Showing papers on "Magnetic circuit published in 1995"

Magnetic tape head with flux sensing element

Abstract: A thin film read-write magnetic head useful in a tape apparatus includes a magnetic circuit consisting of two thin film magnetic layers which form a magnetic yoke that is divided into three closely spaced sections, the central section of at least one of the magnetic layers containing an interspace in which a flux sensing element, such as a magnetoresistive device or Hall effect device, is located. The three section yoke forms a continuous magnetic circuit, except for the transducing gap, which circuit consists of three sections corresponding to the three sections of the yoke. The total gap width determines the width of the data track being recorded. During the write mode, a magnetic valve including an electrical conductor provides a shunt path to bypass the flux sensing means so that all three sections of the head operate for recording. During the read mode, only the central yoke section and its transducing gap portion sense the data signal recorded on the magnetic tape, and the read element detects the sensed signal. A saturation current is directed to the valve conductor during the read mode so that the shunt path is open, thereby allowing the flux sensing means to operate and sense the readout signal.

Air-gap reluctance and inductance calculations for magnetic circuits using a Schwarz-Christoffel transformation

Abstract: A method for calculating the reluctance of air gaps in magnetic circuits making use of a Schwarz-Christoffel transformation is described. The method is applied to the calculation of the inductance of example inductor and transformer configurations and its validity established through comparisons with calculations based on the finite-element method of numerical analysis. >

Introduction to modeling of transformers and coupled inductors

Abstract: A tutorial paper is presented on modeling and design of transformers and coupled inductors. Beginning with a brief review of electromagnetic laws and magnetic circuit models, the magnetic and electric models of transformers and coupled inductors are developed, including both magnetizing and leakage effects. It is shown that while the voltage waveforms on the windings are primarily related by the turns ratio for both devices, the winding currents of transformers and coupled inductors are determined by very different mechanisms. An integrated structure with both transformer and coupled inductor on the same core is also discussed, as well as the special case of the coupled inductor used on a multiple-output transformer-isolated converter. >

Position estimation in solenoid actuators

Abstract: This paper describes a novel method of estimating the position of a plunger inside a solenoid. The solenoid is a single-phase variable reluctance actuator, with a highly nonlinear magnetic circuit. For the proposed method, position is estimated indirectly through the solenoid's incremental inductance in the high current region. It exploits the advantage that motional electromotive force (EMF) is negligible under normal operating condition. The incremental inductance is obtained from the rate of current rise of the pulse-width modulated (PWM) waveform, which in turn, is measured by a dedicated current rise measurement circuit. Position is estimated from a two-dimensional look-up table of incremental inductance and current. The method is simulated and then implemented on a typical industrial solenoid valve. Factors which affect the accuracy of the estimation and methods of overcoming them are also described in the paper.

Linear Circuit Analysis

Abstract: Lapice transfrom analysis- basics Laplace transfrom analysis - circuit applications Laplace transform analysis - transfer function applications time domain circuit response computations the convolution method resonant and bandpass circuits magnetically coupled circuits and transformers two-ports analysis of interconnected two-ports principles of basic filtering Fourier series with applications to electronic circuits. Appendices: introduction to magnetic circuit analysis SPICE for basic circuits.

Flux dam, a method to reduce extra low frequency noise when a superconducting magnetometer is exposed to a magnetic field

Abstract: This letter discusses the effects of a moderate magnetic field applied to a SQUID magnetometer and introduces the invention of the ‘‘flux dam’’ A flux dam is a weak link or Josephson junction in series with the pickup loop which allows magnetic flux to enter and leave the inside of the superconducting loop easily for moderate changes in magnetic field This largely prevents the flux lines from entering and being pinned in the superconducting parts of the magnetometer which would create extra low frequency noise SQUID magnetometers with flux dams in the pickup loop can be operated in the Earth’s magnetic field without a significant increase in low frequency flux noise

Dipole permanent magnet structure

Abstract: A dipole permanent magnet structure having a rectangular gap about a longitudinal axis, in which tapered pole pieces form opposing sides of the rectangular gap to permit establishing a magnetic field in the gap. Permanent magnets having a rectangular shape are coupled to the rear, or base, of each pole piece, and have a magnetic field oriented in the same direction as the pole pieces, perpendicular to longitudinal axis, thereby establishing a magnetic field between the pole pieces. Additional permanent magnets, including a pair of blocking magnets, are coupled to the aforementioned permanent magnets to form a magnetic circuit. The orientation of the magnetic field of each permanent magnet is generally aligned in the direction of the lines of flux in the magnetic circuit to maximize the flux density within the air gap created by formation of the permanent magnets. Moreover, the pair of blocking magnets each form an opposing side of the rectangular gap adjacent to the pole pieces to prevent fringing. The structure is thus capable of generating a magnetic field having a flux density greater than the residual flux density of the magnet material. Indeed, the gap flux density is limited only by the saturation flux density of the pole pieces. Thus, the permanent magnets can be made of magnet material having high coercivity and high saturation magnetization level. An embodiment of the magnet structure is capable of generating a magnetic field in the air gap having a flux density of 2.2 Tesla (22,000 Gauss).

