, the goal is to test the same kind of method in a 2D-TE configuration.
Optimization of a small passive wind turbine generator with multiobjective genetic algorithms
Authors: Abdelli A. , Sareni B. , Roboam X.
Published: December 2018

In this paper Multiobjective Genetic Algorithms (MOGAs) are used for the design of a small wind turbine generator (WTG) coupled to a DC bus through a diode bridge. The originality of the considered system resides in the suppression of the Maximum Power Point Tracker (MPPT). The poor efficiency of the corresponding passive structure is considerably improved by optimizing the generator characteristics associated with the wind turbine in relation to the wind cycle. The optimized configurations are capable of matching very closely the behavior of active wind turbine systems which operate at optimal wind powers by using a MPPT control device.
Combinatorial and multi-level optimizations of a safety isolating transformer
Authors: Tran T.V. , Brisset S. , Brochet P.
Published: December 2018

Two analytical models and two finite element models (2D and 3D) are built and compared in terms of accuracy and computation time. They can be used as a benchmark to compare algorithms for multi-level and combinatorial optimizations. The discrete optimization of the transformer is done using branch and bound methods. The multi-level optimization is performed using one analytical model and the 3D FE model jointly thanks to the space-mapping techniques.
Magnetic properties of Ni-Mn-Fe-Ga ferromagnetic shape memory alloys
Authors: Kanomata Takeshi , Murakami Shuichi , Kikuchi Daisuke , Nashima Osamu , Nishihara Hironori
Published: December 2018

The magnetic measurements on Ni _{50} (Mn _{0.5} Fe _{0.5})_{25+x} Ga _{25-x} (0� x � 5.0) ferromagnetic shape memory alloys are made in the temperature range between 4.5 K and 500 K. A phase diagram of Ni _{50} (Mn _{0.5} Fe _{0.5})_{25+x} Ga _{25-x} is determined from the results of the temperature dependence of the initial permeability. The Curie temperature T _C exhibits only mild dependence when the concentration x increases. The martensitic and reverse martensitic transformation temperatures, T _M and T _R , increase with x. The total moment per formula unit μ _{m} remains constant with x.
Strategies of game theory for the automated optimal design in electromechanics
Authors: Di Barba P.
Published: December 2018

Classical microeconomics and game theory offer a conceptual frame to solve a design problem, characterized by multiple objective functions in mutual conflict. This viewpoint is largely accepted for the design of high-tech products as seen in aerospace engineering. However, for long-established products – like electromechanical and electromagnetic devices – the ongoing evolution in design strategies is not fully influenced by the impact of new design methodologies and software facilities. With this rationale, the shape design of a permanent-magnet three-phase motor is considered as an example of small actuator for house appliances; the analysis of the magnetic field is based on a finite-element model of the device. The design goal is to identify the magnet shape, such that the cogging torque of the motor is minimum for a given value of radial induction at the air-gap. More generally, the problem is cast in terms of multiobjective design: find the set of magnet shapes such that the torque is minimum and the induction is maximum, subject to the given constraints. Solutions in terms of Pareto front and Nash equilibrium are obtained by means of an evolutionary algorithm; during the automated search, discrete-valued design variables were considered, for the sake of a realistic design. The paper shows that the application of multi-objective optimisation in electromechanics gives a powerful design tool. Requirements in terms of timing and facilities are compatible with the resources of a research-and-development(R&D) centre of an industrial company in the area of electrical engineering.
Anti-vibration control of contactless planar actuator with manipulator
Authors: Hao Xiaohong , Mei Xuesong , Gajdusek Michal , Damen A.A.H.
Published: December 2018

