Showing papers on "Magnetic core published in 1996"

Resonant converter with controlled inductor

Abstract: An LC resonant circuit for a resonant converter includes a resonant capacitor and an inductor coupled to a fixed frequency AC supply. A controlled inductor in parallel with the resonant capacitor is controlled by a DC current to vary its inductance. The controlled inductor comprises a magnetic core having one or more power windings, and a control winding wound on the core. The DC current in the control winding produces core flux which effects core permeability. The controlled inductor has the effect of changing the capacitor impedance and thus influences the converter output. Multiple, independently controlled and regulated outputs may be driven by one power switching stage.

Compact and efficient transformerless power conversion system

Abstract: The power conversion system (PCS) developed by the author is a new technology that efficiently transforms power between AC and DC. The conversion process permits the input voltage level to be stepped up or down without the use of magnetic core transformers. The transformation is accomplished using solid state switching devices, capacitors, air-core inductors and an intelligent control system. The technology is based on the property of resonance charging, thereby permitting the use of self commutating switches. The current through the switches, being sinusoidal in nature, has a low dI/dt. This permits the use of slower, less expensive thyristors, similar to those used in high voltage phase control applications. Using these components, a highly efficient inverter can be constructed for a variety of large utility applications.

Radio-frequency accelerating system and ring type accelerator provided with the same

Abstract: In a radio-frequency accelerating system, a loop antenna is coupled with at least one of a plurality of magnetic core groups each including a plurality of magnetic cores or with at least one of the plurality of magnetic cores, and an impedance adjusting means is connected to the loop antenna. A relatively low voltage is applied to the impedance adjusting means. Therefore, the impedance adjusting means may be a circuit element having a low withstand voltage and hence the radio-frequency accelerating system can be formed to have a small construction.

Experimental evaluation of the influence of DC-premagnetization on the properties of power electronic ferrites

Abstract: In many power electronic applications, ferrite cores of magnetic components are biased with a DC or low-frequency premagnetization. Usually however, the influence of the bias on the losses and permeability is not considered in the component design. This paper describes a precise measurement setup to determine the power losses and the magnetization curve of premagnetized ferrites. The measurements on typical ferrites of two major manufacturers prove that the influence of a DC-bias on the material properties cannot be neglected.

A novel soft-switched PWM inverter for AC motor drives

Abstract: A novel soft-switched inverter topology is derived from the passively clamped quasi-resonant link (PCQRL) circuit. By introducing magnetic coupling between the two resonant inductors, the number of auxiliary switches can be reduced from two to one, and only a single magnetic core is required for the resonant DC link. An analysis of this novel PCQRL topology with coupled inductors is presented to reveal the various soft-switching characteristics. In comparison with the conventional passively clamped, continuously resonant DC link inverter, this soft-switched inverter can reduce voltage stresses from more than 2 per unit (pu) to 1.1-1.3 pu. It can also provide soft-switched pulse-width modulated (PWM) operation. Simulations and experiments are performed to backup the analysis.

A comparison of two micromachined inductors (bar- and meander-type) for fully integrated boost DC/DC power converters

Abstract: Two micromachined integrated inductors (bar- and meander-type) are realized on a silicon wafer by using modified, IC-compatible, multilevel metallization techniques. Efforts are made to minimize both the coil resistance and the magnetic reluctance by using thick electroplated conductors, cores, and vias. In the bar-type inductor, a 25-/spl mu/m thick nickel-iron permalloy magnetic core bar is wrapped with 30-/spl mu/m thick multilevel copper conductor lines. For an inductor size of 4 mm/spl times/1.0 mm/spl times/110 /spl mu/m thickness having 33 turns of multilevel coils, the achieved specific inductance is approximately 30 nH/mm/sup 2/ at 1 MHz. In the meander-type inductor, the roles of conductor wire and magnetic core are switched, i.e., a magnetic core is wrapped around a conductor wire. This inductor size is 4 mm/spl times/1.0 mm/spl times/130 /spl mu/m and consists of 30 turns of a 35-/spl mu/m thick nickel-iron permalloy magnetic core around a 10-/spl mu/m thick sputtered aluminum conductor lines. A specific inductance of 35 nH/mm/sup 2/ is achieved at a frequency of 1 MHz. Using these two inductors, switched DC/DC boost converters are demonstrated in a hybrid fashion. The obtained maximum output voltage is approximately double an input voltage of 3 V at switching frequencies of 300 kHz and a duty cycle of 50% for both inductors, demonstrating the usefulness of these integrated planar inductors.