A magnetic shielding type superconducting fault current limiter using a Bi2212 thick film cylinder

Abstract: The application of a superconductor to a fault current limiter in a power system has been researched. The authors developed a magnetic shielding type superconducting fault current limiter using a Bi2212 thick film cylinder. This limiter consists of a primary winding on a superconducting cylinder for generating an AC magnetic field, the cylinder for shielding the field, an iron core for magnetic members and a control ring for controlling fault currents. When a fault occurs, the superconductive cylinder quenches and a magnetic circuit is formed inside the cylinder. As a result, the limiter has a high impedance to limit the fault current. The present study shows the limiting and recovery characteristics of the fault current limiter. >

Machine with transverse flux

Abstract: In order to achieve high potency for magnetic circuits together with a favourable possibility of constructing them in four-phase and two-phase form using radially positioned permanent magnets in flux concentration mode, it is proposed to introduce E-shaped stator pole elements with at least one fanned-out limb each. This gives the most favourable utilisation of the permanent magnets together with high functionality with a view to the maximum obtainable rotor diameter and favourable component manufacture. Both four-phase and two-phase machines may be constructed with the same pole elements. For exclusively two-phase windings there is a possibility of shortening the distance between the part-rotors.

T- Omega method using hierarchal edge elements

Abstract: The edge-element version of the T- Omega method is a 3D finite-element method for computing the fields in and around conducting and magnetic materials at power frequencies. The magnetic field is represented as the sum of two parts: the gradient of a scalar potential and, in the conductors, an additional vector field represented by Whitney edge elements. The method is powerful but uses only a low-order approximation of the magnetic field. The paper describes a version using higher-order polynomials. Three sets of trial function spaces are defined: a set of irrotational spaces and two sets of rotational spaces (one for the impressed coil field and one for the induced eddy currents). By combining spaces from the three sets, a number of representations for the magnetic field is possible on the same mesh. The simplest representation corresponds to the Whitney element; the most accurate is fully quadratic in each tetrahedron. Furthermore, as the spaces are hierarchically constructed, it is possible to mix elements of different types on the same mesh without violating continuity requirements. Results for two test problems are presented: an infinite, current-carrying copper plate, and a copper block in the airgap of a magnetic circuit. The results demonstrate that the higher-order elements give greater accuracy for a given computational cost.

Direct modeling of switched reluctance machine by coupled field-circuit method

Abstract: Transient analysis of a switched reluctance machine (SRM) system is complicated by its unconventional nonsinusoidal operation and highly nonlinear characteristics. The analysis, however, is essential not only for optimizing the SRM magnetic structure but also for proper control of the associated power electronic circuit. In this paper, a direct modeling method for analysis of a SRM system including the power electronic converter, control and the nonlinear magnetic field of the SRM is established. The finite element method is used to model the nonlinear magnetic field, and is coupled to the circuit model of the SRM overall system. Assumptions of current density in FEA and various types of flux-current characteristics in circuit analysis are eliminated. With simultaneous computation over the entire system, the computer model provides abundant information regarding the SRM system. Experimental results are presented to prove the accuracy of the model. >

Transverse flux machine

Abstract: In known transverse flux machines the losses in the magnetically soft body prevent an increase in efficiency. Whilst the production of the winding is remarkable owing to its simplicity, the production of the laminated iron body conveying the magnetic flux incurs high costs. In addition to the saturation in the iron, the use of air gaps restricts any increase in power density. According to the invention the two air gaps (21) are disposed radially externally of the winding (15) and the magnetically hard and/or soft rotor parts (19, 20), which periodically close the magnetic circuit, are disposed axially within the ends of the magnetically soft stator body (18). This air gap arrangement gives rise to an air gap surface which is large relative to the external dimensions and the mass of the machine, and also relieves the load on the housing. Owing to the segmentation of this U-shaped stator body, material wastage during production is minimized and grain-oriented metal sheets can be used which, owing to their favourable properties, enable the efficiency and power density to be increased. Segments of identical construction can be used in machines having different dimensions and power data. The type of construction according to the invention simultaneously reduces costs, weight and losses in transverse flux machines.