This paper addresses the anti-vibration control produced by manipulator movements of contactless planar actuator with manipulator (CPAM). The manipulator on top of the planar actuator has 2-DOF which provides precise linear and rotary movement of the end tip of the manipulator. The successful suppression of the vibration will improve the position accuracy of the CPAM. For the purpose of the anti-vibration control design, a platform of 3-DOF contactless planar actuator with 2-DOF manipulator has been designed and manufactured. The platform, that mimics the magnetic array of the planar actuator, is suspended by 9 voice coils which are distributed into regular array to simulate the topology of the planar actuator and will be used for gravity compensation and for manipulator platform control in 3-DOF: vertically and two tilting angles. The other 3-DOF is fixed by the suspension system consisting of 3 stiff rods. Nine inductive sensors are mounted on the base plate to measure the posture of the platform when the manipulator is working. The CPAM model is based on rigid body dynamics and movement of the manipulator is taken as a disturbance in the platform control. According to the concept of loop shaping, robust H∞ controllers for each of the DOF of the platform are then designed depending on the estimated disturbance force and torque from the manipulator. Control responses in 3-DOF are then presented. The results illustrate high positioning stability.
Numerical analysis of the behavior of magnetic fluid in traveling magnetic field using the ALE GSMAC FEM
Authors: Ido Yasushi , Nakagawa Hideyuki , Kunitomo Takahiro , Kawai Hideki
Published: December 2018

Flow field in a thin layer of magnetic fluid under traveling magnetic field is investigated using the ALE type of GSMAC finite element method. Numerical results are qualitatively agree well with the experimental results reported by H. Kikura [1]. Relation between flow field and volume transportation of fluid is reported. It is shown that the surface velocity is maximized at the certain depth of magnetic fluid layer in case of low frequency of traveling magnetic field.
Implementation of a vector hysteresis model in 2D finite element analysis: Study of a RSST with anisotropic sample
Authors: Leite Jean Vianei , Benabou Abdelkader , Sadowski Nelson , Menach Yvonnick Le , Clenet Stéphane , Da Silva Jr. Pedro Armando
Published: December 2018

This work deals with the implementation of a vector hysteresis model in a 2D finite element code with vector potential formulation. The inverse Jiles-Atherton vector hysteresis model is used to describe the magnetic behavior law. This model allows to write naturally the differential reluctivity tensor which can be directly applied to the field calculation equations. The proposed implementation is then validated with a numerical model of a rotational single sheet tester and comparison with the measurements.
Design of optimal experimental parameters for diffusion-weighted MRI fibre-tracking protocols
Authors: Raguin L. Guy , Majumdar Shantanu , Udpa Satish S.
Published: December 2018

Diffusion-weighted imaging (DWI) has been shown to provide valuable structural information in biological fibrous soft tissues, such as the central and peripheral nervous system and skeletal muscle, based on the acquisition of a series of images that sample q-space. Existing q-space sampling schemes have been compared using several metrics based on diffusion tensor imaging (DTI), which models the restricted diffusion inside fibres as anisotropic unrestricted diffusion. Otherwise, sampling schemes have been optimized using model-independent cost functions. We propose using a model-based framework that connects the experimental noise, the uncertainty in the estimation of the model parameters, and the q-space sampling schemes together, to obtain model-based optimal sampling schemes for the case when the fibre orientation is known a priori to be within a finite region. We apply and validate this framework for the recently proposed quantitative analysis of q-space MRI data (QUAQ) model.
Flow-induced motion of spikes on magnetic fluid droplet
Authors: Yamane Ryuichiro , Sakiyama Nobuhiko , Park Myeong-Kwan
Published: December 2018

In order to fix the magnetic drug to the target a magnetic droplet should be held in position against the flow of the blood. In the present experiment a two-dimensional droplet is placed on the floor of the channel and is held in position by the magnetic force against the flow of the water. The needle-like spikes emerge on the droplet and they move downstream with the flow as if they rotate around the droplet, which will be effective in agitation and mixing inside the droplet. The motion of the spikes is not smooth but intermittent, skipping to the neighboring stable positions.
A method for diagnosis of induction machine fed by PWM vector control
Authors: Kim Mi-Jung , Kim Byong-Kuk , Moon Ji-Woo , Cho Yun-Hyun , Hwang Don-Ha , Kang Dong-Sik
Published: December 2018

