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Showing papers on "Magnetic circuit published in 1993"


Journal ArticleDOI
TL;DR: A nonlinear adaptive state feedback input-output linearizing control is designed for a fifth-order model of an induction motor which includes both electrical and mechanical dynamics under the assumptions of linear magnetic circuits.
Abstract: A nonlinear adaptive state feedback input-output linearizing control is designed for a fifth-order model of an induction motor which includes both electrical and mechanical dynamics under the assumptions of linear magnetic circuits. The control algorithm contains a nonlinear identification scheme which asymptotically tracks the true values of the load torque and rotor resistance which are assumed to be constant but unknown. Once those parameters are identified, the two control goals of regulating rotor speed and rotor flux amplitude are decoupled, so that power efficiency can be improved without affecting speed regulation. Full state measurements are required. >

723 citations


Journal ArticleDOI
D.C. Hamill1
TL;DR: In this paper, a permeance-capacitance analogy for forming lumped equivalent circuits of inductive components is advocated, where magnetic paths are modeled by capacitive circuits and windings are represented by gyrator two-ports.
Abstract: In place of the conventional reluctance-resistance analogy for forming lumped equivalent circuits of inductive components, a permeance-capacitance analogy is advocated. In this approach, magnetic paths are modeled by capacitive circuits and windings are represented by gyrator two-ports. The technique is applied to the integrated magnetics of a zero-ripple isolated Cuk DC-DC converter allowing its electrical and magnetic circuits to be simultaneously simulated with SPICE. >

157 citations


Proceedings ArticleDOI
02 Oct 1993
TL;DR: In this paper, the authors identify and analyze a number of severe fault conditions that can occur in the switched reluctance machine, from the electrical and mechanical points of view, and discuss various electrical configurations of windings and controller circuits, along with methods of fault detection and protection.
Abstract: The paper identifies and analyzes a number of severe fault conditions that can occur in the switched reluctance machine, from the electrical and mechanical points of view. It is shown how the currents, torques, and forces may be estimated, and examples are included showing the possibility of large lateral forces on the rotor. The methods used for analysis include finite-element analysis, magnetic circuit models, and experiments on a small machine specially modified for the measurement of forces and magnetization characteristics when the rotor is off-center. Also described is a computer program (PC-SRD dynamic) which is used for simulating operation under fault conditions as well as normal conditions. The paper discusses various electrical configurations of windings and controller circuits, along with methods of fault detection and protective relaying. The paper attempts to cover several analytical and experimental aspects as well as methods of detection and protection. >

122 citations


Journal ArticleDOI
TL;DR: In this paper, a fully integrated magnetic microactuator using surface micromachining techniques is presented, where low-resistance meander conductors located in a single plane are interwoven with multilevel meander magnetic cores.
Abstract: A fully integrated magnetic microactuator using surface micromachining techniques is presented. To achieve this device, low-resistance meander conductors located in a single plane were interwoven with multilevel meander magnetic cores. This 'wrapped' solenoid (with the core wrapped around the conductor) was fabricated in a fully integrated fashion. A magnetic microactuator was realized by incorporating a surface micromachined nickel-iron cantilever beam as part of the magnetic circuit of the core. The nickel-iron cantilever beam was 2.5 mu m thick, 25 mu m wide, and 780 mu m long, and the magnetic circuit contained seventeen turns of meander-type solenoid coils. Cantilever beam tip deflection of 6 mu m in the vertical direction was achieved when a DC voltage less than 1 V (and resulting drive current of 800 mA) was applied to the coils. This fully integrated multilevel topology offers advantages in a variety of micromagnetic applications, where actuators can be fabricated on the same substrate with an integrated circuit and actuated with low voltages. >

94 citations


Proceedings ArticleDOI
02 Oct 1993
TL;DR: A permeance-tube-based method is developed to allow simple algebraic magnetic circuit analysis and associated prediction of flux linkages regardless of the level of magnetic saturation of the ferromagnetic structure.
Abstract: Unlike its rotary counterpart, the linear switched reluctance machine (LSRM) lends itself to double-sided excitation and multiple translator (or "rotor") configurations that can yield high-force density designs suitable for controlled linear motion in hostile environments. This paper presents the particular design of a 6:4, double-sided, double-translator LSRM that develops 5.1 lb/in/sup 2/ of air gap force shear. The work develops a permeance tube based method to allow simple algebraic magnetic circuit analysis and associated prediction of flux linkages regardless of the level of magnetic saturation of the ferromagnetic structure. Theoretical static thrust predictions are made based on the calculation of change in stored magnetic coenergy per unit distance of translator movement. Laboratory testing of a proof-of-principle LSRM, built up to verify the theoretical predictions, shows that the calculated and measured average thrust values agree within reasonable error over the range of excitation. >

