Showing papers on "Electromagnetic coil published in 1998"

Electrode catheter having coil structure

Abstract: A coil is located at the distal working end of an electrode catheter. The coil includes two parallel electrically conductive strips separated by a narrow gap. The strips are covered with insulation, and are connected respectively to electrical leads having opposite polarity. Electrodes are formed by removing portions of the insulation from the strips. The coil can be expanded to define an increased effective diameter at the working end of the catheter. An RF field produced along the helical path defined by the strips of the coil is unaffected by the expanded state of the coil. The energy from the RF field heats the surrounding venous tissue and causes a reduction in the diameter of the vein. The expanded coil mechanically prevents the vein from shrinking beyond the effective diameter defined by the expanded coil and the patency of the vein is maintained for venous function.

Transcutaneous energy transfer device

Abstract: In the design of transcutaneous energy transfer devices variation in spacing between the coils results in energy transfer efficiency changes. These changes may have other causes. It is proposed to use an autotuning circuit and a voltage control circuit in cooperation with feedback from the internal coil in order to better maintain energy transfer levels as desirable. The feedback is typically provided via IR communication; however, when skin is highly pigmented, IR communication is inefficient. A method and system for using RF signals to accomplish the communication is disclosed.

SAR and B1 field distributions in a heterogeneous human head model within a birdcage coil

Abstract: Calculations of radiofrequency magnetic (B1) field and specific energy absorption rate (SAR) distributions in a sphere of tissue and a multi-tissue human head model in a 12-element birdcage coil are presented. The coil model is driven in linear and quadrature modes at 63, 175, 200, and 300 MHz. Plots of B1 field magnitude and SAR distributions, average SAR, maximum local SAR, and measures of B1 field homogeneity and signal-to-noise ratio are given. SAR levels for arbitrary pulse sequences can be estimated from the calculated data. Maximum local SAR levels are lower at lower frequencies, in quadrature rather than in linear coils, and in linear fields oriented posterior-to-anterior rather than left-to-right in the head. It should be possible to perform many experiments in the head at frequencies up to 300 MHz without exceeding standard limits for local or average SAR levels.

Linear motion electric power generator

Abstract: A linear motion electric power generator for generating electric current from work done by an intermittent force. A moving magnet (2) is confined so that it can move with bi-directional linear, or approximately linear, motion through each of at least two coils (5 and 6). The coils are spaced apart from each other and connected electrically so that current produced in a first coil as a result of movement of the moving magnet is substantially in phase with current produced in said second coil. Embodiments of the invention provide pwoer from extremely low power mechanical forces and are useful for providing power for long life flashlights, for alarm systems and for communication devices located at places where conventional electric power sources are unavailable. Another preferred embodiment is a low profile unit which derives its mechanical power from repetitive forces such as the forces on the heel of a shoe during walking or running.

System and method for servo control of nonlinear electromagnetic actuators

Abstract: Servo control using ferromagnetic core material and electrical windings is based on monitoring of winding currents and voltages and inference of: magnetic flux, a force indication; and a magnetic gap, a position indication. The third order nonlinear servo control is split into nested control loops: a fast non-linear first order inner loop (1636) causing flux to track a target by varying a voltage output; and a slower almost linear second-order outer loop (1650, 1670, 1680) causing magnetic gap to track a target by controlling the flux target of the inner loop.

Fully integrated magnetically actuated micromachined relays

Abstract: A fully integrated magnetically actuated micromachined relay has been successfully fabricated and tested. This particular device uses a single-layer coil to actuate a movable upper magnetically responsive platform. The minimum current for actuation was 180 mA, resulting in an actuation power of 33 mW. Devices have been tested which can make and break 1.2 A of current through the relay contacts when the relay is electromagnetically switched. Operational lifetimes in excess of 850000 operations have been observed. Contact resistances as low as 22.4 m/spl Omega/ have been observed under electromagnetic actuation. Magnetic and structural finite-element (FE) simulations have been performed using ANSYS to calculate both the actuation and contact forces.

Charging device for batteries in a mobile electrical device

Abstract: A device for charging batteries is comprised of a mobile electrical device MD and a charging unit CU and inductively transmits electrical power by means of a alternating magnetic field from at least one primary winding W1, W2 to at least one secondary winding W3, W4 in the mobile device MD. According to the invention, the alternating magnetic field is generated by a self-oscillating push-pull oscillator which contains switches Q1, Q2 that are reciprocally connected with positive feedback and in each push-pull branch, contains a resonance circuit with the effective inductance of at least one primary winding W1 or W2 and with a circuit capacitance C1, C3 or C2, C4, wherein the primary windings W1 and W2 in the charging unit CU are disposed spatially separate from each other so that each generates a magnetic alternating field in a different spatial region and the secondary windings W3, W4 in the mobile device are disposed so that each spatial region is equally loaded.