Electromagnetically actuated rotating machine unbalance compensator

Abstract: An electromagnetically actuated machine balancer (110) including a plurality of peripherally placed magnetic circuits and a power driver which selectively interrupts the magnetic flux (1210) through the circuits, thereby moving unbalanced rotors (350-351) in a desired manner to compensate for machine unbalance. The balancer assembly (110) includes a remote stationary microprocessor based controller (140), operating under stored computer program control and adapted to control assembly (110) in a manner which is specified by the stored program and certain environmental and measured parameters.

Numerical modelling and simulation of hysteresis effects in magnetic cores using transmission-line modelling and the Preisach theory

Abstract: The transmission line modelling method and the Preisach theory are employed to model and simulate the hysteresis effects of magnetic cores. This combined approach provides a useful method, which allows fast and accurate prediction of magnetic core losses, and simple software implementation of the dynamic discrete model. The model can be developed easily, using data provided by core manufacturers and simple measurements. This paper describes, in a tutorial style, the numerical aspects and software implementation of the modelling and simulation of hysteresis for a magnetic core. Step-by-step procedures of the modelling and simulation are included, and demonstrated in a computer simulation. Both simulated and measured results are presented.

Induction machine modeling using finite element and permeance network methods

Abstract: A method to model electrical machines, taking into account electric, magnetic and mechanical coupling, is proposed This method is based on magnetic equivalent circuit associated with bond-graph techniques Simulation results on an induction machine are presented and compared with finite element computation results, showing a good agreement between the two methods >

Theoretical computations for the torque of magnetic coupling

Abstract: The torque of magnetic coupling with different magnetic poles has been investigated by theoretical computations with both FEA and torque formula techniques. The torque of magnetic coupling is sensitive to the number of magnetic poles, and it decreases with increasing the distance between the magnetic rings. From our theoretical computations, we find that we can increase the torque by increasing the number of poles for magnetic coupling between magnetic rings with short distance; however, this is not true for magnetic rings with large separation. We also demonstrate that the theoretical computations of both MagNet software and torque formula established by Furlani (1993) are quite consistent and useful for computing the torque of various magnetic couplings. Finally, the theoretical calculation has been successfully tested by using an experimental data taken from a NdFeB magnetic coupling. >

Design of a three-phase self-excited induction generator

Abstract: The main goals in the design of a self-excited induction generator (SEIG) are minimizing the rotor resistance and increasing the flux density until the magnetic circuit of the generator saturates. In this paper, a computer design package was developed in order to investigate the best way to obtain these goals. By reducing the stator core length by 40%, the frequency regulation and the voltage drop were reduced. The frequency regulation decreased from 10% to 4% and the voltage drop decreased from 30% to 6%. In addition, voltage and frequency regulations in the standard ranges were obtained in the present design without any regulation devices. >

Field strength position sensor with improved bearing tolerance in a reduced space

Abstract: A position sensor has a shaped dual magnet structure carried upon a pole piece having a generally "c" shaped cross-section. The magnet and pole piece define a generally circular linear field which is concentric about the axis of rotation of the complete rotor. A Hall effect device is inserted into the open portion or gap between the two magnets and is exposed to a well defined field. Through the use of selected geometries and particular magnet materials, a precise, compact and yet tolerant magnetic circuit is produced.

Disk drive in-hub radial-gap spindle motor with coils generating axial fields

Abstract: An in-hub brushless permanent magnet DC motor has a radial working gap but uses coils wound in the axial direction of the motor. The coils generate fields that interact with the permanent magnet fields across the radial gap. The stator includes a plurality of angularly spaced stator teeth that have faces radially spaced across the gap from the permanent magnet. The stator teeth are connected to the base and extend axially into a cavity within the hub. The permanent magnet is a magnetically-segmented ring magnet located on an outer rim of the hub radially outwardly from the stator teeth. The magnetic flux from the permanent magnet is directed radially across the gap and into the stator teeth. Each stator tooth has an axially oriented post around which is wound a coil that generates an axial field. The axially-oriented part of each coil forms part of the magnetic circuit. The magnetic flux directed radially into each stator tooth is turned axially into the post and through the coil. The axially directed magnetic flux through the coil and post on each stator tooth is redirected from the axial direction to the circumferential direction by a ring magnetic flux guide. The ring flux guide interconnects the stator teeth and forms part of the magnetic circuit. Because the coils are wrapped around axial posts instead of the stator teeth a larger coil volume is obtained which results in higher motor efficiency and reduced heating of the bearing system. The angular spacing between adjacent teeth can be made very small or even eliminated since there is no need to locate a winding device between them as is required in conventional radial-gap motors. This results in a reduction in the motor cogging torque, which in turn allows a higher tooth/pole symmetry leading to better force balance and lower acoustic noise.

