Showing papers on "Magnetic circuit published in 1997"

Micro-electromechanical relays

Abstract: A micro-electromechanical relay ('micro-relay') designed to both miniaturize and improve upon present day electromechanical relays. The micromachining fabrication process used to make the inventive micro-relay is based upon technology originally used by integrated circuit (IC) manufacturers. In simplest terms, the preferred inventive process consists of three steps, all performed using micromachining techniques. First, a layer of magnetic material is laid down on a substrate and patterned into a desired shape. Next, an electromagnetic coil (3) is created adjacent this material. Finally, a second layer of very efficient magnetic material is laid down adjacent the first two layers, forming a magnetic circuit, and having a portion fashioned into a deflectable structure, such as a cantilever beam (4A). The deflectable structure (4A, 4B) has at least a portion that is suspended over or adjacent to at least one electrical contact. In operation, current passes through the coil (3), clausing the deflectable structure (4A, 4B) to defect, and either make or break contact with the electrical contacts. The invention includes a unique unpowered hold feature. By integrating an electrostatic actuating capacitor into the micro-relay, an electrostatic force can be generated between the cantilever beam and the substrate (1) of the micro-relay that is strong enough to hold the relay in the 'ON' position. Turning the relay 'OFF' requires only that the voltage be removed.

Magnetic film inductors for radio frequency applications

Abstract: Responding to the increasing demand for miniaturization and circuit integration of rf inductors we analyze various aspects of designing planar inductive circuits based on magnetic films as well as demonstrate substantially enhanced inductance characteristics for some prototype structures.

Apparatus for receiving telemetry signals from active implantable medical devices

Abstract: A device for the reception of signals emitted by an active implanted medical device. The device has a signal collector coil for the reception of a magnetic induction which receives a useful signal component (Bs) emitted by the implanted device (26) and a parasitic signal component (Bp) of external origin. There is at least one collecting coil (12) wound on a first portion (14) of a magnetic circuit and at least one compensation coil (22) wound on a second portion (20) of the magnetic circuit, the two portions of the magnetic circuit belonging to a common magnetic element (16) and being configured in a manner such that, when the device is disposed in face of the implanted device, the collecting coil is essentially crossed one time by the magnetic induction field lines of the useful signal component (Bs) and the compensation coil is crossed essentially twice, in opposite direction, by the same magnetic induction field lines, thereby allowing to discriminate the useful signal component for improved signal to noise ratios and high speed data transmission.

A magnetic equivalent circuit approach for predicting PM motor performance

Abstract: Low power industrial motor electrical drives are dominated by the induction motor, followed by permanent magnet, (PM) motors. This paper presents a magnetic equivalent circuit (MEC) method for predicting the performance of surface mounted PM motors at the design stage. The MEC technique is interesting, as it gives fast (minutes), and acceptably accurate results. It provides a trade off between conventional, empirical methods, having fast simulation times (seconds), limited accuracy and flexibility, and the finite element method, which requires long simulation times (hours) but offers high accuracy and flexibility. Important issues such as element types, reluctance network, saturation, sensitivity to element density, and verification of obtained results are described.

Design rules for MR fluid actuators in different working modes

Abstract: The behavior of actuators based on magnetorheological fluids is determined by a variety of parameters. The magnetorheological properties of the MR suspension, the working mode (shear mode, flow mode, squeeze mode) and the design of the magnetic circuit consisting of MR fluid, flux guide and coil all considerably influence the properties of the actuator. This paper presents design rules for MR fluid actuators in different working modes. The behavior of MR fluids in the three working modes was investigated by using a rotational viscometer, a flow mode damper and a new measuring technique working in the squeeze mode. The measurement results for various magnetic flux densities are reported and the results of the different working modes are compared. High dynamic damping forces dependent on the magnetic field can be achieved especially in the squeeze mode. The design of the magnetic circuit of an MR fluid actuator is analyzed by using finite-element-methods. The advantages of integrating permanent magnets into the magnetic circuit of an MR fluid actuator are pointed out. The working point of the actuator can be adjusted by permanent magnets without consuming any power and the maximum power required to drive the actuator can be reduced. From these results design rules for MR fluid actuators are developed.

A large-force, fully-integrated MEMS magnetic actuator

Abstract: A large-force, fully-integrated, electromagnetic actuator for microrelay applications is presented. Designed for high efficiency, the actuator integrates a cantilever beam and planar electromagnetic coil into a low-reluctance magnetic circuit using a combined surface and bulk micromachining process. Experimental testing shows that a coil current of 80 mA generates a 200 /spl mu/N actuation force. Theoretical extrapolation of the data indicates that an actuation force in the millinewton range can be produced by a coil current of 800 mA. The tested actuators have a footprint of less than 8 mm/sup 2/ and their fabrication is potentially compatible with CMOS processing technology.