A generalized dynamic circuit model of magnetic cores for low- and high-frequency applications. I. Theoretical calculation of the equivalent core loss resistance

Abstract: This paper describes the theoretical calculation of the equivalent core loss resistance for a dynamic magnetic core loss model. The equivalent core loss resistance incorporates the effects of both the classical eddy current and anomalous losses. Derivation of a generalized nonlinear core loss resistance expression is presented. This new equivalent core loss resistance can be incorporated into a generalized dynamic magnetic core circuit model suitable for low and high frequency applications.

Magnetic flaw detection apparatus using an E-shaped magnetic sensor and high-pass filter

Abstract: A magnetic sensor in which magnetic leakage flaw detection can be performed with high accuracy without so reducing liftoff, and a magnetic flaw detection method and apparatus to which the magnetic sensor is applied. The magnetic sensor 50 for detecting magnetic flux generated due to a defect portion of a magnetized subject to be inspected has an E-shaped core 51 having magnetic poles (51a, 51b and 51c) arranged in the neighborhood of a steel plate (13) to be inspected, and a search coil (52) wound on the center magnetic pole (51b) of the E-shaped core for detecting the magnetic flux. An external magnetic field floating in the circumference of the E-shaped magnetic sensor passes through the opposite side magnetic poles (51a and 51c) of the E-shaped core 51 but does not cross the center magnetic pole (51b) of the E-shaped core. Accordingly, no voltage due to the external magnetic field is induced in the search coil (52), so that only the magnetic flux caused by the defect portion is detected. Accordingly, the directivity with respect to the external magnetic field is improved so that the generation of a noise voltage due to the external magnetic field is suppressed and S/N at the time of flaw detection is improved.

A generalized dynamic circuit model of magnetic cores for low- and high-frequency applications. II. Circuit model formulation and implementation

Abstract: This paper describes the formulation and implementation of a generalized dynamic magnetic core circuit model suitable for both low- and high-frequency applications. The behavior of magnetic cores with any arbitrary flux waveforms is modeled by a simple ladder network consisting of nonlinear inductors and resistors. The nonlinear B-H loop and the hysteresis loss are incorporated in distributed nonideal inductors and calculated by the Preisach scalar model of magnetic hysteresis. The eddy current and anomalous losses are accounted for by the generalized nonlinear equivalent resistors reported in Part I of the paper. The transmission line modeling method is employed to solve the nonlinear state equations. Numerical aspects and software implementation of the model are discussed. The generalized model has been verified by simulations and measurements at both low- and high-frequency operations.

Particles having a magnetic core and outer glass layer for separating biological material

Abstract: Magnetic glass particles are prepared containing a magnetic core coated with a glass layer having a substantially pore-free glass surface. The particles are used for separating biological material such as nucleic acids. A preferred process of preparing the particles is by forming a mixture of magnetic cores with a sol formed from an alcohol and a metal alkoxide, spray-drying the mixture to coat the cores with a layer of gelled sol, and heating the coated cores to obtain the magnetic glass particles. Preferably, the particles have an average particle size of less than 100 μm and any pores of the glass surface have a diameter of less than 10 nm. The magnetic core may be a composite material containing a mica core and magnetite particles immobilized on the mica core, and the glass layer may contain boron oxide. Magnetic core materials include magnetite (Fe3O4) and Fe2O3. In using the magnetic glass particles to separate a biological material, the particles are contacted with a fluid containing the biological material such that the biological material binds to the glass surface, and the bound biological material is separated from the fluid such as by using a magnetic field. Before applying a magnetic field, the magnetic particles may sediment when contacted with the biological material.

