Showing papers on "Magnetic core published in 2014"

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

Abstract: The applications of exchange coupled bi-magnetic hard/soft and soft/hard ferromagnetic core/shell nanoparticles are reviewed. After a brief description of the main synthesis approaches and the core/shell structural-morphological characterization, the basic static and dynamic magnetic properties are presented. Five different types of perspective applications, based on diverse patents and research articles, are described: permanent magnets, recording media, microwave absorption, biomedical applications and other applications. Both the advantages of the core/shell morphology and some of the remaining challenges are discussed.

New Core Loss Measurement Method for High-Frequency Magnetic Materials

Abstract: Magnetic core loss is an important concern for power converters. As the switching frequency increases and converter size reduced, the core loss will have significant impact to the converter efficiency and temperature. Accurate evaluation is important for magnetic design and converter loss estimation. The classic two-winding method is limited to low frequencies (usually below 1 MHz) because it is sensitive to phase discrepancy. In this paper, a new method is proposed for high-frequency core loss measurement that utilizes capacitive cancellation, which is suitable for HF and VHF core loss measurement. The new method greatly reduces the sensitivity to phase discrepancy, which is the dominating error source in the conventional two-winding method. An experimental demonstration is performed at 10 MHz, and the possible errors are analyzed in detail. With the proposed method, the high-frequency core loss can be accurately measured.

Building Nanocomposite Magnets by Coating a Hard Magnetic Core with a Soft Magnetic Shell

Abstract: Controlling exchange coupling between hard magnetic and soft magnetic phases is the key to the fabrication of advanced magnets with tunable magnetism and high energy density. Using FePt as an example, control over the magnetism in exchange-coupled nanocomposites of hard magnetic face-centered tetragonal (fct) FePt and soft magnetic Co (or Ni, Fe2C) is shown. The dispersible hard magnetic fct-FePt nanoparticles are first prepared with their coercivity (Hc) reaching 33 kOe. Then core/shell fct-FePt/Co (or Ni, Fe2C) nanoparticles are synthesized by reductive thermal decomposition of the proper metal precursors in the presence of fct-FePt nanoparticles. These core/shell nanoparticles are strongly coupled by exchange interactions and their magnetic properties can be rationally tuned by the shell thickness of the soft phase. This work provides an ideal model system for the study of exchange coupling at the nanoscale, which will be essential for building superstrong magnets for various permanent magnet applications in the future.

Fault Diagnosis of PWM DC–DC Converters Based on Magnetic Component Voltages Equation

Abstract: Switch fault diagnosis is an important design aspect for pulse width modulation (PWM) dc-dc power converters. It can prevent power converters from further damage, and also make preparations for remedial actions. In this paper, a fast switch fault diagnostic method is proposed for PWM dc-dc converters operating in continuous conduction mode. The proposed method utilizes the magnetic component (inductor or transformer) voltage for fault diagnosis. Based on the real-time voltage measurement and switch gate-driver signals, characteristics of switch open-circuit faults and short-circuit faults are rapidly extracted, and thus, switch faults can be quickly detected. The magnetic component voltage can be measured by an auxiliary winding in the magnetic core, and gate-driver signals can be easily got from the control circuit. Moreover, the fault detection can be implemented by a low-cost logical hardware circuit, and this circuit can be integrated into the control circuit. The fault diagnosis principle, design considerations, and implementation are discussed in this paper. Experiments are conducted to verify the theoretical analysis.

Leakage Inductance Calculation for Planar Transformers with a Magnetic Shunt

Abstract: The magnetic shunt is generally inserted in a planar transformer to increase the leakage inductance, which can be utilized as the series inductor in resonant circuits such as the LLC resonant converter. This paper presents a calculation methodology for the leakage inductance of the transformer with a magnetic shunt by means of the stored magnetic energy in the primary and secondary sides of the transformer using the magnetomotive force (MMF) variation method, as well as the stored energy in the shunt based on the reluctance model. The detailed calculation method is described. Both the finite-element analysis simulation and the experimental results have proven the validity of the proposed calculation method for leakage inductance.

