Abstract: A degaussing circuit has a degaussing coil, an oscillator, amplifiers, a bias source, a capacitor, a switch and a time period controller. The oscillator supplies high frequency alternating currents which are amplified by the amplifiers to drive the degaussing coil. The bias source and capacitor activate the amplifiers. The capacitor applies a gradually reducing bias to the amplifiers. The switch controls the charging and discharging of the capacitor and thus causes the application of the gradual reducing bias to the amplifiers. The time period controller regulates the operation period of the switch and, therefore, the charge and discharge of the capacitor.

Abstract: A cathode ray tube having degaussing coils attached to an outer side of a glass vessel of a funnel part of a main body of the cathode ray tube, in which the degaussing coils each include a flattened part, extended along the outer front surface at a front side of a funnel part, a circular part having a circular cross-section and a transition part interconnecting the end parts of the flattened part and the circular part and changed in cross-section shape from a flattened rectangle to a circle. The degaussing coil may has shape flattened partially to reduce the outer size of the cathode ray tube and includes a plastic case for retaining the coil in the flattened shape. The degaussing coil is stabilized in shape and is not deformed during transport while its attachability with respect to the cathode ray tube may be improved.

Abstract: A semiconductor memory device having transistors and capacitors on a semiconductor substrate with the lower electrodes and the contact holes for connection with the sources of the transistors formed on a self-alignment basis and a method of producing the same are disclosed. The transistor of the semiconductor memory device formed on the semiconductor substrate has a first insulating layer, a gate electrode, a source portion and a drain portion. The source and drain portions dispose in the vicinity of the gate electrode, on opposite sides of each other relative to the gate electrode, under the first insulating layer and in the semiconductor substrate.

Abstract: An apparatus for erasing information recorded on a magnetic tape wound into a roll having a diameter. The apparatus comprises an erasing coil wound in the form of a solenoid defining a space therein. The space has a width shorter than the diameter of the magnetic tape roll and a length longer than the diameter of the magnetic tape roll. The magnetic tape roll is moved intermittently to different erasing positions in a predetermined sequence so that the magnetic tape roll has different portions placed in the space at the respective erasing positions. A ringing signal is applied to the erasing coil to provide a magnetic field in the space for erasing information recorded on the magnetic tape roll each time the magnetic tape roll is placed at one of the erasing positions.

Abstract: Apparatus for selectively magnetizing and demagnetizing a small tool, such as a screwdriver, by providing an enclosure having a first opening to receive a tool for magnetizing a desired portion of the tool, and a second opening to receive a tool for demagnetizing a selected portion of the tool. The demagnetizing opening is surrounded by a demagnetizing coil that is directly connected through a first switch with a source of alternating current to provide an alternating magnetic field for demagnetizing a tool inserted into the demagnetizing opening. The magnetizing opening is surrounded by a magnetizing coil that is connected through a second switch with the source of alternating current and through a rectifier circuit to provide a continuous magnetic field for magnetizing a tool inserted into the magnetizing opening. Pilot lights are coupled with the respective magnetizing and demagnetizing loops to indicate when the respective loops are energized.

Abstract: A superconducting magnet device which is capable of protecting at the time of quenching a superconducting magnet divided into a plurality of sections comprises a superconducting magnet circuit which is formed by sequentially connecting in series coil pairs 1a, 1b, and 2a, 2b which are positioned symmetrically with respect to a ferromagnetic shield 6, and by connecting in parallel to the superconducting coils 1a, 1b and 2a, 2b superconducting coil protecting elements 3a and 3b which protect the superconducting coils 1a, 1b and 2a, 2b when the voltage at the ends of the coils has exceeded a predetermined value. If quenching occurs at the superconducting coils 1a, 1b and 2a, 2b, generation of an unbalanced electromagnetic force, a local electromagnetic force, etc., against the ferromagnetic shield 6 is prevented, so that the support structure for the superconducting coils and the ferromagnetic shield can be simplified.

Abstract: The invention relates to a demagnetizing device for magnetic recording media, so-called pancakes, wound up in the form of a tape, which device consists of a cylindrical coil (1), the field distribution (3) of which extends essentially parallel to the winding plane (2) of the recording medium (4), while the pancakes (4) can be inserted into the coil (1) in the axial direction by a lifting device (5). The compact form enables an entire pancake stack to be demagnetized at the same time (FIGURE).