Trip device comprising at least one current transformer

Abstract: A trip device comprises at least one current transformer for supplying power to electronic circuits. The current transformer comprises a magnetic circuit, surrounding a primary conductor, a secondary winding wound onto a part of the magnetic circuit forming a core, and a magnetic shunt branch connected on the magnetic core. The magnetic shunt comprises an air-gap. When the current flowing in the primary conductor is of low value, the magnetic flux stopped by the air-gap flows essentially via the core of the secondary winding. At high current levels the induction is greater and a large part of the magnetic flux passes through the shunt via the air-gap. The current transformer has a non-linear current response which limits excess power supplied to the electronic circuits and dissipated in the transformer. The trip device is useful, for example, in a circuit breaker.

Optical pickup for an optical disc player

Abstract: A holder (60) is suspended on a carriage (21), and a magnetic circuit (32, 45, 46, 47) is disposed adjacent to the holder (60). The magnetic circuit has a first magnetic pole (46) and a second magnetic pole (47). A focus coil (63) having a magnetic flux receiving portion (63a) is provided around a vertical axis of the holder (60). A tracking coil (66) having a magnetic flux receiving portion (66a) is provided around a horizontal axis of the holder (60). Both the magnetic flux receiving portions (63a, 66a) are disposed so as not to be overlapped with each other, and are disposed in parallel with one of the surfaces of the first and second magnetic poles (46, 47). Both of the magnetic flux receiving portions (63a, 66a) are flush with each other.

Ignition coil for internal combustion engine

Abstract: PURPOSE:To make it possible to mount a permanent magnet in an ignition coil for an internal combustion engine, in which the permanent magnet is interposed between magnetic circuits, easily and at low cost and at the same time, to ensure the stable ignition of the ignition coil CONSTITUTION:Magnetic circuits are formed of cores 2 and 3, which are respectively wound with a primary coil 12 and a secondary coil 22, and a permanent magnet 5 is interposed between these magnetic circuits This magnet 5 is magnetized after a resin molding is performed and is formed of a magnet material maintaining a prescribed magnetic force into a prescribed form of such a thickness as to allow a mold manufacture For example, the magnet 5 is formed of a 1-5 samarium-cobalt magnet material into a rectangular plate body having a thickness of 15mm or thicker and after the resin molding is performed, the magnet 5 is magnetized Thereby, when the permanent magnet is manufactured by a metal mold, it is never broken and after the resin molding is performed including the permanent magnet, the magnet 5 can be easily magnetized

Design of slotless TORUS generators with reduced voltage regulation

Abstract: The slotless toroidal-stator permanent-magnet machine 'TORUS' can be integrated with an engine to form a compact generating set, but the terminal voltage naturally reduces on load because the armature reaction MMF leads to reduced flux. However, if a stator core of reduced thickness is used, heavy saturation takes place on no-load so that, on load, the armature reaction MMF simply reduces the degree of saturation. The stator coils may then link the same rotating flux whether current is drawn or not, with the terminal voltage without being greatly affected by armature reaction. The design and analysis of the resulting machine with reduced voltage regulation are presented with supporting test results taken from two prototype machines. >

Method and apparatus for limiting high current electrical faults in distribution networks by use of superconducting excitation in transverse flux magnetic circuit

Abstract: The present invention pertains to an electrical fault limiter. The fault limiter comprises a first magnetic core. There is also a second magnetic core opposing the first magnetic core. The fault limiter additionally comprises a third magnetic core adjacent the first magnetic core. Also, there is a fourth magnetic core opposing the third magnetic core and adjacent the second magnetic core. The electrical fault limiter also moreover comprises a rotor disposed between the first and second magnetic cores, and the third and fourth magnetic cores. The rotor is rotatable about a rotor axis. The first and second magnetic cores are disposed on a first side of the rotor axis and the third and fourth magnetic cores are disposed on a second side of the rotor axis. Each core has a first arm, a second arm and a body to which the first and second arms are connected. Each body has a superconducting bias coil disposed about it. Each arm has a conduction mode coil disposed about it. The rotor has a high magnetic reluctance sector and a return flux sector such that when the magnetomotive force from each superconducting bias coil balances with the magnetomotive force from associated load coils on an associated core, there is no force on the rotor. But, when the magnetomotive force from the superconducting bias coil is less than the magnetomotive force from associated load coils on the associated core, then a force is produced on the rotor causing it to accelerate and the reluctance of the primary magnetic circuit is decreased, thereby causing an increase in the self-inductance of the primary coil.

