Showing papers on "Magnetic core published in 1993"

A high frequency transformer model for the EMTP

Abstract: A model to simulate the high-frequency behavior of a power transformer is presented This model is based on the frequency characteristics of the transformer admittance matrix between its terminals over a given range of frequencies The transformer admittance characteristics can be obtained from measurements or from detailed internal models based on the physical layout of the transformer The elements of the nodal admittance matrix are approximated with rational functions consisting of real as well as complex conjugate poles and zeroes These approximations are realized in the form of an RLC network in a format suitable for direct use with the ElectroMagnetics Transient Program (EMTP) The high-frequency transformer model can be used as a stand-alone linear model or as an add-on module of a more comprehensive model where iron core nonlinearities are represented in detail >

Electromagnetic flow meter

Abstract: An electromagnetic flow meter for measuring the flow of blood through a conduit. Flow rate is measured by applying an electromagnetic field around the conduit, with the moving electrolytic blood inducing a current that is sensed by electrodes. The flow meter includes a substantially "E"-shaped magnetic core structure as well as an "E"-shaped hinged cover piece for defining a complete flux loop. In the circuitry, a floating ground arrangement is provided for enhancing the stability and sensitivity of the meter and to ensure appropriate patient isolation. A strong magnetic field, covering the sensing region and with little flux leakage, is alternately switched in polarity. The magnetic coil driver circuit employs an arrangement of switches for facilitating very fast polarity reversal. A two-level current source in the coil current driver greatly enhances the meter's efficiency and power dissipation characteristics. Extensive provisions, both electrical and mechanical, are made to reduce the effects of capacitive coupling, spurious induced currents, electromagnetic interference, and susceptibility to noise and external magnetic fields. A dual gated sample hold circuit samples the sensor signal during steady intervals. A second dual sample-and-hold averaging circuit minimizes the effects of base-line drift in the sense signal and low-frequency noise in the amplifier stage. The flow meter includes a two section error detection circuit which generates an error signal either when the flow signal exceeds power supply limits or when the rate of change of the flow signal exceeds a clinically reasonable rate.

Time domain modeling of eddy current effects for transformer transients

Abstract: Eddy current effects are included in a model of a power transformer for the study of electromagnetic transients. Existing analytical formulae for the calculation of losses in the windings are evaluated. Various equivalent circuits are fitted to represent in the time domain the damping produced by eddy currents in the windings. A frequency dependent model is derived for the iron core, based on the physical distribution of losses and magnetization effects. The parameters of this model are obtained by optimal discretization of the laminations. Simulation show the effects of eddy current in the damping of transients. >

On modelling iron core nonlinearities

Abstract: An algorithm is presented for the computation of the saturation characteristics of transformer iron cores based on supplied conventional V/sub rms/-I/sub rms/ curves and no-load losses at rated frequency. Laboratory measurements on a steel sample were carried out. It is shown that the iron core losses are a nonlinear function of the applied voltage. Taking these losses into account improves the nonlinear flux-current characteristics. >

A fully integrated surface micromachined magnetic microactuator with a multilevel meander magnetic core

Abstract: A fully integrated magnetic microactuator using surface micromachining techniques is presented. To achieve this device, low-resistance meander conductors located in a single plane were interwoven with multilevel meander magnetic cores. This 'wrapped' solenoid (with the core wrapped around the conductor) was fabricated in a fully integrated fashion. A magnetic microactuator was realized by incorporating a surface micromachined nickel-iron cantilever beam as part of the magnetic circuit of the core. The nickel-iron cantilever beam was 2.5 mu m thick, 25 mu m wide, and 780 mu m long, and the magnetic circuit contained seventeen turns of meander-type solenoid coils. Cantilever beam tip deflection of 6 mu m in the vertical direction was achieved when a DC voltage less than 1 V (and resulting drive current of 800 mA) was applied to the coils. This fully integrated multilevel topology offers advantages in a variety of micromagnetic applications, where actuators can be fabricated on the same substrate with an integrated circuit and actuated with low voltages. >

Magnetic structure and magnetic head using the same

Abstract: A magnetic structure and a magnetic head capable of reducing the size thereof and raising the degree of integration is disclosed which has a structure including a substrate having a plurality of ridge-like projections each having slant side-surfaces; the substrate having thereon: a first conductive passage consisting of a plurality of parallel and conductive passages each of which is formed on opposing slant surfaces of adjacent projections and on the bottom surface between the slant surfaces; a first insulating layer stacked on the first conductive passage and the substrate; a magnetic core made of magnetic material enclosed in a groove-shape recess formed by the adjacent projections and the bottom surface; a second insulating layer stacked on the magnetic core; and a second conductive passage formed on the second insulating layer to sequentially connect ends of the first conductive passage to form a helical coil, wherein the magnetic core is separated by the projection so that a plurality of coils are integrally formed on the same substrate.