Abstract: A closed-loop multi-sensor control system for controlling ship signatures positions away from local sensors used to direct local signatures controllers by controlling a field variable signature through local onboard sensors and active coil elements by determining a transfer matrix between discrete local and midrange field values, said determination being based upon virtual sources, M, and control parameters (coil currents) I wherein:M=(M.sub.X1,M.sub.Y.sup.1,M.sub.Z1,M.sub.Z2. . . M.sub.ZX) and I=(I.sub.1,I.sub.2, . . . I.sub.M),wherein local signatures H=A.sub.H I.sub.O +B.sub.H M and wherein midrange signatures K=A.sub.K I+B.sub.H M and wherein the ultimate solution for the coil currents for optimum degaussing is:I=-(A.sub.K.sup.T A.sub.K).sup.-1 A.sub.K.sup.T B.sub.K (B.sub.H.sup.T B.sub.H)..sup.1 B.sub.H.sup.T (H-A.sub.H I.sub.O)=G H.sub.

Abstract: An apparatus for use with magnetically based electronic article surveillance systems employing certain types of markers includes a hollow core having a gap in its perimeter, a coil of wire wrapped around a portion of the core, and appropriate circuitry to drive the combination as an electromagnet. The gap configuration produces an external field of large intensity but limited range, such that the magnetizable portion of a marker is magnetized without affecting magnetic states of the article to which the marker is affixed. Depending on the nature of the circuit, the apparatus may be used as a desensitizer of such markers, or preferably as a resensitizer. The resensitizer incorporates a proportional-integral controller that keeps the level of the alternating current constant.

Abstract: Apparatus for characterizing the magnetic field of a device under test includes a device for nullifying the ambient magnetic field in a test environment area with a constant applied magnetic field, a device for rotating the device under test in the test environment area at least nearly through a complete circle, a device for sensing the magnetic field at a sensor location which is along the circumference of rotation as a function of the rotation angle for successive ones of a set of predetermined orientations of the device under test to obtain a profile of the magnetic field at the sensor location as a function of the rotation angle for each one of the predetermined orientations, a memory for storing the profiles, and a processor coupled to the memory for characterizing the magnetic field of the device from the magnetic field profiles thus obtained.

Abstract: A compact, portable magnetization/demagnetization device comprises a tubular housing internally of which at one end is mounted an electrical coil which surrounds a cavity accessible to screwdrivers and the like. At the opposite end of the housing there is mounted a pair of AC prongs. A manually operated switch on the housing permits the coil to be energized when the prongs are energized to establish a magnetic field in the cavity for the purpose of magnetizing and demagnetizing tools and other objects.

Abstract: A magnetic recording medium such as a magnetic recording tape or disk is demagnetized by applying a saturating magnetic field to the magnetic recording medium, then applying an unsaturating magnetic field to the magnetic recording medium in a direction opposite to the direction of the saturating magnetic field, and finally applying an alternating magnetic field to the magnetic recording medium to remove residual magnetism which has been produced on the magnetic recording medium by the unsaturating magnetic field. The saturating, unsaturating, and alternating magnetic fields are generated respectively by a first DC erasing head, a second DC erasing head, and an AC erasing head, which are arranged at spaced intervals in the order named in the direction in which the magnetic recording medium is continuously moved.

Abstract: An array of nested sets of electromagnetic coils. Each set of two coils is useable both as Helmholtz coils and as deGaussing coils. In each set, the two coils are wound in the same direction and the two coils are on a common axis. The common axes of the three sets are mutually orthogonal. For each set of two coils, the outer two ends of the two coils are connected to two single terminals, while the inner two ends of the two coils are connected to one common terminal. By connecting one side of a DC power supply to one single terminal, and by connecting the other side of the DC power supply to the other single terminal, each set of two coils will operate as Helmholtz coils. By connecting one side of a DC power supply to parallel variable resistors, each resistor in turn being connected to a single terminal, and by connecting the other side of the DC power supply to the common terminal, each set of two coils will operate as deGaussing coils.

Abstract: Noise in the readback signal of a magnetic recording device resulting from spurious pulses in the readback signal produced by transitions of the magnetic remanent state of the yoke in the read/write transducer is eliminated by controlling the occurrence of the spurious pulses. Immediately following the completion of the write process, a decreasing amplitude alternating current is applied to the read/write coil of the transducer to drive the yoke remanent state to a stable or zero remanent state prior to the commencement of the read process.

Abstract: A stray magnetic field control system compensates for the generation of stray magnetic flux by the magnetic structure (body) of a load support shaker apparatus. The circuit includes a Hall effect magnetic field sensor for measuring the stray magnetic field, an amplifier/filter connected to the sensor output, and an A/D converter connected to the output of the amplifier filter. A degauss coil for compensating for the stray flux is energized by an SCR phase controlled power supply which is in turn controlled as to its triggering time by a microprocessor.

