Showing papers on "Electromagnetic coil published in 1996"

Simultaneous acquisition of spatial harmonics (SMASH): ultra-fast imaging with radiofrequency coil arrays

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. Partial signals are acquired simultaneously in the component coils of the array and formed into two or more signals corresponding to orthogonal spatial representations. 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. The signal combining may proceed in a parallel or flow-through fashion, or as post-processing, which in either case reduces the need for time-consuming gradient switching and expensive fast magnet arrangements. In the post-processing approach, stored signals are combined after the fact to yield the full data matrix. In the flow-through approach, a plug-in unit consisting of a coil array with an on board processor outputs two or more sets of combined spatial signals for each spin conditioning cycle, each directly corresponding to a distinct line in k-space. This partially parallel imaging strategy, dubbed SiMultaneous Acquisition of Spatial Harmonics (SMASH), is readily integrated with many existing fast imaging sequences, yielding multiplicative time savings without a significant sacrifice in spatial resolution or signal-to-noise ratio. An experimental system achieved two-fold improvement in image acquisition time with a prototype three-coil array, and larger factors are achievable with ther coil arrangements.

Stretch resistant vaso-occlusive coils

Abstract: A vaso-occlusive coil comprises a primary helically wound coil which may then be wound into a secondary shape. A stretch-resisting member extends through the lumen formed, which stretch-resisting member is fixedly attached, directly or indirectly, to the coil in at least two locations. The stretch-resisting member is preferably somewhat loose within the interior of the lumen so to prevent the coil from collapsing, binding, and therefore stiffening during passage of turns through the human body. This stretch-resisting member is for the primary stretching of the coil during movement of that coil, e.g., by retrieval of repositioning after deployment. The device may have a self-forming secondary shape made from a pre-formed primary linear helically wound coil. The device is typically introduced into the body through a catheter. The device is passed axially through the catheter sheath and assumes its secondary form upon exiting the catheter.

Method and system for navigating a catheter probe

Abstract: A system for navigating a catheter probe through a body cavity includes a sensing coil (14) affixed to a distal end of the probe. Magnetic fields are projected into the body cavity to induce voltage signals in the sensing coil (14) that are sufficient to describe the orientation and position of the probe. A set of magnetic coils (20-26, 30-32, 36-42) each generates a substantially uniform field (27, 33, 43) in a single respective dimension. The orientation angles of the sensing coil may be determined from known values of the unidirectional fields and the measured induced voltage signals. Gradient magnetic fields with components in two dimensions are projected into the body cavity to induce another group of voltage signals. The geometrical intersection of constant voltage surfaces developed by certain gradient fields that produce the measured induced voltage signals is a set of lines on which the catheter is located. The point of intersection of such lines yields the positional coordinates.

Coil fastener applier

Abstract: There is provided a surgical coil fastener applier for use in applying helical coil fasteners in surgical procedures, such as hernia repair, to affix surgical mesh to tissue. The coil fastener applier includes a housing having a handle extending therefrom and a trigger pivotally mounted on the housing. An elongated tubular portion extends from the housing and includes a drive rod rotatably supported therein and slidably supporting a plurality of coil fasteners thereon. A drive assembly is provided within the housing to rotate the drive rod and coil fasteners. The drive assembly includes an anti-reverse mechanism to allow rotation of the drive rod in only one direction. An actuation assembly is provided within the housing to convert the motion of the trigger into rotary motion for supply to the drive assembly. The drive assembly includes structure to limit the amount of rotary motion supplied to the drive assembly. The drive assembly further includes a ratchet and pawl mechanism to prevent a partial cycling of the coil fastener applier. Also provided are various coil fasteners for use with the coil fastener applier.