Methods for fabrication of thin film inductors, inductor networks and integration with other passive and active devices

Abstract: The fabrication of thin film inductors on a substrate, which may include thin film resistors, thin film capacitors, and semiconductor devices. In one embodiment an inductor is fabricated initially on a substrate and then integrated with other devices subsequently formed on the substrate. In this embodiment, process steps used to fabricate such other devices utilize temperatures sufficiently low to prevent damaging or destroying the characteristics of the inductor. In another embodiment the fabrication of an inductor is achieved through photoresist masking and plating techniques. In alternative embodiments, fabrication of an inductor is achieved by sputtering, photoresist processes and etching/ion-milling techniques. A combination of various individual process steps from various embodiments are suitable for use to fabricate the individual layers to achieve a structure of this invention. The inductor fabricated in accordance with this invention is connected to other passive or active components through metal interconnections in order to improve the frequency performance of the inductor. In certain embodiments, parasitic capacitance of the inductor is significantly reduced by fabricating inductor coils on dielectric bridges. In certain embodiments, a magnetic core of ferromagnetic material is used to improve the performance of the inductor at frequencies below about 100 MHz.

Moving coil actuator utilizing flux-focused interleaved magnetic circuit

Abstract: A cylindrically-symmetrical moving coil linear actuator utilizes axially-magnetized cylindrical magnets to provide flux-focused interleaved magnetic circuits. The moving coil linear actuator includes a cylindrical shell that has a closed end and open end. A magnetic core is disposed within the shell to define an annular air gap between the shell and the core. The core includes a first set of axially-magnetized cylindrical permanent magnets having a first direction of magnetization and disposed in proximity to the closed end of the shell. A second set of axially-magnetized cylindrically permanent magnets has a second direction of magnetization which is opposite of the first direction of magnetization and is disposed in proximity to the open end of the shell. A first ferro-magnetic pole piece is disposed between the first set of magnets and the second set of magnets. A second ferro-magnetic pole piece is disposed between the second set of magnets and the open end of the shell. A moving coil assembly is disposed within the annular air gap. The coil assembly includes a non-magnetic coil carrier disposed within the air gap. A first coil winding is formed on the coil carrier in proximity to the first set of magnets and is wound to have a first polarity. A second coil winding is formed on the coil carrier in proximity to the second set of magnets and is wound to have a second polarity opposite to the first polarity such that the first and second coil windings are wound in series opposition.

A planar micromachined spiral inductor for integrated magnetic microactuator applications

Abstract: In this work, planar micromachined spiral inductive structures with relatively high inductance at low (Hz-kHz) frequencies are designed and fabricated for integrated magnetic microactuator applications and other purposes. Two types of multilayer micromachined inductors have been investigated. The first structure is a standard planar inductor spiral. To this structure we have added an electroplated high-permeability nickel-iron (Ni/Fe) magnetic core, which forms a central core to concentrate flux and completely encapsulates the windings, thus minimizing magnetic interference. For a typical 36-turn device 3 mm*3 mm in area, an inductance of approximately 20 mu H was obtained. The structure with a magnetic core has an inductance four to five times greater than a similar structure without a magnetic core. The specific inductance of our structure (inductance per unit area) is 2.2 mu H mm-2 at 10 kHz, which is one of the highest inductance values ever achieved in an integrated planar inductive component at low frequency. Since the structure of the spiral-type inductor is similar to those of planar magnetic microactuators such as micropumps, microvalves and microrelays, several low-frequency microactuator applications are expected to be possible with this inductor.

Discrete modelling of magnetic cores including hysteresis, eddy current and anomalous losses

Abstract: A discrete dynamic model of a magnetic core including hysteresis, eddy current and anomalous losses is proposed. It is suitable for thin laminations and features a simple formulation and fast calculation. The calculations and measurements of an annular ring under different waveforms are presented. The model can be extended to include cores with thick laminations.< >

A practical approach for magnetic core-loss characterization

Abstract: A practical approach for magnetic core loss characterization up to a few megahertz is presented. An error analysis is performed, revealing that corrections are needed to compensate for errors introduced by extra phase shifts inherent in a measurement setup, and by shunt parasitic capacitance associated with an inductive device under test. A simple technique is proposed to control the error, so as to satisfy prescribed tolerances. Extensive meassurements done on a TDK PC40 core yield results which support the analysis. Several sample cores are then characterized at a few megahertz. >