Multi-filar coil medical stent

Abstract: Multi-filar, open and closed coil, tubular medical stents that are introduced to a site in a body lumen and released to expand at the site to provide a passageway through the stent lumen are disclosed. Each stent filar is a coil wound in substantially the same pitch through the majority of its length between the ends thereof. The coils are attached together at least at one coil end to form an end of the stent and wound in an interleaved manner such that the adjacent coils are substantially evenly spaced apart or in close contact in the released state and do not cross over one another. In one open coil stent embodiment, both ends of each coil are attached in respective first and second common attachment junctions, and the resulting coils have relatively even predetermined spacing between adjacent coil turns through the majority of the length of the stent between the first and last coil turns when the stent is released. Preferably, the first and second stent ends are formed by attaching the coil ends in common, and the stent ends are squared by decreasing the pitch of the first coil turn extending from the stent end such that the spacing of the stent end from the adjacent coil is reduced from the predetermined spacing. Additionally, multi-filar closed coil stent embodiments are disclosed having only one end of each coil attached in common and adjacent coil turns in substantial mutual and overlying contact in the restrained state during implantation and non-overlying contact in the released state. Preferably each common attachment junction of attached coil ends and each free coil end is formed into an enlarged stent end in at least one dimension for ease of attachment to and release from a stent delivery catheter. The common attachment junction can be snared or grasped by a stent retrieval system and retracted from the body lumen.

Inductive write head formed with flat yoke and merged with magnetoresistive read transducer

Abstract: A magnetic head includes aligned pole tips and a coil proximally disposed between a pair of first and second magnetic yoke layers which define a closed magnetic path with a transducing gap. The second magnetic yoke layer includes a flat geometry with a substantially level cross-sectional profile. The second yoke layer with less curvature results in less mutual inductance with the coil. Furthermore, the coil can be closely positioned between the first and second yoke layer, thereby allowing the coil to be more efficient in inducing magnetic flux in the yoke layers during data writing, and allowing the intercepted flux to induce current into the coil during data reading if the magnetic head is used as an inductive head.

Alternator for an automotive vehicle

Abstract: The present invention provides a compact, efficient and noiseless alternator for an automotive vehicle which employs a double-layer coil arrangement in a slot for eliminating coil end interference as well as improving the space factor. An automotive alternator comprises a Lundel-type core rotor with 16 poles, and a stator with toothed portions of 96 poles spaced by slots. U-shaped conductor segments are installed in the slots. One portion of the conductor is accommodated in an outer layer portion of a predetermined slot, while the other portion is accommodated in an inner layer portion of a slot phase shifted by an electric angle of 180°. In this manner, all of the slots are separated into the inner and outer layers to accommodate a plurality of conductor segments. These conductor segments are connected only at one side of the stator to form a total of twelve wavy winding coils. These twelve wavy winding coils are divided into three groups each consisting of a serial connection of four wavy windings to constitute one phase of a three-phase stator coil.

Miniaturized position sensor having photolithographic coils for tracking a medical probe

Abstract: A miniature coil assembly for transmitting or receiving magnetic waves comprises a plurality of coils wherein each coil has a respective axis. The coil assembly is assembled such that at least two of the axes are mutually linearly independent, and such that all of the plurality of coils are contained within a volume having a cross-sectional area less than 1.0 mm 2 . At least two of the coils are photolithographic coils.

Radiotherapy machine including magnetic resonance imaging system

Abstract: A radiotherapy machine beam treats a region of a subject while the region and volumes abutting the region are imaged by a magnetic resonance imaging system. The beam and an excitation coil assembly of the imaging system are arranged so the beam is not incident on the coil assembly and magnetic fields derived from the coil assembly do not interact with the beam. The excitation coil assembly includes two spaced winding segments for producing a main DC magnetic field; the segments are located on opposite sides of the region. In one embodiment, wherein the excitation coil assembly is mounted independently of movement of an axis of the beam, the winding segments have a common axis generally aligned with an axis about which the beam axis turns. A treatment couch for the subject fits within aligned central openings of the winding segments. The coil produces main magnetic field lines that extend generally in the same direction as the axis about which the beam turns. In other embodiments, the coil assembly moves with the beam axis and the treatment couch is between the coil segments. In one such embodiment, each winding segment includes a central opening (1) through which the beam axis extends; and (2) generally aligned with magnetic field lines established by and extending between the segments. In another such embodiment, the beam axis extends through a space between the segments, being generally orthogonal to magnetic field lines established by and extending between the segments.