Flux Balancing of Isolation Transformers and Application of “The Magnetic Ear” for Closed-Loop Volt–Second Compensation

Abstract: Semiconductor switches possess nonideal behavior which, in case of isolated dc-dc converters, can generate dc-voltage components which are then applied to the isolation transformer. This dc-voltage component is translated into a dc flux density component in the transformer core, increasing the risk of driving the core into saturation. In this paper, a novel noninvasive flux density measurement principle, called “The Magnetic Ear,” based on sharing of magnetic path between the main and an auxiliary core is proposed. The active compensation of the transformer's dc magnetization level using this transducer is experimentally verified. Additionally, a classification of the previously reported magnetic flux measurement and balancing concepts is performed.

Magnetic Integration of the LCL Filter in Grid-Connected Inverters

Abstract: This letter investigates the magnetic integration of the LCL filter in grid-connected inverters. By sharing an ungapped core and arranging the windings properly, the fundamental fluxes generated by the two inductors of an LCL filter cancel out mostly in the common core. Thus, the common core with low flux level can be dramatically reduced. Although the reluctance of the common core can hardly be zero, which implies an inevitable coupling between the integrated inductors, the proposed magnetic integration scheme is still attractive if the cross-section area and magnetic material of the common core are made reasonable. Experimental results from both single-phase and three-phase grid-connected inverters verify the effectiveness of the proposed method.

Magnetic shielding of wireless power transfer systems

Abstract: This paper deals with the magnetic shielding of the field generated by a wireless power transfer (WPT) system at the frequency of 20 kHz. Different shielding techniques are examined and discussed based on the use of conductive and magnetic material panels. The performances of the WPT system and the magnetic field shielding effectiveness (SE) in presence and in absence of shield panels are calculated and measured.

Solar Plane Propulsion Motors With Precompressed Aluminum Stator Windings

Abstract: This paper reports a propulsion motor for a solar-powered aircraft. The motor uses precompressed aluminum stator windings, with a fill factor of greater than 75%, in a permanent magnet synchronous machine. The motor performance is compared empirically to an identical machine with conventionally wound copper windings. It is shown that there are many advantages to using compressed aluminum windings in terms of weight reduction, thermal improvement, and lower cost, for the same loss and electromagnetic performance, provided a sufficiently high slot fill factor can be achieved. The design and manufacture of the compressed coils is also discussed. A modular stator arrangement is used, in the form of a solid coreback with keyed teeth to allow easy assembly of the compressed windings. It is noted that the electromagnetic performance of the machine is unaffected by the modular nature of the magnetic core. Two prototype motors, one wound with conventional copper and the other with precompressed aluminum windings, are constructed and tested.

Omnimagnet: An Omnidirectional Electromagnet for Controlled Dipole-Field Generation

Abstract: An Omnimagnet is an omnidirectional electromagnet comprising a spherical ferromagnetic core inside of three orthogonal nested solenoids. It generates a magnetic dipole field with both a variable dipole-moment magnitude and orientation with no moving parts. The magnetic and physical properties (e.g., dipole moment, weight, resistance, and inductance) of any Omnimagnet are derived. These general relationships are used to design an optimal Omnimagnet subject to the constraints that it has the same dipole-moment per applied current in any direction, each solenoid has no quadrupole contribution to the magnetic field, and the spherical core size maximizes the strength of the resulting dipole field. This optimal design is analyzed using FEA tools and is verified to be dipole-like in nature. Finally, the optimal design is constructed and its utility is demonstrated by driving a helical capsule-endoscope mockup through a transparent lumen.