Rotating electric machines with magnetic circuit for high voltage and method for manufacturing the same

Abstract: A rotating electric machine for direct connection to all types of high-voltage networks, in which the magnetic circuit adapted for high voltage comprises a rotor, stator and windings. The winding comprising a conductor surrounded by a solid insulation system. The invention also relates to a method for manufacturing the same.

Thin film heads having solenoid coils

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.

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 time-stepping coupled finite element-state space model for induction motor drives. I. Model formulation and machine parameter computation

Abstract: A time-stepping coupled finite element-state-space model for induction motor drives is developed. The model utilizes an iterative approach to include the effects of magnetic nonlinearities, and space harmonics due to the machine magnetic circuits' topology and discrete winding layouts. Model formulation and development, which include an improvement in the layout of the cage circuit representation, are given in this paper. This improvement leads to an enhancement of the "well-posedness", that is, reduction of ill-conditioning in the overall numerical convergence of the model. Meanwhile, in a companion paper results of induction motor performance simulation are compared with no-load and load tests for sinusoidal and inverter operating conditions. Particular attention is given to comparison between sinusoidal and inverter operating losses obtained from this generalized model.

Anisotropic magnet brushless motor having a rotor with elastic insulating support structure

Abstract: A permanent-magnet type brushless motor has a rotor which is made by integrally forming a rotating magnetic pole comprising a cylindrical multi-pole anisotropic magnet, a shaft and an elastic insulating supporting member having rigidity lower than at least that of the shaft. The multi-pole anisotropic magnet causes its magnetic flux to flow to form the closed magnetic circuit, thereby eliminating the necessity of forming the closed magnetic circuit using an inner stator core in the magnet required for the radial anisotropic magnet. A cylindrical casing holding therein a stator core.

Improved simulation of HVDC converter transformers in electromagnetic transient programs

Abstract: In electromagnetic transient simulation HVDC converter transformers are normally represented as magnetically independent single-phase units. However, three-limb converter transformers are often used in HVDC schemes. Single-phase and three-limb three-phase transformer models are derived using a unified magnetic equivalent circuit concept. The new models are verified with laboratory and field data. Also, a comparison is made between the transient performance of HVDC converters with conventional and proposed transformer models.

Analysis of PMLSM using three dimensional equivalent magnetic circuit network method

Abstract: This paper presents characteristics of a permanent magnet linear synchronous motor (PMLSM) considering lateral leakage flux and lateral displacement. In order to analyze the PMLSM with large air gap and finite width, a new three dimensional equivalent magnetic circuit network method (3D EMC) is introduced, which supplements the magnetic equivalent circuit by using numerical techniques. It can model flux ripple three-dimensionally by the teeth and slot structure of the PMLSM, and can take nonlinear magnetic phenomenon into account, which results from using the distributed magnetic circuit parameter, permeance. The analysis considering lateral flux and lateral displacement in the PMLSM which is problematic in 3D is performed using 3D EMC and is compared with the experimental value.

Synchronous compensator plant

Abstract: The magnetic circuit of synchronous compensator plant is included in an electric machine which is directly connected to a high supply voltage of 20-800 kV, preferably higher than 36 kV The electric machine is provided with solid insulation and its winding(s) is/are built up of a cable (6) intended for high voltage comprising one or more current-carrying conductors (31) with a number of strands (36) surrounded by at least one outer and one inner semiconducting layer (34, 32) and intermediate insulating layers (33) The outer semiconducting layer (34) is at earth potential The phases of the winding are Y-connected, and the Y-point may be insulated and protected from over-voltage by means of surge arresters, or else the Y-point is earthed via a suppression filter A procedure is used in the manufacture of a synchronous compensator for such plant, in which the cable used is threaded into the openings in the core for the magnetic circuit of the synchronous compensator

Simulation study of the magnetic coupling between radial magnetic gears

Abstract: The torque of magnetic coupling with different magnetic poles has been investigated by theoretical computations with two dimensional modeling processes of finite element analysis. The torque is sensitive to the number of magnetic poles, the material of the magnetic gears, and the distance between the magnetic gears. For a 2 mm separation distance of two magnetic gears with 20 mm radius, the maximum torque occurs between 6 and 20 poles which is dependent on the thickness of the iron yoke inside the magnets, and on the magnetization configuration within a pole of the magnets. This is explained by analyzing the magnetic coupling strength of each pole. Finally, the computer calculation is tested using an experimental data taken from a sintered NdFeB magnetic gear.

