Showing papers on "Magnetic circuit published in 1988"

Alternating current generator

Abstract: An alternating current generator for supplying the electrical loads on a motor vehicle. The generator has a stator core that carries a three-phase stator or output winding. The rotor of the generator has two claw pole members that are so oriented that the fingers of the pole members are aligned. Disposed between the two pole members is a third pole member having projections disposed between the aligned fingers of the claw pole members. The rotor has two field coils which are so arranged and energized that the magnetic polarity of the two claw pole members is the same and opposite the magnetic polarity of the third pole member. One of the field coils can be replaced by a permanent magnet and when this is done the generator is provided with a magnetic circuit that can divert permanent magnet flux away from the stator core. Flux diversion is controlled by supplying unidirectional current to the field winding under the control of a voltage regulator.

Harmonic field calculation by the combination of finite element analysis and harmonic balance method

Abstract: A finite-element-method (FEM) time-periodic magnetic-field calculation is described. An AC calculation involving saturation characteristics requires many iterations and much storage space. The combination of FEM and the harmonic balance method enables the harmonic magnetic flux distribution under AC magnetization to be calculated economically. The method is applied to the magnetic-field analysis of a reactor and an electromagnet. >

3-D finite element method for analyzing magnetic fields in electrical machines excited from voltage sources

Abstract: A method for analyzing 3-D magnetic fields and currents in electrical machines excited from voltage sources has been developed. It was obtained by expanding the 2-D finite-element method into three dimensions, using the A phi method. The basic idea and the finite-element formulation are described. The effectiveness of the method is shown by some application examples. >

A simplified approach to magnetic equivalent-circuit modeling of induction machines

Abstract: The fundamentals of magnetic equivalent circuit representation of electromechanical systems and the application of these principles to the computation of induction machine dynamics have been previously discussed. Here, some simplifications which clarify the principles of the method and speed up the computation are introduced. The ability of the method to evaluate both time and space variations simultaneously is illustrated with graphs which represent the traveling waves in induction machines on a tooth-by-tooth basis. >

Dynamoelectric machine with diamagnetic flux shield

Abstract: An AC electrical machine which includes a superconducting, diamagentic flux shield cylinder enclosing the stator windings such that the magnetic flux produced by the machine's rotor is bottled within the flux shield.

Electronic transformers and circuits.

Abstract: Transformer Construction, Materials, and Ratings Rectifier Transformers, and Inductors Rectifier Performance Amplifier Transformers Amplifier Circuits Higher--frequency Transformers Saturable Magnetic Circuits High Voltage Pulse and Video Transformers Pulse Circuits Inverter Transformers Inverter Circuits Other Magnetic Devices Index

Applications of yokeless flux confinement

Abstract: A recently developed generalized technique for the production of large confined magnetic fields is used to design a number of novel permanent‐magnet flux sources. The simplest of these produces a transverse field in a long cavity of a rectangular cross section. In such structures, uniform fields that are of the order of the remanence of the material used are obtained easily. Applications include: NMR imaging, general electron device biasing, and the provision of bases for various periodic magnetic structures, such as wigglers, undulators, and twisters. Slight elaboration of such configurations can produce fields of up to three times the remanence. The fields of such structures can be readily adjusted by mechanical means, with continuous variation from zero to the maximum field. The wigglers and twisters afford instantaneous conversion from wiggler to twister and conversely. Adaptations of the basic principles can be used to produce radial, conical, and other unusual field orientations.

High sensitivity magnetic circuit

Abstract: For increased sensitivity a position sensor includes a magnetic circuit in which the stationary portion includes a permanent magnet whose width is optimally 1.5 times the tooth pitch of the exciter portion of the sensor and the magnet face proximate the exciter includes a thin layer of ferromagnetic material over which is centered a narrow magnetic sensing element, such as a magnetoresistor. The sensing element has a width typically less than the tooth width which is between 0.17 and 0.37 the tooth pitch. The needed flux density is typically available simply by appropriate magnet thickness or choice of magnet material without the need of a flux guide.

