Showing papers on "Electromagnetic coil published in 1971"

An Inductively Coupled RF System for the Transmission of 1 kW of Power Through the Skin

Abstract: In systems in which inductive coupling between a pancake-shaped coil on the surface of the body and a similar coil within the body is utilized for the transport of electromagnetic energy, the minimization of temperature rise in the tissue is intimately related to the achievement of minimum losses in the region of the implanted coil. A detailed theoretical analysis indicates the design considerations for achieving minimum losses in the vicinity of the implanted coil and predicts relevant internal losses of about one-half of 1 percent of the transported power. Experimental verification of theoretical expectations has involved an operating frequency of 428 kHz for the transmission of 1 kW of power between a simple water-cooled coil on the surface of the chest and a coil implanted in the chest wall of a dog. A maximum tissue temperature of 103.5° F was observed. Since 1-h operation per day at the 1-kW level would supply the anticipated energy requirements for a patient with an artificial heart, the system may find application in the charging of internal energy storage units of artificial heart systems.

Interturn Short-Circuit Detector for Turbine-Generator Rotor Windings

Abstract: An effective new method of detecting interturn short circuits on round rotor windings is described. The approach used is to measure the rate of change of the air-gap flux density wave when the rotor is at operating speed and excitation is applied to the field winding. The measurements are obtained by the use of a small stationary search coil positioned near the rotor surface. The voltage outputs are recorded by Polaroid pictures from an oscilloscope screen and can be analyzed based on the information presented. The sensitivity obtained from these methods is far superior to previous methods. The data obtained at operating speed identify the coils and slots which have shorted turns, and provide a good indication of the number of turns shorted in a coil if more than one short exists.

Metal base cookware induction heating apparatus having improved power supply and gating control circuit using infra-red temperature sensor and improved induction heating coil arrangement

Abstract: A metal based cookware induction heating apparatus having an improved power supply and control circuit comprised of a chopper inverter including a gate controlled power thyristor coupled to and supplying an induction heating coil with periodic energization currents A full wave rectifier supplies rectified, unfiltered, unidirectional high voltage excitation potential to the chopper inverter which converts the excitation potential to a comparatively high frequency of the order of 20 kilohertz for supply to the induction heating coil A gating circuit is provided for driving the chopper inverter directly from the rectified high voltage excitation potential supplied by the rectifier

Magnetic detection and magnetometer system therefor

Abstract: A highly sensitive magnetometer, consisting of at least one pair of generally rectangular core elements having square hysteresis loops, for use in a guidance system for off-vertical drilling, is disclosed. The primary windings of each of the cores are driven by an oscillator, with the secondary windings of each core being differentially connected through a null circuit, which serves to balance the effects of background fields, and a detector to a suitable indicator. The primary windings of the cores are operated in resonance and the secondary windings are arranged to provide a high null output which eliminates the dead band caused by the threshold value of the diodes in the output detector circuit. This high null output may be accomplished by unbalancing the core windings or by feeding a portion of the primary winding drive current, or a signal synchronous therewith, to the corresponding secondary winding, thereby permitting measurement of the small magnetic fields which previously fell within the dead band of the device.

Low-loss antenna system with counterpoise insulated from earth

Abstract: An improved antenna system for transmitting and/or receiving electromagnetic waves, having a counterpoise insulated from the earth and in which the counterpoise is connected to one terminal of a transmitter or receiver through an inductance. The inductance is tuned in conjunction with the tuning of a conventional loading inductance coil so as to maximize the field strength radiated by the antenna into the far field. The power lost in the earth or other antenna supporting surface is unusually small, so that radiated power is large.

Solid state induction cooking appliance

Abstract: A cooking appliance for inductively heating a cooking utensil comprises a flat induction heating coil mounted beneath a nonmetallic support with a substantially unbroken utensil supporting surface The induction heating coil is driven with an ultrasonic frequency wave generated by a static power conversion circuit typically formed of a rectifier and an inverter The inverter is a series capacitor commutated sine wave inverter with a variable output frequency, variable input voltage, or variable commutating components to adjust the utensil heating level The inverter is also controlled in on-off mode by a utensil temperature sensor

A large volume magnetic field free space for thermal demagnetization and other experiments in palaeomagnetism

Abstract: Three orthogonal coil systems have been constructed within a cube of side 2.5 m to cancel the geomagnetic field to less than 1 gamma over a large volume. The north-south and vertical components are cancelled by systems of four square coils whilst a square Helmholtz pair cancels the east-west component. Cancellation to 1 part in 105 (0.5 gamma in Canberra) is achieved within a sphere of diameter 35 cm, more than 20 times the field-free volume which could be obtained using conventional Helmholtz coils within the available space. Three fluxgate detectors monitor the residual field and their output, taken through a feedback circuit, allows compensation for field variations. The residual field can be maintained to less than 0.5 gamma over the working volume of about 22,000 cm3 during the critical part of a laboratory experiment.

