Showing papers on "Electromagnetic coil published in 1985"

Dual-antenna transceiver

Abstract: A magnetic-field, noise-cancelling transceiver is provided by a dual-coil antenna circuit. In the receive mode, two identical coils 22, 24 connected in series opposition, cancel noise signals common to both coils and receive desired signals present at only one coil. Capacitance 30, 32 in parallel with the series-opposed coils establishes the resonant frequency of the receiver, antenna circuit. In the transmit mode, the two coils, connected in series opposition, have their non-adjacent terminals 26, 28 clamped to ground via two pairs 34, 36 and 38, 40 of oppositely-poled diodes, one pair on each non-adjacent terminal. The transmitter signal, coupled to the junction 20 of the two coils through a capacitance 14, 16 generates additive magnetic fields by causing equal currents to flow in each coil from the common junction, to their respective diode junctions, to ground through the respective, oppositely-poled diode pairs. Series resonance is established by the transmitter coupling capacitance and the parallel combination of the two coils. The transmitter and receiver tuning are independent. The receiver tuning is unaffected by the transmitter circuitry and coupling capacitance because the transmitter is connected to the null between the receiving antenna coils. The transmitter tuning is unaffected by the receiver circuitry and receiver capacitance because the diode pairs provide a relative short across the receiver input during transmission.

Applicator for tying sewing threads

Abstract: The applicator for utilization in combination with an endoscope tube comprises a coil connected to a longitudinal passage through a shaft and comprising hollow turns connected to the shaft passage for reception of a sewing thread, whose proximal extremity is passed through a loop projecting from a radial opening at the distal extremity of the shaft, is then drawn through the shaft passage and fastened to the proximal shaft extremity. Tying the single stitch after piercing the tissues is performed by passing the needle axially through the coil and then around the thread and twisting the coil out of the loop formed thereby to form the first half of a knot which is then complemented by the second half of the knot tied in the same way, the knot being tied by subsequently pulling together the two said halves.

Surface coil system for magnetic resonance imaging

Abstract: A resonance exciting coil (C) excites magnetic resonance in nuclei disposed in an image region in which a main magnetic field and transverse gradients have been produced. A flexible receiving coil (D) includes a flexible plastic sheet (40) on which one or more loops (20) are adhered to receive signals from the resonating nuclei. Velcro straps (46) strap the flexible sheet and the attached coil into close conformity with the surface of the portion of the patient to be imaged. An impedance matching or coil resonant frequency adjusting network (50) is mounted on the flexible sheet for selectively adjusting at least one of an impedance match and the peak sensitivity resonant frequency of the receiving coil. A preamplifier (52) amplifies the received signals prior to transmission on a cable (24). A selectively variable voltage source (70) applies a selectively adjustable DC bias voltage to the cable for selectively adjusting at least one of the impedance match and the LC resonant frequency of the receiving coil. The received signals are amplified by an amplifier (82) and processed by an image processor (30) to form man-readable images of the examined region of the patient for display on a video display (32) or the like.

Solid state NMR probe

Abstract: An in vivo NMR probe (30, 50) is disposed at the distal end of a catheter or endoscope (10) for obtaining NMR spectra from within a patient. The probe (30) is constructed from a passive integrated circuit including a receiving coil (32) and a parametric amplifier (34) for frequency up-converting the received frequency of the NMR emissions. One or more coaxial cables (22) disposed in a lumen (20) of the catheter (10) connect the integrated circuit probe (30) to an external NMR processor. The external processor may also excite the coil to radiate a localized perturbation field prior to obtaining NMR emission data of an area of interest. Alternatively, the probe (50) may be constructed from an active circuit (54) which enables the coil (52A-H) to be tuned to an NMR emission frequency of interest. A closed loop refrigeration circuit utilizing lumens (24) in the catheter or Peltier junction devices on the integrated circuit provide for temperature stability of the active devices.

Noise performance of surface coils for magnetic resonance imaging at 1.5 T.