Magnetic helix non-contacting linear drive

Abstract: A non-contacting linear drive includes a fixed guidance part constructed as a profile part whose magnetic material in the vicinity of helixes (3,4) approaches (8,11,17) the latter and, at a distance from the helixes, forms a return path to the next helix. The rotary part has spaced double helixes, (3,4), a constant magnetic field (7) being produced in the magnetic circuit formed by a double helix and the magnetic return path. A very simple and economic construction and manufacture are consequently possible. The guidance part (2) can be constructed as a profile rail (9) or as a tube (10,15) and has window-like recesses (6), corrugations (11,12) or ribs (17). The double helix (1) can be constructed with permanent magnets (14) placed in the helixes with radial orientation or with permanent magnets (14) provided between soft magnetic helixes in axial orientation.

A modular transmission line/reluctance head model

Abstract: A transmission line model for calculating recording-head fields and efficiencies is described. Exact solutions are obtained for transmission line segments with fixed or varying gap and width. Using these solutions. Thevenin T-reluctance circuit equivalents are obtained for each segment of the total head transmission line structure, and the magnetic flux and fields are obtained by circuit analysis. External fringe fields at edges are also included. Using three basic building blocks: (1) constant-gap, variable or fixed-width regions, (2) graded-gap, variable or fixed-width regions, and (3) external fringe reluctances, in any number and sequence, virtually any head geometry can be quickly and reasonably modeled, without the need for reformulating the problem or respecifying boundary conditions. >

High sensitivity magnetic sensor

Abstract: A magnetic sensor is provided for use in detecting an external magnetic field, typically geomagnetism. Pulse or alternating current is applied across a wire or strip-shaped electrically conductive, magnetic body in its longitudinal direction to create an internal magnetic field in the magnetic body. A pick-up winding is wound around the magnetic body. The sensor detects an electric signal developed in the winding as a result of interaction of the internal and external magnetic fields.

Magnetic read head for a very narrow track

Abstract: Magnetic read head for very narrow track and production process. On a silicon substrate (10) is formed a magnetic circuit (P1, P2, P3), whose thickness is equal to the width of the track to be read. This magnetic circuit is interrupted by a magnetic spacer (20) and two slots (F1, F2), in which are inserted elements sensitive to the magnetic field, e.g. magnetoresistors. The latter are connected to an integrated circuit (12) in the silicon substrate. Application to the reading of information recorded on a magnetic track.

Device for transferring electric power

Abstract: A device for transferring electric power and/or information between two parts which are movable one with respect to the other, in particular between a door frame and a door leaf or an opening window leaf, mounted in this door frame, comprising a first coil wound on a first magnetic core and a second coil wound on a second magnetic core, the first coil being intended to be connected to an electric power source and to be mounted with its core on one of said parts, the second coil being intended to be mounted with its core on the other part, so that both said cores determine a magnetic circuit in at least one determined position of said parts one with respect to the other in order to so allow a variable electric current travelling in said first coil to induce a variable magnetic flux in both cores, and creates an electric current in the second coil when the latter is connected to a closed electric circuit.

System of permanent magnets for an intense magnetic field

Abstract: Permanent magnets for producing an intense field. A main magnetic circuit comprises two magnets (1, 1'), two pole pieces (2, 2') and a yoke (3). Two additional magnets (6, 6') of opposite magnetization reinforce the field in the air gap (5) while extending into the latter between edges (25, 25', 26, 26', 27, 27', 28, 28') of magnets (1, 1') and pole pieces (2, 2'). Application to imaging by magnetic resonance (tomography).