Optimum geometry for torque ripple minimization of switched reluctance motors

Abstract: This paper briefly describes an approach to determine the optimum magnetic circuit parameters to minimize low speed torque ripple for switched reluctance (SR) motors. For prediction of the torque ripple, normalized data obtained from field solution and a neural network approach is used. Comparison of experimental results with computations illustrates the accuracy of the method. The optimization method is briefly described and some results are presented.

Magnetic flux measuring method and apparatus for detecting high frequency components of magnetic flux with high speed orientation

Abstract: A current of predetermined frequency is fed to a coil wound around a ferromagnetic core through a fixed impedance means. A magnetic flux measurement is performed in terms of a level of a DC component of a voltage generated across the coil. A DC bias is added to the current of predetermined frequency, and the resultant current is applied through the fixed impedance means to the coil wound around the ferromagnetic core. A magnetic flux measurement is performed in terms of a level of a DC component of the voltage across the coil. A magnetic flux measuring method and apparatus for embodying the same have a high sensitivity in detecting a minute magnetic flux and an improved temperature characteristic because an output voltage little varies against a temperature variation. A magnetic flux measuring method and apparatus for embodying the same, when they are applied to a leakage flux flaw detection using a saturable magnetic flux sensor, is capable of expanding a measuring span of the magnetic flux sensor, thereby to improve a flaw detection performance.

A dynamic equivalent circuit model for solid magnetic cores for high switching frequency operations

Abstract: This paper presents a dynamic equivalent circuit model of solid magnetic cores for high frequency operations in power electronic circuits. The effects of eddy current, domain wall motion, and hysteresis are taken into account by distributed equivalent resistors and distributed nonideal differential inductors, respectively. The Preisach hysteresis model is employed to simulate hysteresis effects in the inductors. A discrete transform technique based on the transmission line method is adopted to develop a discrete model for numerical dynamic analysis. The resultant model is just a simple tridiagonal system of equations. Good agreement between computer simulations and measurements has confirmed the validity of the new model. >

Fabrication of small flying machines using magnetic thin films

Abstract: A small flying machine based upon a new mechanism was realized. The flying machine driven by magnetic torque had hard magnetic films as wings and a soft magnetic wire as a body, respectively. The wing has two hinges, which create different drag during up and down strokes, and produced lifting force. Shape magnetic anisotropy of the body stabilized the attitude. The flying machine flew without power supply cables and guides when an alternating magnetic field of more than 400 Oe around 12 Hz was applied.

D.C. reactor

Abstract: A D.C. reactor comprising a core structure having two opposed cores separated by a magnetic gap, to form a closed magnetic circuit; a coil wound on one or both of the cores; a pair of permanent magnets for biasing, disposed on the core structure; magnetic flux generation means for causing the bias flux generated by the permanent magnets and the flux generated by the coils to flow in opposite directions; and bypass means for causing the bias flux generated by the permanent magnets to bypass the magnetic gap. The core structure comprises an E-shaped core and an I-shaped core, the magnetic gap is defined between a center leg of the E-shaped core and the I-shaped core, the coil is wound on the center leg of the E-shaped core, and each permanent magnet is shaped into a rectangle and disposed on both side surfaces of the center leg of the E-shaped core. The permanent magnet is a sheet-like permanent magnet magnetized so that each of its longitudinal direction and the direction of thickness forms two poles on each side, and the neutral line of this permanent magnet is brought into conformity with the center line of the magnetic gap and is disposed on both outer side surfaces of the core structure. Since the flux generated by the D.C. reactor does not pass inside the permanent magnet, an eddy current loss decreases, and even when a large current abruptly flows through the coil, the permanent magnet is not demagnetized.

Disk drive spindle motor with radial gap and field generating coils interconnected by ring flux guide

Abstract: A brushless permanent magnet DC motor for use as a disk drive spindle motor has a radial working gap but uses flat coils that generate magnetic fields that interact with the permanent magnet fields across the radial gap. The stator includes a plurality of angularly spaced stator teeth that have faces radially spaced across the gap from the permanent magnet. The magnetic flux from the permanent magnet is directed radially across the gap and into the stator teeth. Each stator tooth has an axially oriented post around which is wound a flat coil that generates an axial field. The central axis of the coil forms part of the magnetic circuit. The magnetic flux directed radially into each stator tooth is turned axially into the post. The axially directed magnetic flux through the coil and post on each tooth is redirected from the axial direction to the circumferential direction by a ring magnetic flux guide. The ring flux guide interconnects the stator teeth and forms part of the magnetic circuit.