Abstract: In this paper we analyze the signal-to-noise ratio (SNR) for surface coil magnetic resonance imaging at 1.5 T. We have applied the treatment of Hoult and Lauterbur to determine the factors that most affect coil performance. We have imaged lossy phantoms with 8-, 10-, and 14-cm-diam circular surface coils and compared the results to body and head coil images. Surface coils can improve SNR by a factor of 4 or more for regions close to the surface. Surface coils are effective for regions up to 6 cm deep in the head and about 12 cm deep in the body. Nonuniformity of image intensity is a necessary requirement for improved SNR in surface coils. Coil losses make only a small contribution to image noise compared to tissue losses at 1.5 T. Surface coils need not be placed in close contact with the patient at 1.5 T.

Control apparatus for brushless motor

Abstract: A control apparatus detects a suitable starting point during rotational oscillation of a rotor at the start of a brushless motor by combining the polarity of a counter electromotive force generated in an armature coil of an armature winding of the brushless motor for a nonexcited phase due to the rotational oscillation of the rotor (when armature coils for particular phases are excited at the start of the brushless motor) with the pulse edge of an excitation switchover signal obtained from the potential of a neutral point of the armature winding having the armature coils connected in star-connection and that of a neutral point of a detecting resistance circuit having resistors connected in star-connection. Each of the resistors of the resistance circuit is arranged in parallel with a corresponding one of the armature coils the armature winding. By driving the brushless motor from the detected suitable starting point, it is possible to effect smooth and quick control of the starting operation of the brushless motor.

Nuclear magnetic resonance imaging antenna subsystem having a plurality of non-orthogonal surface coils

Abstract: An NMR antenna subsystem has a plurality of co-planar surface coils, each comprised of a plurality of segments and elements for tuning the coil to resonance at the Larmor frequency of a nuclei specie to be investigated. Each coil has circuitry for selectively detuning that surface coil when at least one other one of the plurality of surface coils is in use. One of a pair of co-planar surface coils can be utilized for signal reception and includes a parallel-resonant detuning circuit which operates only when a relatively large magnitude RF signal is induced by an excitation signal in a second surface coil. The second surface coil includes a circuit for detuning that coil except when an externally-provided signal is present; this signal may be the RF excitation signal itself or another signal provided simultaneously with the RF excitation signal.

Power transfer for implanted prostheses

Abstract: Apparatus is provided for improving the coupling between an external inductive transmitting coil and an internal inductive receiving coil to transmit power and/or data to the receiving coil from the transmitting coil. The structure includes a coupling coil inductively coupled to the transmitting coil to increase the Q factor and hence the energy transfer between the transmitting coil and the receiving coil.

Electromagnetic valve with permanent magnet armature

Abstract: A modulating valve is described for controlling the flow of a working fluid through a flow orifice. The valve includes a encapsulated armature having a permanent magnet and a pair of soft iron pole pieces within its interior. The armature is axially movable by the passage of current through one or a dual pair of solenoid coils surrounding the armature. A thin webbed sealing disk is stretched over the end of an armature housing extension and acts to close or modulate flow of working fluid by varying the axial clearance between the disk and a stationary annular seat of the flow orifice. The armature is supported on flexure guide springs that allow armature axial motion when axial magnetic forces are applied to the armature. These axial forces are provided by the interaction of the solenoid coil(s) and the field of the permanent magnet. A magnetic field gradient produced by the permanent magnet allows the coil to apply a force to the armature in either the valve opening or valve closing direction, depending on the coil current polarity. An armature velocity signal is used in a closed loop servo control of valve position to suppress valve oscillation and over shoot when a change in valve position is commanded.

Mutual inductance nmr rf coil matching device

Abstract: A matching device uses mutual inductance to couple an NMR radio frequency (RF) coil to an RF power amplifier and RF receiver preamplifier. The device includes a matching coil connected to the RF power amplifier and preamplifier and which is positioned between the NMR RF coil and a decoupling shield in a region where RF flux density, produced by the NMR RF coil, is maximum. This ensures effective coupling to the NMR RF coil and provides a way for adjusting the degree of coupling (hence, input impedance) by varying the area of the matching coil available for intercepting the RF flux.