90 citations


Journal ArticleDOI
TL;DR: In this paper, the frequency dependence of eddy currents for the calculation of the transient recovery voltage across a low voltage transformer breaker interrupting a nearby fault is demonstrated, based on a continued fraction expansion for the frequency dependent magnetizing impedance and a discretization of flux distribution within the lamination.
Abstract: Frequency dependent representations of eddy currents in laminated cores of power transformers are developed. One representation is based on a continued fraction expansion for the frequency dependent magnetizing impedance while the other is based on a discretization of flux distribution within the lamination. Both models are low order and reproduce the frequency characteristics of the transformer magnetizing branch up to 200 kHz with less than 5% error. The importance of modeling the frequency dependence of eddy currents for the calculation of the transient recovery voltage across a low voltage transformer breaker interrupting a nearby fault is demonstrated. >

82 citations


Patent
26 Aug 1993
TL;DR: In this article, a differential pressure transducer for measuring external pressures is described, which uses a ferrofluid contained in two interconnecting chambers, enclosed by two non-magnetic spring diaphragms.
Abstract: A differential pressure transducer for measuring external pressures is disclosed. The pressure transducer uses a ferrofluid contained in two interconnecting chambers, enclosed by two non-magnetic spring diaphragms. In this embodiment, two independent inductance series circuits, each comprising a bar magnet, Hall effect sensor and an iron pole piece, measure variations in the volume of ferrofluid in each of the interconnecting chambers. Changes in pressure displace the non-magnetic spring diaphragms causing the volume in each interconnecting chamber to change in a differential manner. The flux path in the series magnetic circuit is distorted by changes in the volume of the ferrofluid, causing changes in the flux density at the sensing area of the Hall effect sensor, this sensor producing an electrical signal proportional to the flux change. The differential output of the two Hall Effect sensors contained in the two series magnetic circuits produce an electrical signal proportional to the applied differential pressure.

59 citations


Journal ArticleDOI
01 Jul 1993
TL;DR: In this article, a discrete dynamic model of a magnetic core including hysteresis, eddy current and anomalous losses is proposed, suitable for thin laminations and features a simple formulation and fast calculation.
Abstract: A discrete dynamic model of a magnetic core including hysteresis, eddy current and anomalous losses is proposed. It is suitable for thin laminations and features a simple formulation and fast calculation. The calculations and measurements of an annular ring under different waveforms are presented. The model can be extended to include cores with thick laminations.< >

58 citations


Patent
25 Feb 1993
TL;DR: In this article, the phase angle between the previous voltage zero crossing and the time of voltage turn-on is measured by a microprocessor, which is programmed to normalize the phase angles over a range of coil drive voltages.
Abstract: An electrical contactor has first and second contacts movably mounted to engage for achieving continuity in an electrical circuit, via an electromagnet and armature defining a magnetic circuit with an air gap that closes in a first position of the contactor and opens in a second position of the contactor. A controller switches an alternating current voltage to the coil of the electromagnet during a timed portion of each AC half cycle, and senses the current level in the coil in a feedback loop. The controller adjusts the voltage-on time to achieve a predetermined average current as needed for accelerating the armature or coasting during a closing operation, for holding the armature in place when closed, etc. In order to sense whether the contactor is presently open or closed, the controller monitors and stores the phase angle between the previous voltage zero crossing and the time of voltage turn-on. When the inductance of the magnetic circuit including the electromagnet and armature changes rapidly due to opening or closing of the air gap between them, the controller detects a corresponding variation in the phase angle. The controller is preferably a microprocessor, programmed to normalize the phase angle over a range of coil drive voltages. The microprocessors of a number of such contactors can communicate in order to effect coordinated operations.

