Showing papers on "Electromagnetic coil published in 2000"

Self-induction-type stroke sensor

Abstract: Within a body, a sensor member, which has one end supported in a cantilever fashion adjacent a predetermined end of the body and has the other end extending into a space of the body, includes a coil section having a plurality of coil segments that are excitable in a same phase by a predetermined A.C. signal and sequentially arranged along a direction of linear movement of a movable member. The movable member has an inner space to permit entry of the sensor member into the movable member. Inner peripheral wall of the movable member defining the inner space includes a magnetism-responsive substance containing a magnetic or electrically-conductive material. Relative positions of the magnetism-responsive substance and the coil section vary in accordance with a stroke position of the movable member, in response to which respective inductance of the coil segments are caused to vary in such a manner that during movement of the magnetism-responsive substance from one end to the other of a particular one of the coil segments, a voltage across the particular coil segment is caused to progressively decrease or increase.

Feedback stabilization of nonaxisymmetric resistive wall modes in tokamaks. I. Electromagnetic model

Abstract: Active feedback stabilization of pressure-driven modes in tokamaks is studied computationally in toroidal geometry. The stability problem is formulated in terms of open-loop transfer functions for fluxes in sensor coils resulting from currents in feedback coils. The transfer functions are computed by an extended version of the MARS stability code [A. Bondeson et al., Phys. Fluids B 4, 1889 (1992)] and can be accurately modeled by low order rational functions. In the present paper stability is analyzed for a system with an ideal amplifier (current control). It is shown that feedback with modest gain, and a single coil array poloidally, gives substantial stabilization for a range of coil shapes. Optimum design uses sensors for the poloidal field, located inside the resistive wall, in combination with rather wide feedback coils outside the wall. Typically, the feedback does not strongly modify the plasma-generated magnetic field perturbation. A future companion paper [C. M. Fransson et al., Phys. Plasmas (ac...

Partially parallel imaging with localized sensitivities (PILS).

Abstract: In this study a novel partially parallel acquisition method is presented, which can be used to accelerate image acquisition using an RF coil array for spatial encoding. In this technique, Parallel Imaging with Localized Sensitivities (PILS), it is assumed that the individual coils in the array have localized sensitivity patterns, in that their sensitivity is restricted to a finite region of space. Within the PILS model, a detailed, highly accurate RF field map is not needed prior to reconstruction. In PILS, each coil in the array is fully characterized by only two parameters: the center of coil's sensitive region in the FOV and the width of the sensitive region around this center. In this study, it is demonstrated that the incorporation of these coil parameters into a localized Fourier transform allows reconstruction of full FOV images in each of the component coils from data sets acquired with a reduced number of phase encoding steps compared to conventional imaging techniques. After the introduction of the PILS technique, primary focus is given to issues related to the practical implementation of PILS, including coil parameter determination and the SNR and artifact power in the resulting images. Finally, in vivo PILS images are shown which demonstrate the utility of the technique.

Surgical communication and power system

Abstract: An apparatus for determining the position of a wireless catheter probe being used during a surgical procedure. Magnetic fields are projected into an anatomical body to induce voltage signals in a sensing coil that are sufficient to describe the position of a wireless sensor/transmitter. The voltage signals are wirelessly re-transmitted by the sensor/transmitter as positional signals indicative of a current location of the sensor/transmitter in the anatomical body. In a preferred embodiment, the wireless catheter probe is self-powered using the induced voltage signals on a sensing coil. In another embodiment, induced voltage signals of a separate coil are used to power the device.

A noncontact charger using a resonant converter with parallel capacitor of the secondary coil

Abstract: A noncontact charging system using a resonant converter is presented in this paper, where the power transfer ability of a detachable transformer is improved by using a parallel capacitor connected to the secondary coil. A method to get the optimum value of the capacitance which would maximize the charging current is described. A method of application to the practical circuit such as a voltage resonant converter is also described.