A Single-chip Squid Magnetometer

Abstract: THIS PAPER WILL DISCUSS the design and test of a superconducting quantum interference device (SQUID) magnetometer integrated on a single chip. This technique can be used in the construction of a multichannel magnetometer array that could serve as an image sensor in medical and other similar areas. The chip with a pickup coil, sensor, and feedback circuit, fabricated with niobium superconducting thin film on a Si substrate, and is operated at 4.2’K. Conventional RF and dc SQUID magnetometers use analogfeedback circuits, such as lock-in-amplifiers, making integration difficult’. A digital feedback loop using room-temperature electronics, has been tested’. Unlike other types, however, the present design combines a digital feedback circuit on the chip. This circuit must be able to function as a counter and a D/A converter. Its fabrication conventionally requires a large-scale Josephson logic circuit. However, in our chip the feedback circuit was integrated by introducing a circuit t o store magnetic flux quanta in a super-conducting loop, requiring only one write gate. The magnetometer requires only an ac bias and t o produce a digital output, without supplementary circuitry at room temperature: Figure 1. The output pulse can be processed by a digital processor or can, alternatively, be applied to a display instrument through a counter for directly monitoring input magnetic field waveforms. Figure 2 illustrates the circuit. A figure-eight pickup coil transmits the magnetic flux t o be measured t o the sensor through a pair of 20-turn integrated coils. The sensor is an interferometer having two Josephson junctions and two inductors, and has an asymmetric threshold curve; Figure 3a. The interferometer switches from a zero-voltage state to a finite-voltage state of lmV, when the bias current crosses the threshold curve. It is ac-biased and produces a pulse sequence. A positive or negative pulse is generated, depending on whether the input is positive or negative; Figure 3b. It is operative as a comparator by counting the number of positive ( N t ) and negative (N-) pulses. The difference (N’ N-) indicates whether the input is positive or negative; Figure 3c. The digital feedback circuit was fabricated using a superconducting storage loop and an interferometer as a write gate; Figure 2 . The write gate receives a pulse sequence and writes a positive or negative flux quantum to the storage loop when a pulse arrives. The threshold curve of the write gate affords operating-point crossing of the threshold curves twice, as shown by the dashed lines in Figure 4a. The two junctions, J1 and Jz,

Shielding superconducting solenoids

Abstract: A self-shielding system of closed superconducting circuits shields a specific volume from changes in an external magnetic field in which the circuits are located; the configuration of circuits is chosen so that induced currents in the circuits, arising from magnetic flux conservation for each closed circuit, tend to cancel any change in the external magnetic field. In another aspect, a single closed self-shielding superconducting circuit comprised of more than two circular loops connected in series shields a specific volume from changes in an external magnetic field in which the circuit is located; the configuration of the circuit is chosen so that induced currents in the circuit, arising from magnetic flux conservation for the circuit, tends to cancel any change in the external magnetic field.

New magnetooptic head with a built-in generator for a bias magnetic field

Abstract: A high performance magnetooptic head, which generates a bias magnetic field itself, has been developed. It has a moving magnet actuator to drive an objective lens. The moving magnets have two functions. One is to apply a constant magnetic field on the recording medium. The other is to comprise a magnetic circuit for focusing and tracking control. This magnetooptic head is suitable for use in the two-head erase and write method, in which it is not necessary to change the polarity of the bias magnetic field. Moreover, it enables designing a small-sized magnetooptic disk drive, because a bias magnetic field generator is built into the optical head.

Investigation of Magnetic Fields and Forces Arising in Open-Circuit-Type Magnetic Bearings

Abstract: The concept of magnetic bearings consists of using magnetic forces to maintain controlled separation between bearing surfaces. The closed-circuit-type magnetic bearings have been analyzed and reported in literature. In this paper, the development of a theory together with experimental verification for predicting both normal and transverse forces in open-circuit-type magnetic bearings in a quasi-static environment is described. For purposes of analysis, the magnetic bearing system was mathematically modelled by current densities and forces were calculated by using Ampere's law. Very good agreement between the theory and experimental data was observed. Also, experiments were performed to validate the previously developed theory for closed-circuit-type bearings employing high-permeability materials for the case when permanent magnets were used as a battery to energize the magnetic circuit. Presented at the 41st Annual Meeting in Toronto, Ontario, Canada May 12–15, 1986