Electrical breakdown in dielectric liquids-a short overview

Abstract: Power transformers are utilized to convert high voltages normally used in electrical power transmission to lower voltages more suitable for consumers. A transformer consists essentially of a magnetic iron core with primary and secondary copper windings. The alternating current flowing in the primary winding induces a magnetic flux in the core, which in turn creates a current in the secondary windings. If there is a difference in the number of turns in the primary and secondary windings, the secondary voltage will be scaled up or down proportionally to the ratio of the turns. In this way, a high voltage can be transformed to a low voltage. However, the desire to convert increasingly greater electrical loads using smaller power transformers results in both higher electrical and thermal stresses. The materials utilized to insulate the different electrically conductive components from each other must be designed to withstand those stresses. The insulating media often consist of pressboard and an insulating liquid. The liquid performs a double duty as it not only insulates the conductive parts but also functions as a liquid coolant. Here we are primarily interested in the oil as an insulating medium.

3-D–2-D Dynamic Magnetic Modeling of an Axial Flux Permanent Magnet Motor With Soft Magnetic Composites for Hybrid Electric Vehicles

Abstract: Axial flux permanent magnet (AFPM) motors might be an efficient traction solution for hybrid and full electric vehicles. This technology makes the use of soft magnetic composites (SMC) attractive for both manufacturing and performance reasons. Eddy currents in the iron can provide a natural transient damper and/or flux weakener and the iron losses might be compensated by the high torque density of axial structures. The main problematics of magnetic modeling in AFPM motors made with bulk SMC teeth and poles are leakage at the ends, slots effects and finally damping and losses. This paper deals with the material and geometry-dependent magnetic modeling of such a 3-D machine for design purpose considering a maximum a priori effect. Section I begins with the context, state-of-the-art and the geometrical modeling compatible with axial structures. In Section II , the magnetic equivalent circuit (MEC) of the machine is built, then the quasi-static electromagnetic behavior is computed, with time and space harmonics in a steady state. Section III is dedicated to an investigation of magnetic damping and losses, inside lumped parameters, either in a steady state or in a transient state. In Section IV , provided calculations are compared with each other, to the finite element method and to measurements.

A Quantitative Comparison Analysis of Radial-Flux, Transverse-Flux, and Axial-Flux Magnetic Gears

Abstract: The performances of three types of magnetic gears (MGs), which are radial-flux MGs, transverse-flux MGs, and axial-flux MGs, are quantitatively analyzed and compared using 3-D finite-element method of magnetic field and mechanical motion coupled computation. To fairly compare the torque capability of different topologies of MGs, all the MGs under study have the same gear ratio, the same outer diameter, and the same axial stack length. To maximize the torque density, several important structure parameters are optimized. Scenarios using different iron core materials and different magnetization directions of permanent magnets are also studied. Based on the comparative analysis, appropriate topologies of MGs that can achieve a torque density as high as 198 kNm/m 3 are suggested. The results in this paper give a good review of the torque density levels of different MGs, and hence they can be used as application guidelines.

Topology Optimization of Rotor Core Combined With Identification of Current Phase Angle in IPM Motor Using Multistep Genetic Algorithm

Abstract: This paper derives an effective shape of the flux barrier in an interior permanent magnet (IPM) motor. IPM motors generally have many design parameters such as the current phase angle, shape of the rotor and stator's iron core, and shape and position of the magnet. The flux barrier plays an important role in controlling torque characteristics. We apply topology optimization (TO) to the rotor core using a multistep genetic algorithm to determine an effective flux barrier. Furthermore, we extend the TO to combinatorial optimization for considering its effect on the current phase angle. Thus, a reasonable flux barrier with an optimal phase angle is determined.

Magnetic field sensor

Abstract: The invention provides a magnetic field sensor The magnetic field sensor comprises a sensor body, wherein a signal amplifying module, a single-ended turn difference module and a power supply and control module are included in the sensor body The sensor body is used for detecting a magnetic field signal of the environment where the sensor body is located and comprises a magnetic core which is wrapped by an inner cylinder and an induction coil which is wound on the periphery of the inner cylinder, and a middle tap of the induction coil is connected with the ground The signal amplifying module is connected with the two ends of the induction coil, is used for amplifying the magnetic field signal detected by the sensor body, and outputs the signal through a single-ended mode, the single-ended turn difference module is connected with the signal amplifying module and used for converting the magnetic field signal output by the signal amplifying module in the single-ended mode into the difference type signal, and the power supply and control module is used for supplying power sources to the signal amplifying module and the single-ended turn difference module and outputs the difference type detected signal output by the single-ended turn difference module According to the magnetic field sensor, a hollow coil is replaced by a structure with a magnetic core coil, and under the situation that the number of turns is not changed, compared with the hollow coil which improves the sensitivity of the sensor by increasing the area of a single turn, the sensitivity of the sensor is improved by selecting the suitable magnetic core coil