A totally implantable cochlear prosthesis

Abstract: A totally implantable cochlear prosthesis is presented. Said prosthesis is designed to function for hours or days without any external components. An externally-activated subcutaneous pressure switch enables the user to adjust the perceived volume by pressing against the skin with a finger. A similar second pressure switch provides a safety 'off/on' feature. A pliable bridge connecting two hermetically sealed housing sections, and corrugated conductor lines, provide for future dimensional changes due to head growth. A titanium encapsulated microphone is positioned underneath the skin in the posterior wall of the external auditory canal. A modiolus-hugging electrode array is inserted into one of the cochlea scala. Periodic charging of the implanted battery (contained within one of the housing sections) is required, such charging accomplished via an external mechanically held head-mounted device containing an external coil, said external coil inductively coupling electrical power to an implanted receiving coil. The external and implanted coils can also be used as a communication link to program the implanted electronics.

Reduction of resonant RF heating in intravascular catheters using coaxial chokes

Abstract: The incorporation of RF coils into the tips of intravascular devices has been shown to enable the localization of catheters and guidewires under MR guidance. Furthermore, such coils can be used for endoluminal imaging. The long cable required to connect the coil with the scanner input inadvertently acts as a dipole antenna which picks up RF energy from the body coil during transmit. Currents are induced on the cable which can lead to localized heating of surrounding tissue. Cables of various lengths were measured to determine if a resonance in the heating as a function of cable length could be found. Coaxial chokes with a length of lambda/4 were added to coaxial cables to reduce the amplitude of the currents induced on the cable shield. A 0.7-mm diameter triaxial cable, small enough to fit into a standard intravascular device, was developed and measured both with and without a coaxial choke. It is demonstrated that resonant heating does occur and that it can be significantly reduced by avoiding a resonant length of cable and by including coaxial chokes on the cable.

Method and System for Navigating a Catheter Probe in the Presence of Field-Influencing Objects

Abstract: A system for and method of determining and compensating for the effect of a field influencing object on a field sensor, preferably a coil, that is within a navigational domain. The navigational domain contains navigational magnetic energy and disturbing magnetic energy, and the field influencing object produces the disturbing magnetic energy in response to the navigational magnetic energy. The correction system includes a first transmitter for projecting into the navigational domain field energy in a first waveform sufficient to induce a first signal value in the sensing coil. The system also includes a second transmitter for projecting into the navigational domain field energy in a second waveform sufficient to induce a second signal value in the sensing coil. The system further includes a signal processor for receiving the second signal value to determine the effect of the electrically conductive object on the field sensor.

Improvement of the quality factor of RF integrated inductors by layout optimization

Abstract: A systematic method to improve the quality (Q) factor of RF integrated inductors is presented in this paper. The proposed method is based on the layout optimization to minimize the series resistance of the inductor coil, taking into account both ohmic losses, due to conduction currents, and magnetically induced losses, due to eddy currents. The technique is particularly useful when applied to inductors in which the fabrication process includes integration substrate removal. However, it is also applicable to inductors on low-loss substrates. The method optimizes the width of the metal strip for each turn of the inductor coil, leading to a variable strip-width layout. The optimization procedure has been successfully applied to the design of square spiral inductors in a silicon-based multichip-module technology, complemented with silicon micromachining postprocessing. The obtained experimental results corroborate the validity of the proposed method. A Q factor of about 17 have been obtained for a 35-nH inductor at 1.5 GHz, with Q values higher than 40 predicted for a 20-nH inductor working at 3.5 GHz. The latter is up to a 60% better than the best results for a single strip-width inductor working at the same frequency.

Electromagnetic field source with detection of position of secondary coil in relation to multiple primary coils

Abstract: An electromagnetic field source (EFS) for providing electromagnetic energy to a secondary coil, including two or more primary coils that each carry a time-varying current to produce an electromagnetic field, and a controller that selectively provides current to one or more primary coils based on their position with respect to the secondary coil. The secondary coil may be implanted in a human recipient and used to provide power for the operation of a medical device, such as an artificial heart or ventricular assist device. The invention also provides such a secondary coil and EFS, collectively referred to as a transcutaneous energy transfer (TET) device. The primary coils of the EFS or TET may be housed in furniture. For example, they may be housed in a bed mattress or mattress pad on which the recipient rests, or in a blanket for covering the recipient. The controller includes a proximity detector that identifies those primary coils that are closest to the secondary coil, and a current director that, responsive to the proximity detector, selectively directs time-varying currents through the closest primary coils. The controller may also include an orientation detector, coupled to the current director, that determines an orientation of the secondary coil with respect to the closest primary coils. In one implementation, the proximity detector identifies the quantity of closest primary coils utilizing a resonance frequency shift detector that detects a shift in inductance of one or more primary coils due to the proximity of the secondary coil.

