Showing papers on "Magnetic circuit published in 1996"

Principles of Electric Machines and Power Electronics

Abstract: Magnetic circuits transformers electromechanical energy conversion DC machines induction (asynchronous) machines synchronous machines single-phase motors special machines transients and dynamics power semiconductor converters. Appendices: windings units and constants Laplace transforms.

A method for dynamic simulation of air-gap eccentricity in induction machines

Abstract: In this paper, a method is proposed which enables the simulation of the air-gap eccentricity in induction machines. The method is based on the coupled magnetic circuit approach. The model is derived by means of winding functions, and no symmetry in windings layout is assumed. The parameters of the model are calculated directly from the geometry and winding layout of the machine. The effect of eccentricity is included in calculation of machine inductances. It is shown that by proper modeling of the induction motor it is possible to determine the effect of eccentricity on the machine startup, whether the machine is running off a sinusoidal supply or a converter. Theoretical foundations of the technique, as well as the detailed differential equations describing the machine performance under rotor eccentricity are presented.

Magnetic field sensor and current and/or energy sensor

Abstract: A magnetic field sensor has two flux concentrators which serve to strengthen a magnetic field to be measured and which are separated by an air gap. Two Hall elements are arranged outside the air gap in such a way that at least a part of the field lines which lead from the first to the second flux concentrator pass through the two Hall elements in approximately opposite directions. Such a magnetic field sensor is less sensitive to external interference fields. It is suitable for the measurement of very weak magnetic fields and also for use as a current and/or energy sensor.

Novel permanent magnet motor drives for electric vehicles

Abstract: Novel permanent magnet (PM) motor drives have been successfully developed to fulfil the special requirements for electric vehicles such as high power density, high efficiency, high starting torque, and high cruising speed. These PM motors are all brushless and consist of various types, namely rectangular-fed, sinusoidal-fed, surface-magnet, buried-magnet, and hybrid. The advent of novel motor configurations lies on the unique electromagnetic topology, including the concept of multipole magnetic circuit and full slot-pitch coil span arrangements, leading to a reduction in both magnetic yoke and copper, decoupling of each phase flux path, and hence an increase in both power density and efficiency. Moreover, with the use of fractional number of slots per pole per phase, the cogging torque can be eliminated. On the other hand, by employing the claw-type rotor structure and fixing an additional field winding as the inner stator, these PM hybrid motors can further provide excellent controllability and improve efficiency map. In the PM motors, by purposely making use of the transformer EMF to prevent the current regulator from saturation, a novel control approach is developed to allow for attaining high-speed constant-power operation which is particularly essential for electric vehicles during cruising. Their design philosophy, control strategy, theoretical analysis, computer simulation, experimental tests and application to electric vehicles are described.

A new miniature magnetic field probe for measuring three-dimensional fields in planar high-frequency circuits

Abstract: A new noncontacting miniature magnetic field probe for measuring the surface current distribution on high-frequency planar circuits in x-, y-, z-directions in the 1-20 GHz band has been designed, fabricated and tested. The field probes have very small dimensions and do not need any connection to the operating circuit under test, therefore there is almost no perturbation of the circuit properties. This simple and practical magnetic field probes can be used to assist the design of microwave circuits, antenna diagnostics and to test products in industry. This paper describes the production procedure of the magnetic field probes, a scanning diagnostic system, measurement examples and comparisons between measurements and calculations. The measurement results agree very well with theoretically expected field distributions.

Concealed magnetic ID code and antitheft tag

Abstract: The invention relates to a special type of magnetic tag that serves both as an identifier of the article to which it is attached and as an antitheft device. The former attribute is especially important should stolen property be recovered. Identification comes about through the use of an array of individual magnetic elements that are closely spaced, preferably along and perpendicular to an amorphous wire or strip. The magnetic elements can take the form of magnetic ink, high coercivity wire, thin foil, or amorphous wire. The array may be personalized (coded) by leaving out elements of the array or driving selected elements to saturation while others remain demagnetized. The elements can also be in the form of a double array to constitute `1`s and `0`s to form a code. Reading of the elements is accomplished with a special reading head consisting or one or more small magnetic circuits coupled to one or more pickup loops. A longer length of soft magnetic wire or thin strip is used to trigger an anti-theft alarm when activated by an external field from a magnetic gate.

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.

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.

An augmented circuit model for magnetic bearings including eddy currents, fringing, and leakage

Abstract: Magnetic bearings are often designed using magnetic circuit theory. When these bearings are built, however, effects not included in the usual circuit theory formulation have a significant influence on bearing performance. Two significant sources of error in the circuit theory approach are the neglect of leakage and fringing effects and the neglect of eddy current effects. This work formulates an augmented circuit model in which eddy current and flux leakage and fringing effects are included. Electrical impedance predictions from the model are found to be in good agreement with experimental data from a typical magnetic bearing.