In this study, we propose a diagnosis method for the rotor eccentricity in induction machines fed by a PWM converter by considering the harmonics in a transient magnetic phenomenon. The influences of the asymmetrical whirling motions are studied using the back EMF of a search coil, which enables the detection of motor faults. The analysis results of the rotor eccentricity could be obtained by comparing the characteristics of motors fabricated with normal and irregular air gaps, and the validity is verified from the experimental results. The simulation and experimental results can be useful for the online faults detection monitoring system of induction machines.
Optimization of electromagnetic coupling in induction heating systems excited by solenoidal and axial windings
Authors: Carrillo E.
Published: December 2018

A dimensionless analysis of eddy current distribution on massive conductors was undertaken, using configurations for two excitation sources co-axial to a cylindrical induction device: a solenoidal type, as found in most coreless furnaces, and an axial type, similar to that used in induction motors. The mathematical model is based on a one-dimension solution of the electromagnetic diffusion equation in an infinitely long cylinder utilizing the Newton shooting method. The simulated electromagnetic performance is compared for both configurations for a minimum in either the operational frequency or the size of a given induction heating system. The theoretical results show that workpieces powered by single-phase axial winding, featuring one pair of magnetic poles, release ohmic losses equivalent to the solenoidal counterpart using half of its frequency or the square root of its radius.
Power transmission through an unbounded elastic plate using a finite piezoelectric actuator and a finite piezoelectric power harvester
Authors: Xu Limei , Geng Yunlong , Zhang Ying , Fan Hui
Published: December 2018

Recently thickness vibrations of an unbounded elastic plate with an unbounded piezoelectric actuator and an unbounded piezoelectric power harvester have been studied for power transmission through an elastic wall with various potential applications. In this paper we analyze the more realistic geometric configuration of a structure with finite piezoelectric transducers on unbounded plates operating with slowly varying thickness modes via the first-order lamination theory for plates. In addition to the output voltage and transmitted power, confinement and localization of the vibration energy is also studied which is of practical importance and can only be understood from analyzing vibrations of finite transducers.
The behavior of two parallel non-symmetric interface cracks in a magneto-electro-elastic material strip under an anti-plane shear stress loading
Authors: Zhou Zhen-Gong , Wang Jia-Zhi , Wu Lin-Zhi
Published: December 2018

In this paper, the behavior of two parallel non-symmetric interface cracks in a magneto-electro-elastic material strip subjected to a uniform anti-plane shear stress loading was studied using Schmidt method. The problem was formulated through Fourier transform into two pairs of dual integral equations, in which the unknown variables are jumps of displacements across crack surfaces. To solve the dual integral equations, the jumps of displacements across crack surfaces were directly expanded as a series of Jacobi polynomials. Finally, the relations among the electric filed, the magnetic flux field and the stress field were obtained. The solution of the present paper shows the effect of the distance between two parallel cracks, the thickness of the layers and the level distance between two center points of two parallel non-symmetric cracks upon the stress, electric displacement and magnetic flux intensity factors at crack tips. It is also revealed that the crack shielding effect presents in magneto-electro-elastic materials.
Optimized model for magnetic hysteresis in silicon-iron sheets by using the simulated annealing algorithm
Authors: Boukhtache S. , Azoui B. , Féliachi M.
Published: December 2018

To characterize magnetic materials it is very important to take into account the initial magnetization curve and the magnetic hysteresis loop. Several approaches have been used to model these characteristics. However, some problems related to the accuracy of the results, especially at the knee of the curves have been encountered. This paper presents a contribution to solve this problem using both a simulated annealing algorithm to optimize the parameters of the Jiles-Atherton magnetic hysteresis model and the Brillouin theory to express the anhysteritic magnetization. The obtained results are in good agreement with measurements performed on silicon- iron sheets.
Multi-objective optimization of shielding devices for eddy-currents using niching evolution strategies
Authors: Cranganu-Cretu Bogdan , Jaindl Michael , Köstinger Alice , Magele Christian , Renhart Werner , Smajic Jasmin
Published: December 2018