Apparatus and method for multi-zone high-density inductively-coupled plasma generation

Abstract: A multi-zone high-density inductively-coupled plasma source includes a first individually controlled RF antenna segment for producing a plasma from a process gas. A second individually controlled coil segment is included in the ICP source for producing a plasma from a process gas. In various embodiments, more than two sets of individually controlled coil segments may be used. In one embodiment, a separate power supply may be used for each coil segment individually. Another aspect of this invention is a hermetically-sealed inductively-coupled plasma source structure and method of fabrication which eliminates the possibility of process contamination, improves the source hardware reliability and functionality, and improves the vacuum integrity and ultimate base pressure of the plasma system.

Implantable medical device with external recharging coil electrical connection

Abstract: A rechargeable implantable medical device with an improved external recharging coil electrical connection resistant to corrosion is disclosed. The electrical connection couples the external recharging coil to a recharge feedthrough. The rechargeable implantable medical device can be a medical device such as a neuro stimulator, drug delivery pump, pacemaker, defibrillator, diagnostic recorder, cochlear implant, and the like. The implantable medical device has a housing, electronics carried in the housing configured to perform a medical therapy, a rechargeable power source, and a recharging coil.

Methods and devices for filtering fluid flow through a body structure

Abstract: An intravascular filter having a filament which expands a filter element. The filament is a coil which is stretched to reduce the diameter of the coil for introduction. The filter element is preferably biased toward the closed position and is opened by the coil when tension is released on the coil. The filament slides along the internal surface of the filter element so that the filter element may assume intermediate positions.

A transmit-only/receive-only (TORO) RF system for high-field MRI/MRS applications.

Abstract: The design and operation of a detunable shielded hybrid birdcage RF head coil optimized for human brain imaging at 170 MHz is presented. A high duty-cycle and rapid-switching decoupling scheme that allows uniform RF transmission with the head coil and reception with a surface coil within the volume of the head coil is also demonstrated. In addition, the circumscribing hybrid coil can be biased to operate as a conventional transmit/receive head coil. Our RF design allows the use of higher sensitivity surface coils or phased-array coils at very high magnetic fields where body RF resonators are not currently available or whose use is precluded by specific-absorption ratio restrictions. The design also allows the use of receive-only coils within head gradient inserts, which normally do not allow transmission with an RF body resonator at any field strength.

Thin film write head with universal coil design

Abstract: In at least one embodiment, a thin film write head having a conductor with a coil structure having a central axis perpendicular to an air bearing surface. The conductor having a first contact centrally located at a first end of the conductor. The conductor having plurality of contacts located distal from the first contact. The plurality of contacts having at least one contact on either side of the central axis of the write head.

Improvement in calculation of the self- and mutual inductance of thin-wall solenoids and disk coils

Abstract: The self-inductance expressions given by Yu and Han (1987) for air-core circular coils with rectangular cross sections, thin solenoids, and disk coils can be solved only by the numerical integration methods. We propose as an alternative a combined analytic and numeric approach. The approach brings some improvement in the calculations of self-inductance of thin-wall solenoids and disk coils that can be encountered in superconducting magnetic energy storage (SMES) problems. We also give a method for the calculation of mutual inductance of disk coils and of thin-wall solenoids. The results are obtained in an analytical form over the complete elliptic integrals of the first and second kind and Heuman's Lambda function. It is important to mention that the kernels of these integrals are always continuous functions on intervals of integration, so singularities are avoided. The results enable one to calculate the self-inductance and the mutual inductance of any thin air-core coil precisely and fast. For practical applications, the results are so simple to use that we recommend them to avoid the problems of solving the singular cases.