Microwave ablation catheters having antennas with distal fire capabilities

Abstract: A variety of improved antenna arrangements for ablation catheters and methods for constructing catheter with these antenna arrangements are described. In various apparatus aspects of the invention, the catheter includes an elongated flexible tubular member adapted to be inserted into a vessel in the body of a patient. A transmission line suitable for transmitting electromagnetic energy is received within the tubular member. An antenna is coupled to the transmission line for generating an electric field sufficiently strong to cause tissue ablation. In one embodiment, the antenna takes the form of an antenna coil that is oriented such that its longitudinal axis extends substantially perpendicular to the longitudinal axis of the flexible tubular member. In another embodiment, a plurality of such laterally oriented antenna coils are provided at longitudinally spaced locations relative to the catheter axis. In other embodiments, the antenna coil is spirally wound. A variety of spiral antenna arrangements are contemplated. In some embodiments, the coil is wound in a substantially conical or frusto-conical manner expanding either distally or proximately. In still another embodiment, the antenna coil is wound in a substantially flat coil.

Planar magnetic element

Abstract: Disclosed herein is a planar magnetic element comprising a substrate, a first magnetic layer arranged over the substrate, a first insulation layer arranged over the first magnetic layer, a planer coil formed of a conductor, having a plurality of turns, arranged over the first insulation layer and having a gap aspect ratio of at least 1, the gap aspect ratio being the ratio of the thickness of the conductor to the gap between any adjacent two of the turns, a second insulation layer arranged over the planar coil, and a second magnetic layer arranged over the second insulation layer. When used as an inductor, the planar magnetic element has a great quality coefficient Q. When used as a transformer, it has a large gain and a high voltage ratio. Since the element is small and thin, it is suitable for use in an integrated circuit, and can greatly contribute to miniaturization of electronic devices.

Implantable and external hearing systems having a floating mass transducer

Abstract: A floating mass transducer for improving hearing in a hearing impaired person is provided. The floating mass transducer (100) may be implanted or mounted externally for producing vibrations in a vibratory structure of an ear. In an exemplary embodiment, the floating mass transducer comprises a magnet assembly (12) and a coil (14) secured inside a housing (10) which is fixed to an ossicle of a middle ear. The coil is more rigidly secured to the housing than the magnet. The magnet assembly and coil are configured such that conducting alternating electrical current through the coil results in vibration of the magnet assembly and coil relative to one another. The vibration is caused by the interaction of the magnetic fields of the magnet assembly and coil. Because the coil is more rigidly secured to the housing than the magnet assembly, the vibrations of the coil cause the housing to vibrate. The vibrations of the housing are conducted to the oval window of the ear via the ossicles. In alternate embodiments, the floating mass transducer produces vibrations using piezoelectric materials.

Endoluminal coil delivery system having a mechanical release mechanism

Abstract: The invention provides endoluminal coil delivery systems (10) and methods for positioning a coil (13) within a body lumen (44). In particular, the device uses a mechanical latch in the form of jaws to positively engage the coil (13) during positioning. The coil may be restrained in a straight configuration from within the coil (13), using an internal coil wire (22), or from outside using a catheter. Thus, the mechanism for releasing the coil (13) to form its relaxed convoluted shape is separate from the mechanism for disengaging the coil (13) from the delivery system (10). The use of an internal core wire allows a coil having a helical outer surface to be torqued against a fallopian tube or other body lumen wall, thereby firmly anchoring the coil (13) in the target position prior to disengaging the delivery system (10).

High resolution intravascular MRI and MRS by using a catheter receiver coil

Abstract: Potentially important diagnostic information about atherosclerosis can be obtained by using magnetic resonance imaging and spectroscopy techniques. Because critical vessels such as the aorta, coronary arteries, and renal arteries are not near the surface of the body, surface coils are not adequate to increase the data quality to desired levels. A few catheter MR receiver coil designs have been proposed for imaging the walls of large blood vessels such as the aorta. These coils have limited longitudinal coverage and they are too thick to be placed into small vessels. A flexible, long and narrow receiver coil that can be placed on the tip of a catheter and will enable multi-slice high resolution imaging of small vessels has been developed. The authors describe the theory of the coil design technique, derive formulae for the signal-to-noise ratio characteristics of the coil, and show examples of high resolution cross-sectional images from isolated human aortas acquired by using this catheter coil. In addition, high resolution in vivo rabbit aorta images were obtained as well as a set of spatially resolved chemical shift spectra from a dog circumflex coronary artery.

