Showing papers on "Electromagnetic coil published in 1988"

High speed digital telemetry system for implantable devices

Abstract: A high speed digital telemetry system (10) includes a transmitter (12) and a receiver (14), at least one of which is adapted for use in an implantable device. The transmitter includes a data encoder (14), modulator (16), transmitting coil (20), and transmitting coil drive circuit (18). The data encoder examines prescribed incoming data bits and prior encoded data bits, generating an encoded data stream (36) that includes a data transition only when a prescribed correlation is noted amongst the examined bits. The modulator modulates a carrier signal (34) with the encoded data stream, causing a phase reversal of the carrier at each data transition of the encoded data stream. The transmitting coil drive circuit applies the modulated carrier (38) to the transmitting coil. The receiver includes a receiving coil (22) and associated amplifier (24) and bandpass filter (26) for detecting the transmitted modulated carrier. The bandpass filter is centered at the frequency of the carrier, passing the carrier only when no phase reversals are present. This results in an on-off signal at the frequency of the carrier. An AM detector (28) detects when the signal is present and when it is not, and appropriate decision logic (30) applies a suitable acceptance criteria to the detected signal to define the received binary data.

Ingestible size continuously transmitting temperature monitoring pill

Abstract: A temperature responsive transmitter is disclosed. The transmitter utilizes a unique circuit design that allows encapsulation in an ingestible size capsule. The inventive circuit design uses a one transistor inverting amplifier with a tank circuit forming the link between the transistor's collector and the battery. The tank circuit is tuned to provide a lagging capacitive load which causes the inverting amplifier to oscillate. The tank circuit contains a coil inductor that emits a near field magnetic communications field containing temperature information. The ingestible size temperature pill can be configured in a rechargeable embodiment. In this embodiment the pill uses the inductive coil in the tank circuit as the magnetic pickup to charge a rechargeable nickel cadmium battery.

Steerable guidewire with deflectable tip

Abstract: The present invention is directed to a steerable guidewire. More specifically, the invention is directed to a guidewire which comprises flexible tubing having proximal and distal ends and inner and outer surfaces, a helically wound flexible spring coil having proximal and distal ends, the proximal end of the spring coil being attached to the flexible tubing and the distal end of the spring coil comprising stretched coils, a deflection wire extending through the flexible tubing and spring coil, the deflection wire having proximal and distal ends, optionally a control wire having proximal and distal ends, the proximal end of the control wire being attached to the spring coil proximal to the stretched coils, and a rounded tip engaging the distal end of the spring coil, the distal end of the deflection wire, and the distal end of the control wire.

RF powering of millimeter- and submillimeter-sized neural prosthetic implants

Abstract: The size of the transducers for neural stimulation has shrunk steadily with application of thin-film techniques to electrode design. The feasibility is examined of designing millimeter- and submillimeter-sized power sources based on RF coupling that could be integrated into these implants to provide power without a tethering power cable. The coupling between a transmitter coil and receiver coil when the coil diameters are markedly different is analyzed, and for these circumstances, a simple Thevenin equivalent model is developed to describe the power transmission between the transmitter and receiver. The equivalent circuit developed gives insight into the way that coil diameters, frequency, and turns affect coupling between large and small coils. Several examples demonstrate that milliwatt range power sources can be implemented with millimeter- and submillimeter-diameter receivers. >

Impulse testing of power transformers using the transfer function method

Abstract: The transfer function of a transformer winding is deconvoluted in the frequency domain from the digitally recorded neutral current and high voltage applied during impulse tests. The integrity of the winding insulation is determined by comparing the transfer function obtained at full and reduced test voltage. Differences between the transfer function plots reveal local breakdowns in the winding that can be dissociated from partial discharges. Thus the method permits unambiguous acceptance or rejection if the transformer and, since the transfer function is theoretically immune to changes in the applied impulse, also allows evaluation of the chopped-impulse test. Some 100 windings of large HV power transformers have been tested using the transfer function method, which on several occasions has revealed transformer faults as well a test setup problems that would have been missed or misinterpreted by conventional techniques. >

Dual coil steerable guidewire

Abstract: A steerable guidewire has an elongate main wire (10) having a tapered distal portion (12A) and a helical coil (16) mounted about the distal portion. The distal end (12) of the coil extends beyond the distal tip (14) of the tapered distal portion of the main wire. An inner helical coil (22) is disposed within the outer coil is secured at its proximal end (24) to the distal tip of the tapered distal portion of the main wire and at its distal end to the distal end of the outer coil. The device does not have a separate safety wire, the inner coil serving as the sole safety connection between the main wire and the outer coil. The omission of the conventional safety wire and the use of the dual coil construction provides a tip which is equally flexible in all directions. Gradual selected transitions in stiffness may be achieved by varying the spacing of the individual turns of the inner and outer coils. The guidewire also provides for a change in the radiopacity of the distal portion of the guidewire to provide a more radiopaque segment at the distal portion than at the more proximal portions by forming the inner coil from a more radiopaque material than the outer coil.