Magnetic head with a toroidal coil encompassing only one yoke layer

Abstract: A magnetic head includes first and second magnetic yoke layers which contact each other at a back closure region at one end and delineate a transducer gap at another end. A toroidal coil encompasses one of the yoke layers. The coil axis of the toroidal coil passes through the encompassed yoke layer. During data writing, electrical current passes through the toroidal coil inducing magnetic flux along the coil axis, which flux is efficiently and directly delivered to the transducer gap for writing on a recording medium. During data reading, magnetic flux intercepted by the transducer gap flows along the encompassed yoke layer and efficiently induces electrical current in the toroidal coil for amplification. In alternative embodiments, separate read transducers are disposed adjacent to the toroidal coils to form merged heads.

Surface temperature sensor

Abstract: A surface temperature sensor includes a thermally conductive surface contact means for contacting a surface to be thermally measured and a coil. The coil contains an insulated thermal sensing element in thermal contact with the surface contact means and provides support for the surface contact means.

Near field magneto-optical head made using wafer processing techniques

Abstract: The method of making and self-aligning a magneto-optical head at a wafer level is as follows: A flat optical substrate is molded or heat pressed in batches as a wafer level to form the desired lens shapes. Coil cavities or depressions are simultaneously formed with the lens to accommodate the coil assembly. Conductive plugs are formed in proximity to the cutting lines, for wire bonding attachment to the coil. The plugs are filled with a conductive material such as copper. The plugs do not extend through the entire depth of the optical wafer, thus further facilitating the mass production of the integrated heads. The slider body wafer is formed from silicon or other appropriate material. The slider body wafer and the lens/coil wafer are bonded. Coils and pedestals are formed on the lens / coil plate using thin-film processing techniques. Reflective surfaces are deposited on the bottom surface of the substrate, opposite the lens. The mirror material around the pedestal areas and plugs is masked and removed. An alumina layer is then deposited to define the air bearing surface and the pedestal. Yokes are then formed by means of lithography and plating in the base and sides of the depressions to assume a desired shape. A series of alternating insulating layers and conductive coil layers is formed. A protective layer seals the coil assembly, and is lapped to correct the lens thickness and to provide proper focal plane.

Numerical simulation of SAR and B/sub 1/-field inhomogeneity of shielded RF coils loaded with the human head

Abstract: The finite-difference time-domain (FDTD) method is combined with the method of moments (MoM) to compute the electromagnetic fields of shielded radio-frequency (RF) coils loaded with an anatomically accurate model of a human head for high-frequency magnetic resonance imaging (MRI) applications. The combined method can predict both the specific energy absorption rate (SAR) and the magnetic field (known as the B/sub 1/ field) excited by any RF coils. Results for SAR and B/sub 1/ field distribution, excited by shielded and end-capped birdcage coils, are calculated at 64, 128, 171, and 256 MHz. The results show that the value of SAR increases when the frequency of the B/sub 1/ field increases and the B/sub 1/ field exhibits a strong inhomogeneity at high frequencies.

Inductive angle sensor

Abstract: An inductive angle sensor includes: a stator element having an exciting coil with a periodic AC voltage applied thereto and several receiving coils; a rotor element that affects a strength of inductive coupling between the exciting coil and receiving coils as a function of its angular position relative to the stator element; and an evaluation circuit for determining an angular position of the rotor element relative to the stator element from voltage signals induced in the receiving coils. The rotor element forms at least one closed-loop lead that, at least over a partial area, forms a periodic repeating bend structure in a direction of a circumference of the rotor element. The inductive angle sensor provides a compact structure, a high resolution, and a particularly high degree of insensitivity to production and installation tolerances.

Apparatus for magnetically decoupling an rfid tag

Abstract: A resonant circuit tag (12) includes an integrated circuit (18) for storing data and an antenna circuit (22) for generating a first local field and resonating at a first predetermined radio frequency. A second circuit including an inductive coil (30) selectively generates a second local field such that a sum of the first and second local fields approaches zero. The second circuit thus allows the resonant tag (12) to be selectively decoupled from its environment.