Design considerations for an inductive high T/sub c/ superconducting fault current limiter

Abstract: The authors investigate the design feasibility of an inductive iron core superconducting fault current limiter. A simplified thermo-electromagnetic analysis of the operating behavior of the fault current limiter is presented. This design is based on a high temperature superconducting shield surrounding a magnetic circuit with a primary winding generating an AC magnetic field. During fault conditions the field penetrates the core resulting in a large impedance, and thus a limitation of the fault current. In the analysis of this design, for voltages and currents up to 25 kV root-mean-square (RMS) and 2000 A RMS, it is shown that recuperation times for superconductors operating at liquid nitrogen temperatures are acceptable. >

Electromagnetic wave absorbing, surface modified magnetic particles for use in medical applications, and their method of production

Abstract: This invention describes an electromagnetic wave-absorbing surface modified magnetic particle for use in medical applications. The magnetic particles are coated with an amphipathic organic compound and an amphipathic vesicle forming lipid. These particles may be used in a method of treatment of cancer, as well as for the treatment of infectious disease. For cancer treatment the invention comprises providing a patient said coated particles, absorbing the coated particle intracellularly into the cancer cell, and subjecting the patient to an alternating electromagnetic field to inductively heat the magnetic core particle along with the cancer cells. The inductive heating of the magnetic core particle is then continued so as to achieve an increase in intracellular temperature which selectively kills the cancer cells.

Toroidal transformer with magnetic shunt

Abstract: A transformer or inductor is made by wrapping a magnetic core material about a toroid-like structure made up of one or more electrical windings. A ferroresonant transformer may be constructed by including a slotted washer between primary and secondary windings. By shorting one of the windings, the ferroresonant transformer can be made into a gapped inductor with the gap totally enclosed within the core.

Load characteristics of a spiral coil type thin film microtransformer

Abstract: A spiral coil type thin film microtransformer with a size of 2.4*3.1 mm/sup 2/ is fabricated using photolithography techniques for application in megahertz region switching regulators. An amorphous magnetic film of a multilayered CoNbZr/SiO/sub 2/ is used as a magnetic core. Load characteristics are measured at 10 MHz. A comparatively high efficiency of 67% and an acceptable excitation current of 25 mA are obtained, in spite of the small size of the microtransformer. >

Generalised transformer model based on the analysis of its magnetic core circuit

Abstract: In this paper a new transformer model, named ‘geometrical’, is developed, based on the circuit analysis of its magnetic core. The method is general and can be used for any type of multiphase multiwinding transformer. The model simulates the transformer as a set of coupled branches and can be incorporated into the widely known electromagnetic transients program (EMTP). A basic advantage of the model is that it can represent any asymmetry of the transformer magnetic circuit. As a study case, the model of an actual 280 MVA autotransformer is derived and used for the simulation of various steady state and transient conditions.

Floating magnetic head

Abstract: PURPOSE:To avoid danger of a head crash by inserting a piezoelectric element between a flexure and a slider CONSTITUTION:The flexure 14 is attached at a tip of a load beam 10 and the piezoelectric element 24 is provided on the flexure 14 and besides the slider 16 having a magnetic core 26 is attached to the piezoelectric element 24 and a magnetic head is composed At a stopped time of a rotation of a magnetic disk 22, a thickness of the piezoelectric element 24 is shrunk by a voltage impressed on the piezoelectric element 24 and the slider 16 is set at such a position that the slider is not allowed to contact with the magnetic disk 22 Also at an operating time, the magnetic disk 22 rotates at a regular speed and a voltage applied to the piezoelectric element 24 is suppressed by making it coincide with the generation of a high speed of air flow having a sufficient floating force Thus a contact sliding between the magnetic head and the magnetic disk 22 is eliminated and the damage is avoided

High-current high-precision openable-core AC and AC/DC current transformers

Abstract: The application of an electronic technique, which greatly increases the apparent permeability of the magnetic core of a current transformer, to high-current high-precision openable-core AC and AC/DC current transformers is described. The openable-core AC/DC current transformer can be used to measure accurately alternating current only or direct current only, or both alternating and direct currents simultaneously. Test results of two prototypes, 5000 A/5 A openable-core AC and 2000 A/1 A openable-core AC/DC current transformers, indicate an AC current measurement accuracy of both types of transformers on the order of 10 p.p.m. and a DC current transformer of better than 100 p.p.m. >

Partial gap magnetic core apparatus

Abstract: Potted wire-wound loop-core structures are based on cores which include partial gapped inductors or transformers with their reduced dependence of inductance on current during operation. Total enclosure of gaps by encircling core material is both magnetic and physical, thereby avoiding fringing magnetic fields as well as joint failure due to differential expansion of potting material.