Flywheel energy storage

Abstract: PROBLEM TO BE SOLVED: To provide a flywheel energy storage which eliminates influence of running vibration, yawing, pitching, etc., at the time of being loaded on a self-running machine such as an electric motorcar, etc. SOLUTION: A rotary shaft 14 is arranged vertically within a device housing 9, and a discoidal flywheel 2 is integrated with the bottom of the rotary shaft 14. The rotary shaft 14 is supported rotatably by an upper ball bearing 16 and a lower ball bearing 17 of roller bearings, and a magnetic ball bearing 1 of a magnetic energizing means. The magnetic bearing 1 is a passive thrust magnetic bearing which constitutes a magnetic circuit of a magnetic rotor 25 and a magnetic stator 26, and it energizes the rotary shaft 14 upward with the energizing force corresponding to the weight of the rotary shaft 14, the flywheel 2, etc., and the pre-load of the lower ball bearing 17. Moreover, damping rings 19 and 20 of vibration attenuating means having large rigidity and an attenuating function are interposed between the device housing 9 and both ball bearings 16 and 17. COPYRIGHT: (C)1999,JPO

Rotating electrical machine plants

Abstract: The present invention relates to installations for transformerless generation of HVDC and wherein the installation comprises rotating high-voltage single-winding/multiple-winding machines and converters. The single-winding/multiple-winding machine comprises a magnetic circuit with one or more magnetic cores and one or more windings, phase-shifted in space, which comprise a cable with one or more current-carrying conductors (2), each conductor comprising a number of strands, around each strand there being arranged an inner semiconducting layer (3), around which is arranged an insulating layer (4) of solid insulation, around which is arranged an outer semiconducting layer (5).

Energy storage flywheel apparatus and methods

Abstract: A flywheel energy conversion device (10) provides highly efficient conversion between kinetic and electrical energy. The flywheel (10) produces increased output by providing armature coils (44) in an air gap (46) formed about the flywheel (both radial and axial embodiments are described). In preferred embodiments, field coils (30, 32) of a magnetic circuit are energized with DC drive current that creates homopolar flux within a rotating solid rotor (12) having teeth (14) 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 (14) passing across an armature air gap (46). Air gap armature coils (44) 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.

Low-noise toroidal thin film head with solenoidal coil

Abstract: The invention relates to a low-noise toroidal TFH device including a solenoidal or helical coil with low coil resistance and inductance, especially suitable for very high magnetic recording areal densities and channel frequencies. The length of a solenoidal coil turn is only about 20-30% that 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). Also, the solenoidal coil coupling efficiency between each turn and the magnetic core is practically 100%, thereby improving the write and read-back efficiencies. Other features of the invention include a non-via large back-closure contact area between the bottom and top magnetic poles along their entire back-side width, and elimination of all other open branches and loose ends in the magnetic circuit. 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.

Comparison of lumped parameter and finite element magnetic modeling in a brushless DC motor

Abstract: The FEM is a favored motor design tool for its high accuracy. Magnetic equivalent circuit analysis, an alternative to FEM, is becoming popular for its fair accuracy and quick repetition of computation. An equivalent circuit model of a brushless DC motor is developed and its ability to accurately predict various motor performance parameters is assessed.

Artificial molecule realization of a magnetic wall

Abstract: The design of magnetic materials can be achieved with artificial magnetic molecules formed by electrically small loop antennas loaded with passive electrical circuit elements. A time derivative Lorentz material response is achieved with a series resistor and capacitor load. It is shown that the parameters of this magnetic molecule can be selected to yield a time derivative Lorentz material that acts as a highly conducting magnetic wall.

Comparison of techniques for measurement of shaft currents in rotating machines

Abstract: Irregularities in the magnetic circuits of motors may result in spurious voltages that lead to shaft currents through the shaft, bearings, bearing supports and closing through the machine framework. The IEEE Standard Test Procedure for Polyphase Induction Motors and Generators discusses the shaft current and presents a measurement method for recording either the voltage across the ends of the shaft or the current. This paper discusses an alternative measurement approach and its application to the identification of shaft current in a large induction machine. Procedures were developed for measuring the shaft current. The procedures include the shunt current method and the measurement using the Rogowski coil. Only the Rogowski coil measurement yields accurate measurements of shaft currents whereas the other method either yields inaccurate measurement or may result in other problems for the machine's integrity. The theory and justification for the superiority of the Rogowski coil method is presented along with supporting test data.

Sensor arranged for detecting angular displacement and direction of valve axle

Abstract: A sensor used to detect an opening angle of, for example, a throttle valve comprising: a pivotable valve axle arranged so as to be pivoted through a pivoted angle; a magnet; a first magnetic circuit, through which a first magnetic flux branched from a total magnetic flux developed from the magnet is passed; a second magnetic circuit, through which a second magnetic flux branched from the total magnetic flux developed from the magnet is passed; a pair of first and second Hall effect devices, the first Hall effect device being interposed in the first magnetic circuit so as to output a first signal according to the first magnetic flux passing therethrough and the second Hall effect device being interposed in the second magnetic circuit so as to output a second signal according to the second magnetic flux passing therethrough; and a calculation circuit, in response to the first and second signals of the first and second Hall effect devices, for calculating a level of a detection signal (So1, So2) of the sensor from the first and second signals outputted from the first and second Hall effect devices and for outputting the detection signal, the level of the detection signal being linearly varied according to the pivoted angle of the valve axle.