Magnetic shielding and shunting in industrial devices is crucial for keeping stray losses and hot-spot appearances as low as possible. Nevertheless, the additional costs for magnetic shunts and conductive shields have to be taken into account. Therefore, an optimal trade-off between a remarkable reduction of the stray losses and the design and position of the shielding devices has to be found. A higher order evolution strategy is applied to perform this task. The relevant objectives are merged into a single number by applying a fuzzy membership function to each objective, respectively. These membership functions can be implemented as static ones or in a way, that they adjust themselves dynamically during the optimization process. In general multi-objective problems show a number of local solutions besides the global one and it is worth to investigate as many of the local solutions as possible as well. Therefore, a most desirable behaviour would be if the optimization strategy behaves globally and yields additional information about local minima detected on the way to the global solution. This goal can be achieved by clustering the population prior to the recombination process and by performing the recombination in a cluster sensitive way.
Gradient based optimization of semi-numerical models with symbolic sensitivity: Application to a simple ferromagnetic MEMS switch device
Authors: Delinchant B. , Rakotoarison H.L. , Ardon V. , Chadebec O. , Cugat O.
Published: December 2018

This paper deals with electromagnetic modeling dedicated to constrained optimization needs. A tool dedicated to magnetic devices with simple shapes is presented and applied to the design of magnetic MEMS. This tool allows semi-numerical modeling and provides symbolic gradient computation. A multi-level optimization strategy is used to ensure fast and global convergence of magnetic latch micro device.
Optimization and identification in regional hyperthermia
Authors: Weiser Martin
Published: December 2018

Regional hyperthermia is a cancer therapy aiming at heating tumors using phased array applicators. This article provides an overview over current mathematical challenges of delivering individually optimal treatments. The focus is on therapy planning and identification of technical as well as physiological quantities from magnetic resonance (MR) thermometry measurements.
Inverse algorithm for electromagnetic wire inspection based on GMR-sensor arrays
Authors: Kreutzbruck Marc , Allweins Kai , Strackbein Chris , Bernau Hendrick
Published: December 2018

To meet the increasing fabrication quality standards and the high throughput requirements NDE techniques are reliant on efficient reconstruction tools and visualization tools. In this work we present an inverse algorithm for a modern electromagnetic non-destructive testing approach using a small GMR sensor array to inspect superconducting wires. Four sensitive GMR sensors are positioned around the wire. Small defects of 100 μm in size could be detected in a depth of 200 μm with a signal-to-noise ratio of better than 400. Surface defects could be detected with a SNR of up to 10,000. This remarkably SNR and the small extent of GMR sensors results in a spatial resolution which offers new visualisation techniques for defect localisation, defect characterization and future tomography-like mapping techniques. We developed several inverse algorithms based on either a Finite Element Method or an analytical approach leading to defect localization with an accuracy of a few 10 μm.
Coupled electromagnetic thermal and kinetic modeling for microwave processing of polymers with temperature- and cure-dependent permittivity using 3D FEM
Authors: Sun Rensheng , Kempel Leo C. , Zong Liming , Hawley Martin C. , Benard Andre
Published: December 2018

This paper presents a self-consistent 3D marching-in-time multiphysics model, which includes electromagnetic field distribution, microwave power absorption, heat transfer, and polymer curing kinetics. Temperature- and cure-dependent permittivity and curing kinetics for DGEBA/DDS based on experimental data are explicitly included in the model. An edge-based finite element method (FEM) is implemented for the electromagnetic model, whereas node-based FEM is used in the heat transfer model. The numerical results can be used to determine the time-dependent temperature distribution and curing profile across the polymer sample, as well as the electromagnetic field distribution within the cavity applicator. The numerical results are compared with the measured data and a good agreement is achieved.
Quantitative NDE of cellular metallic materials and structures by using eddy current testing technique
Authors: Zhang Dongli , Chen Zhenmao , Xu Minglong , Lu Tian-jian
Published: December 2018

