Showing papers on "Magnetic core published in 2009"

Magnetic−Plasmonic Core−Shell Nanoparticles

Abstract: Nanoparticles composed of magnetic cores with continuous Au shell layers simultaneously possess both magnetic and plasmonic properties. Faceted and tetracubic nanocrystals consisting of wustite with magnetite-rich corners and edges retain magnetic properties when coated with a Au shell layer, with the composite nanostructures showing ferrimagnetic behavior. The plasmonic properties are profoundly influenced by the high dielectric constant of the mixed iron oxide nanocrystalline core. A comprehensive theoretical analysis that examines the geometric plasmon tunability over a range of core permittivities enables us to identify the dielectric properties of the mixed oxide magnetic core directly from the plasmonic behavior of the core−shell nanoparticle.

Review of On-Chip Inductor Structures With Magnetic Films

Abstract: A comparison of on-chip inductors with magnetic materials from previous studies is presented and examined. Results from on-chip inductors with magnetic material integrated into a 90 nm CMOS processes are presented. The inductors use copper metallization and amorphous Co-Zr-Ta magnetic material. Inductance densities of up to 1700 nH/mm2 were obtained thanks to inductance increases of up to 31 times, significantly greater than previously published on-chip inductors. With such improvements, the effects of eddy currents, skin effect, and proximity effect become clearly visible at higher frequencies. Co-Zr-Ta was chosen for its good combination of high permeability, good stability at high temperature (> 250degC), high saturation magnetization, low magnetostriction, high resistivity, minimal hysteretic loss, and compatibility with silicon technology. The Co-Zr-Ta alloy can operate at frequencies up to 9.8 GHz, but trade-offs exist between frequency, inductance, and quality factor. Our inductors with thick copper and thicker magnetic films have dc resistances as low as 0.04 Omega, and quality factors of up to 8 at frequencies as low as 40 MHz.

A novel core-shell structured magnetic organic-inorganic nanohybrid involving drug-intercalated layered double hydroxides coated on a magnesium ferrite core for magnetically controlled drug release

Abstract: A novel magnetic nanohybrid involving non-steroid anti-inflammatory drug diclofenac (DIC) intercalated Mg–Al layered double hydroxides (LDH) coated on magnesium ferrite particles was assembled via a one step coprecipitation self-assembly method. The XRD, FT-IR and ICP measurements reveal that the magnetic nanohybrid consists of both DIC-LDH nanocrystallite and magnesium ferrite phases. The TEM image shows that the magnetic nanohybrid presents well-defined core-shell structure with diameter in the range of 90–150 nm. Compared to pure DIC-LDH, an obviously smaller dimension and less sharp hexagonal morphology of the coated DIC-LDH nanocrystallites in magnetic hybrids is observed due to a heterogeneous nucleation and crystal growth process with the introduction of the magnetic core. The in vitro drug release rate of the magnetic nanohybrid was thus enhanced owing to the much smaller size of the coated DIC-LDH nanoparticles on the surface of the magnetic core. However, under an external magnetic field of 0.15 Tesla, the drug release rate of the magnetic nanohybrid decreases dramatically owing to the aggregation of the magnetic nanohybrid particles triggered by non-contact magnetic force. The kinetic data reveal that the release of DIC from the magnetic nanohybrid is controlled by particle diffusion, and the release rate is mainly affected by the particle size and the aggregation extent of the hybrid magnetic particles. Additionally, the obtained nanohybrid has a strong magnetization response, implying the possibility of application in magnetic drug targeting.

Resonator for wireless power transmission

Abstract: Disclosed is a resonator for wireless power transmission used in a mobile device. The resonator includes a substrate, at least one microstrip line, and a magnetic core. The microstrip line is formed on the substrate and is provided at one side thereof with a slit to have an open-loop shape. The magnetic core is formed on the substrate and is disposed on a space defined by the microstrip line to increase coupling strength.