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.

A simple dynamic model for eddy currents in a magnetic actuator

Abstract: This paper presents a simple dynamic model of eddy currents in a magnetic actuator. The model is based on the application of Maxwell's equations to a homogeneous ferromagnetic conductive material. The resulting diffusion equation is solved in two dimensions for a cross-sectional cut through a rectangular bar; boundary conditions are imposed by a sinusoidally varying actuator coil current. The utility of the new modeling approach is illustrated by predicting the dynamic performance of a magnetic bearing actuator. The predictions are found to be in good agreement with measured values. The model provides a new and convenient method of modeling the relationships among voltage, current, force, and flux in magnetic circuits containing eddy currents.

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.

Electrical current sensor with magnetic field detector

Abstract: The invention concerns an electrical current sensor comprising a magnetic circuit (3), with an air gap (3a), a winding (4) on the magnetic circuit in which a current to be measured flows, a magnetic field detector (5) arranged in the air gap, and a support plate (2) carrying an electrical circuit (6) configured to amplify an output signal from the magnetic field detector. The support plate (2) comprises a main part (21) and a lateral extension (23), the entire unit having an area cut away from the overall rectangular shape of the plate. The turns (4a) of the winding (4) are arranged at that area in such a way that the thickness of the sensor depends on the transverse dimensions of the winding.

A nodal analysis approach for 2D and 3D magnetic-circuit coupled problems

Abstract: This paper presents a unified approach for magnetic-circuit coupled problems in 2D and 3D. The approach is based on the A/spl I.oarr/-V formulation with the Coulomb gauge for low frequency eddy currents, and the modified nodal analysis method for electric circuit simulation. It supports static, time-harmonic and transient analysis types. Both stranded coils without eddy currents and massive conductors with eddy currents are included. Compared to other methods, the present approach can be easily implemented in existing finite element electromagnetic codes. Numerical examples are presented to validate the theory.

Controllable fluid rehabilitation device including a reservoir of fluid

Abstract: A controllable fluid device (20) for rehabilitation of injured or weakened complex appendages such as the hands and feet. The controllable fluid device (20)includes a reservoir (34)which contains a sufficient amount of controllable fluid (52)such as a Magnetorheological (MR) fluid. A magnetic field generator (36)provides the magnetic field (H) which is applied to the controllable fluid (52) by a magnetic circuit (60). In one aspect, an electromagnet including a coil (58) and core (54) provides the magnetic field (H). The intensity of the magnetic field is controlled via a controller (38). In another aspect, the magnetic field (H) is provided by a permanent magnet (44) and a mechanical shunt mechanism (42) is used to vary the magnetic field intensity. Other embodiments include a heater unit (66) with optional thermostat (74).

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.

Inductive measuring device for measuring alternating current components superposed to a high direct current

Abstract: A direct current of high intensity having alternating current components superposed thereon is flowing in a conductor 1 through a magnetic circuit 5, 6. Two measuring coils 7, 8 are arranged inside opposite air-gaps of the magnetic circuit and are connected in an electric measuring circuit in series with each other and in parallel to voltage dividers 12, 13 and 14, 15. The alternating current components induce voltages in the coils 7 and 8 which add up, the sum thereof appearing across the series-connection of resistors 13, 15. This voltage is integrated by an integrating circuit 10 and then filtered in a band-pass filter 11. The magnetic circuit 5, 6 is screened by lateral screening members 30, 31 so that the remaining field lines of a lateral parasitic magnetic field produce in the magnetic circuit flux portions which are approximately equal and which are added to the useful flux in one air-gap and are substracted from the useful flux in the other air-gap.

Integrated motor/generator/flywheel utilizing a solid steel rotor

Abstract: A flywheel energy conversion device provides highly efficient conversion between kinetic and electrical energy The flywheel produces increased output by providing armature coils in an air gap formed about the flywheel (both radial and axial embodiments are described) In preferred embodiments, field coils of a magnetic circuit are energized with DC drive current that creates homopolar flux within a rotating solid rotor having teeth cut from a flat disk The total reluctance of the magnetic circuit and total flux remain substantially constant as the rotor rotates The flux may travel radially outward and exit the flat disk through the teeth passing across an armature air gap Airgap armature coils are preferably utilized in which the changing flux density (due to the rotating teeth) induces an output voltage in the coils The flux is diffused before returning to the rotor in one of several ways such that core losses are effectively reduced, thereby enabling the flywheel to operate efficiently at high frequencies

Induction heat fusing device

Abstract: An induction heating device for printers, copiers and the like includes a magnetic coil assembly and a heated metal body that form a closed magnetic circuit. To compensate for the effects of heat radiation at the ends of the heated metal body, a greater amount of heat is generated at the ends of the body than at the center thereof. In one approach, the amount of heat is varied by changing physical parameters of the magnetic circuit, such as the spacing of the coil assemblies from the heated body, the relative sizes of the cores, and/or the relative magnetic permeability of the cores. In another approach, the electrical connection of the coils of multiple assemblies are arranged such that the coils in the center of the heated body are in parallel, and the coils at the ends of the body are in series with the parallel central coils.

