Showing papers on "Electromagnetic coil published in 1990"

A model of the stimulation of a nerve fiber by electromagnetic induction

Abstract: A model is presented to explain the physics of nerve stimulations by electromagnetic induction. Maxwell's equations predict the induced electric field distribution that is produced when a capacitor is discharged through a stimulating coil. A nonlinear Hodgkin-Huxley cable model describes the response of the nerve fiber to this induced electric field. Once the coil's position, orientation, and shape are given and the resistance, capacitance, and initial voltage of the stimulating circuit are specified, this model predicts the resulting transmembrane potential of the fiber as a function of distance and time. It is shown that the nerve fiber is stimulated by the gradient of the component of the induced electric field that is parallel to the fiber, which hyperpolarizes or depolarizes the membrane and may stimulate an action potential. The model predicts complicated dynamics such as action potential annihilation and dispersion. >

Hollow lumen cable apparatus

Abstract: A hollow lumen cable is formed by helically winding inner and outer coils with the helices of each coil being in an abutting relationship and the outer coil inner peripheral diameter being less than the outer peripheral diameter of the inner coil. Preferably, each coil is multifilar. After the coils are wound, an unwinding force is applied to the outer coil and the inner coil is inserted into the outer coil to have its winding inclined opposite to that of the outer coil; and thence, the outer coil is allowed to contract to form an interference fit with the inner coil. The cable may be incorporated as part of a medical apparatus. The cable is bendable about the tight radii and has a high torque transfer resolution while having a small cable outer diameter, a relatively long life, and has a hollow lumen in which there is no structure or through which fluid, wires or medial devices may pass. Also, there is a handle assembly for operating a movable guide wire between positions for straightening the guide wire and allowing it to assume its generally J-shape.

Control of the Vertical Instability in Tokamaks

Abstract: The problem of control of the vertical instability is studied for a massless filamentary plasma with finite resistivity included for the shell and active control coil. Stability boundaries are determined. The system can be stabilized up to a critical decay index, which is predominantly a function of the geometry of the passive stabilizing shell. A second, smaller, critical index, which is a function of the geometry of the control coils, determines the limit of stability in the absence of derivative gain in the control circuit. The system is also studied numerically in order to incorporate the non-linear effects of power supply dynamics. The power supply bandwidth requirement is determined by the open-loop growth rate of the instability. The system is studied for a number of control coil options which are available on the DIII-D tokamak. It is found that many of the coils will not provide adequate stabilization and that the use of inboard coils is advantageous in stabilizing the system up to the critical index. A hybrid control system which utilizes such inboard coils on a time-scale which is faster than the vessel L/R time is proposed. Experiments carried out on DIII-D confirm the appropriateness of the model. Using the results of the model study, DIII-D plasmas with decay indices exceeding 90% of the critical index have been stabilized. Measurement of the plasma vertical position is also discussed.

Flexible guide with safety tip

Abstract: An elongated guide for use in medical procedures is provided, the guide having a flexible metal core and a forward portion comprising an elongated, helically wound wire coil providing a flexible tip. A flexible safety wire extends forwardly within the coil and terminates forwardly in an integral, enlarged diameter portion defining a plug carried adjacent the forward end of the coil, the plug having a diameter at least approximately equal to the inner diameter of the coil at its forward end and substantially filling the lumen of the coil. A bonding agent such as a polymeric resin, solder or the like is employed to adhere the plug to the coil.

Electric power transmitting device with inductive coupling

Abstract: An electric power transmitting device transmits electric energy from one coil to another coil through an inductive coupling therebetween. One of the coils has an end bent in the axial direction of the coil. When the other coil is to be inserted into said one coil, it can be inserted in not only the axial direction of said one coil, but also a direction transverse to the axial direction through the bent end of the coil. Said one of the coils is typically housed in a holder, and the other coil in the grip of a gun-shaped, hand-held bar-code scanner. When the grip is inserted into a groove defined in the holder, the coils are magnetically coupled to each other, thus providing an inductive coupling. The bar-code scanner can easily be placed on and removed from the holder.

