Showing papers on "Magnetic circuit published in 1985"

Prediction of No-Load Flux Density Distribution in Permanent Magnet Machines

Abstract: Both the average output torque as well as the output torque pulsations of permanent magnet (PM) motors depend on the air gap flux density waveform produced by the magnets. An analytical model is presented, which uses the two-dimensional field theory in polar coordinates to determine the flux density waveforms at the stator and rotor surfaces of PM machines and also the amount of magnetic flux entering these surfaces. The analysis is valid for dc as well as for synchronous brushless motors with magnets which are magnetized in either the radial or the parallel direction. The results obtained by the model are verified by comparison with results obtained by finite-element analysis as well as with test results.

Compensating circuit for a magnetic field sensor

Abstract: A circuit which compensates for fluctuations in the transfer characteristic of a magnetic field sensor is disclosed. More particularly, an auxiliary magnetic field is generated preferably by a coil which is connected to a voltage generator by way of a voltage/current transducer. The auxiliary magnetic field along with the magnetic field to be measured is detected by the magnetic field sensor. The portion of the sensor output signal due to the auxiliary magnetic field is correlated with the voltage produced by the voltage generator by means of a correlator circuit. If the portion of the magnetic field sensor output due to the auxiliary magnetic field is not properly correlated with the signal from the voltage generator a feedback signal is sent to the magnetic field sensor to adjust the transfer characteristic.

High switching frequency converter auxiliary magnetic winding and snubber circuit

Abstract: An integrated magnetic assembly for use in the direct current output circuit of a high frequency electronic switching power supply, comprising magnetic core sections for the output transformer and inductor windings and a common magnetic core segment completing the magnetic flux paths for the transformer and inductor windings An auxiliary winding on one or both of the core sections is supplied with energy from the capacitor of a snubber circuit connected across the primary side of the magnetic output circuit This auxiliary winding is magnetically coupled to the secondary side of the magnetic circuit to transfer energy to the power supply output during a portion of the switched current cycle

Brushless D.C. dynamoelectric machine having ferrite material magnetic circuit

Abstract: A dynamoelectric machine which may operate in a motor mode or a generator mode is described wherein substantially the entire magnetic circuit is provided by ferrite material. In one particular embodiment, hard ferrite permanent magnet segments are mounted on a rotor plate while soft ferrite magnet segments with electrical coil windings mounted thereon are provided in a stator spaced apart from the rotor by an air gap. Other embodiments of the concept are described.

Integrated transformer and inductor

Abstract: An electrical transformer comprises a hollow form exhibiting high magnetic permeability and interior projections extending between separable halves of the form to provide a low magnetic leakage transformer core. Primary and secondary windings are disposed around the central projections. Furthermore, there is included means internal to the form for providing a lower permeability magnetic circuit shunt path. The internal shunt path means is typically either a cylinder or disc structure. A reduction in stray magnetic flux is desirable since it means that smaller, less expensive transformers may be constructed. The transformer of the present invention is particularly useful in electronic ballast circuits for gas discharge lamps because the magnetic shunt path acts as a current-limiting inductor. Moreover, since the transformers of the present invention do not generate external magnetic fields, flux shields are not required to maintain high efficiency.

Electromagnetic linear motor and pump apparatus

Abstract: An electromagnetic linear motor having a variable length stroke and providing a substantially large force in both its power stroke and return stroke includes concentric inner and outer magnetic circuits arranged coaxially for movement relative to one another in a rectilinear path with reciprocating motion in response to the interaction of magnetic fields produced by the inner and outer magnetic circuits, respectively. The length of the stroke and the rate of reciprocation are directly proportional to the magnitude of the voltage used to excite primary and secondary coils which generate the respective magnetic fields and the rate at which the polarity of the voltage applied to the secondary coil is changed between negative and positive polarities. The invention further resides in a central core pump having a pumping tube connected for movement with the outer magnetic circuit and in coaxially alignment with inlet and discharge tubes and each of the three tubes having a check valve to form variable volume chambers between the pumping and inlet and pumping and outlet tubes respectively so that one or more successive volumes of fluid are drawn into one and discharged from the other when the outer circuit moves in one direction and discharged from one and drawn into the other when the outer circuit moves in the opposite direction. The invention further resides in the electromagnetic linear motor being arranged with a central core pump to provide fuel injection to an internal combustion engine.