High frequency plasma generation apparatus

Abstract: In a high frequency plasma generation apparatus used in a reactive ion etching apparatus, an ion shower apparatus, a sputter apparatus, etc. for fabricating thin films or semiconductor devices for which a fine patterning process is required, electrical breakdown is apt to be provoked at the surface of a high frequency coil, because the high frequency coil is usually inserted in a plasma. In order to remove this drawback, according to this invention, the high frequency coil is disposed in the plasma production chamber at the neighborhood of the cylindrical side wall, and thus a plasma confinement domain is formed inside of this high frequency coil by use of a magnetic field production device which generates a multi-cusp magnetic field so that the plasma confinement domain is separated from the high frequency coil. In this way, electrical breakdown on the surface of the high frequency coil is prevented and thus the apparatus according to this invention can work stably for a long time.

Variable force solenoid

Abstract: A variable force solenoid for operating a hydraulic pressure regulating valve which includes an actuator shaft aligned with the central axis of the valve and solenoid, a coil of electrical conducting wire, a cylindrical core on which the wire is wound and through which the induced magnetic flux flows, an actuator actuates shaft spaced by a non-working air gap from the casing and moveable axially toward and away from the edge of the core, flexible bearings at opposite axial ends of the actuator shaft and a compression spring. A force is applied to the actuator shaft by a unique double spring combination. The flexible bearings restrict lateral displacement of the actuator and permit frictionless axial displacement of the actuator. The hydraulic valve has a valve spool that moves due, to the position of the actuator, from a position that produces maximum pressure when the coil is de-energized to a position that produces zero pressure when the coil is energized. A zero pressure adjustment and maximum pressure adjustment establish the correct position of the valve spool within the valve body.

Hybrid excited generator with flux control of consequent-pole rotor

Abstract: An electrical machine utilizes a consequent pole rotor with a polyphase stator assembly and a control coil to produce a widely variable voltage output. Either constant-speed--variable-voltage performance, or variable-speed--constant-voltage performance may be easily achieved by varying the magnitude and level of D.C. current supplied to the control coil. Single and double rotor embodiments are disclosed, with cogging being easily suppressible in the double rotor embodiments.

Nmr spectroscopy body probes with at least one surface coil

Abstract: An NMR spectroscopy body probe is comprised of at least one surface coil, each coil having at least one turn and positioned adjacent to a first surface of an insulative member; an electric-field-reducing shield is fabricated upon the other surface of the relatively flexible substrate. The shield surface of the probe is to be positioned closest to the sample. A plurality of surface coil-bearing substrates can be stacked, one adjacent to the other with the planes thereof substantially parallel to each other and to the plane of the electric-field shield, and with each individual surface coil being separately tunable to a different nuclei species resonance frequency. Each surface coil can be utilized for both transmission and reception, or can be used for only reception of the re-radiated signal from the sample, with a separate excitation coil being provided with a radius substantially greater than the average radius of the (receiver) surface coil and positioned in the plane of any of the at least one receiving surface coils.

Induction sealing of paperboard

Abstract: A method and apparatus for use in form, fill, and seal machines wherein a polyfoil material is compressed between two jaws, one jaw having a secondary induction coil which passes through an electromagnetic field and induces a current in the metallic layer of the polyfoil, to heat and then seal the polyfoil. In a preferred embodiment, a plurality of nonconductive sealing jaws, each containing a secondary induction coil, are mounted on an endless carrying means and a plurality of opposing corresponding rigid pressure jaws are also mounted on an endless carrying means and are arranged so that, as the carrying means advance continuously, each sealing jaw and corresponding pressure jaw contact and compress together facing thermoplastic layers of a polyfoil material and each secondary coil passes through an electromagnetic field to induce a current in the secondary induction coil which in turn induces a current in the area of the metallic foil layer proximate to the secondary induction coil to heat the foil and soften the adjacent thermoplastic materials which, because they are pressed together, will fuse and harden upon cooling. In continuous transverse sealing of a filled polyfoil tube, the pressure jaws may include a knife to sever the seals, the polyfoil tube may be preformed before it is sealed, and the sealing and pressure jaws may have an alignment means to facilitate severing and sealing. The secondary induction coil is preferably an elongated twin loop coil folded so that one loop is fully subjected to the electromagnetic field and the second loop induces a current in the polyfoil tube.