The feasibility of Eddy Current Testing (ECT) for the nondestructive evaluation of cellular metallic materials is investigated. The inspection target is focused on the welding joints connecting the surface and inner layers of a typical cellular material – metallic sandwich plate. Through numerical simulations, it is found that the defects in the welding zone cause ECT signals of significant different phase property with those caused by welding bead. The multi-frequency signal processing algorithm (MFA) is used to process the signals in order to improve the S/N ratio, which enables the recognition of crack indication from the mixed signals of welding joint. In addition, through profile reconstruction of a crack in the welding zone by means of a deterministic inverse analysis and MFA, it is demonstrated that ECT is a suitable quantitative NDE technique for the matrix sandwich material.
A new analytical technique for analysis of the rotor eccentricity in rotating electrical machines
Authors: Kiyoumarsi Arash , Zadeh Mohammad Reza Hassan
Published: December 2018

In this paper three different rotor eccentricities, i.e., static, dynamic and a combination of them, in the rotor of rotating electrical machines are studied by considering a relative permeance function in which variations of the airgap length have been included. The airgap flux density distribution that involves the effects of rotor eccentricity is calculated using the new relative permeance function. In this study, the cylindrical rotor shape is considered. The comparison of the results of this analytical method with which obtained by transient finite element method will also be considered in future studies.
TE-wave scattering from a shallow circular channel in a perfectly conducting plane
Authors: Tsaur Deng-How , Chang Kao-Hao
Published: December 2018

The problem of TE-wave scattering by a shallow circular channel in a perfectly conducting plane is considered and its rigorous series solution is also derived. By the region-matching technique, a semi-circular auxiliary boundary is introduced to divide the analyzed region into two subregions. The magnetic field of each subregion is represented in terms of an infinite series of wavefunctions with unknown coefficients. To include more practical applications, the wave source is assumed to be a Gaussian beam. The Kozaki's approximate expansion for Gaussian-beam incidence is adopted, which can convert into the plane-wave expansion with a special condition. With the enforcement of interface continuity conditions and the satisfaction of the channel surface boundary condition through the Graf's addition formula, the unknown expansion coefficients are determined. Comparisons for the semi-circular channel case with available data in the literature indicate excellent agreement. Pronounced effects of the depth-to-half-width ratio of the channel on backscattering width, far-field radiation pattern and equi-amplitude distribution of the magnetic field are illustrated by graphical results. The flexible and tunable features of the presented geometry make it easily applicable to the design and fabrication of multiple finite channels for optical devices.
On smoothening the singular field developed in the vicinity of metallic edges
Authors: Valagiannopoulos Constantine A.
Published: December 2018

Metallic wedges can be considered as parts of corner reflectors, open-ended waveguides, transmission lines and other devices with polygonal shape existing in an electromagnetics laboratory. The fields developed in the vicinity of these conducting edges possess substantial magnitudes which can affect negatively the conducted experiments and the measurement procedures. In this work, a cylindrical cap of lossy material is used to weaken the damaging radiation of the edge. The influence of the cylinder's radius, the material's permittivity and conductivity and the angular extent of the wedge on the interfering field is illustrated through various numerical examples.
Modification of the weak form to enforce electromagnetic field interface conditions in element-free Galerkin method
Authors: Yang Enhui , Mo Jinqiu , Liu Handan , Xu Wei , Wang Shigang
Published: December 2018