Accurate AC measurements of standard resistors between 1 and 20 Hz

Abstract: A new version of an AC bridge for low-frequency (1-20-Hz) measurements of resistance ratios is designed. The bridge is based on an alternating current comparator operating at room temperature. The current comparator uses a single magnetic core of high permeability provided with a tuned detection winding enclosed in electrostatic and magnetic shields. Comparators with ratios equal to 1/1, 100/1, 64.53/1, and 129.06/1 were built, allowing the calibration of 1- and 100- Omega resistance standards in terms of the quantized Hall resistance. Ratio windings are formed by the series connection of strands from a set of individually guarded cables, a technique which provides low ratio error, not exceeding a few parts in 10/sup 9/ at 1 Hz. The AC behavior of 1- Omega DC standard resistors from different manufacturers is studied using this bridge. The time constant of these resistors is on the order of 1 mu s. If the frequency does not exceed 1 Hz, the AC/DC resistance difference due to eddy currents in the metallic can enclosing the resistors is lower than one part in 10/sup 9/. At 1 Hz, the AC-DC difference due to the Peltier effect is found to be less than a few parts in 10/sup 9/, with the exception of two particular resistors for which the difference was on the order of one part in 10/sup 8/. >

On a circuit theory approach to evaluate the stray capacitances of two coupled inductors

Abstract: This paper provides a method for evaluating three lumped equivalent capacitances which take into account the physical effects of stray capacitances in two coupled inductors. Capacitance evaluation is performed in two steps: (i) initially, the resistance and leakage inductance of each winding, together with the magnetic core equivalent impedance, are evaluated by means of discrete parameter estimation; (ii) successively, the three equivalent capacitances are evaluated by resolving a linear set of three algebraical equations after the natural oscillation frequencies of the two coupled inductors in experimental tests are determined. The paper provides both the definitions and the mathematical theory on which the method is based. The actual response of two coupled inductors was compared with the response of the identified model; tests showed a good correlation between them. >

Rotary armature and method of forming armature coil

Abstract: A central conductor portion of a coil is formed with a potbelly-shaped cross-sectional form and a flat-shaped face of an insulated coating film of the potbelly-shaped cross-sectional form coil is made thinner than an arc-shaped face of the insulated coating film of the potbelly-shaped cross-sectional form coil. An insulated coating wire having a circular-shaped cross-sectional form is formed to a coil having a potbelly-shaped cross-sectional form by rolling process at a normal temperature. A dead space in a slot is lessened and the magnetic resistance of a magnetic core is decreased, thereby a small size and a high output electric motor can be obtained. A method of forming a rotary armature coil having a high space factor in the slot can be attained.

Coin analyzer sensor configuration and system

Abstract: A coin analyzer system includes a coin detecting sensor having a body defined by a magnetic core with spaced apart sides to define there-between an air gap that is large enough to position any size coin which may be deposited. A coil that is magnetically coupled to the core generates a uniform magnetic flux through the air gap from one side to the other so that the positioning of the coin in the air gap is not critical. A return path is provided in the core for returning the magnetic flux to the one side from the other side and thereby completing the magnetic circuit. The arms surrounding the coin sensing region define facing surfaces which converge outwardly from the bite portion in order to produce a uniform magnetic circuit reluctance for all portions of the facing surfaces. The core may be divided into two core portions separated by a secondary air gap in the return path with a pair of coils provided, one magnetically coupled with each of the core portions. One coil may serve as a transmitting coil and the other as a receiving coil. Various detection circuits are disclosed for connection with the sensor coils in order to determine the denomination of the test coin.

Electromagnetic induction heater

Abstract: An induction coil is formed by winding an electrically conductive wire around an iron core, and at least one turn of a pipe of electrically conductive material is wound around the induction coil. The pipe is short-circuited at positions other than where the pipe is wound around the induction coil. An A.C. power source is connected to the induction and preheated fluid is supplied to the pipe to be further heated by induction within the pipe. Since the pipe has a large heat transfer area, efficient heat exchange can be obtained. This heating system is connected to a steam generator, which supplies the preheated fluid to it. The steam generator includes an induction coil of an electrically conductive wire wound on an iron core and a metal material forming a plate disposed on the iron core. The bottom surface of the metal material provides a magnetic flux path for the induction coil. An A.C. power source is connected to the induction coil to induce induction heating in the plate and thus to vaporize water or other fluid supplied to the steam generator into a space within the steam generator above the plate. The steam generator also includes a gas-liquid separator above the plate for separating steam from condensed droplets.