High-Speed Forming of Metal Sheets by Electromagnetic Force

Abstract: A numerical method to simulate the high-speed free forming of a clamped circular disk in an electromagnetic forming system using a flat spiral coil is presented. The method combines field penetration into the disk and dynamic elasto-plastic deformation of the disk. The spiral coil is approximated by coaxial circular loops carrying the discharge current from a capacitor bank. The penetration of the magnetic field of the coil into the disk is formulated as a boundary-value problem for the diffusion equation. Magnetic field, eddy currents and electromagnetic force density in the disk are calculated. An equation of motion for the disk loaded by the magnetic force is combined with the field equation as well as an equivalent circuit equation. Plane stress condition is assumed. Strain-rate effect on the work-hardening law of the disk material is taken into account. An experiment on the free bulging of annealed aluminum disks is also presented, showing fairly good agreement with the numerical solution.

Digital protection method for power transformers based on an equivalent circuit composed of inverse inductance

Abstract: An algorithm for the protection of power transformers is described in which transformers are represented by a universal equivalent circuit composed of inverse inductance, without reference to an internal fault. The circuit is derived from multiterminal network analysis of the windings. The intrinsic characteristics of the equivalent circuit elements are clarified by calculations for actual power transformers. The characteristics of the inverse inductance obtained by sampling voltage and current at each terminal are used to discriminate between internal faults and magnetizing inrush. Computer simulations for large power transformers and experimental studies on actual model transformers have confirmed that the algorithm can distinguish internal faults from a magnetizing inrush at very high speed. >

Microstrip phase scan antenna array

Abstract: A microstrip phase scan antenna array is provided having a columnar array microstrip radiating patches mounted on a dielectric substrate. Each column of the array is fed by a separate variable, reciprocal ferrite rod phase shifter which is mounted on the substrate and is coupled to the column which it controls and to a source of millimeter wave energy by microstrip to dielectric waveguide transitions. Each of the phase shifters is controlled by a helical biasing coil surrounding the ferrite rod. All of the biasing coils are serially interconnected by a single scanning control drive wire and the numbers of turns of the coils are related to each other by an arithmetic progression in which the number of turns of a particular biasing coil differs from the number of turns of the adjacent biasing coil in the sequence of biasing coils controlling the array by a constant amount.

Superconductive magnetic resonance magnet without cryogens

Abstract: A superconductive magnet for magnetic resonance imaging not requiring consumable cryogens or requiring cryogen liquid or vapor cooling of superconducting coils is provided having a resin impregnated coil of superconductor wire Heat conductive means having a thermal conductivity greater than the resin, contact the impregnated coil along the length of at least one of the impregnated coil surfaces A thermal radiation shield is spaced away from and surrounds the resin impregnated coil and heat conductive means An evacuable housing is spaced away from and surrounds the shield The housing supports the shield, heat conductive means and the impregnated coil A multiple stage cryocooler is mounted in the housing with one stage of the cryocooler thermally coupled to the radiation shield and with another stage capable of achieving lower temperatures than the stage coupled to the shield, thermally coupled to the heat conductive means, so that superconductive operation in a vacuum can occur without the coil being immersed in cryogen liquid or vapor

Magnetically levitated fine motion robot wrist with programmable compliance

Abstract: Selective compliance in up to six degress of freedom in a magnetically levitated fine motion device, or robot wrist, with limited motion in X,Y,Z, ROLL, PITCH, YAW, is provided by controlled actuation currents applied to six electrodynamic forcer elements. The wrist has a stator support base defining a dual periphery, carrying a number of stator magnet units. A shell flotor unit nests within the stator support base dual periphery, and carries forcer coils at locations corresponding to respective magnet units. The magnet unit and related flotor coil form a forcer element. There are a number of forcer elements. The vector sum of all the translational forces and rotational torques established at the forcer elements determines the X,Y,Z, ROLL, PITCH, and YAW motion of the flotor. The flotor carries an end effector which may be a tool. Position and orientation of the flotor is monitored by light emitting diodes and lateral effect cells. Coil currents are controlled as a composite of present position, desired final position, and desired compliance. As the fine motion device approaches its final position, the control unit changes forcer coil current patterns at various sets of forcer elements, to provide selected compliance in one or more degrees of freedom while approaching and finally while maintaining the desired position. Cooling is provided as needed; docking and locking provision is made to allow de-energizing the coils for cooling, motion of the base, or shutdown.