Design and analysis of interior-magnet outer-rotor concentric magnetic gears

Abstract: In this paper, a new topology of concentric magnetic gears is proposed and implemented. The key of the new topology is to bury permanent magnets (PMs) of the outer rotor into the iron core in a new way so that the mechanical integrity can be improved, and the PM material can be saved while the torque density is maintained. The proposed gear is designed with the speed reduction ratio of 7.33 and optimized by using the three-dimensional finite element method (3D-FEM). The key of the 3D-FEM is to employ scalar magnetic potential to reduce the required memory and time for data manipulation and computation. After prototyping, the measured maximum static torque well agrees with the calculated one, hence verifying the proposed design and analysis.

Comparison of Models for Estimating Magnetic Core Losses in Electrical Machines Using the Finite-Element Method

Abstract: This paper focuses on the modeling and prediction of core losses in nonoriented magnetic materials of electrical machines. The aim is to investigate the accuracy, efficiency, and stability of certain models, including the commonly used and the advanced ones, and to discuss their advantages and disadvantages when they are implemented in the finite-element method (FEM). It is shown in the paper that the traditional technique based on the loss separation theory can efficiently produce reasonable results in specific operation conditions but can, on the other hand, over- or underestimate the core losses in other circumstances. The advanced model based on solving the one-dimensional (1-D) Maxwell equations can give accurate results for the prediction of core losses in a lamination strip, but its accuracy, stability, and computational burden are put under scrutiny when it is applied to the prediction of core losses in an electrical machine. A third technique, referred to as the hybrid model, which captures the advantages of the traditional and advanced techniques and merges them into one, has been found to be the best compromise. The principal aim of the hybrid model is to avoid the numerical procedure of the 1-D Maxwell equations while maintaining relatively accurate predictions with a reasonable computational burden. A comparative investigation has been conducted for the three core-loss models that have been incorporated into the 2-D FEM analysis of a 37-kW induction motor on which experiments were carried out for comparisons.

Synthesis, Characterization, and Magnetically Controlled Release Behavior of Novel Core-Shell Structural Magnetic Ibuprofen-Intercalated LDH Nanohybrids

Abstract: LDH (layered double hydroxides)-based magnetic-sensitive drug−inorganic nanohybrids were assembled by a one-step co-precipitation method. The effect of a magnetic substance on the microstructure and drug release behavior of ibuprofen (IBU)-intercalated Mg−Al−LDH in magnetic nanohybrids was systematically studied via XRD, TEM, XPS, and VSM methods and in vitro release with and without an external magnetic field (MF). The results reveal a well-defined core−shell structure with a gray IBU−LDH shell coated onto the surface of a dark magnetic core and superior magnetic sensitivity of the magnetic nanohybrids. Compared with the clear platelets of the pure IBU−LDH, the IBU−LDH coatings in magnetic nanohybrids exhibit more like a compact stacking film fully covering the magnetic core and their particle sizes and thickness decrease with increasing core contents, explaining an enhanced release rate under no MF. While under a 1500 G MF, the release rate is greatly reduced with increasing core content due to the inst...

Coupled Inductor Characterization for a High Performance Interleaved Boost Converter

Abstract: Interleaved power converter topologies have received increasing attention in recent years for high power and high performance applications. The advantages of interleaved boost converters include increased efficiency, reduced size, reduced electromagnetic emission, faster transient response, and improved reliability. The front end inductors in an interleaved boost converter are magnetically coupled to improve electrical performance and reduce size and weight. Compared to a direct coupled configuration, inverse coupling provides the advantages of lower inductor ripple current and negligible dc flux levels in the core. In this paper, we explore the possible advantages of core geometry on core losses and converter efficiency. Analysis of FEA simulation and empirical characterization data indicates a potential superiority of a square core, with symmetric 45deg energy storage corner gaps, for providing both ac flux balance and maximum dc flux cancellation when wound in an inverse coupled configuration.