Planar motor with linear coil arrays

Abstract: A planar electric motor comprising a magnet array having a plurality of magnets with magnetic fields of alternating polarity and a coil array positioned adjacent to the magnet array and operable to interact with said magnetic fields to generate an electromagnetic force between the coil array and the magnet array The coil array includes a first linear coil array having a plurality of polygonal shaped coils extending longitudinally in a first direction, and a second linear coil array having a plurality of oval shaped coils extending longitudinally in a second direction generally orthogonal to said first direction The motor is for use in moving a stage within an exposure apparatus having an optical system for imaging a pattern formed in a reticle onto an article supported by the stage

A novel integrated current doubler rectifier

Abstract: This paper presents an innovative current doubler rectifier, which integrates all the magnetic components into a single core and minimizes the number of high current windings. Compared to the conventional approach, the proposed integrated magnetic structure features reduced core loss, smaller core size, and reduced AC conduction losses, all while still reducing winding losses. The new rectification circuit can be applied to many topologies. An asymmetrical half-bridge converter was used as one attractive example to demonstrate the operation and performance of the proposed structure. A prototype featuring 400 V input, 48 V output, 200 kHz switching frequency, and 1 kW output power was also developed based on this topology.

Disk drive employing seek time vcm ir voltage calibration for velocity control of an actuator arm

Abstract: A disk drive is disclosed comprising a disk, a head, an actuator arm for actuating the head radially over the disk during a seek operation, and a voice coil motor (VCM) for rotating the actuator arm about a pivot, the VCM comprising a coil comprising a VCM resistance R. A back EMF voltage detector measures a back EMF voltage across the coil, and a current detector detects a current I flowing through the coil. An IR voltage detector, responsive to the current I detected by the current detector, detects an IR voltage proportional to the current I times the VCM resistance R. A voltage compensator substantially cancels the IR voltage from the measured back EMF voltage to generate a compensated back EMF voltage. A control voltage generator, responsive the compensated back EMF voltage, generates a control voltage applied to the coil to generate the current I flowing through the coil. A memory stores a first compensated back EMF voltage generated at a first time period of the seek operation. A comparator compares the first compensated back EMF voltage stored in the memory to a second compensated back EMF voltage generated at a second time period of the seek operation. A calibrator, responsive to the comparator, calibrates the IR voltage detector.

Method for manufacturing a magnetic write element

Abstract: The present invention provides a magnetic write element for use in a magnetic data recording system such as a disk drive. The invention provides a method of manufacturing a well defined coil, which avoids the problem of shallow wall angle problems exhibited by prior art methods due to coil mask shrinkage during high temperature bake. A series of trenches are provided in the coil mask, the trenches being shallower than the coil pattern, and not extending completely through the coil pattern. During the high temperature baking process shrinkage of the coil mask will be absorbed by the trenches and not transferred to the coil pattern, preventing deformation of the coil wall portion of the mask.

Coil structures and methods for generating magnetic fields

Abstract: An apparatus for determining a location of a sensor in a surgical navigation domain includes a first magnetic field generator having a first coil set (402-414), a second magnetic field generator having a second coil set (408-428). The first and second coil sets (420-428) are disposed substantially within a common plane. The apparatus further includes a processor configured to receive a plurality of signals and calculates the location of the sensor from the plurality of signals. The sensor produces the plurality of signals in response to magnetic fields generated by the first and second magnetic field generators.

Method and apparatus for electrical stimulation adjunct (add-on) treatment of urinary incontinence and urological disorders using an external stimulator

Abstract: An apparatus and method for neuromodulation therapy for urinary incontinence and urological disorders comprises an implantable lead-receiver, and an external stimulator having a power source, controlling circuitry, and predetermined programs. The stimulator further includes a primary coil which inductively transfers electrical signals to the lead-receiver, which is also in electric contact with the sacral nerves. The external stimulator emits electrical pulses to stimulate the sacral plexus according to a predetermined program. In a second mode of operation, an operator may manually override the predetermined sequence of stimulation.

Load models and their application in the design of loosely coupled inductive power transfer systems

Abstract: Load models are developed as a design tool for loosely coupled inductive power transfer systems. The models are used to investigate the sensitivity of these systems to variations in operational frequency and load. The results of the investigation can then be used to determine the power transfer capability and controllability of the system.