Faraday rotator which generates a uniform magnetic field in a magnetic optical element

Abstract: A Faraday rotator which includes a magnetic optical element and a magnetic field generating unit. The magnetic optical element has an optical path extending therethrough. The magnetic field generating unit is positioned so as not to obstruct the optical path, and generates a uniform magnetic field in the magnetic optical element. The magnetic field generating unit can include a first magnet unit and a second magnet unit. The first magnet unit is positioned so as not to obstruct the optical path and generates a magnetic field passing through the magnetic optical element. The second magnet unit is positioned so as not to obstruct the optical path and generates a magnetic field passing through the magnetic optical element. The magnetic field generated by the second magnet unit is perpendicular to the magnetic field generated by the first magnet unit and combines with the magnetic field generated by the first magnet unit to produce a uniform magnetic field in the magnetic optical crystal.

Miniature device for executing a predetermined function, in particular microrelay

Abstract: This miniature relay is obtained by micromachining on a substrate using etroforming, photolithography and/or similar techniques, all its components being obtained on the substrate by integration operations similar to those used for fabricating integrated circuits. A mobile contact (26) is borne by an elastic lever (19) attached, overhanging, to the substrate (1). A lever (19) forms a rocker and is attached to the substrate (1) by means of a deformable connection. At each of its free ends is provided an armature (20, 21) of a magnetic circuit which defines a seat against which the armature can be applied with a magnetic force opposite that generated by the elastic deformation of the lever (19). Each magnetic circuit is additionally provided with at least one coil (10a, 10b, 11a, 11b) which can be selectively excited and can generate a second magnetic force, opposite that of the magnetic circuit, in order, when the armature is applied onto its seat, to release the armature associated with this coil and apply the other armature onto its seat by tilting the lever (19).

System for concealed serialization utilizing a soft magnetic antitheft element

Abstract: The invention relates to a special type of magnetic tag that serves both as an identifier of the article to which it is attached and as an antitheft device. Identification comes about through the use of an array of individual magnetic elements that are closely spaced, preferably along and perpendicular to an amorphous wire or strip. The wire or strip forms an integral part of the identification array and can be used as an anti-theft device to trigger an alarm when activated by an external field from a magnetic gate. The array may be personalized (coded) by leaving out elements of the array or by driving selected elements to saturation while others remain demagnetized. The elements can also be in the form of a double array to constitute `l`s and `0`s to form a code. Reading of the elements (code) is accomplished with a special reading head consisting of one or more small magnetic circuits coupled to one or more pickup loops utilizing, in some cases, the Matteucci effect.

Magnetic circuit modelling of the field regulated reluctance machine. Part I: model development

Abstract: A transient magnetic circuit model of a field regulated reluctance machine is presented. The model is based on flux loop equations rather than node equations as have previously been employed. A key feature of this approach is that magnetic circuit models based on loop equations permit an entire machine to be represented by only one equivalent pole.

Finite elements coupled to electrical circuit equations in the simulation of switched reluctance drives: attention to mechanical behaviour

Abstract: A method to model the switched reluctance motor is presented in this paper. The methodology is based on the simultaneous solution of the magnetic field, represented by the two-dimensional finite element method, with electrical circuit equations. With this model, the currents in the windings are calculated and the force distribution on the stator teeth is obtained. The mechanical response to magnetic forces is calculated by a finite element code.

Accelerator with closed electron drift

Abstract: The invention is related to a plasma technology field, in particular, to plasma accelerators, used in a space technology, in scientific researches and in industry. A technical result is that the accelerator has an increased lifetime which is achieved by reducing in wear of discharge chamber walls. An accelerator with closed electron drift includes a ring anode 1 with an anode cavity 2, a magnetic circuit 3, field coils 4 and pole tips 5 with a ring interpole gap, external 6 and internal 7 ring cathodes, a cathode-compensator 8, a power supply 9, a means forming positive gradient of magnetic field 10 which can be formed by walls of the anode 1 made of ferromagnetic material. Outlet edges of the anode 1 are provided with nozzles 11 made of nonmagnetic material; a nozzle shape coincides with shape of the magnetic field line of force which is tangential to outlet edges of the anode. The anode 1 is connected with a system supplying with gaseous active substance by means of the hole 12.