Mathematical and Numerical Modelling in Electrical Engineering Theory and Applications

Abstract: Glossary of Symbols. Foreword. 1. Introduction. 2. Mathematical Modelling of Physical Phenomena. 3. Mathematical Background. 4. Finite Elements. 5. Conjugate Gradients. 6. Magnetic Potential of Transformer Window. 7. Calculation of Nonlinear Stationary Magnetic Fields. 8. Steady-State Radiation Heat Transfer Problem. 9. Nonlinear Anisotropic Heat Conduction in a Transformer Magnetic Core. 10. Stationary Semiconductor Equations. 11. Nonstationary Heat Conduction in a Stator. 12. The Time-Harmonic Maxwell Equations. 13. Approximation of the Maxwell Equations in Anisotropic Inhomogeneous Media. 14. Methods for Optimal Shape Design of Electrical Devices. References. Author index. Subject index.

High-resolution micro-fluxgate sensing elements using closely coupled coil structures

Abstract: This paper describes high-resolution micro-fluxgate magnetic sensing elements using magnetic thin films and closely coupled excitation and pick-up coils based on a solenoid-shaped coil structure. In order to improve the sensitivity of the sensing element, the optimal coupling structure between excitation and pick-up coils, and the formation method of permalloy magnetic films are investigated. The closely coupled coil structure allows the magnetic core to be excited in an optimal condition with reduced excitation current. The addition of indium to the permalloy plating bath greatly reduces the degradation of the magnetic core due to the thermal treatment process. The sensitivity of the fabricated sensing element is measured to be 2700 VT −1 at an excitation frequency of 3 MHz. The noise level, or resolution in d.c. to 10 Hz bandwidth is measured to be about 40 nT p−p .

Integrated-magnetic filter having a lossy shunt

Abstract: A two-winding, integrated-magnetic EMI filter provides damped common-mode and differential-mode inductances. The preferred embodiment of the filter has a magnetic core structure that incorporates a high-permeability C-core, a high-permeability I-core, and a low-permeability, lossy shunt. The three core pieces are assembled so as to form a structure that, similar to an E-I configuration, has two winding windows. The loss in the shunt aids in dissipating noise and it diminishes the effects of unwanted parasitic resonances by providing damping for the differential-mode inductance. Damping for the common-mode inductance is provided by losses in the C and I core pieces. Varying the reluctance of the shunt allows the differential-mode inductance to be adjusted separately from the common-mode inductance in order to tune the filter to remove desired noise frequencies. Another embodiment of the invention incorporates a high-permeability toroid core and a low-permeability, lossy shunt.

Two-phase permanent-magnet electric rotating machine

Abstract: A three-phase permanent-magnet electric rotating machine having necessary performance which can be realized easily at a low cost, wherein a stator includes a stator iron core having a disc portion and 3n magnetic poles formed so as to be erected at right angles from an outer circumference of the disc portion, and excitation windings mounted on the magnetic poles so as to have a predetermined width in the axial direction, and wherein a rotor is constituted by permanent magnets magnetized into N and S poles arranged alternately in the direction of rotation of the rotor and the rotor is supported so as to face the top ends of the respective magnetic poles of the stator through a predetermined air gap. In this case, the number n is an integer not smaller than 1. Alternatively, n may be selected to be an even number not smaller than 2 so that the excitation windings may be mounted on every other one of the magnetic poles. Preferably, a plurality of magnetic teeth of a predetermined shape may be formed on each of the top end portions of the magnetic poles formed in the stator iron core. Further preferably, excitation windings are mounted on first and second stator iron cores which are doubly arranged so as to be concentric with each other to thereby form a stator provided with a double structure of the magnetic poles.

Antenna for transponder and transponder

Abstract: An antenna for a transponder comprises a magnetic core composed of layered amorphous metallic thin plates or composite plates of soft magnetic flakes and a synthetic resin, and a coil wound on the magnetic core. A transponder comprises two antennas set forth above, and a spiral antenna.