The disposal of interface conditions is a key problem for the application of meshless method in numerical computation of engineering electromagnetic field. Due to the meshless methods employing moving least square approximation scheme can not verify the Kronecker-δ property, the interface conditions can not be enforced automatically as done in FEM. This paper applies methods based on the modification of the weak form, such as Lagrange multiplier method and penalty method, to impose electromagnetic field interface conditions. Using above methods, the general models of electromagnetic field interface conditions expressed by A-φ-A approach are implemented by using the element-free Galerkin method. Then, a rectangular cross section solenoid with analytical solution is employed to validate the effect of the imposition of electromagnetic field interface conditions, and discuss the potential problems when using above two methods in different cases.
A study of head instabilities in TMR sensors using in high density perpendicular magnetic recoding systems
Authors: Tongsomporn Damrongsak , Afzulpurkar Nitin , Sitthisak Onjira
Published: December 2018

We did an experimental study to examine head instabilities and noise of tunneling magnetoresistance (TMR) sensors using in high-density perpendicular recording systems. It found that the instability signatures on the transfer curves could be categorized into two groups; permanent magnet/free layer (PM/FL) failure and synthetic antiferromagnetic layers/antiferromagnetic layer (SAF/AFM) failure. The thermal-mechanical stress from the adaptive flying height (AFH) heater as well as head-disk interaction potentially degrades PM resulting in the reduction of the FL stabilizing field, therefore TMR ratio and signal increases. The non-uniformity of PM remnant magnetization and the switching of PM grains especially near the edge potentially degrade the biasing field. Scanning electron microscope images of these weak heads show rough surface and scratches close to the active area of read sensor. The deep scratches by particles in the head-disk interaction and shallow scratches by the slider lapping process is a potential cause to degrade PM. In another group, the thermal-mechanical stress from AFH heater potentially reduces the exchange-bias field and thermal stability of SAF/AFM layers allowing partial flipping of SAF edge magnetization, consequently it induces voltage fluctuations and hysteresis loops in the transfer curves.
Numerical modeling of electromagnetic welding
Authors: Kore S.D. , Dhanesh P. , Kulkarni S.V. , Date P.P.
Published: December 2018

Feasibility of electromagnetic welding of flat sheets is ascertained by comparing the minimum impact velocities determined by using software ANSYS/EMAG and ABAQUS with the required minimum velocity obtained from analytical considerations. Magnetic forces acting on the sheets are computed from ANSYS/EMAG simulations. The velocity of impact and the pressure profile acting on the sheets are found from ABAQUS simulations. A criterion for weld formation is subsequently arrived at based on the simulations, which is further validated using experimental results. The reasons for no-weld zone in Al-to-Al EM weld and complete metal continuity (absence of no-weld zone) in Al-to-SS EM weld have been analyzed based on the numerical and experimental results.
Solution of a low-frequency coupled electromagnetic problem using the wavelet-Galerkin method
Authors: Kaushik K. , Kulkarni S.V.
Published: December 2018

In this paper, we present an analysis of a two-dimensional electric circuit-electromagnetic field coupled problem using the wavelet-Galerkin method. For illustration, the bar-plate configuration, a basic model for analysing eddy current phenomenon in electrical apparatus, is chosen. Firstly, a brief description of wavelet theory and its application in computational electromagnetics is provided. Then, a description of the two-dimensional coupled problem formulation and its solution using the wavelet-Galerkin method is given. Finally, results obtained using simulation are presented.
Time domain microwave imaging for a buried dielectric cylinder by dynamic differential evolution
Authors: Li Ching-Lieh , Chien Wei , Huang Chung-Hsin , Chiu Chien-Ching
Published: December 2018

This paper presents the studies of time domain inverse scattering for a two dimensional homogeneous dielectric cylinder buried in a half-space which are based on the finite difference time domain (FDTD) method and the dynamic differential evolution (DDE). For the forward scattering, the FDTD method is employed to calculate the scattered E fields, while for the inverse scattering the DDE scheme is utilized to determine the shape, location and the permittivity of the buried cylindrical scatterer with arbitrary cross section. The subgirdding technique is implemented for the FDTD code in order to model the shape of the cylinder more smoothly. In additions, in order to describe an unknown cylinder with arbitrary cross section more effectively during the course of searching, the closed cubic-spline expansion is adopted to represent the scatterer contour instead of the frequently used trigonometric series. Numerical results demonstrate that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In addition, the effects of Gaussian noise on the reconstruction results are investigated. Numerical results show that even the measured scattered fields are contaminated with Gaussian noise, DDE is able to yield good reconstructed quality.
Conformal PML with vector ABC undersurface for scattering problem
Authors: Zhang Yongjie , Sun Qin
Published: December 2018