High-temperature superconducting magnetic bearing

Abstract: A passive magnetic bearing structure for radially supporting a rotor with respect to a stator is provided, in which a magnetic circuit is mounted on the rotor or stator for generating two strongly different axial magnetic fields in two concentric angular gaps coaxial to the rotation axis and radially spaced from one another. At least three shortened superconducting turns are mounted on the stator circumferentially around the rotation axis so that under any tolerable shift of the rotor, one edge of every turn will be placed in one annular gap comprising magnetic field, and the radially opposite edge will be placed in the other gap. The invention is also directed to a linear magnetic bearing structure for restricting unwanted movement of a slider, comprising the slider, a guideway, and a magnetic circuit mounted on the slider or guideway for generating two strongly different magnetic fields perpendicular to the movement direction, in two different layers lengthened in the sliding direction and spaced from one another in the direction normal to both the sliding and magnetic field directions. A shortened superconducting turn is mounted on the slider or guideway so that any tolerable shift of the slider, one edge of every turn will be placed in one layer comprising magnetic field, and the radially opposite edge will be placed in the other layer.

Permanent-magnet type rotary electric machine

Abstract: PURPOSE: To increase only the effective magnetic flux amount contributing to the generating efficiency in the motor efficiency by employing a member coexisting a ferromagnetic part and a non-magnetic part in a rotor yoke, and disposing the non-magnetic part at the rotor yoke position for causing a leakage magnetic flux. CONSTITUTION: A rotor yoke 65 is made of the laminate of thin plates 67, and formed of a member coexisting a ferromagnetic part 650 and a non- magnetic part 660. A permanent magnet 1 is inserted into a through hole 68, and closely fixed in the yoke 65. Poles N, S of total four poles are formed on the outer periphery of a rotor 10 of the magnet 1. Since the part 660 indicated by a shade is the non-magnetic part, no short-circuit occurs in the magnetic flux in the yoke 65, and hence leakage magnetic flux is extremely small. As a result, the leakage magnetic flux generated between the poles formed at the permanent magnet or between the adjacent magnets can be suppressed, and a rotary electric machine having efficient magnetic circuit can be formed. COPYRIGHT: (C)1996,JPO

Method for making magnetic and electromagnetic circuit components having embedded magnetic materials in a high density interconnect structure

Abstract: A magnetic or electromagnetic circuit component includes an embedded magnetic material (e.g., ferromagnetic) in an HDI structure with alternating dielectric and metal or winding layers. In one embodiment, the ferromagnetic material is situated in a substrate well, or cavity, with or without an adhesive. Alternatively, the ferromagnetic material is co-fired with the ceramic substrate and then machined to achieve a required core shape. An electroplating process is employed to construct the metal layers, such process including differential plating for varying the thickness of metal layers and/or other portions of the circuit. Laser ablation or any other suitable technique is employed to make through-holes for insertion of the posts of a ferromagnetic core plate used to complete a magnetic circuit, if required. Advantageously, a magnetic or electromagnetic component may have a height of less than about 0.1 inch. Furthermore, such magnetic or electromagnetic circuit components allow for very low inductance interconnections between these components and other circuit elements. Moreover, in a power supply, for example, not only can the complete power supply be built using HDI technology, but power density is increased at relatively low cost and at a high level of reproducibility.

Application of harmonic balance-finite element method (HBFEM) in the design of switching power supplies

Abstract: Numerical modeling and analysis are effective techniques to assist in the design of high-frequency switching power supplies. Striving for high power densities and higher efficiencies has pushed the operating frequencies up, resulting in new circuit configurations and different component architecture. This paper presents a numerical method that is used to analyze magnetic systems for switching power supplies, in particular the switching resonant DC-DC converters. The method uses the harmonic balance technique combined with finite element methods and is referred to as the harmonic balance-finite element method (HBFEM). The HBFEM is used to solve various harmonic, eddy-current, hysteresis, and nonlinear problems applied to magnetic circuits used in switching power supplies. To evaluate the numerical results, comparisons are made with experimental results.

A permanent magnet ac machine structure with true field weakening capability

Abstract: New doubly salient ac machines in which the field excitation is developed by stationary permanent magnets has recently been undergoing development at the University of Wisconsin. Because of the unique geometry of the stator, these permanent magnets are readily accessible. Therefore, for experimental purposes, simple iron blocks have been used to “short” a large portion of the permanent magnet flux and thus reduce the back emf developed within the machine. However, for practical applications, field weakening schemes involving miniature linear actuators or high torque stepper motors are being explored, as well as machine designs with combined PM and electrical excitation. Preliminary experimental results show that a substantial reduction in the back emf can be readily obtained thus lending credibility to the concept of weakening air gap fields produced by stationary permanent magnets.