Nuclear magnetic resonance apparatus with a permanent magnet

Abstract: In a nuclear magnetic resonance apparatus the permanent magnetic material of the main magnet is formed by magnetized bars bounded by flat planes which surround a field space with a polygonal cross-section. Fitted around the permanent magnetic material is a return yoke of high-permeability material whose geometry can be matched to the locally prevailing flux. Extra magnetic devices can be fitted to improve the field uniformity in the field space enclosed by the magnetic material.

YIG thin film tuned MIC oscillator

Abstract: A tuned oscillator is disclosed which comprises an active element, a resonator electrically connected to the active element and made of a magnetic material using ferro-magnetic resonance phenomenon, and a magnetic circuit for applying a magnetic field to the resonator. The resonator is made of an YIG (yttrium, iron and garnet) thin film magnetic resonance element formed by a thin film forming technique and utilizes an uniform mode ferro-magnetic resonance in the YIG thin film, and operating under the application of magnetic field of the magnetic circuit.

Variable reluctance actuators having improved constant force control and position-sensing features

Abstract: A variable reluctance actuator, of either the linear or rotary type, having a moving element operated by a solenoid, is controlled by a Hall effect sensor signal representative of flux density in the magnetic circuit of the actuator. The actuator may be operated in either a constant-force control mode, or a position-sensing or control mode. Substantially constant force, independent of position of the actuator's movable element, is obtained by varying, rather than stabilizing, the sensed magnetic field during movement. Position sensing, independent of actuator force, is obtained by variably controlling the magnitude of the excitation current of the Hall effect sensor in response to the magnitude of the coil current and Hall sensor output.

Differential twin track vertical read/write magnetic head structure

Abstract: An improved twin track read/write head structure that is differential in its response, thereby eliminating common mode noise signals is described. It also has a low electrical offset, increased linearity and reduction or elimination of any bias fields interfering with the magnetic recording medium. The structure utilizes a dual coupled film magneto resistive sensor bridging the legs of two magnetically permeable coupling members so that the dual magnetic sensors are in a series magnetic circuit with the coupling members. The dual coupled film magnetic sensors are connected together in a center tapped arrangement and are oppositely magnetically biased. Opposing voltages changes occur when the pair are subjected to a magnetic flux field passing serially through them. This produces a differential output signal that rejects unwanted common mode noise of all types. In addition, during read back when the sensors are biased by a magnetic flux field into their sensitive range, the balanced differential structure of the head presents equal magneto motive forces at both ends of the sensor where they connect to the flux coupling legs. As a consequence, there is no net flux available at the other ends of the coupling legs and no flux is coupled to the media.

Coupling the circuit equations to the non-linear time dependent field solution in inverter driven induction motors

Abstract: The conventional way of analysing electric machinery has been to impose currents or current densities, to calculate from them the electromagnetic field and from that the self and mutual inductances of the windings. Circuit equations using these inductances would give correct values for the currents in the windings. In this paper, the field and circuit equations are coupled, giving a time dependent set of nonlinear equations, the solution of which gives the magnetic vector potential at every point in the cross section of the machine and the electric field intensity at the cross section of the conductors. The method is of particular interest when the harmonic content of the excitation is large, prohibiting the calculation of permeability of iron from only the fundamental.

Solution of magnetic fields and electrical circuits combined problems

Abstract: A finite element formulation is developed to analyse the magnetic fields in constrained electrical circuits by combining field and circuit equations. The terminal voltages are specified and the corresponding magnetizing currents assumed as unknown. This method takes into account the eddy currents and it has a symmetric coefficient matrix with respect to the ones mentioned in the literature. This approach makes it possible the computation of the characteristics of induction motor, specially squirrel cage induction motor, excited by constant voltage power sources. It is verified using a magnetic relay and a 4-pole shaded-pole motor.