Multiconductor transmission-line model for the line-end coil of large AC machines

Abstract: This paper describes how the PE2D finite-elements field package is used to calculate the distributed L and C parameters of a multiconductor transmission-line model for the line-end coil of a large AC motor. Under steady-state AC conditions, the package produces field distributions from which self and mutual inductances and capacitances can be calculated. Distributed shunt and series losses are included in the model, and there is no need for any assumptions about surge velocities in evaluating the coil response. Separate parameters are calculated for the slot and overhang regions and the various sections of uniform multiconductor transmission lines are joined in series to represent the complete coil. The coil response is then computed using a Fourier transform technique. The input waveform is broken down into its spectral components and the steady-state transmission-line equations are solved at each component frequency. The response at each frequency is then used in the inverse Fourier transform to arrive at the solution in the time domain. Responses calculated from the model are compared to test responses on a laboratory model of the line-end coil and are found to be in good agreement. Several parameter variations are then investigated on the theoretical model.

Printed coil unit for small size actuator

Abstract: A printed coil unit for use in a very thin type flat brushless motor or a linear actuator, in which a magnetic sensor element having a thickness smaller than 0.6 mm is embedded integrally within the coil unit without projecting therefrom in a region located outside and in the vicinity of spiral conductor coil patterns. The printed coil unit includes a single printed coil sheet or a lamination of such coil sheets each having more than one spiral conductor patterns on the same plane. A magnetic sensor element, such as Hall element or magneto-resistance element having a thickness equal to or smaller than that of the printed coil sheet is embedded within the coil sheet at blank regions located between adjacent spiral conductor patterns, or regions made availably by diminishing the size of a selected one of the spiral conductor patterns. A moving speed detecting coil or patterned conductor can be additionally provided on the other available area of the coil sheet.

Method and apparatus for producing electromagnetic surveillance fields

Abstract: A system for producing alternating electromagnetic fields for use in theft detection and surveillance systems, including an arrangement of field-generating inductance coils for disposition on opposite sides of a passage to be monitored by the electromagnetic field produced by such coils. In a preferred such arrangement, upper and lower coils are used on each side of the passage and such coils are mutually distinct from one another and separately energizeable so as to generate separate components of a resulting composite electromagnetic field. The upper and lower coils in each such set are preferably disposed in coplanar alignment with one another but have at least portions of one coil overlapping portions of the other, so as to enhance uniformity in the resulting electromagnetic field. The array of separately-energizeable coils provides for resultant flux vector variation in the magnetic field along three mutually orthogonal axes as a function of coil drive excitation phase variation. The specification further discloses preferred coil-drive circuitry for accomplishing such purposes.

Thin-film magnetic head with a double gap for a recording medium to be magnetized vertically

Abstract: A thin-film magnetic head with a layer-wise build-up on a nonmagnetic substrate for a recording medium which can be magnetized vertically comprises a magnetic conduction body carrying the magnetic flux, with two outer magnet legs and a further central magnet leg, the poles of which facing the recording medium are arranged one behind the other as seen in the direction of motion of the head, and with predetermined gap widths between each other, where the current conductors of a write/read coil arrangement extend through spaces formed between the central magnet leg and a respective outer magnet leg adjacent thereto. With this magnetic head it is possible to generate a magnetic writing field, the field pattern of which has a pronounced largely symmetrical maximum. It is provided that the current conductors of the coil arrangement also run through a further space where the current flow directions in the current conductors arranged on both sides of the central magnet leg are opposed to each other. It is particularly advantageous if the central magnet leg has, at least in the vicinity of the pole, a higher saturation magnetization than the outer magnet legs, so that these magnet legs are in magnetic saturation sooner than the central leg during writing.

Rotational position detection device

Abstract: The rotational position detection device comprises a stator section (1) including primary and secondary windings (W1, W2) and a rotor section (2) disposed in such a manner that it is capable of performing relative rotational displacement with respect to the stator section. A conductive substance portion (2b) is provided in the form of a predetermined pattern. The amount of flux passing through the conductive substance portion of the rotor section (2) changes in accordance with a relative rotational position of the rotor section with respect to the stator section (1) and therefore an eddy current flows through the conductive substance portion. Reluctance is caused to change by a loss due to this eddy current and a secondary output signal corresponding to the rotational position is produced in the windings of the stator section. The pattern of the conductive substance portion (2b) can be formed easily by using electro-plating or other surface processing technique. The rotor section (2) may be of a shape such that the rate of the reluctance change is enhanced by the combination of the magnetic substance portion (2a) and the conductive substance portion.