Gapped transformer design methodology and implementation for LLC resonant converters

Abstract: In the LLC resonant converter, the air gap is generally positioned in the core of the transformer for proper magnetizing inductance. Traditional transformer design methods assume infinite permeability of the core and no energy stored in the core. The improved design methodology for the gapped transformer is proposed with the optimum relative permeability and gap selection to meet the temperature rise and the magnetizing inductance requirements. The magnetizing current influences the magnetic flux in the core leading to the core saturation and core loss, while the resonant current contributes to the winding loss. The transformer design for a 200 W, 90 kHz LLC resonant converter is presented and experimental results validate the proposed methodology.

A Novel Integrated Magnetic Core Structure Suitable for Transformer-Linked Interleaved Boost Chopper Circuit

Abstract: A novel integrated magnetic structure suitable for the transformer-linked interleaved boost chopper circuit is proposed in this paper. The coupled inductor is known to be effective for miniaturization in high coupling area because the DC flux in the core can be canceled and the inductor current ripple become to high frequency. However, coupled inductor with E-E core and E-I core are realistically difficult to obtain necessary leakage inductance in high coupling area. The cause is fringing effect and the effects leads to complication of magnetic design. To solve this problem, novel integrated magnetic structure with reduction of fringing flux and high frequency ripple current performance, is proposed. Furthermore, the design method for novel integrated magnetic structure suitable for coupled inductor is proposed from analyzing of the magnetic circuit model. Finally, effectiveness of reduction of fringing flux and design method for novel coupled inductor are discussed from experimental point of view.

Direct protein detection in the sample solution by monitoring rotational dynamics of nickel nanorods.

Abstract: The feasibility of a recently introduced homogeneous immunodiagnostic approach to directly detect analyte binding by optical observation of the hydrodynamic properties of magnetically rotated nanorods ("PlasMag") is demonstrated experimentally. Specifically, it is shown that the phase lag of the long axis of nickel nanorods (magnetic core parameters: length 182 nm, diameter 26 nm) with respect to externally applied rotating magnetic fields significantly increases on the adhesion of bovine serum albumin (BSA) protein to their surfaces. To validate these results, the amount of bound protein molecules is independently determined by analysis of the electrophoretic mobility of the nanorods. Furthermore, the data also demonstrate the applicability of recently developed empirical models based on numerical solutions of the Fokker-Planck equation for describing the dynamics of magnetic nanoparticles in rotating magnetic fields.

Core Loss Computation in a Permanent Magnet Transverse Flux Motor With Rotating Fluxes

Abstract: This paper presents the core loss computation in a permanent magnet transverse flux motor (TFM) with soft magnetic composite stator core and mild steel rotor yoke, in which the magnetic fluxes rotate. The computation is based on modified core loss models and finite element magnetic field analysis (FEA). The coefficients for the core loss models are obtained by curve-fitting measurements on samples, and the magnetic flux density patterns in the motor are obtained by time-stepping FEA while operating conditions are considered. The computations of the motor core losses agree with the measured values on the TFM prototype. Index Terms—Core loss, finite element analysis, rotating magnetic flux, soft magnetic composite, transverse flux motor.