Wide Frequency Range Current Transformers

Abstract: Current transformers with resistive loads are examined experimentally to determine some of the limitations to high frequency response. Coil resonances are avoided by placement of damping resistors around the secondary winding. This permits a relatively large number of secondary turns (50 or 100), improving low frequency response and increasing the i×t product, even for the highest frequency transformers. Uniform response to several gigahertz is obtained in a transformer with 6.4 mm window, while a range ∼1 Hz to ∼300 MHz is found in a larger transformer (12.7 cm diam and 2.5 cm window). Both ferrite and iron alloy cores are utilized.

Static magnetic field metal detector

Abstract: A static magnetic field detector senses the passage of ferrous or magnetic objects, employing a balanced pick up coil configuration providing substantial self-cancellation of spurious background signals. The pick up coils are disposed in a uniform static magnetic field and are cooperatively effective to sense the presence of such objects with respect to an extended passage way by reacting to the field distortion caused by the object to produce an alarm or control signal. Further reduction of the effects of spurious background signals is afforded by novel means for processing the signals generated within the detector coils providing filtering and threshold functions. An adaptive threshold control circuit provides automatic adjustment of the threshold level of object detection.

High precision wide dynamic range viscous loss measuring apparatus

Abstract: A viscosity measuring system especially useful in pollution and chemical process control applications. A variable gain amplifier drives a magnetic coil which causes a torsion member to oscillate. The amplitude of the oscillations is sensed by a transducer, and converted to a DC voltage by an amplitude monitoring circuit. The DC voltage, which represents the instantaneous amplitude of mechanical oscillation, is compared to a reference DC voltage which represents the desired amplitude of oscillation. The resulting error signal is utilized to control the gain of the amplifier in such a manner that the amplitude of mechanical oscillation is maintained constant and equal to the desired amplitude. The viscosity of the fluid in which the torsion member is immersed is obtained by providing an output signal which is a measure of the power provided by the amplifier to the magnetic coil in order to maintain the desired constant amplitude of oscillation. Preferably, the output signal is obtained from the voltage developed across a resistor in series with the magnetic coil.

Apparatus for producing super heated fluids

Abstract: The disclosure relates to an apparatus for producing super heated fluids by converting electromagnetic energy into thermal energy within the fluid. A coil of low dielectric tubing is placed in a microwave resonant chamber and extends from a fluid inlet to a vapor outlet. The fluid to be super heated passes through the coil and is vaporized directly by microwave energy. The invention is particularly applicable to a vapor powered vehicle that produces no environmental pollution.

Power Transformer Core Behavior Under Transient Conditions

Abstract: The solution of an electric circuit problem is only valid if the circuit elements have been validly modelled. The iron-cored coil is a common nonlinear circuit element, especially in power system circuits, where the iron core is laminated grain-oriented silicon-iron sheet. This paper attempts to show that eddy-current loss modelling in such a core is at least as important as hysteresis loss modelling, and demonstrates the accuracy of linear modelling of the eddy-current effect. If the circuit analyst has confidence in this complete model he can then decide which aspects of the model can be ignored with impunity when studying such circuit phenomena as ferroresonance, subharmonics and inrush current.

Apparatus for the adjustment of the working pressure of a tool

Abstract: A machining tool is attached to a current carrying annular coil which is mounted for axial movements in an associated annular gap of a magnetic circuit, energized by at least one suitable permanent magnet and/or electromagnet. The terminal leads of the coil are connected to a variable current source. In this arrangement the working pressure of the tool against a workpiece may be very accurately regulated by suitable adjustment of the current supplied to the coil from the variable current source.

A Nanosecond Risetime Megampere Current Monitor

Abstract: An integrating Rogowski coil has been used for measuring megampere current pulses in large electric fields. The coil has a risetime of about 2 nsec and a typical sensitivity of 300 V/MA.

Electromagnetic linear motion device

Abstract: Herein disclosed is an electromagnetic linear motion device having an armature or movable core which is wrapped with a control coil cutting across a magnetic field established through a rectilinear air gap which is defined by inner and outer pole pieces having opposite polarities and positioned in parallel to and at least partly coextensive to each other. The device uses a support mechanism including bearings to longitudinally movably support the movable core and resilient suspension means which is adapted to have the movable core balanced in the longitudinal direction of the device. Such device can be used as a linear motor or a signal generator where minute and precise linear motions are required.