Ferromagnetic microdisks as carriers for biomedical applications

Abstract: We report the fabrication process, magnetic behavior, as well as the surface modification of ferromagnetic microdisks suspended in aqueous solution. They posses unique properties such as high magnetization of saturation, zero remanence due to spin vortex formation, intrinsic spin resonance at low frequencies, and the capability of delivering various biomolecules at once. Furthermore, because of their anisotropic shape, our magnetic particles rotate under alternating magnetic fields of small amplitude. This can be used to promote the idea of advanced therapies, which include combined drug delivery and magnetomechanical cell destruction when targeting tumor cells. The approach enables us to fabricate suitable magnetic carriers with excellent size tolerances, and then release them from the wafer into solution, ready for surface modification and therapeutic use. The particles have a magnetic core and are covered with few nanometers of gold on each side to provide stability at ambient conditions as well as biocompatibility and selective adhesion functions. A successful attempt to bind thiolates, including SH-modified antibody, to the disk’s surface was demonstrated.

Microwave-assisted three-dimensional multilayer magnetic recording

Abstract: Layer-selective writing of two layer bit patterned media is demonstrated by performing micromagnetic finite element simulations. Selectivity is achieved by controlling the frequency of an oscillating magnetic field in the gigahertz range, applied in addition to the head field. Generation of the microwave field by means of a wire next to the tip of a single pole head is proposed. The Oersted field from the alternating current induces magnetic oscillations in the pole tip which create a high frequency field that is superimposed to the perpendicular write field. The amplitude of the ac field component is in the order of 0.1 T.

Module having a stacked magnetic device and semiconductor device and method of forming the same

Abstract: A module having a stacked magnetic device and semiconductor device, and method of forming the same. In one embodiment, the module includes a printed wiring board including a patterned conductor formed on an upper surface thereof. The module also includes a magnetic core mounted on the upper surface of the printed wiring board proximate the patterned conductor and a semiconductor device mounted on an upper surface of the magnetic core.

Motor modeling for EMC simulation by 3-D electromagnetic field analysis

Abstract: A building technique of high-frequency motor models by 3-D electromagnetic field analysis has been developed to establish the simulation technology for EMC estimation in the design stage of motor drive systems. Stray capacitance of each part of a motor was calculated by static electric field analysis, while inductance and resistance of its stator windings were calculated by magnetic field analysis. A motor equivalent circuit was then built with these circuit constants to compute frequency characteristics of motor impedance. In order to take eddy current in laminated iron core into account precisely, we analyzed a 3-D model of half thickness of one laminated steel sheet, and a simplified 3-D model of coil end of a motor. We also took the difference between magnetic field distribution of common mode and that of differential mode into account by setting different coil current and boundary conditions in the analyses. The frequency dependence of calculated inductance and resistance was introduced into circuit simulations. As a result, we have obtained frequency characteristics of motor impedance, whose basic features are similar to those of measured data. Possible causes of the discrepancy have also been discussed.

Fixer, image forming apparatus including same, and fixing method

Abstract: A fixer includes a fixing member with a rotary heat generator, a pressure member, an excitation coil disposed facing a heat generation layer of the rotary heat generator to generate magnetic flux that inductively heats the heat generation layer, a loop-shaped demagnetization coil unit disposed facing the heat generation layer to generate magnetic flux that partly counteracts the magnetic flux generated by the excitation coil, a first magnetic core disposed in a first area that is enclosed by both the excitation coil and the demagnetization coil unit, and a second magnetic core disposed in a second area that is outside a loop of the demagnetization coil unit and enclosed by the excitation coil. The first magnetic core and the second magnetic core are magnetically continuous in a rotary axial direction of the rotary heat generator. A fixing method fixes an image on the sheet used in a fixer.

Characteristic Analysis of Claw-Pole Machine Using Improved Equivalent Magnetic Circuit

Abstract: Magnetic field analysis of claw-pole machines using improved equivalent magnetic circuit (EMC) is presented in this paper. On the basis of 3-D geometry, improved EMC, which consists of magneto motive-force (MMF) source and permeance considering main and leakage flux distribution, is composed and field analysis is performed. Nonlinear characteristics of magnetic core are considered for precise analysis results. Three-dimensional finite element analysis (FEA) is performed to verify calculated results and flux density in rotor and stator areas are compared. In addition, calculated and experimental back-EMF versus MMF of field and rotor speed is compared. From the verification with calculated and experimental results, it is proved that improved EMC compared with 3-D FEA provided reasonable results in initial design of claw-pole machine having asymmetric structure.