Intracavity probe and interface device for MRI imaging and spectroscopy

Abstract: An insertable pickup probe and interface network for magnetic resonance imaging and spectroscopy. The pickup probe in the preferred embodiment is for use in imaging the male prostate and comprises an elongated shaft supporting a patient interface balloon at its distal end which contains a RF receiving coil. The interface balloon comprises an inflatable inner balloon enclosed by a flexible outer balloon. The receiving coil is positioned between the inner and outer balloons and placed intimately adjacent the region of interest by inflating the inner balloon to expand outwardly against the outer balloon. In addition, a non-stretchable planar material is provided on the surface on the inner balloon adjacent the receiving coil for ensuring that the receiving coil is placed adjacent the region of interest. The inner balloon is inflated by an inflator cuff connected to the shaft and communicated to the inner balloon by a first lumen in the shaft. The receiving coil is electrically connected to an interconnecting cable which is connected to the proximal end of the shaft and communicated to the receiving coil by a second lumen in the shaft. The interface network receives the interconnecting cable of the pickup probe and includes impedance matching means, tuning means, and decoupling means for interfacing the probe with a magnetic resonance imaging scanner. In addition, the interface includes an electronic circuit for automatically adjusting the control voltage of a varactor diode in a Pi network which comprises the tuning means.

The distribution of induced currents in magnetic stimulation of the nervous system.

Abstract: Magnetic stimulation of the nervous system is being used as an alternative to electrical stimulation, principally because it is painless. The spatial distribution of induced currents from the stimulating coil is calculated from a computer model with graphical output. Two configurations of a plane circular coil are considered: parallel to the tissue surface and perpendicular to the surface. The surface is assumed planar and infinite in extent. The tissue is modelled as a uniform, isotropic volume conductor. A quasi-static approximation is made in calculating the electric field. Maps of current density, J, as a function of position, including depth, are shown. In both configurations, J is always parallel to the surface, and is maximum at the surface. There is no perpendicular (vertical) current. For a one-turn 10 cm diameter coil, spaced 1 cm from conducting tissue and parallel to it, with rate of change of current 10(8) A s(-1), Jmax = 6.8 A m(-2) (assuming conductivity 0.2 omega -1 m(-1)). In the perpendicular configuration Jmax = 4.1 A m(-2). These results suggest that nerve fibres running parallel to the skin surface are more likely to be stimulated than those running obliquely; and that it is extremely difficult to stimulate nerve fibres running perpendicularly. This model can be used to characterise the performance of other shapes of stimulating coils and the dependence on fibre orientation.

Automatic headlight dimmer apparatus

Abstract: An apparatus within a vehicle including a plurality of high beams in electrical communication with an automatic circuit to direct voltage to each associated high beam, wherein a photo-transistor is arranged in parallel circuitry to a relay coil and resistor, with the junction transistor arranged to interface between the first and the second parallel circuit, including the photo-transistor and adjustable resistor respectively. A modified detector circuit includes a second resistor in series with the resistor, and a third resistor in parallel relationship to the relay coil to effect a time delay in actuation of the high beam members of the vehicle. A third junction transistor is arranged in a third circuit parallel to the first and second circuit to direct current to the respective high beam for increased sensitivity relative to the incoming light source from a remote vehicle.

Method and apparatus for tracking catheters

Abstract: A device for tracking catheters includes an oscillator which is coupled to a transmit coil The transmit coil is rotated in a direction transverse to the longitudinal axis of the transmit coil A receive coil situated on the guide wire of a catheter inserted into a patient's body receives the signal transmitted from the transmit coil A rectifier rectifies the received signal, and a filter filters the rectified received signal A strobe circuit provides strobes of light in response to the rectified received signal and cooperates with bar image forming circuitry and structure to provide an image of a bar which is aligned with the longitudinal axis of the receive coil, which is indicative of the orientation of the catheter and guide wire on which the receive coil is situated A bar display indicates the relative proximity of the transmit coil to the receive coil, and a numeric display provides a read-out of the distance between the transmit coil and the receive coil

Method of manufacturing a planar coil construction

Abstract: A planar coil construction, especially adapted for use in a force-producing device such as a de-icer, includes first and second sheet-like members, each defined by a continuous electrical conductor having a plurality of turns and first and second ends. The first end of the first conductor defines an electrical input to the coil, while the second end of the second conductor defines an electrical output from the coil. The second end of the first conductor and the first end of the second conductor are electrically connected. The sheet-like members are superimposed such that current flow through adjacent turns of the conductors is in the same direction. Within each sheet-like member, adjacent conductors also have current flow in the same direction. The invention includes a technique for spacing the conductors by means of a dielectric layer, and a technique for encapsulating the sheet-like members. Alternative embodiments are provided wherein different relationships among the sheet-like members are possible as they might be used for force-producing elements in a de-icer.