Solid state induction cooking appliances and circuits

Abstract: An economical smooth-top cooking appliance for inductively heating cooking utensils preferably comprises a flat air-core induction heating coil driven at an ultrasonic frequency by a simplified one-thyristor, one-transistor, or two-transistor resonant inverter. The series and parallel resonant circuits in the inverters are formed by a capacitor and the induction heating coil. The one-thyristor series resonant circuit is desirable because power control to adjust the cooking temperature is obtained by the combined effect of increasing the frequency and amplitude of the sinusoidal current pulses supplied to the coil. The coil is also movable to change the gap spacing between coil and utensil to vary the coupled power. Flux beneath the coil is used for warming purposes.

Method and apparatus for scrap coil transfer in continuous strip processing lines

Abstract: An apparatus and method are disclosed for accelerating the usually time-consuming operation, in a continuous stripprocessing line, of removing the tail-end scrap from the line prior to bringing in a new coil A swingable arm supports a transfer mandrel which aligns with the conventional pay-out mandrel in one position, and can swing to another position out of the way of an incoming new coil After a given coil has been run down to the tail-end scrap, its rotation is halted, the strip is severed, the scrap coil is pushed off onto the aligned transfer mandrel, and the latter is swung to the other position where a conventional scrap-coiler unwinds the tail-end scrap from the transfer mandrel

System for the magnetic non-destructive testing of materials for long and short defects

Abstract: A system for electroinductively testing elongated products comprising; a coil system for detecting short defects as seen in the longitudinal direction of the product and inducing a magnetic field in the product to be tested; and a sensing means, e.g. including induction coils, Hall elements or the like, rotating around the product and cooperating with said magnetic field for detecting long defects as seen in the longitudinal direction of the product.

Automatically resettable fault indicator

Abstract: A pair of opposed L-shaped pole pieces of demagnetizable low coercive force material is arranged to embrace an alternating current carrying conductor with the short legs in opposition and the long legs carrying reset windings which are energized with unidirectional current from a capacitor that is charged by a rectifier energized from a capacitor plate electrostatically related to the conductor or a secondary winding of a transformer the primary winding of which is energized from the conductor A four pole fault indicating rotor is held in a normal position by the magnetic fields from the short legs A biasing permanent magnet, having magnetic poles of opposite polarity, is offset from the short legs and biases the rotor to fault indicating position when the L-shaped pole pieces are demagnetized by alternating magnetic flux generated by flow of fault current in the conductor Permanent magnets at the distal ends of the long legs of the L-shaped pole pieces are effective to change the fault current response of the rotor

Field sub-assembly for universal electric motors

Abstract: For a universal electric motor, a wound field sub-assembly including a core and a pair of coils wound in slots therein, wherein the solid, magnet wire of the coils is connected to the stranded, lead wire via a simplified and improved connector and process. A connector, insulatively mounted on the field core, receives the magnet wire and provides for later connection to stranded lead wire or another circuit element. The process includes, in addition to the conventional winding of the coils on the core, the step of mechanically securing the start and end portions of the wound coil to the terminal before control thereof is released by the winding apparatus.

Magnetic core structure

Abstract: A circular magnetic core structure comprises a plurality of laminations of prestressed oriented silicon steel secured together near their juxtaposed ends which are biased into mutual engagement and are separable to receive an alternating current carrying conductor to induce into the core alternating magnetic flux which induces alternating current into a coil on the core corresponding to the current in the conductor. The core and coil are encapsulated in insulating material. In one embodiment self curing cement is applied to the juxtaposed ends after the core is applied to the conductor to seal them together. In another embodiment the ends are provided with interlocking separable coupling extensions of corrosion resisting magnetic material.

Permanent magnet armature valve

Abstract: A solenoid-type valve for use in a fuel injection system has a non-magnetic valve body and a coil with an axially extending nonmagnetic core, a portion of which is tapered. Translatable within the core is valve means including a permanent magnet armature, the pole regions of which are spaced generally proximate the pole regions of opposite polarity of the coil. The coil upon energization provides a magnetic field that builds up rapidly in the core. This field has a density which increases axially from one pole region at the wide end of the core to a pole region of opposite polarity at the small end. The valve means is normally biased to a closed position when the coil is deenergized, and the field of the coil when energized cooperates with the permanent magnet armature to immediately effect a force to translate the valve means in the direction of increasing field density to an open position.