53 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the feasibility of an inductive iron core superconducting fault current limiter, which is based on a high temperature super-conducting shield surrounding a magnetic circuit with a primary winding.
Abstract: The authors investigate the design feasibility of an inductive iron core superconducting fault current limiter. A simplified thermo-electromagnetic analysis of the operating behavior of the fault current limiter is presented. This design is based on a high temperature superconducting shield surrounding a magnetic circuit with a primary winding generating an AC magnetic field. During fault conditions the field penetrates the core resulting in a large impedance, and thus a limitation of the fault current. In the analysis of this design, for voltages and currents up to 25 kV root-mean-square (RMS) and 2000 A RMS, it is shown that recuperation times for superconductors operating at liquid nitrogen temperatures are acceptable. >

49 citations


Patent
21 Jun 1993
TL;DR: In this paper, the magnetic field has a minimum induction in the transition area in the vicinity of the anode (25), the absolute induction value of the field increasing again upstream of the buffer chamber (23) in order to produce a magnetic mirror effect.
Abstract: A PLASMA ACCELERATOR OF SHORT LENGTH WITH CLOSED ELECTRON DRIFT The means (31 to 33, 34 to 38) for generating a magnetic field in the main channel of the plasma accelerator are adapted to produce, in the main channel (24) an essentially radial magnetic field at the downstream end (225) of the channel (24), its induction being maximum at this point. The magnetic field has a minimum induction in the transition area in the vicinity of the anode (25), the absolute induction value of the field increasing again upstream of the anode (25), in the region of the buffer chamber (23) in order to produce a magnetic mirror effect. The magnetic field lines include, between the anode (25) and the downstream end (225) of the channel (24), a concavity oriented downstream, causing focusing of ions, the maximum ionisation density area being located downstream of the anode (25). The magnetic field generating means comprise several distinct magnetic field generating means (31 to 33) and inner (35) and outer (34) radial, plane pole pieces (34, 35) disposed at the outlet face on either side of the main channel (24) and linked to one another by a central core (38), a yoke (36) and a peripheral magnetic circuit (37) axially disposed outside of the main channel (24). The yoke (36) consists of radial elements located in the immediate vicinity of the anode (25) and passing through the annular buffer chamber (23), thereby creating spaces (13) for communication between the annular buffer chamber (23) and the main channel (24).

Patent
06 Jul 1993
TL;DR: In this article, an arrangement using sensing coils for obtaining flux rate of change information in a magnetic circuit was proposed, where active (electric powered) circuitry was used to implement closed loop control of flux rate.
Abstract: An arrangement using sensing coils for obtaining flux rate of change information in a magnetic circuit. The arrangement can be used for vibration attenuation in a magnetic forcer system. Active (electric powered) circuitry is used to implement closed loop control of flux rate. The control loop is "broadband" since a broad range of vibration frequencies are attenuated. The arrangement can be applied to magnetic forcer/suspension systems in which vibrations due to magnetic mechanical/magnetic runouts, system mechanical resonances, or external vibration sources are present. The arrangement is particularly applicable for systems with a large number of varying vibration frequencies.

Journal ArticleDOI
TL;DR: In this paper, a self-oscillated class C converter for noncontact charging of the rechargeable cell with electromagnetic coupling is proposed, which matches the condition of the transformer, the output voltage is always sinusoidal, and the noise of the circuit and the core loss due to harmonics are small.
Abstract: A converter using a self-oscillated class C converter for noncontact charging of the rechargeable cell with electromagnetic coupling is proposed. The oscillating condition of the circuit matches the condition of the transformer, the output voltage is always sinusoidal, and the noise of the circuit and the core loss of the transformer due to harmonics are small. The oscillating condition as a class C converter is automatically adjusted by a simple bias circuit which is composed of a diode and a resistor. >

Patent
31 Mar 1993
TL;DR: A leakage current protection device, such as a ground fault circuit interrupter (GFCI), is provided that can be used in single phase or polyphase systems, with a range of input voltages from 70 to 264 volts AC, frequencies of 50 or 60 hertz, and ground fault trip currents of 6 to 30 milliamperes as discussed by the authors.
Abstract: A leakage current protection device, such as a ground fault circuit interrupter (GFCI), is provided that can be used in single phase or polyphase systems, with a range of input voltages from 70 to 264 volts AC, frequencies of 50 or 60 hertz, and ground fault trip currents of 6 to 30 milliamperes. A leading power factor circuit is connected to the secondary winding of the GFCI differential transformer to permit the magnetic circuit to respond to pulsating DC signals. Provision is made for continuing to provide GFCI protection in the event of an open neutral lead, with a timing circuit to prevent current flow to the ground lead until current flow in the neutral lead is completely discontinued. Various types of circuit interrupting devices, such as a circuit breaker or a power converter, may be selectively utilized.