Shielded electromagnetic transducer

Abstract: An electrical to electromagnetic transducer for applying electromagnetic energy to damaged potions of the living body, which provides high efficiency generation of electromagnetic fields for electromagnetic therapy by directing electromagnetic radiation to the damaged body part. Electromagnetic radiation is initially generated by a dipole consisting of a bar of high permeability material wrapped with an electrically conductive coil. The dipole is placed between a conductive shield and the damaged body part. An electrical signal passes through the coil which causes a magnetic field to be generated through and around the high permeability material. The field radiation pattern of the dipole is directed toward the damaged body part by a conductive shield. Magnetic fields which are generated away from the damaged body part intersect the conductive shield and establish eddy currents. These eddy currents in turn generate magnetic fields opposite and nearly equal to the magnetic fields generated by the electromagnetic source. These resultant redirected electromagnetic fields then reinforce the electromagnetic field directed towards the damaged body part and diminish the electromagnetic field directed away from the damaged body part.

Correction for intensity falloff in surface coil magnetic resonance imaging

Abstract: A method has been developed to compensate for sensitivity variation in surface coil images. An algorithm to derive the surface coil profile by acquiring a crude body coil image of the region under study is presented and tested using a homogeneous phantom. Practical application is demonstrated on images of a tomato and rabbit acquired with a 2 T 33‐cm bore magnetic resonance imager/spectrometer.

Antenna structure for providing a uniform field

Abstract: An apparatus for radiating a magnetic field of substantially uniform magnitude along an axis in a volume of space having width, height and depth directions, said apparatus comprising: a first coil arranged in the width and height directions and having a first imaginary point at its centre, a second coil arranged in the width and height directions, having a second imaginary point at its centre, the second coil being spaced from said first coil, said first and said second coils each having a side and a predetermined configuration and being positioned adjacent each other, in opposite and facing configuration, the first and second coils being spaced by a distance in the range of 2.0 to 0.1 times the length of one of the coil sides, wherein: said first and said second coils are adapted to provide in response to a current applied to the coils, said substantially uniform field within said space, said space being located between said first imaginary point and said second imaginary point and extending in the depth direction. Also an antenna structure for providing a three dimensional powering field of substantially constant magnitude comprising three orthogonal coil pairs.

Charging apparatus for an electronic device

Abstract: An apparatus for charging a power storage device provided within an electronic device. A power source provides direct current which is alternated in direction through a pair of primary coils for inducing alternating current in a secondary coil of the electronic device. The pair of primary coils are fixed to a coil yoke all of which are supported within a casing of the apparatus. During charging of the power storage device, the electronic device is mounted to the outside surface of the casing whereby substantially all of the magnetic flux of the magnetic field produced by the pair of primary coils flows through the secondary coil and coil yoke. The frequency of the oscillating signal is preset to provide the maximum induced current which will not adversely affect the movement of the analog mechanisms within the electronic device.

Method of making a multilayer electrical coil

Abstract: A monolithic multilayer electrical coil uses advanced printed wiring board technology to create a monolithic component having plural parallel multi turn planar coils interconnected by solid vias of plated metal on a single substrate preferably designed as a surface mounted device.

Synchrotron radiation source having adjustable fixed curved coil windings

Abstract: A synchrotron radiation source contains a particle track with a curved track section. A beam guiding chamber surrounding the particle track has an exit opening for the synchrotron radiation leading in an outward direction. A magnetic device has superconducting coil windings located on both sides of the particle track having a peripheral outer rim. In addition, a device for the mechanical fixation of the superconducting coil windings is provided. The fixation device has at least one support element at the peripheral outer rim of the magnetic device. The support element is located further outward than the exit opening for the synchrotron radiation and acts substantially perpendicular to the direction of the radiation. The support element is covered from the synchrotron radiation by a radiation absorber. The use of a support element provides simple and safe support for the superconducting coil windings in the area of the radiation exit opening.