On the E - H mode transition in RF inductive discharges

Abstract: In inductively coupled radio frequency (RF) plasmas a mode transition between a low-power mode with dominant capacitive coupling (E-mode) and a high-power mode with dominant inductive coupling (H-mode) has been frequently reported in the literature We investigate this transition, which results in an increase of the light emission by up to two orders of magnitude Furthermore we observe a hysteresis of this mode transition Two major aspects of the transition are addressed in this paper First we propose an explanation for the discontinuous character of the mode transition The analysis is based on a simple, electrodynamic model of the inductive discharge This analysis shows that a certain minimum maintenance RF coil current is required for the operation of an inductive discharge and that the skin effect of the RF field is essential for stable discharge operation This point is supported by experimental observations In the second part of the paper we present a simple, self-consistent analytic description of the discharge, which enables us to calculate the minimum maintenance RF coil current The theoretical results are found to be in reasonable agreement with the measured minimum maintenance coil currents

Transcutaneous energy transmission circuit for implantable medical device

Abstract: An improved transcutaneous energy transmission device (50) is disclosed for charging rechargeable batteries (13) in an implanted medical device (14). A current with a sinusoidal waveform is applied to a resonant circuit comprising a primary coil (9) and a capacitor (25). Current is induced in a secondary coil (10) attached to the implanted medical device. Two solid state switches (21, 22) are used to generate the sinusoidal waveform by alternately switching on and off input voltage to the resonant circuit. The sinusoidal waveform reduces eddy current effects in the implanted device which detrimentally increases the temperature of the implanted device. The present invention charges the batteries using a charging protocol that reduces charging current as the charge level in the battery increases. The controller preferably is constructed as a pulse width modulation device (23) with a variable duty cycle to control the current level applied to the primary coil. An alignment indicator (40) also is provided to insure proper alignment between the energy transmission device and the implanted medical device.

Calculation and measurement of unbalanced magnetic pull in cage induction motors with eccentric rotors. I. Analytical model

Abstract: The paper describes an analytical model for cage induction motors with a static eccentric rotor. The method is based on an airgap permeance approach including stator and rotor MMF harmonics. The stator windings are resolved into harmonic conductor density distributions that allow different series/parallel winding connections to be accommodated in a straightforward manner. Sinusoidal and homopolar airgap field components are identified and the total airgap field distribution is used to determine the radial forces on the rotor. The model examines the principal harmonic interactions that influence the unbalanced magnetic pull.

Method of internal magnetic resonance imaging and spectroscopic analysis and associated apparatus

Abstract: The invention provides a method for magnetic resonance imaging and spectroscopic analysis of the interior of a specimen (4) which includes positioning the specimen within a main magnetic field, introducing an invasive probe having an elongated receiver coil (22) into or adjacent to the specimen with the coil having at least one pair of elongated electrical conductors (24, 26), preferably, generally parallel to each other disposed within a dielectric material (30) and having a pair of ends electrically connected to each other (32). The method involves employing a flexible receiver coil which has uniform sensitivity along the coil. Tuning capacitance may be distributed along the length of the coil and/or a Faraday screen provided to minimize dielectric losses between the coil and the surrounding material of the specimen. In a preferred use the probe is introduced into small blood vessels of a patient to facilitate determination of atherosclerotic plaque. A corresponding apparatus is provided.

Endoscope provided with function of being locked to flexibility of insertion part which is set by flexibility modifying operation member

Abstract: A densely wound coil and a wire which passes through the coil are inserted into a flexible part which has a flexibility. The coil which is fixed in the vicinity of a distal end of the wire has a proximal end thereof which is regulated in movement toward a rearward side by a stopper. The wire which extends rearward from the proximal end of the coil has a proximal end thereof which is drawn or pulled toward the rearward side by angular movement of an adjustment knob which is provided in the vicinity of a forward end of an operation part. By this traction, a compressive force is relatively applied to the coil to make flexibility of the coil changeable. By an O-ring which is urged against the adjustment knob, even if a hand is removed after the adjustment knob has been operated, the adjustment knob can be locked to the state by a frictional force.