Journal ArticleDOI
01 Jul 1993
TL;DR: In this paper, a geometrical transformer model based on the circuit analysis of its magnetic core was developed, which can be used for any type of multiphase multiwinding transformer.
Abstract: In this paper a new transformer model, named ‘geometrical’, is developed, based on the circuit analysis of its magnetic core. The method is general and can be used for any type of multiphase multiwinding transformer. The model simulates the transformer as a set of coupled branches and can be incorporated into the widely known electromagnetic transients program (EMTP). A basic advantage of the model is that it can represent any asymmetry of the transformer magnetic circuit. As a study case, the model of an actual 280 MVA autotransformer is derived and used for the simulation of various steady state and transient conditions.

Patent
29 Jan 1993
TL;DR: In this article, the magnetic circuit is constructed such that its number of slots per each pole and each phase is 0.5 and that its winding system is of concentrated winding, and the total length of its stator coils can be reduced compared with that of the conventional machine.
Abstract: An AC generator for use in motor vehicles which is high in power generation and cooling efficiency. The magnetic circuit is so constructed that its number of slots per each pole and each phase is 0.5 and that its winding system is of concentrated winding. With such a construction, the total length of its stator coils can be reduced compared with that of the conventional machine. In addition, its output and efficiency are improved by the reduced temperature rise and a reduction in its structure and cost can be achieved by the reduced consumption of copper.

Patent
26 Oct 1993
TL;DR: In this paper, a pole piece or tip is laminated using relatively large bar-shaped laminations instead of the usual thin sheet material and small insulating gaps are filled with low loss insulating liquid filler material.
Abstract: An MRI magnet member (e.g., a pole piece or tip) is laminated using relatively large bar-shaped laminations instead of the usual thin sheet material. One or more layers of such bar-shaped laminations are arrayed with small insulating gaps into which a low loss insulating liquid filler material is flowed and then cured to a hardened solid state. This simultaneously produces insulated pole tip laminations which have been robustly integrated together into a unitary structure. The resulting robust laminated pole tip is relatively easy to manufacture and is also capable of withstanding rather large magnetic forces and maintaining relatively uniform magnetic field distribution within an MRI imaging region while yet providing providing sufficient eddy current reduction so as to efficiently permit rapidly changing magnetic gradient coil currents to be established.

Patent
17 Jun 1993
TL;DR: In this paper, it is shown that magnetic flux passing through the magnetic body converges in one direction so as to apply a rotational torque to the rotational output shaft no force opposing movement of a rotor or movable element is generated.
Abstract: A motive power generating device comprises a permanent magnet disposed around a rotational output shaft for rotation therewith, the output shaft being mounted on a support member for rotation, a magnetic body disposed in concentric relationship with the permanent magnet for rotation with the rotational output shaft, the magnetic body being subjected to magnetic flux generated by the permanent magnet, a plurality of electromagnets fixedly mounted to the support member in such a manner that they are spaced at predetermined distances around the periphery of the magnetic body, each magnetic circuit of the electromagnets being adapted to be independent of one another, and excitation change-over means for the electromagnets, the excitation change-over means being adapted to sequentially magnetize one of the electromagnets which is positioned forwardly with regard to a rotational direction of the rotational output shaft, so as to impart to the particular electromagnet a magnetic polarity opposite to that of the magnetic pole of the permanent magnet, whereby magnetic flux passing through the magnetic body converges in one direction so as to apply a rotational torque to the rotational output shaft No force opposing movement of a rotor or movable element is generated

Proceedings ArticleDOI
07 Mar 1993
TL;DR: In this paper, a circuit model for the magnetic regulator was derived and was shown to contain a current-controlled leakage inductance, which was used to verify the model on an experimental device.
Abstract: A method of providing regulation in a resonant power supply uses a device called a magnetic regulator which resembles an ordinary AC transformer. Through the use of additional control windings, the conversion ratio of the magnetic regulator can be electronically varied, thus achieving control. A circuit model for the magnetic regulator is derived and is shown to contain a current-controlled leakage inductance. Measurements made on an experimental device verify the model. Two additional structures are described. >