Electromagnetic contactor with energy balanced closing system

Abstract: An electromagnetic contactor or motor controller is taught in which an energy efficient bounceless contact closing operation is utilized. An electromagnetic closing coil voltage is sensed by the contactor control system and compared against a memory menu of stored delay angles for a wide range of sensed voltages. The delay angles are applied to the conduction interval of a triac or similar gated device which is connected in series with the coil for controlling current flow therethrough. Depending upon the voltage sensed the amount of current flowing through the coil on a half cycle by half cycle basis is varied by the control system. The energy supplied to the armature of the electromagnetic closing coil is such that the armature attains a predetermined velocity during its closing operation which predetermined velocity is approximately sufficient to allow the armature to move to its final fixed closed disposition where the air gap between it and a permanent magnet is reduced to zero at a velocity of approximately zero. Generally only that much energy is supplied to the armature which is just needed to close the contacts and no more within practical limits.

Use of Helmholtz coils for magnetic measurements

Abstract: Helmholtz coils can be used for the measurement of open-circuit magnetization of most permanent magnet materials. The author describes the physics of the measurement, lists the materials that can be measured, derives the coil constant, and derives a correction factor for the measurement of arc magnets. A measurement is made by placing the magnet at the center of the coils, and zeroing the integrating voltmeter or fluxmeter. The magnet is then removed from the coil, parallel to the coil axis, to a distance such that the sample has no influence on the reading, typically 75 to 100 cm. The open-circuit magnetization of the sample is related to the time-integrated voltage. >

Hall-effect controller

Abstract: A Hall-effect control apparatus incorporating an actuator member having a magnetic core, and which is pivotally mounted on a base for movement in X-axis and Y-axis directions. An electrically energized coil excited with a. c. voltage produces a fluctuating magnetic field in the vicinity of the core. Four Hall-effect sensors are mounted on the base, and are arranged to sense changes in the a. c. field as the core member moves. The output of the Hall-effect sensors is both d. c. and a. c.; an electrical circuit connected therewith processes these voltages so as to cancel out any d. c. components thereof. The output of the electrical circuit in turn provides two voltages which are indicative of the X-axis and the Y-axis positions of the actuator member. The device is immune to interruption arising from d. c. fields, such as that of the earth; also significant immunity against error due to temperature fluctuations is realizeable, as is immunity to error arising from aging of the various components. There is thus achieved improved accuracy and linearity as compared to the various devices of the prior art.

Horizontal field iron core magnetic resonance scanner

Abstract: A patient is disposed on a patient couch (A) and positioned longitudinally and vertically to bring a region of interest within the patient into a gap between a pair of magnetic pole pieces (20, 22). Magnetic field driver(s) (50', 50, 52) generates a magnetic field through a U-shaped ferrous member (B) connected with the pole pieces and through the gap therebetween. The U-shaped ferrous member extends below the gap such that open access is provided to the patient from above. Shielding coils (62, 64, 66) are disposed between the U-shaped ferrous portion and the gap to compensate for distortion of the magnetic field in the gap attributable to magnetic flux through the U-shaped member. Magnetic resonance is excited in the region of interest of the patient between the pole pieces and magnetic resonance signals emanating therefrom are received, such as with a crossed elliptical quadrature coil (72). The received magnetic resonance signals are processed by processing circuitry (E) and image representations for display on a monitor (82).

Quasistatic biological cell and tissue modifier

Abstract: A quasistatic biological cell and tissue modifier is provided that presents a controlled electromagnetic environment which produces beneficial effects in biological material. The electromagnetic environment consists of a static magnetic field and a time-varying field. The static magnetic field potentiates the effect of the time-varying magnetic field and further modulates the amplitude at which the time-varying field is biologically active. The static field is provided by a permanent magnet or through electromagnetic means. In one embodiment the coil that produces the time-varying field is a single coplanar helical coil. In another embodiment it is a plurality of coplanar helical coil segments connected in parallel. In these two embodiments the coil is a flexible printed circuit that can be contoured around an organ. The static magnetic component is provided by a flexible permanent magnet or by the net bias of the time-varying field itself. A third embodiment with two small rigid coils uses a clamp to attach the coils to a patient's ear or other part of the body.