Disk drive employing VCM demand current to calibrate VCM IR voltage for velocity control of an actuator arm

Abstract: A disk drive is disclosed comprising a disk, a head, an actuator arm for actuating the head radially over the disk, a fixed object, and a voice coil motor (VCM) for rotating the actuator arm about a pivot, the VCM comprising a coil comprising a VCM resistance R A back EMF voltage detector measures a back EMF voltage across the coil, and a current detector detects a current I flowing through the coil An IR voltage detector, responsive to the current I detected by the current detector, detects an IR voltage proportional to the current I times the VCM resistance R A voltage compensator substantially cancels the IR voltage from the measured back EMF voltage to generate a compensated back EMF voltage A control voltage generator, responsive the compensated back EMF voltage, generates a control voltage applied to the coil to generate the current I flowing through the coil A voltage calibrator, responsive to the current I detected by the current detector, calibrates the IR voltage detector by generating a calibration command input applied to the control voltage generator to move the actuator arm until it presses against the fixed object The IR voltage detector is programmed to detect an initial IR voltage, and then adjusted to incrementally change the detected IR voltage until the current I detected by the current detector reaches a predetermined level

Magnetic stimulation coil and circuit design

Abstract: A detailed analysis of the membrane voltage rise commensurate with the electrical charging circuit of a typical magnetic stimulator is presented. The analysis shows how the membrane voltage is linked to the energy, reluctance, and resonant frequency of the electrical charging circuit. There is an optimum resonant frequency for any nerve membrane depending on its capacitive time constant. The analysis also shows why a larger membrane voltage will be registered on the second phase of a biphasic pulse excitation. Typical constraints on three key quantities voltage, current, and silicone controlled rectifier (SCR) switching time dictate key components such as capacitance, inductance, and choice of turns.

Power transmission system, electromagnetic field generator, and electromagnetic field receiver

Abstract: PROBLEM TO BE SOLVED: To realize a noncontact IC card system, having a wide operating range by solving an important problem to, efficiently supply power from a reader/writer side to IC card side, which requires matching the impedance of the transmitter and receiver for power and signals, although, an effective range has been limited, because efficient power supply is limited within a range in which impedance is matched. SOLUTION: This system includes an impedance matching circuit, connected with an antenna coil on a transmitter or a receiver and detects transmission and receiving conditions of power simultaneously, determines whether impedance matching is satisfied, and according to the result, switches the matching conditions automatically.

Disk drive control system and method for determining the temperature of an actuator coil

Abstract: A hard disk drive comprising an actuator control system that measures the temperature of an actuator coil and methods for providing the same. The control system comprises a controller and a current source controlled by the controller that generates a flow of current through the actuator so as to reposition a transducer of the drive. The control system further comprises sampling means for sampling at least one electrical characteristic of a conducting path defined by the coil. The control system measures the temperature by monitoring the current flowing through the coil and/or the voltage across the coil and by extracting the coil temperature from the monitored values. In one embodiment, the control system obtains a measurement of the coil by successively approximating the resistance of the coil until an estimated back emf component of the voltage across the coil.

Seek distance dependent variable max VCM seek current to control thermal rise in VCM's

Abstract: A disk drive and methods for preventing a coil in a voice coil motor from overheating due to the application of excess current. The disk drive comprises a servo control system. The servo control system is adapted for applying a current to a coil of the voice coil motor thereby causing the voice coil motor to move the head according to a seek distance. The servo control system generates a plurality of seek profiles for each of a plurality of seek distances and a plurality of current limits for the plurality of seek profiles. Each of the plurality of seek profiles defines a plan for controlling the current to be applied to the coil while the voice coil motor is operated over the seek distance. The plurality of current limits each define a maximum current allowed while controlling the current to be applied to the coil.

Radio IC card

Abstract: A first antenna coil (22) is formed on a surface of an IC chip (23). A second coil (31) and a third coil (32) are formed on a module board (30). The IC chip (23) is mounted on the module board (30) such that the first antenna coil (22) of the IC chip (23) is opposed to the second antenna coil (21).