Patent
23 Dec 1993
TL;DR: In this article, the magnetic flux density of the static magnetic field is determined, taking into consideration the frequency of the high-frequency wave or the microwave, so that the same is not lower than the magnetic density at which electron cyclotron resonance occurs.
Abstract: A plasma processing method for processing a thin film formed on a substrate or forming a thin film on a substrate within a vacuum vessel provides for supplying a gas into the vacuum vessel, producing a plasma in the vacuum vessel by applying a microwave to the gas, and creating a static magnetic field represented by magnetic lines of force parallel to the direction of propagation of the microwave in the vacuum vessel by a magnetic circuit. The field intensity of the static magnetic field is determined taking into consideration the frequency of the microwave so that the same is lower than the field intensity at which electron cyclotron resonance occurs. The magnetic flux density of the static magnetic field is determined, taking into consideration the frequency of the high-frequency wave or the microwave, so that the same is not lower than the magnetic flux density at which electron cyclotron resonance occurs, and the density of the plasma is determined so that the left-hand circularly polarized wave is cut off.

Patent
01 Sep 1993
TL;DR: A coin analyzer system includes a coin detecting sensor having a body defined by a magnetic core with spaced apart sides to define there-between an air gap that is large enough to position any size coin which may be deposited as mentioned in this paper.
Abstract: A coin analyzer system includes a coin detecting sensor having a body defined by a magnetic core with spaced apart sides to define there-between an air gap that is large enough to position any size coin which may be deposited. A coil that is magnetically coupled to the core generates a uniform magnetic flux through the air gap from one side to the other so that the positioning of the coin in the air gap is not critical. A return path is provided in the core for returning the magnetic flux to the one side from the other side and thereby completing the magnetic circuit. The arms surrounding the coin sensing region define facing surfaces which converge outwardly from the bite portion in order to produce a uniform magnetic circuit reluctance for all portions of the facing surfaces. The core may be divided into two core portions separated by a secondary air gap in the return path with a pair of coils provided, one magnetically coupled with each of the core portions. One coil may serve as a transmitting coil and the other as a receiving coil. Various detection circuits are disclosed for connection with the sensor coils in order to determine the denomination of the test coin.

Book
22 Oct 1993
TL;DR: In this article, the basic AC circuit concepts are discussed and a detailed analysis of the power system components and their properties are presented, including faults, protection, and stability, as well as power flow solutions.
Abstract: Energy Resources and Electric Energy Conversion. Power System Components and Analysis. Basic AC Circuit Concepts. Magnetic Circuits and Transformers. Fundamentals of Rotating Machines. DC Machines. Synchronous Machines. Induction Motors. Transmission Lines. Power Flow Solutions. Faults, Protection, and Stability. Appendices. Index.

Journal ArticleDOI
TL;DR: An extension to the theory of General Magnetic Reconnection (GMR) is presented in this article, where a new analytical relation between the rate of change of newly connected magnetic flux and the maximum possible value of the parallel component of the electric field integrated along the magnetic field is derived.

Journal ArticleDOI
TL;DR: In this article, the results of a measurement and a theoretical program to study the magnetic field performance of a double circuit 230 kV line with only one circuit energized and with both circuits paralleled in a low reactance configuration are presented.
Abstract: Power engineers have been trying to find transmission line geometries that will reduce fields. One of the reduced field geometries is the double circuit, low reactance line. The results of a measurement and a theoretical program to study the magnetic field performance of such a double circuit 230 kV line with only one circuit energized and with both circuits paralleled in a low reactance configuration are presented. The measurements show that the reduced field line is more sensitive to deviations from balanced currents. >

Patent
Hideo Yamasaki1, Makoto Nagasato1
30 Apr 1993
TL;DR: In an electro-magnetic actuator, a pair of magnetic circuits are separately arranged in a tracking direction and a carriage is located between the magnetic circuits and is movably supported or guide rails extending along the tracking direction as discussed by the authors.
Abstract: In an electro-magnetic actuator, a pair of magnetic circuits are separately arranged in a tracking direction and a carriage is located between the magnetic circuits and is movably supported or guide rails extending along the tracking direction. On the carriage, a lens holder for holding an objective lens is movably suspended and focusing coils are fixed on side surfaces of the lens holder. A tracking coil is fixed in the carriage and is extended in the magnetic circuit. Focusing permanent magnets of the magnetic circuits are so extended along the tracking direction as to produce, focusing magnetic fluxes penetrating the focusing coil and leakage magnetic fluxes penetrating the tracking coil. A focus drive force is generated by an interaction between a current supplied to the focusing coil and the focusing magnetic fluxes and a biasing track drive force is generated by an interaction between a current supplied to the tracking coil and the leakage magnetic fluxes.