Choke coil for eliminating common mode noise and normal mode noise

Abstract: There is provided a choke coil having a sufficient noise eliminating effect against common mode and normal mode noises. The choke coil has two bobbins, a pair of windings wound around the respective bobbins, first and second magnetic cores which are each inserted in cylindrical body portions of the bobbins at one side thereof, and a support member for supporting the cores. The first magnetic core is in the form of the character B and made of a material having lower permeability. The second magnetic core is in the form of the character D and made of a material having higher permeability. A predetermined gap is maintained between the cores by a spacer provided on the top surface of the support member.

Cylindrical Hall device

Abstract: We present a new magnetic sensor based on the Hall effect, sensitive to a cylindrical magnetic field. Such a field is found around a wire carrying a current or under the gap between magnetic concentrators. Compared to traditional (plate-like) Hall devices, the geometry of the cylindrical Hall device allows lower bias voltage and lower offset to be achieved. The combination of this new device with integrated magnetic concentrators results in a very high detectivity magnetic sensor.

Toroidal thin film head

Abstract: A low-noise toroidal thin film head ("TFH") device has low coil resistance and inductance, especially suitable for very high magnetic recording areal densities and channel frequencies. The length of a toroidal coil turn is only about 20-30% that of the length of an average turn in the conventional planar spiral coil design. This allows either reduction of the device thermal noise (by about 6 dB) and/or increase of the device operational frequency bandwidth (by a factor of 3-5). The toroidal coil coupling efficiency between each turn and the magnetic core is practically 100%, thereby improving the write and read-back efficiencies. In one embodiment a non-via large back-closure contact area is provided between the bottom and top magnetic poles along their entire back-side width, and all other open branches and loose ends in the magnetic circuit are eliminated. The magnetic core has a gradual, smooth toroidal (or a horse-shoe) shape with no loose ends, nooks, crevices, or sharp corners. The larger back-closure contact area decreases the magnetic core reluctance and improves the device efficiency. Utilization of a soft non-magnetic seed-layer, such as gold, eliminates interference noise due to the conventional magnetic (NiFe) seed-layer. Slight mechanical texturing (scratching) of the seed-layer along the intended easy axis helps to define and induce strong magnetic uniaxial anisotropy in the plated magnetic poles. All these features facilitate significant reduction of Barkhausen and other sources of device noise. Embodiments include conventional TFH's, Planar TFH's, Pinched-Gap TFH's, and various versions of Magnetoresistive (MR) TFH's.

A simple method to determine dynamic hysteresis loops of soft magnetic materials

Abstract: An approach to plotting hysteresis curves of soft magnetic materials using a personal computer assisted measuring system is presented. The resulting hysteresis curves provide enough detail to allow determination of the parameters required for a simulation with PSPICE (Jiles-Atherton model) or the Hodgdon/Carpenter model. The magnetic core loss for different materials and core shapes can be determined at frequencies up to 200 kHz and at voltages up to 500 V.

Method for realizing magnetic circuits in an integrated circuit

Abstract: Inductive structures make highly efficient use of the magnetic flux generd, and are consistent with integrated circuit manufacturing techniques. The structures include electrically conductive layers and interconnecting conductor filled vias to define a helical winding surrounding a closed magnetic core. The magnetic core may also be formed by semiconductor manufacturing techinuqes. A method of making the structures on a semiconductor substrate concurrently with the formation of the integrated circuit itself is also disclosed.

A comparison of micromachined inductors with different magnetic core materials

Abstract: Two integrated inductors with different electroplated cores, permalloy (Ni(80%)-Fe(20%)) and orthonol (Ni(50%)-Fe(50%)) cores, are designed, fabricated, tested, and compared in order to reach optimum designs for integrated inductors and transformers. These integrated inductors were realized on a silicon wafer by using micromachining techniques to fabricate wrapped coils wound around a 'bar' of high permeability core material. These devices have high current capability (up to 2A steady DC current) and are suitable for application in DC/DC converters. The total inductor size is 4 mm/spl times/1.0 mm/spl times/0.13 mm having 30 turns of multilevel copper coils (40 /spl mu/m thick). Each inductor has nominally identical geometry and core thickness (15 /spl mu/m), implying that differences in performance would be due entirely to differences in core behavior. The permalloy core inductor has a slightly higher inductance than the orthonol core inductor. However, the DC saturation current of the orthonol core inductor is much higher than the permalloy core inductor. In many high power applications, high saturation flux density is more important than permeability, because DC saturation current is proportional to saturation flux density. The measured behavior confirms on in-situ electroplated samples and fabricated components the trends expected from bulk properties of these nickel-iron alloys.