A Giant Magneto Resistive (GMR) Effect Based Current Sensor With a Toroidal Magnetic Core as Flux Concentrator and Closed-Loop Configuration

Abstract: This paper presents a novel current sensor, which includes a giant magnetoresistance (GMR) chip, a toroidal magnetic core, and a feedback winding on the core. The mathematical model of the sensor was built, which was used to analyze the influence factors of the closed-loop current sensor. The closed-loop configuration with the magnetic core and the feedback winding improved the sensitivity of the sensor, eliminated the offset and drift related to temperature of the chip, and greatly reduced the error caused by magnetic hysteresis phenomenon. The simulation and test results showed that the novel current sensor has very low linear error (less than ± 0.7%). The designed sensor can measure frequency of currents up to 100 kHz. The current sensor has high linearity with the range from 10 mA to 20 A.

Magnetic integrated device and power conversion circuit

Abstract: Disclosed are a magnetic integrated device and a power conversion circuit. The magnetic integrated device comprises a first magnetic core base, a second magnetic core base, and a first magnetic core column, a second magnetic core column, and a third magnetic core column that are located between the first magnetic core base and the second magnetic core base, said bases and columns being parallel to each other. A first winding, a second winding, and a third winding are respectively wound on the first magnetic core column, the second magnetic core column, and the third magnetic core column in the same manner, to form a closed magnetic flux loop. The first winding, the second winding, and the third winding are respectively used for connecting to a single-phase branch of a three-phase parallel circuit, currents flowing through all the single-phase branches of the three-phase parallel circuit have the same value, and every two of the currents have a phase difference of 120 degrees. In the present invention, by using the magnetic flux coupling relationship, single-phase branches of the three-phase parallel circuit interact with each other in the magnetic integrated device, and once the magnetic flux of one phase changes, the magnetic fluxes of the other two phases are adjusted at the same time. Whereby, automatic current equalization is realized, achieving the effect of automatically balancing the currents of different phases.

Accurate Measurement of the Air-Core Inductance of Iron-Core Transformers With a Non-Ideal Low-Power Rectifier

Abstract: The air-core inductance of power transformers is measured using a nonideal low-power rectifier. Its dc output serves to drive the transformer into deep saturation, and its ripple provides low-amplitude variable excitation. The principal advantage of the proposed method is its simplicity. For validation, the experimental results are compared with 3-D finite-element simulations.

Design of a 3-D Rotational Magnetic Properties Measurement Structure for Soft Magnetic Materials

Abstract: Three-dimensional magnetic properties of the soft magnetic materials should be considered and comprehensively analyzed in electrical engineering, compared with the traditional 1-D and 2-D testing method. A novel 3-D magnetic properties measurement structure with symmetrical “C-type” cores has been designed and modeled. To guarantee the experimental precision and accurately analyze the 3-D magnetic properties of the soft magnetic materials, especially for laminated silicon steel, a symmetrical 3-D magnetic flux path in the magnetization structure fit for given dimension of the cubic specimen has been calculated and modeled. Magnetic flux in each direction has been homogenized and concentrated on the top of the core poles by means of finite element analysis. Therefore, magnetic properties measurement in each direction of the specimen can become practical.

Template-assisted nano-patterning of magnetic core–shell particles in gradient fields

Abstract: A method is proposed for controlling the assembly of colloidal magnetic core–shell nanoparticles into patterned monolayer structures with nanoscale feature resolution. The method is based on magnetic field-directed self-assembly that is enhanced using soft-magnetic template elements. The elements are embedded in a nonmagnetic substrate and magnetized using a uniform bias field. A key feature of this approach is the combined use of a uniform field with induced gradient-fields produced by the template elements. This enables the customization of a force field with localized regions of attractive and repulsive magnetic forces that provide extraordinary control of particle motion during assembly. The method is demonstrated using a computational model that simulates the assembly process taking into account magnetic and hydrodynamic forces including interparticle interactions, Brownian diffusion, van der Waals force and effects of surfactants. The analysis shows that extended geometric patterns of particles can be assembled with nanoscale resolution, beyond that of the template elements, within milliseconds. This is achieved by tailoring key parameters including the template geometry to produce a force field that focuses the particles into prescribed patterns; the thickness of the dielectric particle shell to control the magnetic dipole–dipole force upon contact and the particle volume fraction to suppress undesired aggregation during assembly. The proposed method broadly applies to arbitrary template geometries and multi-layered core–shell particles with at least one magnetic component. It can enable the self-assembly of complex patterns of nanoparticles and open up opportunities for the scalable fabrication of multifunctional nanostructured materials for a broad range of applications.