Method of preparing insulated coil in slotted core

Abstract: A process for applying a coating of insulating, heat hardenable resin to coil turns or windings for use in electrical apparatus, by placing coils of turns or windings in slots of a core of magnetic material, packing the interstices between the turns or windings and the slot walls with a powder of heat hardenable resin while vibrating the apparatus, heating the assembly of the apparatus, coils, and the powder to cure the resin, and applying the powdered resin to melt and the heated end portions of the coils external of additional slots to obtain a cured resinous coating thereon.

Metal object sensor, particularly for railway wheels

Abstract: A sensor for sensing movement of a metal object, such as a railway wheel, along a given path, comprising three sensing coils, all tuned to the same operating frequency, spaced along the path with their axes intersecting the path, and connected in series in three consecutive arms of a pentagon bridge. An oscillator, connected to the remaining two bridge arms, excites the coils at their operating frequency. A metal object moving along the path disturbs the fields of the coils in a sequence depending upon its direction of movement; the direction and velocity of the metal object are indicated in output signals derived by additively combining and synchronously detecting the signal voltages developed at the bridge terminals. In the preferred construction, the two end coils each include a few turns encompassing the central coil to reduce mutual coupling between adjacent coils.

Magnetic resonance probe system

Abstract: A magnetic resonance probe system having an impedance bridge wherein a sample containing coil forms one leg of the bridge and is positioned in a magnetic field for producing resonance in the sample; an RF generator connected to bridge input terminals for exciting the sample; and means differentially comparing the potentials at the midpoint or null terminals.

Auditory training device with radio receiver and hearing aid

Abstract: An auditory training device to be worn by the hard-of-hearing wherein a radio receiver is housed in a case having a chamber into which a pocket-type hearing aid with an input induction coil may be inserted. An output induction coil encircles the chamber and is connected to the output terminals of the radio receiver to generate an electromagnetic field in the chamber. A radio signal transmitted from an instructor is received by the radio receiver and converted to an audio frequency output signal which is conducted to the output induction coil to establish an electromagnetic field in the chamber. The input induction coil of the hearing aid is coupled by the field and the output signal is induced in the input coil of the hearing aid when the hearing aid is in the chamber, thus permitting a hard-of-hearing person to hear the audio frequency output signal over his hearing aid.

Hydraulically controlled device for modulating the mud

Abstract: A hydraulically controlled device to transmit measurements taken at the bottom of a well to the surface, in the form of pressure modulations created by periodical restrictions on the passage of the drilling fluid, characterized by the use of a servovalve which operates the drilling fluid flow-restriction system, and the hydraulic control fluid of which is uniformly related, in quantity and direction, to the electric intensity passing through its coil.

Method and apparatus for tool orientation in a bore hole

Abstract: An orienting device for a gun or jet perforator or the like to permit setting at a selected angle to a ferrous element such as an adjacent casing string, comprising an exciter coil producing an alternating electromagnetic field and a pair of receiver coils longitudinally spaced from the exciter coils, the disposition of the receiver coils being such that the voltages induced therein vary differentially with the angle presented by the ferrous element by reason of the distortion of the otherwise axially symmetrical field. Electronic means are provided to convert the differential voltages to a pulsed signal which is received at the surface and caused to register the orientation angle. Motor means are provided to rotate the device. All operating power, control signals, and information signals are transmitted by a single conductor cable serving also to suspend the device.

Automatic focusing camera

Abstract: An automatic focusing camera having a driving mechanism for moving a taking lens on the basis of a signal provided by a distance measuring device. The lens position is controlling by a cam member capable of being turned stepwise in one direction about the optical axis of a taking lens by a pulse signal given by the distance measuring device. The driving mechanism has a light quantity controlling movable coil member and a taking lens driving and controlling movable coil member. Both the light quantity controlling movable coil member and the taking lens driving and controlling movable coil member are disposed within a gap and exposed to a common magnetic field.

Metal detector for identifying and discriminating between objects of different size, shape, orientation and ferrous content and including an auto nulling circuit

Abstract: A metal detector comprising a sensor coil positioned relative to an excited field coil for minimum mutual inductive coupling therebetween to provide a null output from the sensor coil in the absence of objects to be detected. The coils are rigidly secured in a lightweight epoxy casting to preclude deformation of the coils and relative displacement therebetween under varying environmental conditions to preclude drift of the null output. Low frequency excitation on the order of a few hundred up to a few thousand hertz is applied to the field coil to obtain a high degree of insensitivity to moisture conditions existing in the vicinity of the detector for further maintaining constancy of the null output. An auto-nulling circuit for automatically compensating for any long term drift of the detector output is also optionally included.