Performance characteristics of brushless DC drives

Abstract: A simulation model for the performance prediction of brushless DC drives is used to investigate the speed control obtained from modulation index and commutation advance variations for a motor of complex magnetic circuit geometry powered by a sine-coded PWM (pulsewidth modulation) inverter. The results of the study show the effects of motor model complexity on voltage and torque. Optimum performance conditions in the field-weakening mode are determined, and the value of motors using sinusoidal induced voltages is explored. >

Gas cycle machine

Abstract: A gas cycle machine includes a moving coil composed of a first moving coil portion and a second moving coil portion opposing to the first moving coil portion and a magnetic circuit is constituted such that magnetic flux in a first gap in which the first moving coil portion is disposed passes through the first moving coil portion inwardly and magnetic flux in a second gap in which the second moving coil portion is disposed passes through the latter outwardly. Magnetic flux of a permanent magnet passes through the first and the second gaps in opposite directions, respectively, and, therefore, a closed magnetic circuit is composed of the permanent magnet, a cylinder of soft iron and an annular disc, which eliminates the necessity of providing a large circular disc as in the conventional engine.

Impact of load on winding inductances of permanent magnet generators with multiple damping circuits using energy perturbation

Abstract: A computer-aided method for determining the impact of load on winding inductances and other machine parameters of permanent magnet generators with multiple damping circuits is presented. The method is general in nature so that it can be applied to detailed computer-aided design processes of permanent magnet generator systems. The method is based on use of the abc frame of reference for development of the necessary state equations. >

Electric current sensing device of the magnetic field compensationtype

Abstract: A magnetic circuit is coupled with a primary conductor in which flows the current to be sensed. The magnetic circuit has an air gap with a magnetic field detector and is coupled with a measuring coil producing a magnetic flux for compensation the flux generated by the primary current. The necessary current in the measuring coil to achieve such flux compensation is a measure for the primary current. A yoke part of high magnetic permeability is arranged in the vicinity of the air gap inside the measuring coil so as to form a magnetic shunt between the two magnetic circuit portions forming the air gap.

A document detecting arrangement

Abstract: An arrangement for detecting bank notes having magnetic properties, comprising transport means (11) for transport­ing documents past a magnetic detector (12-14). The ob­ject of the invention is to increase the possibility and the reliability of distinguishing bank notes which are not genuine from genuine bank notes and bank notes of a given denomination/kind from bank notes of another denomination/­kind. The detector includes a permanent magnet (12) and a mag­netic circuit (13) having detector means (14) for detect­ing changes in the magnetic field through the magnetic circuit (13). The output side of the detecting means (14) is connected to a signal processing means (20) for gener­ating signals in response to the magnetic properties of bank notes transported through the arrangement. The magnetic circuit (13) includes an air gap (131) which is located closely adjacent the bank note transport path (0-0). The magnetic flux of the permanent magnet (12) in the air gap (131) is directed in a plane at right angles to the direction of the transport path (0-0) closely ad­jacent the air gap.

Modeling of transients in permanent magnet generators with multiple damping circuits using the natural abc frame of reference

Abstract: A computer-aided method for modeling the transient performance of permanent magnet generators and determining their parameters is presented The method is based on the development and use of state models in the natural abc frame of reference, in which the abc machine-winding parameters were determined from combined energy-current perturbation and finite-element magnetic field computation methods The method is applied to a two-pole, 75 kVA, 208 V, 24000 r/min permanent-magnet generator with multiple damping circuits, to study the effects of various generator faults on generator transient characteristics, starting from no-load and rated-load initial conditions >