Thin film magnetic head having magnetic film of Co-Ni-Fe alloy

Abstract: A thin film magnetic head comprising a lower magnetic film, an upper magnetic film which is formed over the lower magnetic film and in which one end is come into contact with one end of the lower magnetic film and the other end faces the other end of the lower magnetic film through a magnetic gap and thereby forming a magnetic circuit which has a magnetic gap in a part thereof, together with the lower magnetic film, and a conductor coil forming a coil of a predetermined number of turns and passing between the upper and lower magnetic films and crossing the magnetic circuit. Each of the upper and lower magnetic films is formed of a Co-Ni-Fe ternary alloy having a face-centered cubic crystal structure. Also, uniaxial anisotropy is alternately and perpendicularly given in every layer of a predetermined thickness stacked in the direction of thickness of the film.

Magnetron sputter device using the same pole piece for coupling separate confining magnetic field to separate targets subject to separate discharges

Abstract: A magnetron sputter device includes separate first and second targets over which first and second discharges are formed by separate ionizing electric fields and separate confining magnetic fields. The separate confining magneticfields include first and second magnetic circuits through the first and second targets, respectively. The first magnetic circuit includes first and second pole pieces for coupling magnetic flux from a first magnetic field source to the first target. The second magnetic circuit includes the second pole piece and a third pole piece for coupling magnetic flux from a second magnetic field source to the second target. The magnetic circuits and the magnetic field sources are arranged so that magnetic fluxes from the first and second magnetic field sources flow in opposite directions through the second pole piece.

Positioning device of magnetic suspension type

Abstract: A positioning device of magnetic suspension type is disclosed, which comprises a cylindrical stationary member and a cylindrical floating member arranged coaxially with the stationary member. The floating member is supported in non-contact state with respect to the stationary member by the magnetic forces produced by a plurality of magnetic circuits. The device further includes at least one control coil disposed such that it crosses the flux passing through the magnetic circuit. When the control coil is energized, it receives an electromagnetic force for displacing the floating member in co-operation with the flux from the magnetic circuit.

Impact of Winding Inductances and Other Parameters on The Design and Performance of Brushless DC Motors

Abstract: The computer aided design process of two electronically operated brushless dc motors intended for use in electric vehicle propulsion is described. The components of this process are a time domain dynamic simulation model of the brushless dc motor system in which the machine paramenters, inductances and emfs, are obtained entirely from finite element field analysis of the magnetic circuit arrived at by the designer. This computer aided design process is used to determine the correct winding configurations for two machines, the permanent magnet rotor one of which is of samarium cobalt, and of ferrite for the other. Both machines are required to achieve 15 hp continuous and 35 hp peak ratings as motors, subject to the constraints of a maximum dc supply voltage of 120 V and a maximum current of 400 A due to limitations on the available power switching components. In addition, the effects of changes in the firing angle of the inverter transistors, with respect to the induced winding emf's, are examined. The results of this work demonstrate that the performance of such systems is inductance limited especially in high speed (frequency) applications. The two machine designs selected as a result of this analysis were fabricated and subsequently tested in the laboratory. Both machines met the desired performance goals as predicted by the computer aided design process.

Constant flux magneto resistive magnetic reluctance sensing apparatus

Abstract: Disclosed is an improved method and apparatus for sensing magnetic reluctance variations. The invention may be used for magnetic ink character reading, such as is employed on bank checks, or for any of a variety of magnetic reluctance pickup applications. An improved magnetic reluctance sensor head utilizes an essentially U or C-shaped magnetically permeable member having a magnetizing coil encircling it. The coil is arranged to deliver essentially a constant magnetic flux to the U or C-shaped member. The tips of the U or C are placed adjacent to the element whose variation of reluctance is to be detected and a magneto resistive or other similar magnetic sensor is connected in the magnetic circuit either in parallel or in series with the variable reluctance which is to be sensed.