Novel permanent magnet motor drives for electric vehicles

Abstract: Novel permanent magnet (PM) motor drives have been successfully developed to fulfil the special requirements for electric vehicles such as high power density, high efficiency, high starting torque, and high cruising speed. These PM motors are all brushless and consist of various types, namely rectangular-fed, sinusoidal-fed, surface-magnet, buried-magnet, and hybrid. The advent of novel motor configurations lies on the unique electromagnetic topology, including the concept of multipole magnetic circuit and full slot-pitch coil span arrangements, leading to a reduction in both magnetic yoke and copper, decoupling of each phase flux path, and hence an increase in both power density and efficiency. Moreover, with the use of fractional number of slots per pole per phase, the cogging torque can be eliminated. On the other hand, by employing the claw-type rotor structure and fixing an additional field winding as the inner stator, these PM hybrid motors can further provide excellent controllability and improve efficiency map. In the PM motors, by purposely making use of the transformer EMF to prevent the current regulator from saturation, a novel control approach is developed to allow for attaining high-speed constant-power operation which is particularly essential for electric vehicles during cruising. Their design philosophy, control strategy, theoretical analysis, computer simulation, experimental tests and application to electric vehicles are described.

Advanced designs of floating mass transducers

Abstract: A floating mass transducer for assisting hearing in a person is provided. Inertial vibration in the floating mass transducer (100) produces vibrations in the inner ear. In an exemplary embodiment, the floating mass transducer comprises a magnet assembly (12) and a coil (14) secured inside a housing (10) which is attached to bone within the middle ear. The coil is more rigidly secured to the housing than the magnet. The magnet assembly and coil are configured such that conducting alternating electrical current through the coil results in vibration of the magnet assembly and coil relative to one another. The vibration is caused by the interaction of the magnetic fields of the magnet assembly and coil. Because the coil is more rigidly secured to the housing than the magnet assembly, the vibrations of the coil cause the housing to vibrate. The floating mass transducer may generate vibrations in the inner ear by being attached to the skull or through a mouthpiece.

Guidewire having bimetallic coil

Abstract: An embodiment of the invention provides a guidewire having a coil which comprises at least a distal coil segment (24) and a proximal coil segment (22), one of the coil segments being more radiopaque than at least one of the other coil segments An elongate wire (14) may extend within the lumen of the coil In a two segment coil, the distal end of the distal coil segment is attached to the wire (14) and the proximal end of the distal coil segment is attached to the distal end of the proximal coil segment while the proximal end of the proximal coil segment is attached to the wire (14)

Surface coil phased arrays for high‐resolution imaging of the carotid arteries

Abstract: An MR phased-array coil assembly was developed to obtain high-resolution images of atherosclerotic plaques in the carotid artery. Images of volunteers and patients obtained by using alternative coil designs provided a subjective assessment of the coils' performance, field of view, ease of use, and susceptibility to motion artifacts. A quantitative measurement performed on a phantom indicated that a two-coil phased-array design should produce a 37% better signal-to-noise ratio at the carotids than would a conventional single 3-inch surface coil.

Embolic coils with offset helical and twisted helical shapes

Abstract: This is a surgical device that, in particular, is for forming a vasoocclusion or embolism. Typically, it is a helically wound coil in which the helix is wound in such a way as to have multiple axially offset, longitudinal or focal axes. Another important facet of the invention is the presence of small diameter secondary coil windings adjacent large diameter coil windings. The device is sufficiently flexible and small that it may be delivered to a site within the vasculature of the human body using a pusher and a catheter. The device is generally linear when within the catheter but relaxes to form the multi-focal form after delivery from the distal end of the catheter lumen. Various mechanical connections may also be used to discharge the inventive coil from its pusher. Similarly, the coil may be attached to a pusher using a sacrificial joint, which sacrificial joint is dissolved by imposition of a small voltage within the human body. The device may be used alone or in conjunction with other coils or with a fibrous thrombotic attachments or the substrate to localize subsequent infusion of tissue adhesives, other particulate embolization devices, or chemotherapeutic agents in abnormal blood vessels and tissues.