Journal ArticleDOI
13 Apr 1993
TL;DR: In this paper, a thin gap is introduced into the sandwich-structured planar inductors between a pair of magnetic plates, in one of which a meander coil is embedded.
Abstract: New structure planar inductors are developed for miniaturized DC-DC converters. A thin gap is introduced into the sandwich-structured planar inductors between a pair of magnetic plates, in one of which a meander coil is embedded. Due to the thin air gap introduced, the flux density in the magnetic plates becomes uniform, resulting in low iron loss. Planar inductors using NiZn ferrite thin plates are successfully applied to a 10-W-class buck converter operated at 2 MHz. The efficiency is higher than 82%, and the effective volume of the inductor is 0.2 cm/sup 3/ (1 cm square and 2 mm thick). >

Patent
29 Sep 1993
TL;DR: In this article, a DC current is supplied to a DC excitation winding for a permanent magnet synchronous rotating machine to increase rotational speed without using demagnetization control operation and to reduce an iron loss without lowering the efficiency of the rotating machine.
Abstract: PURPOSE:To increase rotational speed without using a demagnetization control operation and to reduce an iron loss without lowering the efficiency of the title rotating machine by a method wherein a magnetic flux by a permanent magnet and a DC magnetic flux by a DC excitation winding are adjusted to be strong and weak. CONSTITUTION:When a DC current is supplied to a DC excitation winding 5 for a permanent-magnet synchronous rotating machine, a closed magnetic circuit is formed in the route of an armature yoke 4, an S-pole-side iron core 2b, a gap, an S-pole-side salient-pole-shaped part 12aS, a rotor core 12, a rotor yoke 14, the rotor core 12, an N-pole-side salient-pole-shaped part 12aN, the gap, an N-pole-side iron core 2a and the yoke 4. In this case, the direction of a magnetic flux can be controlled by the direction of the DC current, and its magnitude can be controlled by the magnitude of the current. As a result, field strength can be adjusted easily, a torque can be increased easily within a constant torque range, an induced voltage can be reduced easily within a constant output range, an available range can be increased, a DC excitation input become extremely small, the efficiency of the rotation machine can be increased, and an iron loss can be reduced sharply by reducing the magnetic flux in a high-speed region.

Journal ArticleDOI
TL;DR: In this paper, some of the more fruitful approaches to the use of high coercivity/high remanence magnet materials in magnetic circuit design and how the application of comparatively few and simple techniques can result in a large number of useful devices are discussed.
Abstract: Discusses some of the more fruitful approaches to the use of high coercivity/high remanence magnet materials in magnetic circuit design and how the application of comparatively few and simple techniques can result in a large number of useful devices. The approaches discussed are the estimation of permeances, magnetic cladding, equivalent pole densities and current sheets, analytic application of Maxwell's equations, the magnetic moment rotation theorem and magnetic mirrors. Some novel devices resulting from these applications are cited. >

Patent
16 Jul 1993
TL;DR: The sensitivity of an induction-type motion sensor to small movements increases when a stator (2) is devised with a core containing a permanent magnet (12) and an air gap (9), an electrical coil (3) is constructed around the stator and a rotor (1) is designed with a ferromagnetic moving element (4, 5) which passes in and out of the air gap.
Abstract: The sensitivity of an induction-type motion sensor (1), comprising a magnetic circuit with a permanent magnet (12), to small movements increases when a stator (2) is devised with a core containing a permanent magnet (12) and an air gap (9), an electrical coil (3) is devised around the stator (2) and a rotor (1) is devised with a ferromagnetic moving element (4, 5) which, when the motion sensor is subjected to movement stress, passes in and out of the air gap (9), alternating the magnetic field in the stator (2) and inducing a current in the electrical coil (3).

Patent
11 May 1993
TL;DR: In this paper, an external magnetic field application device for use in an optical information recording and reproducing apparatus is described, which includes a heat dissipation member arranged to contact an outer periphery of the winding for conducting heat generated in the winding, when the winding is energized, to the magnetic plate.
Abstract: Disclosed is an external magnetic field application device for use in an optical information recording and reproducing apparatus. The device has a winding wound on an outer periphery of a magnetic pole piece and a magnetic plate attached to the magnetic pole piece to form a magnetic circuit. The device includes a heat dissipation member arranged to contact an outer periphery of the winding for conducting heat generated in the winding, when the winding is energized, to the magnetic plate, and a metal plate arranged on top of the heat dissipation member for dissipating heat of the heat dissipation member.