Reader/writer having coil arrangements to restrain electromagnetic field intensity at a distance

Abstract: The present invention provides a reader and/or writer for performing both the supply of operating power to an IC card and transmission of a communication signal to the IC card or transmission and reception thereof to and from the IC card, wherein a main coil or a spiral antenna for generating an electromagnetic field for the two or at least power supply, and auxiliary coils or spiral antennas for generating magnetic fields opposite in phase to the electromagnetic field generated by the main coil or spiral antenna to thereby restrain the intensity of the electromagnetic field in the distance are provided side by side.

Brushless dc motor control

Abstract: An electronically commutated brushless DC motor primarily for fractional horsepower applications of the type where at any instant one motor winding is unpowered and used to detect back EMF zero-crossings which information is used to initiate winding commutations. The duration of the pulse produced in this winding due to dissipation of stored energy by free-wheel diodes in parallel with the commutation devices after supply of current has been removed from this winding is used to provide a measure of motor current. This allows for simplified commutation device current limiting circuits and is available for control purposes which are a function of motor torque. There is also disclosed a method for maximising useful power output by reducing the phase angle between the motor current and the back EMF. This is accomplished by introducing a delay in commutating the motor windings beyond the occurrence of each back EMF zero-crossing, with the delay being a function of the time between commutations.

Focusing and targeting of magnetic brain stimulation using multiple coils

Abstract: Neurones can be excited by an externally applied time-varying electromagnetic field. Focused magnetic brain stimulation is attained using multiple small coils instead of one large coil, the resultant induced electric field being a superposition of the fields from each coil. In multichannel magnetic brain stimulation, partial cancellation of fields from individual coils provides a significant improvement in the focusing of the stimulating field, and independent coil channels allow targeting of the stimuli on a given spot without moving the coils. The problem of shaping the stimulating field in multichannel stimulation is analysed, and a method is derived that yields the driving currents required to induce a field with a user-defined shape. The formulation makes use of lead fields and minimumnorm estimation from magneto-encephalography. Using these methods, some properties of multichannel coil arrays are examined. Computer-assisted multichannel stimulation of the cortex will enable several new studies, including quick determination of the cortical regions, the stimulation of which disrupts cortical processing required by a task.

Composite ic module and composite ic card

Abstract: A composite IC card is provided with an IC module which has both a contact type function of receiving supplied electric power and transmitting/receiving signals through an electric contact and a non-contact type function of receiving supplied electric power and transmitting/receiving signals in a non-contact way by electromagnetic coupling without providing any electric contact on the IC card, and a non-contact transmission antenna. The IC module and antenna are provided with first and second coupling coils so arranged as to be coupled closely to each other, respectively. The IC module and antenna are coupled with each other in a non-contact way by transformer coupling. The coil of the antenna is so disposed that the coil does not overlap with an IC module fitting section which is the area of a contact type external terminal electrode, an emboss area, and a magnetic stripe area.

Rechargeable battery pack and charging stand for charging the rechargeable battery pack by electromagnetic induction

Abstract: A battery pack having at least one rechargeable battery and a secondary coil, which is electromagnetically coupled to a primary coil contained inside of a charging stand. The battery pack also includes a control circuit which controls electric power induced in the secondary coil for charging the rechargeable batteries. The secondary coil of the battery pack is positioned close to the bottom of a battery pack case with its center axis oriented along the elongated direction of the case. The charging stand contains the primary coil, which is located so as to be close to the secondary coil when the battery pack is mounted on the charging stand.

Antenna unit and digital television receiver

Abstract: An antenna unit comprising a conductor base plate and an antenna element arranged near the conductor base plate. The antenna element includes a predetermined portion as a coil or zigzagged conductor and has one end grounded through the conductor base plate. The antenna element may include the coil or zigzagged conductor at its one end in such a manner that the coil or zigzagged conductor is connected with the other part of the antenna element on an insulator provided on the conductor base plate.