Three-dimensional integrated circuit inductor

Abstract: PROBLEM TO BE SOLVED: To increase an inductor and reduce an area and a volume by a method, wherein there is provided the inductor in which a plurality of first and second conductor wires and a conductive via are positioned relatively, in order to form successive conductive coils around a magnetic core. SOLUTION: In an inductor, a plurality of first planar conductor wires 10 are separated from a second pair of planar conductor wires 70 by a magnetic core 40. Both the pairs of planar conductor wires are electrically connected to each other by a conductive via 60, and a loop encircling the magnetic core 40 is formed. Further, an insulation layer in which the magnetic core 40 is respectively separated from the conductive wires 10, 70 is formed. Here, the magnetic core 40 is selected from a group containing a Permalloy (R) and a ferromagnetic body and is disposed horizontally on a substrate. Further, first and second conductor wires 10, 70 have an 'L'-shaped configuration, respectively.

Fluorescent lamp ballast with current feedback using a dual-function magnetic device

Abstract: A fluorescent lamp ballast utilizes a single a transformer for providing both tank inductance and current mode feedback to the ballast driver circuitry. The transformer has an "EE" core with inductor windings on the center legs and gate windings on one of the outer legs. The center leg is gapped to avoid magnetic core saturation and to adjust inductance to a desired value. Coupling can be adjusted further by gapping one or the other of the outer legs.

Thin film magnetic head with differing saturation magnetic flux density films and spacer between floating surface and coil patterns

Abstract: A thin film magnetic head includes lower and upper magnetic cores, an upper magnetic core distal end portion, a magnetic gap layer, coil layers, and insulating layers. The lower magnetic core has a distal end portion facing a magnetic head floating surface. The upper magnetic core distal end portion opposes the distal end portion of the lower magnetic core through a magnetic gap. The lower magnetic core and the upper magnetic head distal end portion are heated at a temperature T1 to have a saturation magnetic flux density BS1. The upper magnetic core magnetically connects the lower magnetic core and the upper magnetic core distal end portion to constitute a magnetic core and is heated at a temperature T2 to have a saturation magnetic flux density BS2. Note that T2

Composite magnetic material and product for eliminating electromagnetic interference

Abstract: A composite magnetic material is provided for use as an electromagnetic interference suppressor member for effectively suppressing an electromagnetic interference within a high frequency apparatus including a mobile communication terminal. The composite magnetic material consists essentially of a soft magnetic powder and an organic binder and is electrically non-conductive and has at least two magnetic resonances caused by at lest two anisotropic magnetic fields (Hk). In the composite magnetic material, the anisotropic magnetic fields (Hk) are different in strength from each other.

High-Frequency Dimensional Effects in Ferrite-Core Magnetic Devices

Abstract: (ABSTRACT) MnZn ferrites are widely used in power electronics applications where the switching frequency is in the range of several tens of kilohertz to a megahertz. In this range of frequencies the combination of relatively high permeability and relatively low conductivity found in MnZn ferrite helps to minimize the size of magnetic devices while maintaining high efficiency. The continuing improvement in semiconductor switches and circuit topologies has led to use of high-frequency switching circuits at ever increasing power levels. The magnetic devices for these high-power, high-frequency circuits require magnetic CORES that are significantly larger than standard ferrite-core devices used at lower power levels. Often such large ferrite cores must be custom designed, and at present this custom design is based on available material information without regard for the physical size of the structure. This thesis examines the issues encountered in the use of larger MnZn ferrite cores for high-frequency, high-power applications. The two main issues of concern are the increased power dissipation due to induced currents in the structure and the change in inductance that results as the flux within the core is redistributed at higher frequencies. In order to model these problems using either numerical or analytical methods requires a reliable and complete set of material information. A significant portion of this work is devoted to methods for acquiring such material information since such information is not generally available from the manufacturers. Once the material constants required for the analysis are determined, they are used in both closed-form and numerical model to illustrate that large ferrite cores suffer significant increases in loss and significant decreases in inductance for frequencies as low as several hundred kilohertz. The separate impacts of the electrical and magnetic losses in the core are illustrated through the use of linear finite element analyses of several example core structures. The device impedances calculated using the FEA tools show fair agreement with measurement. An analysis of gapped structures and segmented cross-sections shows that these design options can reduce the severity of the dimensional problems for some designs. Acknowledgments I would like to express my sincere appreciation to my advisor, Dr. Fred C. Lee, for the support and encouragement he provided throughout the course of this research. His extensive experience in the power electronics field has been a tremendous aid in focusing this work on the practical issues that face designers. I would also like to thank Dr. …