Inductive coupler for electric vehicle charger

Abstract: An inductive coupler for use in a battery charging system for an electric vehicle has a primary device having a primary coil and a core and a secondary device having a secondary coil and core. The primary and secondary devices are coupleable together with the primary coil placed within an open space defined by the secondary coil. The secondary coil is formed and sized so as to have a greater dimension than the primary coil as measured in the longitudinal direction of an electric vehicle parked for battery charging so that a space interval between the two coils in the longitudinal direction of the vehicle is greater than that in the lateral direction of the vehicle.

Therapeutic appliance releasing device

Abstract: This invention is a device (10) for releasing a therapeutic appliance, such as an embolic coil (12) inside an aneurysm (16). The device includes a coupling (24) of a shape memory alloy which is responsive to a change in temperature beyond a predetermined transformation point so as to change the shape of the coupling from a first configuration, wherein the coupling receives and holds the proximal end (72) of the coil, to a second configuration wherein the coil can be released from the coupling. An energy receiver (46) is operably associated with the coupling to heat the coupling to a temperature above the transformation point with laser or electrical energy received from an external source.

Multi-degree of freedom magnetorheological devices and system for using same

Abstract: A semi-active device (20) for damping motion between structures having multi-degrees of freedom. A magnetic field produced by a permanent magnet, a coil, or a combination thereof, change the rheological properties of an MR fluid (40) to effectively lock up the components and the structures to which they are attached to serve as a brake or damper of the associated compound motion. A system (21) employing the MR devices (20) includes a motion detection sensor (15) and a controller (19) to actuate the MR devices (20) when a predetermined motion threshold is exceeded.

Lumped parameter models for single- and multiple-layer inductors

Abstract: A method for modeling inductors under high-frequency operation is presented. The method is based on analytical approaches which can predict turn inductances, turn-to-turn and turn-to-core capacitances using physical structure of windings. Turn inductances, turn-to-turn and turn-to-core capacitances of coils are then introduced into suitable lumped parameter equivalent circuits of inductors. The overall inductance and stray capacitance can be obtained through the use of the equivalent circuits. Both single- and multiple-layer inductors are considered. The method was tested with experimental measurements. The accuracy of the results was good in most cases. The derived expressions can be useful for the design of HF inductors and can also be used for simulation purposes.

Methods and apparatus for measuring temperatures at high potential

Abstract: A thermocouple is provided which measures the temperatures of structures at high RF potential, such as an RF electrode within a plasma CVD or plasma etch reactor. The thermocouple includes an outer conductive sheath that connects to the RF electrode at a first location, and a wire pair, connected to a second location of the RF electrode, that is used to sense the RF electrode temperature. The sheath--or a conductive member connected in circuit with the sheath--is wound into a coil to form an inductor with an impedance much greater than the impedance of the RF electrode. A large capacitor grounds the coil so that the thermocouple wires, extending through the sheath, and through and out of the coil, are available for diagnostic purposes. While RF current flows through the sheath, the wires experience the same magnetic field generated by the inductive coil, substantially grounding the thermocouple. Preferably, signal conditioning electronics remove any remaining DC bias voltages. In the case of a reactor for plasma CVD or etch, the thermocouple can be enclosed within a vacuum-sealed RF feedthrough that conducts the RF energy to the electrode.

Conformal positioning assembly for microwave ablation catheter

Abstract: An ablation catheter includes an elongated flexible tubular member adapted to be inserted into a vessel in the body of a patient. A transmission line is disposed within the tubular member and a transducer is coupled to the transmission line for generating an electric field sufficiently strong to cause tissue ablation. A shape memory wire is positioned at a distal portion of the catheter adjacent the transducer to facilitate straightening the catheter tip after use. In one preferred embodiment, the shape memory wire may a flat wire which is formed from copper beryllium, a steel alloy, or nickel titanium. In another embodiment, the transmission line of the catheter is a coaxial cable, and the transducer is a helical antenna coil that is adapted to radiate electromagnetic energy in the microwave frequency range. In yet another embodiment, the shape memory wire is positioned within the antenna coil. Methods for manufacturing and using such ablation catheters are also described.