Tire inspection device

Abstract: The present invention provides a device for inspecting the pressure, temperature, etc. in the tire (1) and which is composed of a pressure sensor (9) attached to the valve (4) fixed to the tire fixing rim (2) and of which the output varies depending upon the tire internal pressure and a resonator (10) including a resonant coil (8) which resonates with an external radiation electromagnetic wave and a capacitor. The oscillation coil (30) of an oscillator (24) which generates the above-mentioned ra­diation electromagnetic wave is installed as projected from the main body (20) in which the main body (20) of the inspection device comprises a signal processor (25) which detects and processes any change in oscillation state which has take place at the oscillator as caused by the resonance state of the resonator (10) and a display (26) to display the result of the processing made at the signal processor (25).

Multiple coil eddy current probe and method of flaw detection

Abstract: An improved eddy current probe system and method for simultaneously detecting different types of flaws at different depths within a metallic wall, such as a section of Inconel tubing, is disclosed herein. The system comprises a current generator for generating alternating currents of substantially different frequencies, a probe head including first, second and third concentrically arranged coils in separate communication with the current generator, shielding material disposed between the coils for preventing cross talk between each coil and the pulsating magnetic field of the coils adjacent to it, and a detector circuit which may include an inductive bridge for providing an electrical output representative of the impedance changes in the respective coils. In operation, each of the coils conduct currents having substantially different frequencies, the highest frequency being conducted by the smallest-diametered coil and the lowest frequency being conducted by the largest-diametered coil. The different levels of magnetic field penetration provided by the coils as it is helically moved around the inside surface of a section on Inconel tubing not only allows the probe system to detect diverse kinds of flaws such as cracks, pits, or regions of thinning, but also flaws located at different depths throughout the tube wall. In the method of the invention, a computer is used to adjust the frequencies of the alternating currents conducted through the coils during the scanning operation in order to maximize the impedance changes in each coil, thereby maximizing the resolution of the probe system.

Third harmonic commutation control system and method

Abstract: A system for determining rotor position information from the back emf of a permanent magnet motor includes extracting the third harmonic from the back emf of the motor by summing the terminal voltages of the motor. The phase angle of the third harmonic of the back emf is a function of the position of the rotor, and a signal is produced when the phase angle of the third harmonic (measured with respect to the voltage on the neutral conductor of the motor) reaches a predetermined angle. Electronically controlled switches selectively apply power to the phase windings of the motor in response to the detection of predetermined phase angles of the third harmonic.

Magnet for installation in the middle ear

Abstract: A magnet assembly for location around portions of bones in the middle ear where one portion of the assembly is a magnet and another portion of the assembly is a magnetic material, the portions being hinged to one another so that they are held around the bone by the magnetic field and being adapted for optimal coupling with a magnetic field produced by a coil in a magnetic induction hearing aid.

Demand defrost control method and apparatus

Abstract: A demand defrost controller for a heat pump. The controller compares the temperature of an outdoor heat exchange coil with an enable temperature. A timer is activated when the coil temperature is less than the enable temperature. When the timer senses the compressor has run for a predetermined time the controller checks outdoor and coil temperatures to determine if a defrost cycle of the heat pump should be conducted. A defrost cycle is achieved by reversing refrigerant flow in the heat pump system for a predetermined period or until the outdoor heat exchange coil has been heated to a termination temperature.

Implantable helical coil microwave antenna for interstitial hyperthermia

Abstract: An implantable helical coil microwave antenna has been developed for improved localization and control of interstitial hyperthermia for deep-seated tumours. A helical coil structure was employed as an extension of the inner conductor at the terminal portion of a miniature semi-rigid coaxial cable. The antennas were constructed with three different connection configurations of the helical coil to the feedline, and with several coil turn densities during the optimization of heating characteristics. In order to compare relative antenna heating performance, a set of quantitative parameters was introduced. Power deposition profiles of 2450 MHz helical coil antennas were studied in both phantom models and muscle tissue in vivo, and compared to those of commonly used dipole antennas. Optimal antenna performance was obtained with a 10-turn per 1 cm helical coil connected to the inner conductor at the tip and separated from the outer conductor by a 0.1 cm gap (HCS-10). These antennas produced a well-localized heating pattern with a sharp falloff of temperature in both directions axially from the coil element. For half-wavelength insertion depths, the effective heating length (50 per cent of maximum SAR) of HCS-10 antennas matched that of standard dipole antennas, but was shifted down towards the tip. For shorter and deeper antenna insertion depths the HCS-10 heating pattern remained similarly localized to the region surrounding the helical coil with minimal cold zone at the tip. In contrast, the dipole antenna heating pattern changed significantly depending on insertion depth, with an unavoidable 0.2-0.7 cm cold region at the antenna tip and elevated surface temperatures for short insertion depths.