Coin selection apparatus

Abstract: A coin selection apparatus comprises a plurality of detection coils and an oscillation circuit which detects changes of impedances of the detection coils caused when a coin pass through the detection coils, as a change of a voltage output. The plurality of detection coils include at least two sets of detection coils each including two detection coils opposingly arranged to the coin path. One set of detection coils has its two coils connected in series and in phase and the other set of detection coil has its two coils connected in series and in phase opposition. The two sets of coils are arranged at a spacing along the coin path smaller than a minimum diameter of a coin to be selected and all of the coils are connected in series and connected as a resonance element of the oscillation circuit. Thus, material, thickness and diameter and other appearance characteristic of the coin are detected based on the voltage output of the oscillation circuit. Accordingly, the coin selection apparatus is of simple construction and has a small number of components.

Control for guiding a boring tool

Abstract: A control system guides a boring tool in a borehole. The tool has a longitudinal tool axis and includes a driver for advancing the tool axially through the earth and steering mechanism for directing the motion of the tool relative to the tool axis in response to control signals. The control system includes an axial electromagnetic source for generating an axial alternating magnetic field directed along an axial source axis. A sensing assembly remote from the source means includes first and second pickup coils for sensing the alternating magnetic field. Each of the first and second pickup coils has a respective coil axis and is rigidly mounted in respect to the other with their respective axes at a substantial angle with respect to each other, defining a sensing assembly axis substantially normal to both coil axes. Each coil generates a respective null electrical signal when the lines of magnetic flux at the respective coil are normal to the respective coil axis. Either the source of the sensing assembly is rigidly mounted on the tool, preferably the source. The outputs of the sensing coils are used to determine the direction of lines of magnetic flux at the sensing assembly, and indicate the attitude of the source relative to the sensing assembly. This permits guiding of the tool by control signals sent to the tool.

Reluctance type linear position detection device

Abstract: This detection device comprises a coil section and a rod section which is capable of linear displacement relative to the coil section The rod section has a magnetic substance portion changing reluctance of a magnetic circuit passing through the coil section in accordance with the linear displacement and a conductive substance portion provided in part of the rod section where the reluctance is caused to increase relatively in such a manner that an eddy current path will be formed relative to flux By this arrangement, in places where reluctance increases due to absence of the magnetic substance, reluctance is caused to further increase by the eddy current loss produced by presence of the conductive substance portion whereby the secondary side induced voltage level is further attenuated and the accuracy of detection can be improved The rod section may be so constructed as to produce only the reluctance change due to the conductive substance portion This detection device is applicable to detection of a piston rod position of a fluid powered cylinder

Solar tracking mechanisms

Abstract: A solar self-tracking mechanism for continuously tracking the movement of the sun with time comprises a solar radiant energy receiver secured to a base settled on a ground to be rotatable about a rotating shaftwhich extends horizontally in an east-west direction and plurality of compound parabolic concentrators secured to both longitudinal edges of the solar receiving mechanism in parallel to the rotating shaft The sun energy concentrated on suitable means such as shape memory alloy coil or solar cell module located at a position coincident with the focal line of the compound parabolic concentrator is transferred to a mechanism for driving the rotating shaft of the solar radiant energy receiver thereby to rotate the same and continuously obtain the solar radiant energy

Compensating circuit for a magnetic field sensor

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

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

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

Improved surface coil imaging in MR: decoupling of the excitation and receiver coils.

Abstract: We obtained magnetic resonance images with good sensitivity and radio frequency (RF) uniformity using separate transmitter and receiver coils. The excitation, namely, the rotation of the magnetization vector into a plane perpendicular to the magnetic field, was done by applying a homogeneous RF magnetic field produced by a large saddle-shaped coil. Surface coils were used for detection only. Because two coils that operated on the same resonance frequency were used, a coupling problem developed. This problem, which involved inhomogeneity of the RF magnetic field caused by the large current induced in the surface coil during excitation, could only be solved by minimizing the mutual inductance or maximizing the impedance of the surface coil resonance circuit during excitation. We were able to solve this problem using an electronic detuning method.

Integrated transformer and inductor

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