Non-buckling thin-walled sheath for the percutaneous insertion of intraluminal catheters

Abstract: An introducer sheath includes an extremely thin, flat wire metal coil that is surrounded only on its exterior surface with a plastic tube or coating. The flat wire coil optimizes the resistance of the sheath to buckling while minimizing the wall thickness of the sheath. The plastic covering being only on the outside of the metal coil optimizes the thinness of the introducer sheath wall while still providing a smooth outer surface for easy percutaneous insertion into an artery or other vessel of a living body. The higher density of the metal coil as compared to the plastic tubes of existing introducer sheaths, maximizes the radiopacity of the sheath for this thin-walled design. An alternative embodiment consists of two flat wire metal coils, one wound over the other, with a plastic covering the outer surface of the outer metal coil.

Analysis of an electromagnetic induction detector for real-time location of buried objects

Abstract: Spatial response characteristics of an electromagnetic induction sensor as it passes over a metallic object are investigated using a simple analytical technique. In this low-frequency technique, one replaces a metallic object with equivalent electric and magnetic dipoles and then applies the principles of reciprocity to obtain the induced EMF in a sensor coil. Analysis is carried out for a sensor employing rectangular coils, and the object set is confined to a sphere and a prolate spheroid. The simple approach, which is illustrated with both numerical and experimental data, is found to be adequate to understand the effect on the response characteristics of parameters such as object depth, orientation, aspect ratio, and material properties. >

A comparison of magnetic and electrical stimulation of spinal nerves.

Abstract: We compared magnetic stimulation using different coil designs (2 rounded coils and a butterfly-prototype coil) with electrical stimulation of the median and ulnar nerves in 5 normal subjects. Using magnetic stimulation we were able to record technically satisfactory maximal sensory and motor responses only with the butterfly coil. Submaximal electrical stimuli preferentially activated sensory rather than motor axons, but submaximal magnetic stimuli did not. The onset latency, amplitude, area and duration of responses elicited electrically or magnetically with the butterfly coil during routine sensory and motor nerve conduction studies were similar, and motor and sensory conduction velocities were comparable when studied over long segments of nerve. However, the motor conduction velocities with magnetic and electrical stimulation differed by as much as 18 m/sec in the across-elbow segment of ulnar nerve. Thus, recent developments in magnetic stimulator design have improved the focality of the stimulus, but the present butterfly coil design cannot replace electrical stimulation for the detection of focal changes in nerve conduction velocity at common entrapment sites, such as in the across-elbow segment of the ulnar nerve.

A theoretical calculation of the electric field induced by magnetic stimulation of a peripheral nerve.

Abstract: A mathematical model is presented that predicts the electric field induced in the arm during magnetic stimulation of a peripheral nerve. The arm is represented as a homogeneous, cylindrical volume conductor. The electric field arises from two sources: the time-varying magnetic field and the accumulation of charge on the arm surface. In magnetic stimulation both of these contributions are significant. The magnitude of the electric field is greatest near the surface of the arm, and is well localized. Various coil orientations are examined; the smallest electric fields are induced when the coil is perpendicular to the arm surface, the largest when the coil is parallel. These results are consistent with many experimental observations in the literature, and aid in the basic understanding of magnetic stimulation of the peripheral nervous system.

Clinical use of the magnetic stimulator in the investigation of peripheral conduction time.