Transcutaneous electromagnetic energy transfer

Abstract: A method and apparatus for enhancing transcutaneous energy transfer to provide power to a medical device that is disposed within the body of a patient. A magnetic field is created by an external transmitting coil (200), which induces an electrical current in a receiving coil (300) that has been placed under the patient's skin (100). The flux path magnetic permeability between the receiving and transmitting coils is enhanced by the implantation of particles (120) into dermis (104) within the skin at that site. The particles, which comprise soft iron or other material having a characteristic high magnetic permeability, are preferably implanted using either a hypodermic needle (150) or a medical air injection device (160). A biocompatible material such as Teflon™ is applied as a coating (123) to the particles. To implant the particles, they are preferably first suspended in a liquid, forming a mixture that is readily delivered to the desired location. The particles are dispersed in a deposit below the epidermis, so that the deposit is between pole faces of the transmitting and the receiving coils. The efficiency of transcutaneous power transfer increases because the magnetic flux density coupling the transmitting and receiving coils is improved by the particles.

Inductively coupled parallel-plate plasma reactor with a conical dome

Abstract: A plasma reactor appropriate for fabrication, especially etching, of semiconductor integrated circuits and similar processes in which the chamber has a top comprising a truncated conical dome and, preferably, a counter electrode disposed at the top of the conical dome. An RF coil is wrapped around the conical dome to inductively couple RF energy into a plasma within the chamber dome. The dome temperature can be controlled in a number of ways. A heat sink can be attached to the outside rim of the dome. A rigid conical thermal control sheath can be fit to the outside of the dome, and any differential thermal expansion between the two is accommodated by the conical geometry, thus assuring good thermal contact. The rigid thermal control sheath can include resistive heating, fluid cooling, or both. Alternatively, a flexible resistive heater can be wrapped around the dome inside the RF coil. The resistive heater includes a heater wire wound in a serpentine path that has straight portions overlying and perpendicular to the RF coil but has bends located away from the RF coil. The path prevents the heater wire from shorting the azimuthal electric field induced by the RF coil and also acts as a Faraday shield preventing capacitive coupling from the coil into the chamber plasma.

Non-destructive evaluation of pipes and tubes using magnetostrictive sensors

Abstract: A method and apparatus for the inspection of ferromagnetic and non-ferromagnetic pipes (14) or other cylindrical shell structures utilizing the magnetostrictive effect to detect defects within the structure. The invention constitutes an active testing application, wherein a transmitting coil element (16) generates a mechanical pulse (15) within a cylindrical shell structure through the magnetostrictive effect and a second coil (24) detects reflected mechanical waves (15) within the pipe, or a single sensor (10) functions as both transmitter and detector. The present invention also anticipates a passive monitoring application with a detection coil (16) that continuously monitors ferromagnetic or non-ferromagnetic cylindrical structures for mechanical or acoustic wave emissions (15). Non-ferromagnetic structures (14) are made amenable to inspection by attaching a layer of ferromagnetic material such as nickel on a wall of the structure by plating or bonding such material in a local area where the sensor is to be placed.

Optimal realization of arbitrary forces in a magnetic stereotaxis system

Abstract: Very small implanted permanent magnets guided by large electromagnetic coils have been proposed previously as a method for delivering hyperthermia to or guiding catheters through brain tissue. This procedure is termed "magnetic stereotaxis". Early efforts employed a single coil on a movable boom, a design that proved logistically difficult to use on human patients. The present work deals instead with a design where several stationary coils are employed to develop a force on the implanted magnet. The coil current-to-force relationship is developed for this type of machine, and several optimal solutions for realizing an arbitrary static force are presented for various constraints on the orientation of the implanted permanent magnet. Costs of the different solutions are compared in several examples using a mathematical model based on the Magnetic Stereotaxis System (MSS) developed by Stereotaxis, Inc., the University of Virginia, and Wang NMR.