Single dipole permanent magnet structure with linear gradient magnetic field intensity

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 pole pieces and blocking magnets are tapered along the longitudinal axis such that the rectangular gap narrows from the proximate end to the distal end of the gap. The structure is thus capable of generating a magnetic field having a linear range of flux densities from a relatively low flux density to 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 range of 0.5 Tesla or less to 2.0 Tesla or more.

Computational algorithms for linear variable differential transformers (LVDTs)

Abstract: The authors present an equivalent magnetic circuit for a solenoid linear variable differential transformer. Using magnetic circuit theory, the calculations for its magnetic circuit reluctance, mutual inductance, output voltage and sensitivity are provided. Experimental tests are used to verify the calculations.

Magnetic Field Sensors for Magnetic Position Sensing in Automotive Applications

Abstract: Magnetic position sensors are transducers whose output is an electrical signal that is a function of a mechanical motion. They consist of a permanent magnet, a magnetic field sensor, and a moving magnetic circuit. Being contactless, they do not wear out. Unlike optical systems, they are impervious to contamination. With the proliferation of microprocessor control in many on-board automotive applications, magnetic position sensing becomes a crucial function, found e.g. in cam and crankshaft sensors used for ignition timing and engine misfire detection, in brushless electrical motors, in wheel speed sensors and in other applications. This paper first reviews the requirements put on the magnetic field sensors in these applications. Five main types of field sensors are used: Si Hall sensors with integrated amplifiers, GaAs Hall sensors, InSb-based magnetoresistors, anisotropie magnetoresistors (AMR), and metal-multilayer magnetoresistors (GMR). Magnetoresistors are almost always used as differential pairs, either in Wheatstone bridges or with matched constant current sources. The two characteristics of each type of field sensors that matter most are their sensitivity to magnetic field, and the smallest amount of field modulation they can detect, i.e. their resolution, which is mainly limited by the drift of the outputs with temperature. These parameters are measured and reported here on the 5 types of sensors; the work is an update of a 1993 review by the author.

Three-dimensional magnetic field analysis of electrodes for VCBs [vacuum circuit breakers]

Abstract: This paper describes the application of three-dimensional magnetic field analysis, including eddy current effects on the axial magnetic field electrodes of vacuum circuit breakers. The accuracy of the analysis is verified with both basic and full models of the electrodes. The analytical results were compared with measured values obtained by a Hall sensor system. The effect of the electrode slit length and the electrical conductivity of the contact on the magnetic flux density and phase difference was analyzed with the full model. The magnetic field in the gap was simulated when the arc ignites between the electrodes. These results demonstrated that the magnetic design of the electrodes can be carried out on an engineering workstation.

A device for casting in a mould

Abstract: A device, for continuous or semicontinuous casting of metal in a casting mould, for braking and splitting up a primary flow of hot melt supplied to a casting mould, and controlling the flow of melt in the non-solidified portions of a cast strand which is formed in the casting mould. The device comprises a plurality of water box beams (51, 52) which support and cool the casting mould and supply a coolant to the casting mould, and a magnetic brake. The magnetic brake is adapted to generate at least one static or periodic low-frequency magnetic field to act in the path of the inflowing melt and comprises at least one or more magnets (71, 72, 710, 720, 730, 740) to generate the magnetic field, one or more cores to transmit the magnetic field generated by the magnet to the casting mould and the cast strand present in the casting mould, and one or more magnetic return paths to close the magnetic circuit. The water box beam is completely or partially arranged in a magnetically conducting material. A magnetic brake comprises one or more magnetic circuits, each of which, in addition to the magnet, the core and the return path, also comprising the casting mould and the cast strand present in the casting mould into a magnetic circuit. The magnet (71, 72, 710, 720, 730, 740) is arranged in a recess (91, 92) in a water box beam. The magnet and the magnetic return path are arranged integrated into the water box beam such that the magnet and the magnetic return path in their entirety are arranged inside the rear wall of the water box beam.

High-voltage transformer

Abstract: PROBLEM TO BE SOLVED: To provide a high-voltage transformer which hardly causes discharge accidents and can be reduced in size SOLUTION: In a high-voltage transformer, a plurality of secondary coils 3 and 4 which commonly use magnetic fluxes generated from primary coils 1 and 2 are wound in the opposite directions and connected in parallel with each other Major magnetic circuits are formed of soft ferrite cores and the secondary coils 3 and 4 are arranged at different positions in the circumference of the cores COPYRIGHT: (C)1998,JPO