Actuator for dot matrix printhead

Abstract: An improved dot matrix actuator is provided which includes a magnetic circuit formed of a yoke assembly and a pivotal armature The armature is pivotally supported with respect to the yoke by means of a flexure assembly which eliminates the need for a true pivot between the two elements The elements are shaped so as to maintain a constant small air gap therebetween so as to maximize the magnetic efficiency of the device while eliminating wear The device is operated just below saturation of the magnetic circuit in order to maximize efficiency In addition, the actuator includes several features for maximizing its speed and operational efficiency

Finite element analysis of magnetic fields taking into account hysteresis characteristics

Abstract: A new technique for taking into account hysteresis has been developed. The paper describes the details of the method and the usefulness of the technique is clarified by applying it to the analysis of magnetic fields in single-phase transformer cores. The calculated results are in good agreement with the measured ones.

Electromagnetic induction device for heating metal elements

Abstract: An electromagnetic induction apparatus for heating metal elements has at least one flat loop magnetic circuit open at its two facing ends, with an inductor wound onto the magnetic circuit. The inductor has two windings wound onto the magnetic circuit, respectively in the vicinity of the two ends of the loop, which windings are supplied by in-phase alternating currents. Each end of the flat loop is chamfered, the ends forming an air gap therebetween, in which the element to be heated is placed.

Noiseless electromagnet and a contactor using such an electromagnet

Abstract: The electromagnet comprises a fixed magnetic circuit, a mobile magnetic circuit forming, with the fixed magnetic circuit, at least one air gap and a coil. The distance over which the mobile magnetic circuit travels with respect to the fixed magnetic circuit is limited by at least one working position stop determining the working position, this stop being provided with at least one working position damper.

Three pole single element magnetic read/write head

Abstract: A magnetic head has three pole pieces that form a magnetic circuit. The magnetic pole pieces are arranged in a common plane so that the two outside pole pieces are each spaced from the central pole piece to form a transducing gap between each of the outside pole pieces and the central pole piece. A first and a second coil, each having the same magnetic sense, is wound on the magnetic structure between an outside and the center pole piece. The coils are connected in series for a write operation so that the flux in the outside pole pieces is additive for writing, and the coils are connected in series opposition for a read operation so that the flux produced in the center pole by a previously recorded magnetic transition in the magnetic recording medium adjacent to the transducing gaps is sensed additively in the coils.

Optimum Magnetic Circuit Configurations for Permanent Magnet Aerospace Generators

Abstract: In the design of high-speed low-power electrical generators for unmanned aircraft and spacecraft, maximization of specific output (power/weight) is of prime importance. Several magnetic circuit configurations (radial-field, axial-field, flux-squeezing, homopolar) have been proposed, and in this paper the relative merits of these configurations are subjected to a quantitative investigation over the speed range 10 000-100 000 rev/min and power range 250 W-10 kW. The advantages of incorporating new high energy-density magnetic materials are described. Part 1 deals with establishing an equivalent circuit for permanent-magnet generators. For each configuration the equivalent circuit parameters are related to the physical dimensions of the generator components and an optimization procedure produces a minimum volume design at discrete output powers and operating speeds. The technique is illustrated by a quantitative comparison of the specific outputs of conventional radial-field generators with samarium cobalt and alnico magnets. In Part II the specific outputs of conventional, flux-squeezing, and claw-rotor magnetic circuit configurations are compared. The flux-squeezing configuration is shown to produce the highest specifilc output for small sizes whereas the conventional configuration is best at large sizes. For all sizes the claw-rotor configuration is significantly inferior. In Part I1l the power densities available from axial-field and flux-switching magnetic circuit configurations are maximized, over the power range 0.25-10 kW and speed range 10 000-100 000 rpm, and compared to the results of Parts I & II. For the axial-field configuration the power density is always less than that of the conventional and flux-squeezing radial-field configurations.

Electromagnetically-operated fuel injection valve

Abstract: An electromagnetically-operated fuel injection valve has a magnetic circuit comprising a valve casing, a stator core on which an electromagnetic coil is wound, an armature core, and an air gap between the stator core and the armature core. At least one of the valve casing, the stator core and the armature core is so configuared that the magnetic flux passing therethrough is saturated substantially at the time the armature core is fully attracted to inject fuel. A magnetic restrictor at which the cross-sectional area for the magnetic flux is reduced than that at the other portion is provided at least at a portion of the valve casing, the stator core and the armature core so that the magnetic flux is saturated thereat substantially at the time the armature core is attracted fully.