Coil array autocalibration MR imaging

Abstract: A magnetic resonance (MR) imaging apparatus and technique exploits spatial information inherent in a surface coil array to increase MR image acquisition speed, resolution and/or field of view. Magnetic resonance response signals are acquired simultaneously in the component coils of the array and, using an autocalibration procedure, are formed into two or more signals to fill a corresponding number of lines in the signal measurement data matrix. In a Fourier embodiment, lines of the k-space matrix required for image production are formed using a set of separate, preferably linear combinations of the component coil signals to substitute for spatial modulations normally produced by phase encoding gradients. One or a few additional gradients are applied to acquire autocalibration (ACS) signals extending elsewhere in the data space, and the measured signals are fitted to the ACS signals to develop weights or coefficients for filling additional lines of the matrix from each measurement set. The ACS lines may be taken offset from or in a different orientation than the measured signals, for example, between or across the measured lines. Furthermore, they may be acquired at different positions in k-space, may be performed at times before, during or after the principal imaging sequence, and may be selectively acquired to optimized the fitting for a particular tissue region or feature size. The in vivo fitting procedure is readily automated or implemented in hardware, and produces an enhancement of image speed and/or quality even in highly heterogeneous tissue. A dedicated coil assembly automatically performs the calibration procedure and applies it to measured lines to produce multiple correctly spaced output signals. One application of the internal calibration technique to a subencoding imaging process applies the ACS in the central region of a sparse set of measured signals to quickly form a full FOV low resolution image. The full FOV image is then used to determine coil sensitivity related information and dealias folded images produced from the sparse set.

Articulated magnetic guidance systems and devices and methods for using same for magnetically-assisted surgery

Abstract: An articulated magnet assembly optionally includes one or two additional fixed magnets to guide or move such as by pulling or pushing a magnetic structure in the body. The magnetic structure may be a magnetic tip of a catheter or a magnetic seed, or other such magnetic assembly, implant or device. The device is arranged to facilitate biplanar, real-time, X-ray imaging of the patient. The moved magnet can be a large, strong permanent magnet or a cored solenoid. The added, fixed electromagnets may have either normally conducting or superconducting coils. The magnet on the articulated magnet assembly can move radially, along a polar direction, and at an azimuthal angle, and may also pivot in place to direct an opposite pole of the magnet in the direction of the patient. Magnetically-assisted surgery can be performed, in some instances, by pivoting the magnet on one or two axes without withdrawing it from the vicinity of the patient to control the direction and/or orientation of a temporarily or permanently implanted magnetic surgical device. If the magnet is an electromagnetic coil, this pivoting may or may not have to be accompanied by a ramping of current in the coil.

Method and apparatus for generating a plasma

Abstract: A method and apparatus for generating a plasma by inductively coupling electromagnetic energy into the plasma. In one embodiment, first and second antenna coils are disposed about the circumference of the plasma containment area. The first and second antenna coils are relatively spaced along the longitudinal axis of the plasma containment area. A current is generated in the first and second antenna coils. A phase shift regulating network establishes a difference between the phase of the current in the first antenna and the phase of the current in the second antenna. The phase difference corresponds to the phase difference required to launch a helicon wave in the plasma. In a second embodiment, a chamber shield is made of a conductive material and is coupled to the RF source such that the shield functions as an RF antenna. The shield may be coupled in series to a coil surrounding the shield to increase the resultant flux density.

Signal-to-noise ratio in MRI.

Abstract: in RF receiving coil design. However, modern is proportional to 0 , so that their population imaging techniques often demand very high speed difference is larger at high values of 0 . Since the and spatial resolution, so that the highest possible ratio of the energy difference to thermal energy is SNR is still required to avoid poor image quality. very small, the population difference increases in In this commentary, the physics underlying the direct proportion to 0 , as does the size of the variation of SNR with static field strength will be nuclear magnetic dipole moment. Secondly, the briefly reviewed, practical methods of optimizing Larmor frequency at which the dipole moment SNR will be outlined, including a discussion of the precesses is proportional to 0 so that the rate of principles of quadrature and phased-array RF change of flux linked to the RF coil also increases coils, and methods of measuring SNR for acceptin proportion to 0 . Therefore, by Faraday’s law ance testing and quality assurance will be of electromagnetic induction, the signal produced discussed. by a dipole magnetic moment of constant magni-

Radio frequency identification transponder having non-encapsulated IC chip

Abstract: The present invention is directed to an identification element having an integrated circuit and an antenna coil ( RFID transponder) connected to the integrated circuit, as well as to a method of manufacturing such an identification element. The present invention provides an economically priced identification element and a method of manufacturing such an identification element. The integration circuit is a non-encapsulated chip and the antenna coil comprises at least one layer of a metallic coating.

Radio-frequency amplifier based on a niobium dc superconducting quantum interference device with microstrip input coupling

Abstract: A dc superconducting quantum interference device (SQUID) was used to amplify radio-frequency signals that were coupled to one end of the microstrip formed by the input coil and the SQUID washer. For one device, the resonant frequency of the microstrip was increased from about 200 to 620 MHz by progressively shortening the length of the coil. At an operating temperature of 4.2 K, the gain was typically 18 dB, and the system noise temperature ranged from 0.5±0.3 K at 80 MHz to 3.0±0.7 K at 500 MHz.