Perfectly matched layers (PML) are the layers of electromagnetic wave absorbing elements designed for the mesh truncation of an open domain in a harmonic or modal analysis. It is an artificial anisotropic material that is transparent and heavily lossy to incoming electromagnetic waves. Conformal PML(CPML) is a convex and smooth shell region made up of lossy anisotropic medium. Generally, a conformal PML region is backed by a PEC boundary condition or a PMC boundary condition. But there are some reflections back into the computational domain by the PEC (PMC) boundary condition. In order to reduce the reflections, the traditional PEC (PMC) boundary condition is changed into vector absorbing boundary condition (ABC), and functional formula of conformal PML backed by vector ABC is deduced in this paper. Numerical experiments show that conformal PML backed by vector ABC is high-precision and high-efficiency.
Study on axial unbalance mechanism of radial passive magnetic bearings and its effects
Authors: Xiu Shichao , Tan Qingchang
Published: December 2018

According to the static magnetics viewpoint, the no-friction passive magnetic bearings are not stable in their non-load direction. So its position must be limited by certain means for its applications in engineering. Based on the theory of equivalent magnetic charges, the mathematical models for the axial displacement and force of radial passive magnetic bearings were established without any hypothesis and simplifications. In addition, the numerical simulations and the experiments for the axial and radial forces of radial passive magnetic bearing were performed. It shows that the simulations results tally with the experimental results primarily, and the relative axial displacement between the inner ring and the outer ring of the magnetic bearing not only weakens the radial bearing load capacity regularly, but also induces the axial force and makes the bearings unbalance in axial direction. The researches provide an effective approach to study the performance, the load capacity and the structure of the no-friction passive magnetic bearings.
Iron loss properties of a practical rotating machine stator core at each manufacturing stage
Authors: Nakazaki Osamu , Kai Yuichiro , Todaka Takashi , Enokizono Masato
Published: December 2018

This paper presents measured iron loss properties of a rotating machine's stator core at each manufacturing stage. It is well known that the magnetic properties deteriorate in constructed cores due to stress in manufacturing process and the iron loss increases in comparison with one of the ideal material used in designing, and then the building factor becomes more than one. In this paper, knowledge obtained in development of a simplified evaluation method of iron losses in actual stator cores of rotating machines is presented.
Design and finite element analysis of a novel structure brushless synchronous machine
Authors: Deng Xianming , Wang Lei , Zhang Jiamin , Wang Kang
Published: December 2018

In order to solve problems of complicated structure and huge volume of synchronous machine (SM), this paper presents a brushless synchronous machine with the structure of single stator core and single rotor core. Power windings and excitation windings of stator are laid in the same stator core. Correspondingly, DC excitation windings and AC windings of rotor are laid in the same rotor core, fixed in the machine's rotor by the rotating rectifier which is formed of commutation diodes. Magnetic field of the new structure machine is analyzed and calculated by ANSYS. The results show that the designed brushless synchronous machine has characteristics such as simple structure and superior performance. Therefore, it has a good application prospect.
Study of magnet rotor type non-contact transformer
Authors: Hasegawa Hitoshi , Kashiwagi Takayuki , Sakamoto Yasuaki , Sasakawa Takashi
Published: December 2018

This paper describes the realization of the magnet rotor type non-contact transformer that is possible to transmit electric power and a torque by non-contact. As for the large air gap as well, this device can transmit electric power and a torque efficiently which compensates for exciting current in the transformer by the permanent magnet flux.