Three-Phase Transformer Model Including Magnetic Hysteresis and Eddy Currents Effects

Abstract: In this paper, a three-phase transformer model is developed to be suitable for slow transient and power-quality studies. The proposed model takes into account the eddy currents, the magnetic core topology, and the nonlinear characteristics of the core material. In order to model the eddy currents effects in the magnetic core, Bertotti's work for the eddy currents is used and nonlinear resistors dependent on the magnetic core topology are proposed. A systematic procedure is developed for the determination of the incremental self and mutual inductances of the windings. The nonlinear characteristics of the core material are represented either by a magnetization curve or by a hysteresis loop. The hysteresis loop is introduced either by the mathematical model proposed by Tellinen or by the macroscopic model presented by Jiles-Atherton. Simulations results are compared to published measurements in order to verify the proposed model.

High efficiency magnetic core electrical machine

Abstract: A magnetic core electrical machine includes a plurality of “U”-shaped stator yokes arranged circumferentially with respect to a rotor and either staggered to form a continuous flux return path or displaced relative to permanent magnets of the rotor in order to reduce cogging. Various mechanisms and/or circuits are provided to limit an output of the electrical machine at high speeds, and boost the voltage output at low speeds.

Analysis of Microinductor Performance in a 20-100 MHz DC/DC Converter

Abstract: This paper presents a low-profile thin-film microfabricated inductor on silicon and its performance in a high-frequency low-power DC/DC converter. The design of the inductors has focused on maximizing efficiency while maintaining a relatively flat frequency response up to 30 MHz. The inductance at 20 MHz is approximately 150 nH with a resistance of 1.8 ?. The performance of the microinductor has been compared to two conventional commercially available 150-nH chip inductors. One of the chip inductors has a magnetic-material core and the other is an air core. The maximum efficiency of the microinductor, which relates the power loss of the microinductor to output power loss of the converter, is measured to be approximately 93% at 20 MHz. The low-power DC/DC converter operates in the tens of milliwatts output power range, with an input voltage of 1.8 V and an output voltage programmable between 0 and 1.8 V. The converter maximum efficiency when using the microinductor on silicon is 78.5% at 20 MHz, which is approximately 2% lower than the efficiency using the conventional chip inductors.

High sensitivity differential current transformer for insulation health monitoring

Abstract: A current transformer is provided. The current transformer comprises an inner magnetic core having a central opening, an outer sense core circumscribing the inner magnetic core, at least one pair of conductors extending through the central opening and positioned symmetrically with respect to a center point of the inner magnetic core, and one or more coils disposed on the inner magnetic core, the outer sense core, or both, in a magnetically balanced configuration relative to a magnetic neutral axis of the inner magnetic core.

Performance Test of a 100 kW HTS Generator Operating at 67 K–77 K

Abstract: A systematic test program is in progress to fully characterize a 100 kW HTS synchronous generator which was successfully constructed in 2004. The machine was one of the first HTS synchronous generator/motors to operate at liquid nitrogen temperatures while achieving a power rating relevant to practical application. It has a conventional 3-phase stator and a cold rotor with a magnetic core and a superconducting winding consisting of 10 HTS Bi2223 pancake coils separated by magnetic flux diverters. The test program includes a series of tests at various speeds, field currents and temperatures (65 K-77 K) with the machine in open circuit to determine the critical currents of the HTS rotor, the waveform and harmonic characteristics of generated voltage at different levels of iron saturation. Stationary measurements of the rotor critical current are carried out using dc current in the stator windings to quantify the influence of stator field on the performance of the superconducting winding. The voltages and temperatures of the rotor are measured using a radio frequency telemetry system.