Low profile coupled inductors and integrated magnetics

Abstract: In a dc-to-dc converter, input and output inductors loosely coupled and isolation transformer windings closely coupled are implemented on a UI magnetic core in such a manner as to satisfy a zero-ripple condition k 1 =n of current in the output inductor, where n is a turns ratio of the loosely coupled input and output inductors, and both inductors are chosen to have the same number of turns, and that number is an integer such that the value of the coupling coefficient k 1 required to satisfy the zero-ripple condition is one achieved by modeling of core leakages instead of by adjusting the turns ratio n, thus making it feasible to implement the coupled inductors, and the transformer windings as well, in a single UI core and modeling the core losses by configuring the core. It is then possible to implement the core legs that are long enough to just accommodate a printed circuit board on which all of the windings are manufactured for a low profile package with both inductor windings on the same leg opposite the transformer windings. If the input inductor is on the same leg of the core as the transformer windings, adding an external inductor in series with the input inductor will filter any ripple current coupled into it by the transformer flux.

Distribution of two-dimensional magnetic properties in three-phase induction motor model core

Abstract: This paper presents the result for the local magnetic properties in a three-phase induction motor model core. The relationship between the magnetic field strength vector H and the magnetic flux density vector B, is obtained through measurements with a special sensor, which utilizes the H-coil method and the double needle method. As a result, the relationship between the H-vector and the B-vector is made clear, and it is shown that the local properties in an actual core are vectorial in nature.

Determination of anisotropic equivalent conductivity of laminated cores for numerical computation

Abstract: For the accurate electromagnetic simulation of devices containing laminated conductive cores including eddy current effects it often turns out that the full discretization of each sheet of a laminated core and the space between two sheets is computationally costly. The factors considered in reducing the effort refer to the finite integration method. By means of an analytical model the equivalent conductivity of a laminated iron core in the direction normal to the sheets is determined. The applicability of the model is demonstrated by comparison of measured shading ring sensor data and numerical results, performed by the W3 module of the program package MAFIA.

An energy-based design criterion for magnetic microactuators

Abstract: Magnetic actuators can be divided into two types: those in which motion changes the gap separation (type I) and those in which motion changes the gap overlap area but not the gap separation (type II). In conventional magnetic actuators of both types, it is assumed that most of the magnetic energy is stored in the gap due to the large reluctance of the gap compared with the negligibly small reluctance of the magnetic core. However, in magnetic microactuators, the fabrication limitations on the achievable cross-sectional area of the magnetic core as well as the finite core permeability increase the core reluctance to the point that this assumption may no longer be valid. In this case, the magnetic energy is distributed in both the gap and the magnetic core, in which the energy distribution is in proportion to the reluctance of the gap and the reluctance of the core respectively. Using an elementary structure of a magnetic actuator, it is shown that for type I microactuators, when the initial gap of the actuator is fixed (e.g., determining the stroke of the actuator), the generated magnetic force has maximum value when the gap overlap area is designed such that the reluctance of the gap is equal to the reluctance of the magnetic core (i.e., ). For type II actuators, the initial overlap area of the actuator is fixed (determining the stroke); therefore the generated magnetic force has a maximum value when the gap separation is designed such that the above equality holds. This paper details both analytical and finite element method (FEM) analysis confirmation for type I actuators. Extension to type II actuators is straightforward.