Eddy current type decelerator

Abstract: PURPOSE: To eliminate a conduction at the time of braking and to brake by a simple operation by altering the superposing state of a permanent magnet and a switch plate to generate a braking force at a rotor. CONSTITUTION: A magnetic circuit is composed of adjacent permanent magnets 6 and a switch plate 7 in a state that the magnets 6 are superposed by half over the adjacent plate 7. Since a magnetic flux generated from the magnet 6 does not operate the cylinder 9-1 of a rotor 9, no eddy current is generated on the cylinder 9-1, and it is in an OFF braking state. When a hydraulic cylinder 10 is operated to rotate an arm 5-1 and the magnet 6 and the plate 7 are superposed, a magnetic circuit is composed of the adjacent magnet 6, the adjacent plate 7 and the cylinder 9-1. Thus, since the magnetic flux from the magnet 6 is operated at the cylinder 9-1 to generate an eddy current, it becomes an ON braking state. COPYRIGHT: (C)1989,JPO&Japio

Compensation principle current sensor

Abstract: In this sensor, the magnetic field generated in a magnetic core by the current to be measured is compensated by a compensation current, at least one strip-shaped element of amorphous soft-magnetic material being arranged for controlling the compensation current in the magnetic circuit of the magnetic core, which element is magnetised in a bipolar pulse-shaped manner with the aid of an indicator winding so that the imbalance of the current or, respectively, voltage amplitudes can be used for determining and evaluating the misalignment

Static electricity discharge device for a magnetic head

Abstract: A static electricity discharge device for a magnetic head formed by providing a recess to expose one of the conductors connected to the head's magnetic circuits. Static electricity buildup on the conductors discharges through the exposed portion of the conductor rather than through the pole pieces of the magnetic circuits.

Circuit for detecting AC magnetic field due to magnetic resonance with a variable resistance for noise suppression

Abstract: In a signal detecting circuit of, for example, an NMR apparatus, a signal transmission path transmits an AC magnetic flux signal to be superposed on a DC magnetic field whose strength does not change with time during a period of signal detection. The signal transmission path comprises a superconducting closed loop including a receiving coil receiving the AC magnetic flux signal, an input coil applying the received AC magnetic flux signal as an input to a flux meter, and a variable resistor replacing part of the superconducting closed loop and having its resistance value changed in relation to a change in the strength of the DC magnetic field.

Film magnetic head for high frequency recording

Abstract: A film magnetic head in which a soft metal magnetic film having uniaxial magnetic anisotropy is employed as a magnetic pole material, and a magnetic circuit having a magnetic path direction substantially perpendicular to the easy axis direction thereof is provided. The magnetic head records and reproduces signals having frequencies of 1 MHz and higher. According to a first embodiment of the invention the length W of a magnetic pole film in the easy axis direction forming a magnetic path is defined as follows: 0.2≦d/W≦0.3, or d/W≦0.15, where d is the 180° magnetic domain wall distance in the magnetic pole film. Alternatively, the length W of a magnetic pole film in the easy axis direction forming a magnetic path and the uniaxial anisotropic constant Ku is defined as follows: 50 μm≦W≦200 μm and 100 J/m.sup.3 ≦Ku≦400 J/m 3 , or 700 μm≦W, and Ku≦300 J/m.sup.3. Thus, the magnetic permeability of the magnetic core in the high frequency range is improved, and therefore the signal recording and reproducing efficiency is excellent.

Manufacture of thin film magnetic head

Abstract: PURPOSE:To improve the yield of a thin film magnetic head by forming a magnetic circuit part at a pitch smaller than a cut-pitch and cutting off the head chip so as to arrange a non-defective magnetic circuit to a prescribed location in the head cut. CONSTITUTION:The pitch (l) of the cut of the magnetic circuit part 11 is formed so as to be made smaller than a cut pitch L in case of the cut-off of the head chip. The slicing is applied with a prescribed cut pitch L and in cutting plural head chips, as a result of check, if the magnetic circuits 11a, 11b are assumed to be defective, then slicing is applied at a position of a cut line having a prescribed cut pitch L, that is, a position of cut line (a) shown in alternate long and short dash lines in figure at the outside of the location of the circuits 11a, 11b to form plural head chips. Thus, defective magnetic circuits 11a, 11b are not worked and non-defective parts only are cut off selectively to improve the yield.