Synthesis of Fe3O4/SiO2/CeO2 core-shell magnetic and their application as photocatalyst.

Abstract: The Fe3O4/SiO2/CeO2 core-shell magnetic has been successfully synthesized by three steps of hydrothermal, sonochemical and homogeneous precipitation by coating CeO2 nanoparticles onto Fe3O4/SiO2 magnetic core. The prepared samples were characterized by X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM) connected with energy dispersive X-ray analysis system (EDS), high resolution transmission electron microscopy (HRTEM), Nitrogen adsorption-desorption analyses (BET), and vibrating sample magnetometer (VSM). The photocatalytic activities for Fe3O4/SiO2/CeO2 core-shell magnetic under UV and visible lights were measured by determining the degradation rate of formic and oxalic acid in spiral reactor for 120 min. The amounts of CO2 generated during the process were compared between the magnetic catalyst and bare CeO2. After the finished photocatalytic degradation, the magnetic catalyst was recovered by external magnetic field at the end of each experiment. The results showed that the photocatalytic activity of Fe3O4/SiO2/CeO2 core-shell magnetic had higher than that of bare CeO2 and was found to be constant for three cycles of the recycled use.

Core Loss Estimation of Various Materials Magnetized With the Symmetrical/Asymmetrical Rectangular Voltage

Abstract: Core losses were estimated for various magnetic core materials magnetized with a duty-cycle-changed symmetrical and asymmetrical rectangular voltage. Each voltage waveform is applied to a transformer and a dc reactor in a dc/dc converter, respectively. Core losses were measured for the four typical magnetic core materials often used in power electronics: 3% grain-oriented silicon steel sheet, 6.5% silicon steel sheet, amorphous material, and nanocrystalline material. Measurement results were evaluated by the loss separation model. An approximation method was proposed for the core loss magnetized with asymmetrical rectangular voltage that divides the total core loss into the core loss of the magnetization from -B m to B m and that of the magnetization from B m to -B m . This method was confirmed to approximate the core loss accurately except for silicon steel sheet in an extreme duty cycle condition. However, it was demonstrated experimentally that dc component of the magnetic field strength caused this error.

Coupling inductor and power converter

Abstract: A coupled inductor and a power converter includes at least two input ends, an output end, a common magnetic core, at least two first windings, and at least two second windings The common magnetic core includes at least two magnetic cylinders, and the number of the at least two magnetic cylinders corresponds to the number of the at least two input ends; and one first winding and one second winding are twined in parallel on each cylinder among the at least two magnetic cylinders, and the first windings and the second windings on the at least two magnetic cylinders are mutually connected between the at least two input ends and the output end to form mutually coupled inductances and when currents that flow into the at least two input ends are equal, make the first winding and the second winding on each cylinder generate opposite magnetic potentials

Magnetic Bearings and Synchronous Magnetic Axial Coupling for the Enhancement of the Driving Performance of Magnetic Wireless Pumps

Abstract: In this paper, we introduce the property and effects of using magnetic bearings for the synchronous magnetic axial coupling operation of magnetic wireless pumps. Typically, the developed magnetic wireless pump can be driven by both synchronous radial and axial coupling. However, because of the radial direction of magnetization in the fully magnetic impeller and the strong coupling force, synchronous magnetic radial coupling has been used for magnetic wireless pumps. To utilize a synchronous axial coupling with weaker coupling force to driving the pump, we considered a magnetic bearing mechanism using the magnetic array of rectangular Nd-Fe-B magnets (14 pieces). The proposed magnetic bearing resulted in a magnetically levitated effect, stable operation, and wide torque variation in the magnetic axial coupling. We investigated the magnetic properties and the enhanced driving performance of the magnetic wireless pump through simulation with experiments.