Design and characterization of a microwire fluxgate magnetometer

Abstract: This paper deals with the characterization of fluxgate magnetometers that adopt a FeSiB microwire as magnetic core. The proposed device has a number of peculiarities that make this sensor very interesting. In fact this magnetometer affords the detection of weak magnetic targets with a very high spatial resolution and low power consumption. The readout strategy is based on the use of the “Residence Times Difference”; the DC magnetic field information is derived from the temporal positions of the output waveform spikes. In the paper an accurate device characterization is performed with particular regards to sensor resolution, sensitivity and power consumption; moreover, some comparisons between the FeSiB microwire fluxgate and a “ribbon” Magnetic Alloy FR4-fluxgate, previously developed by the authors, are presented. Finally exhaustive experimental characterization results demonstrate the possibility to use the microwire fluxgate as a low power system (with high spatial resolution) operating with a sinusoidal bias current of 5 mA pp .

Plasmon antenna with magnetic core for thermally assisted magnetic recording

Abstract: A TAMR (Thermal Assisted Magnetic Recording) write head uses the energy of optical-laser generated plasmons in a plasmon antenna to locally heat a magnetic recording medium and reduce its coercivity and magnetic anisotropy. To enable the TAMR head to operate most effectively, the maximum gradient of the magnetic recording field should be concentrated in the small region being heated. Typically this does not occur because the spot being heated by the antenna is offset from the position at which the magnetic pole concentrates its magnetic field. The present invention incorporates a magnetic core within a plasmon antenna, so the antenna effectively becomes an extension of the magnetic pole and produces a magnetic field whose maximum gradient overlaps the region being heated by edge plasmons being generated in a conducting layer surrounding the antenna's magnetic core.

Wireless power transmission for implantable devices using inductive component of closed magnetic circuit

Abstract: A mechanically flexible wireless power transmission module for implantable systems with enhanced transmission efficiency using a closed magnetic circuit (CMC) is presented. The CMC-based power transmission module consists of a primary inductor for power transmission and a secondary inductor for power reception. The CMC is fabricated by electroplating the Permalloy, composed of 81% nickel and 19% iron, on the inductors. For an open magnetic circuit (OMC), the measured power transmission efficiency was 13% when the distance between the two inductors was 5%mm. However, the efficiency was enhanced to 27% and 34% for the proposed two types of CMCs.

Finite Element Three-Phase Transformer Modeling Taking Into Account a Vector Hysteresis Model

Abstract: In this work an approach for modeling a transformer core taking into account magnetic hysteresis is presented. For this purpose, the inverse vector Jiles-Atherton hysteresis model is incorporated in a 2D finite element code. This model allows writing naturally the differential reluctivity tensor which can be directly used in the magnetic field equations. A three-phase transformer is modeled. The excitation characteristics of the transformer, as well as hysteresis loops at specific points, are presented. The proposed model was verified with obtained experimental data.

Antenna coil and antenna device

Abstract: An antenna coil is obtained by winding a flexible substrate around a magnetic core. Conductors are provided on the flexible substrate, whereby a first coil portion and a second coil portion are provided on either side of the magnetic core except for in a middle portion. A non-winding portion including no conductors is provided between the first coil portion and the second coil portion on a main surface of the magnetic core.

Compact, two stage, zero flux electronically compensated current or voltage transducer employing dual magnetic cores having substantially dissimilar magnetic characteristics

Abstract: A device for sensing electrical current or voltage in an electrical distribution system using an actively compensated current ratio transformer that includes a first magnetic core having a first permeability and a second magnetic core having a second permeability higher than the first permeability. A primary winding having P turns is coupled with the first and second magnetic cores, a measurement winding having M turns is coupled with the first and second magnetic cores so that current in the primary winding induces current in the measurement winding, and a sense winding having S turns is coupled with the second magnetic core. An amplifier coupled to the sense winding receives a voltage developed across the sense winding and produces a compensation current in response to the received voltage. The amplifier has an output coupled to the sense winding to feed the compensation current through the sense winding to reduce the voltage developed across the sense winding voltage to substantially zero. A burden resistor is coupled to the measurement winding and the sense winding for receiving the sum of the current induced in the measurement winding and the compensation current.