Study of thin film micro transformer with high operating frequency and coupling coefficient

Abstract: For miniaturization of magnetic devices, it is necessary to increase the operating frequencies. A thin film microinductor is studied in order to realize a high operating frequency and reduce iron losses. A thin film microtransformer is proposed, with high operating frequency achieved by the application of multilayered magnetic film to the core. The transformer is designed to be able to obtain a high coupling coefficient. The magnetic core is made of amorphous CoFeSiB film of CoFeSiB/SiO/sub 2/ multilayered film. The induced magnetic anisotropy is controlled so that the exciting direction of the coil is along the hard axis. The experimental transformers show that a multilayered core is useful to improve the transmission loss of the transformer at high operating frequency. A thin film transformer whose transmission loss is 2.7 dB from 100 MHz to 250 MHz is developed. >

The inductance of planar structures

Abstract: A method for calculating the inductance of planar-spiral structures in the presence, and in the absence, of magnetic core material is presented. In this method, the current is assumed to flow in the exact center of the planar conductor. Simplified expressions for the self inductance of each turn comprising the inductor, and the mutual inductance between turns on the same layer of the inductor are developed. An expression for the leakage flux between turns on adjacent layers is presented. The effect of a magnetic core on the inductance is considered, and an equivalent magnetic circuit for the core is developed. At the measurement frequency of 100 kHz, the new expressions exhibit better agreement with measurements than do existing ones presented in the literature. >

Hybrid excitation-type permanent-magnet synchronous rotating machine

Abstract: PURPOSE:To increase rotational speed without using a demagnetization control operation and to reduce an iron loss without lowering the efficiency of the title rotating machine by a method wherein a magnetic flux by a permanent magnet and a DC magnetic flux by a DC excitation winding are adjusted to be strong and weak. CONSTITUTION:When a DC current is supplied to a DC excitation winding 5 for a permanent-magnet synchronous rotating machine, a closed magnetic circuit is formed in the route of an armature yoke 4, an S-pole-side iron core 2b, a gap, an S-pole-side salient-pole-shaped part 12aS, a rotor core 12, a rotor yoke 14, the rotor core 12, an N-pole-side salient-pole-shaped part 12aN, the gap, an N-pole-side iron core 2a and the yoke 4. In this case, the direction of a magnetic flux can be controlled by the direction of the DC current, and its magnitude can be controlled by the magnitude of the current. As a result, field strength can be adjusted easily, a torque can be increased easily within a constant torque range, an induced voltage can be reduced easily within a constant output range, an available range can be increased, a DC excitation input become extremely small, the efficiency of the rotation machine can be increased, and an iron loss can be reduced sharply by reducing the magnetic flux in a high-speed region.

Current transformer for earth-leakage circuit breakers which are sensitive to current pulses

Abstract: It is proposed that a magnetic core having a remanence ratio Br/Bs 0.7. The magnetic properties are achieved using magnetic cores consisting of a fine-crystalline iron-based alloy which has been subjected to two-stage heat treatment.

Method of producing low iron loss grain-oriented silicon steel sheet having low-noise and superior shape characteristics

Abstract: A method of producing a low iron loss grain oriented silicon steel sheet which generates improved magnetostrictive characteristics when used as a stacked iron core and low noise when used in a stacked transformer, as well as superior shape characteristics. A grain oriented finish-annealed silicon steel sheet is coated with an insulating film. The surface of the grain oriented silicon steel sheet is irradiated with an electron beam along a multiplicity of spaced paths so as to refine the magnetic domains. The irradiation with the electron beam is conducted continuously or intermittently along a waveform path on the surface of the grain oriented silicon steel, and the wave-form, such as a zigzag form, has a period length much smaller than the width of the grain oriented silicon steel sheet, and line interconnecting the centers of successive waves extends substantially perpendicularly to the direction of rolling of the grain oriented silicon steel sheet.

IC memory card with non-contact power and data connection

Abstract: A non-contact electrical transformer coupling is disclosed that provides electrical power and full duplex digital communications between a host computer and a removable IC memory card. A unique two-part host magnetic core assembly having a quadrafid design forming multiple poles is provided with printed circuit windings and is disposed to receive the IC memory card embedded with core pole pieces and associated printed circuit card windings to complete the magnetic flux paths and transformer coupling. The configuration of the poles and windings form completely independent channels, each of which behaves like a wide-band ferrite core transformer. The independence of each channel enables this unique magnetic core and associated windings to couple relatively large amounts of power to the circuitry of the IC memory card and establish a high-speed bidirectional data link between the host and card.