Abstract: The application of rapidly changing magnetic fields (magnetic stimulation) over the neck or lower back elicits EMG responses in the muscles of the arm or leg respectively. Such responses have stable onset latencies but their amplitudes vary depending on the position of the coil over the neck or lower back. Supramaximal responses could not be obtained. Comparison of onset latencies with estimates of peripheral conduction time using a conventional F-wave technique suggest that the site of excitation of the motor axons is about 1.3 msec conduction time distal to the cervical motoneurons and 3 msec distal to the lumbosacral motoneurons. Response configuration after paravertebral magnetic stimulation was similar to that of the standard electrically evoked M-wave in the small hand muscles but not in lower limb muscles. Responses in lower limb muscles after paravertebral magnetic stimulation may consist of additional F-wave and H-reflex components. The possible clinical role of paravertebral magnetic stimulation in the investigation of peripheral and central motor pathways is discussed in the light of these findings.

Electrical terminal representation of conductor loss in transformers

Abstract: The formulation of a general, complete electrical terminal representation of eddy-current loss in transformer windings is presented. It is shown that the effects of mutual resistances must be considered in addition to the familiar winding resistances (self resistances) for a complete description of eddy-current loss. A simple two-foil winding structure is analyzed to display the features of the self- and mutual-resistance terms. The example illustrates that leakage resistance, i.e. resistance associated with opposing winding currents of equal amp turns, provides only a partial description of eddy-current loss. The analysis is extended to multiple windings, with a simple three-foil winding structure as an example. >

Inductive-coupling connector for a well head equipment

Abstract: The invention relates to an electrical connector for transmitting electrical signals between the outside and the inside of a well having a well head (20) terminated by a valve assembly (10). The connector comprises at least two inductively coupled electrical coils (1A, 1B; 5A, 5B) whose respective winding axes are aligned with the axis (zz') of the well head. The coils are integrated in the fluid connector interconnecting the valve assembly and the well head, with one of the coils being releasably fixed to the valve assembly (10) while the other coil is releasably fixed to the well head (20).

Catheter with body temperature glass transition region

Abstract: A catheter consists of a torque transmitting portion which has rigidity sufficient for torque transmission and a flexible portion made of a material having a glass transition temperature for giving rigidity before insertion and flexibility after insertion. The torque transmitting portion maintains torque transmitting ability before, during and after insertion. The flexible portion maintains appropriate rigidity before and during insertion, which enables easy insertion, and gains flexibility after insertion by the body heat, which avoids hurting of the vulnerable insertion walls. Further, the torque transmitting portion may have a structure wherein a reinforcement of a coil or a braid of linear metal wires, specifically flat rectangular wires, is attached thereto to afford torque transmitting ability. Catheters having various functions and structures can be easily manufactured by extrusion-molding, or the like.

A complete model characterization of brushless DC motors

Abstract: The authors address the modeling problem associated with brushless DC motors (BLDCMs) with nonuniform air gaps that operate in a range where magnetic saturation may exist. The mathematical model includes the effects of reluctance variations as well as magnetic saturation to guarantee proper modeling of the system. An experimental procedure is developed and implemented in a laboratory environment to identify the electromagnetic characteristics of a BLDCM in the presence of magnetic saturation. It is demonstrated that the modeling problem associated with the class of BLDCMs can be formulated in terms of mathematically modeling a set of multidimensional surfaces corresponding to the electromagnetic torque function and the flux linkages associated with the motor phase windings. The accuracy of the mathematical model constructed by the developed method is checked against experimental measurements. >

Solenoid closure detection

Abstract: A method and apparatus for electronically detecting when a solenoid has closed, or nearly closed, indirectly senses changes in the inductance of the solenoid's coil as the solenoid closes. When the inductance has changed by a selected amount, the solenoid is assumed to have closed, or nearly closed, and current through the coil is promptly reduced. Preferably, changes in the inductance of the coil are sensed by establishing a plurality of current peaks in the coil, and sensing the current's decay time between peaks. When the decay time of a measured current peak exceeds the decay time of a previously measured current peak by a selected amount, it is assumed that the solenoid has closed, or nearly closed.

Electrical connector using shape memory alloy coil springs

Abstract: An electrical connector (39) provides high density interconnections through contact paths of printed circuit pads (12, 31) via flexible circuit (22) having contact pads (26, 28) driven by a canted coil spring (40) formed of a shape memory alloy selectively responsive to variations in temperature applied to the coil through a medium, heated or cooled and supplied via passage (62) in the connector.