Controlled synthesis of core/shell magnetic iron oxide/carbon systems via a self-template method

Abstract: A sol-gel assembly process was developed for the synthesis of magnetic core/carbon shell materials with porous networks. Fe(CO)5 was assembled into the pore channels of mesoporous silicavia a sol-gel method at 18 °C, by using the block copolymer F127 as the template and Fe(CO)5 as an additional precursor. At this temperature, the magnetic precursor Fe(CO)5 was pre-organized into hydrophobic cores of micelles by self-assembly of F127. In the subsequent carbonization of the assembly under an Ar atmosphere, Fe(CO)5 transformed into magnetic nanoparticles and surfactant F127 transferred into carbon shells enveloping the magnetic nanoparticles, forming magnetic iron oxide core/carbon shell structures. The removal of the silica with 5% HF acid resulted in the core/shell nanoporous composite. The obtained system demonstrates a saturation magnetic value of 3 emu g−1 as well as a high surface area (98 cm2 g−1) and pore volume (0.21 m3 g−1), which would benefit its potential applications as adsorbents and catalysts, or applications in targeted drug delivery systems. This facile strategy would provide an efficient approach for tailoring core/shell porous materials with desired functionalities and structures by adjusting precursors and structure-directing agents.

Small-Resistance and High-Quality-Factor Magnetic Integrated Inductors on PCB

Abstract: We have designed and fabricated both single-coil and parallel-coil magnetic integrated inductors with extremely small resistances and high quality factors on an 8-in-round printed circuit board (PCB) substrate for microprocessor power delivery applications. The dc resistances of these inductors are less than 12 mOmega. Soft magnetic material CoFeHfO was successfully integrated into the inductor fabrication to increase the inductance. The quality factors are more than 80 in a frequency range of 1.5-2 GHz for air-core inductors and more than 23 in a range of 200-300 MHz for magnetic inductors. The net inductance improvement of the magnetic inductor over air-core inductor is about 12%, which could be further enhanced with a thicker magnetic core, according to our theoretic calculation and HFSS simulation. We also characterized the permeability spectra of CoFeHfO material on the PCB substrate, simulated the high-frequency performance of the magnetic integrated inductor by HFSS, and, for the first time, reached a good agreement with the experimental data. The experimental and simulation results of the magnetic inductors as compared to those of the air-core inductors point out the future direction to further optimize magnetic integrated inductors.

Power converter magnetic devices

Abstract: Magnetic structures for use in components utilized in switched mode power supplies can be combined to provide space and cost savings. Portions of magnetic cores can be utilized to form more than one component and/or separate magnetic cores can be combined into a single core. Further, a layer of material that has a higher flux density saturation point than the core and that is lower in permeability than the core (but higher than that of air) can be placed adjacent to the air gap in a core to decrease the magnetic flux passing through the vicinity surrounding the core so as to reduce EMI. A differential-mode choke and a separate common-mode choke can be combined onto a single core. An extra leg for a PFC choke core can be added to an isolation transformer core to form a single combined core. A pair of E-E core structures can be combined into a single core structure such as could be used to combine a pair of separate PFC chokes into an integrated pair of PFC chokes.

Finite-Element Modeling of Saturation Effect Excited by Differential-Mode Current in a Common-Mode Choke

Abstract: This letter presents a method for modeling of the differential-mode (DM) current-excited core saturation effect in a common-mode (CM) choke. This is performed by finite-element analysis (FEA) and computation of 3-D magnetic field distribution in the magnetic core of CM choke. The simulation result shows that the DM-current-excited flux is not canceled completely in the core, and some leakage flux remains, which increases the flux density in the core and gives rise to partial saturation of the core. In order to determine the CM inductance of the CM choke when its core is partially saturated by DM current excitation, the letter then presents a method to calculate the dynamic inductance at the operation point of the CM choke with assistance of FEA. Finally, an experiment for CM inductance measurement of a prototype of CM choke under DM DC bias is carried out to validate the method of dynamic inductance calculation.