A method of modeling permanent magnets for analytical approach to electrical machinery

Abstract: A method of simulating permanent magnets in analytical approach for the transfer-matrix-method is given. The method is suited for deriving analytical expressions of the magnetic fields and electromagnetic forces in electrical machines containing permanent magnets. The method was applied to the analysis of a long-stator linear synchronous motor with permanent magnet excitation. Measurements of the forces in the 150-pole Samarium-Cobalt type linear synchronous motor for electric propulsion were used to verify this permanent magnet modeling analysis. Comparison with experimentally obtained results shows a very good agreement.

Magnetic recording and reproducing system with composite magnetic head

Abstract: The invention discloses a magnetic recording and reproducing system using a composite magnetic head whose surface facing a magnetic recording medium is composed primarily of a ferromagnetic metal and a high permeability ferrite single crystal, and which has a region close to a gap and composed of the ferromagnetic metal, wherein the composite magnetic head is arranged in such a fashion that the {110} plane of the high permeability ferrite single crystal is made to substantially coincide with a plane forming a principal magnetic circuit of the composite magnetic head, that the direction lying inside the {110} plane is inclined at an angle of from 15° to 75° with respect to a direction perpendicular to the surface facing the magnetic recording medium, and that the magnetic recording medium travels in a direction which is relatively the same as, and parallel to, a vector formed by projecting a vector extending from the inside to the outside of the surface facing the magnetic recording medium in the direction, on the surface facing the magnetic recording medium. This magnetic recording and reproducing system can remarkably reduce the step occurring on the surface facing the magnetic recording medium due to wear caused by the travel of the recording medium, and can reduce any output deterioration and fluctuation resulting from the step.

Multiple coils for reduction of stray magnetic fields in disk file actuators

Abstract: A linear disk actuator is disclosed incorporating a magnetic circuit for reducing stray magnetic fields in the region of the disks and recording heads of a magnetic recording disk system. The moving part of the actuator is provided with a plurality of coils mounted thereon, at least two of which are energized simultaneously and in magnetically opposing relationship to reduce the amplitude of the stray magnetic fields. Movement of the actuator is achieved by both energized coils interacting with a set of alternating poles positioned on the stationary part of the actuator.

A design of a superconducting split-coil open gradient magnetic separator

Abstract: Similarity properties of magnetic fields in axial coil systems are utilised together with extensive computations of various coil geometries to establish a set of design parameters α = 137, β 1 = 025 and β 2 = 0625 defining the optimum split-coil configuration for the superconducting open gradient magnetic separator An example of such a separator with magnetic force densities of 48 × 108Nm-3is presented and analaysed

Method of magnetic cylinder assembly

Abstract: A magnetic cylinder and plate for offset printing. The cylinder has annular magnets and pole pieces. The magnetic circuit is completed through a printing plate. The magnetic flux substantially saturates the pole pieces and plates. The area ratio of the pole pieces to the magnets is greater than about 0.45 to 1 and preferably about 0.6 to 1. In assembling the magnets and cylinder, the magnets are wrapped into slots between the pole pieces. The magnets are angularly displaced so that the leading magnet is positioned between the pole pieces before it is in proximity to the trailing magnet and demagnetization of the magnets is minimized.

Method and apparatus for the pressing and alignment of radially oriented toroidal magnets

Abstract: A method and apparatus for pressing magnetic powder in a toroidal-shape we in a radial magnetic field. A magnetic flux is produced and carried by a die rod through the axial center of toroidally-shaped magnetic powder. An annular portion coaxially surrounding the die rod and magnetic powder is connected to a yoke member which carries the magnetic flux back to the magnetic flux producing means. This completes the magnetic circuit, and creates a radial magnetic field across the toroidally-shaped magnetic powder between the die rod and the annular portion. This radial magnetic field aligns the granules of the toroidally shaped magnetic powder during pressing.