Plural-coil non-contact ic card having pot cores and shielding walls

Abstract: In a non-contact IC card based on an electromagnetic induction system, N small thin-film coils formed by thin-film technology are arranged to perform N-bit parallel data transfer at an increased data transfer rate. Each thin-film coil may be constructed with a pot core to solve a problem relating to errors in positioning the card relative to a terminal unit and thereby improving the reliability of data transfer. Shielding walls may be provided between the adjacent thin-film coils to prevent interference therebetween. The N thin-film coils are integrally formed as a thin-film coil module.

Wireless low-frequency medical treatment device

Abstract: A wireless low-frequency medical treatment device having a sending section for sending data for low-frequency medical treatment and a pulse applying section for receiving the above data and applying a low-frequency pulse corresponding to the data on a living body, the device being characterized in that the sending section comprises a plurality of sending coils, whose axes cross each other in a space, and a sending coil driving circuit for supplying the sending coils with resonating currents having different phases, respectively, the currents indicating a signal corresponding to the data; and that the pulse applying section comprises a receiving coil for receiving the signal sent from the sending coils through electromagnetic induction.

Flexible coil assembly for reflectance-mode nondestructive eddy-current examination

Abstract: An improved flexible coil array for nondestructive reflective-mode eddy-current testing of conductive members is disclosed. The assembly comprises a flexible substrate having a first array of coils formed on one side thereof. The first array of coils are connected in series in parallel columns. One end of each of the rows is connected to a common ground connection, while the other ends of each row are successively connected to a source of excitation energy. A second array of series-connected rows of coils, orthogonal to the columns, is formed on the opposite side of the substrate. Again, one end of each of the rows is connected to a common point while the other end of each of the rows is successively connected to means for detecting a voltage induced on the coils of the row. The voltage will vary if one of the coils is disposed in juxtaposition to a discontinuity of the member to be inspected. Comparison of voltages induced on the various rows of coils, together with indication of the column of driver coils which is being driven at the time of detection of a variation in the voltage, locates any discontinuity in the member to be inspected. The coils may be made up of pairs of half-coils connected in series to form the rows and columns.

Azimuthally oriented coil array for MWD resistivity logging

Abstract: A coil array which is installed on a MWD drill collar for use in a resistivity logging system. The drill collar is provided with upper and lower coil support rings. These are toroids which support individual coil segments, and are connected by suitable magnetic shorting bars. The coil segments and shorting bars inscribe a specified solid angle or azimuthal extent. By connecting the outputs of the several coils through a combining circuit, the coils on a single coil form can be connected in series additive, or subtractive relationship. Through the use of two such coil forms with aligned coils on each, an azimuthally oriented window is thereby defined. By proper switching multiple azimuthally oriented windows can be made operative so that there is an azimuthal orientation to the current flow pattern relative to the MWD resistivity logging tool.

Steerable guide wire

Abstract: A steerable guide wire for use in a medical procedure, such as coronary angioplasty, which requires positioning a catheter or other device at a remote location within the body by way of the cardiovascular system or other passage way. The guide wire has a solid core wire which runs the entire length. The distal end of the core wire is tapered to an intermediate diameter to permit insertion into a short flexible coil, or a combination of a flat wire coil and round wire coil attach to each other at a brazed joint. The flexible coil has an outside diameter approximately equal to the outside diameter of the core wire proximal to the taper. The proximal end of the flexible coil is fixedly attached to the taper. The distal tip of the core wire is further tapered and optionally flattened to enhance the handling characteristics as well as flexibility. The distal tip of the core wire and a flexible round wire coil are coextensive, and attached distally to form a smooth tip for the guide wire. The entire guide wire can be coated with a polymer or other suitable material to control, and reduce friction over the length of the guide wire.

Appropriate modelling of conductive losses in the design of magnetic components

Abstract: An analytical method to calculate the AC resistance of round conductor windings is derived It is shown that the skin effect and proximity effect are orthogonal to each other, which means that their losses can be calculated separately and then simply added together It is shown that this method of calculation is inherently much more accurate than a popular existing method using an equivalent rectangular conductor and a one-dimensional cartesian coordinate system solution >