Abstract: Auto transformer supplying current to the object to be demagnetized (chuck), this current controlled by an ON set of transformers, and a DEMAG set of transformers. Each set includes a pair of secondaries providing pulsating current for respective half cycles of AC, of opposite polarity. The opposite polarity of pulsating current is produced in intervals of decreasing time and voltage, until the magnetism in the object is at or near zero. The control transformer sets are controlled by a unit establishing selected values of voltage, that voltage controlling a cross-over unit which includes transistors, which in turn control the intervals of the control transformers. A CMOS oscillator circuit, with an oscillator chip, including NAND gates, effects alternate energization of the control transformers.

Abstract: A device for treatment of ferromagnetic materials comprising means for developing a magnetic field of a selected intensity, duration, and cycle, which field is passed through materials to be processed, such as cutting tools and drill bits that have been sharpened or resharpened and other parts that have internal stresses. The magnetic field through the material provides stress relief of the stresses from welding, forming, heating cooling or sharpening or loading. The treatment increases surface wear resistance, decreases the coefficient of friction on the surfaces that are so treated, and increases the strength and modulus of elasticity. In certain types of materials, an increase in the surface concentration of such alloying metals such as wolfram, molybdenum, and tungsten, as well as oxygen and carbon is achieved. The structure comprises a coil and a controlled source of electrical power that generates a magnetic field for achieving the desired results.

Abstract: A chuck and a power transformer having a pair of secondaries for applying continuous unidirectional DC to the chuck. A pair of control transformers each having a pair of secondaries related to respective ones of the power secondaries, for producing opposite polarities on the chuck. A timer operable through a maximum time interval for controlling the control transformers and thereby producing DC on the chuck of a level according to that time interval, and settable to lesser time intervals for producing DC of correspondingly lesser levels. Means for producing DC in each of oppositee polarities, and each throughout a corresponding time interval according to the setting of the timer. Oscillator means controlling the control transformers for thereby controlling the power transformer for producing DC of opposite polarities in a series of steps, and interposing resistances of successively greater values in the steps to reduce the charge on the chuck to zero at the last step.

Abstract: An apparatus for demagnetizing parts after they have been subjected to the action of a magnetic field having coils (1,2) connected to an a-c power supply source and disposed one inside the other at one and the same angle with respect to a trough (3) extending through the inner coil. The coils (1,2) are mounted in such a manner that the angle (.alpha.) therebetween can be adjusted.

Abstract: The invention concerns processes for immunizing nautical vessels against the disturbances that they cause to the magnetic field of the earth, consisting in supplying immunization loops of such a vessel with a set of alternating currents producing inside the volume of the vessel a homogeneous and alternating inductor field, isolating the alternating signal issuing from the alternating field at the measuring base and calculating the induced magnetization, wherein it allows to separate the induced magnetization from the permanent magnetization in the magnetic signature of a vessel while reducing the duration of measuring time required.

Abstract: In the magnetic chuck control disclosed herein, the chuck winding is selectively energized in one direction or the other through respective triggerable semiconductor current switching devices. Successively reducing current levels are applied in successive phases of operation, the polarity of the current being reversed in successive phases. During a first portion of each phase the device is triggered to apply a corresponding preselectable voltage. During a second portion of each phase the switching devices are triggered quite late to provide an average voltage which opposes the current flow which was induced during the first portion thereby to quickly reduce the level of current flowing in the winding.

Abstract: The invention concerns demagnetization devices used in particular for demagnetizing vessels or submarines in fixed stations, wherein one embodiment comprises: three sets of conductors for demagnetizing a vessel according to three directions; a direct current generator; an array of capacitors, a bridge switching device, an inductance coil; a switch allowing to select one of the three assemblies of conductors; a servo device for controlling the charge voltage of the array of capacitors; magnetometers; and a screen and keyboard allowing especially to supply a microprocessor with a reference value fixing the value of the desired residual magnetization; the demagnetization consisting of sending into each set of conductors a sequence of discharges, of smaller and smaller intensity and servo-controlled to the value of the remaining magnetization, in order to cause the magnetization to converge towards the desired value.

Abstract: A display device comprising a cabinet and an electromagnetic deflection yoke and a horizontal width adjusting coil received is the cabinet comprises a canceling coil for cancelling electromagnetic field noise generated from the electromagnetic deflection yoke received in the cabinet.

Abstract: An electromagnet control apparatus having a remote control switch assembly switchable between a number of positions representing full, variable, residual and zero levels of magnetization. Means are provided for causing the electromagnet to be fully energized for several seconds before being dropped to the residual level of magnetization whenever the switch assembly is switched to a residual setting.

Abstract: The item to be demagnetized is placed in a chamber surrounded by electrical windings defining a pair of coils that are disposed in a mutually orthogonal configuration. Currents for the two coils are developed in a microprocessor-controlled inverter circuit and are applied through semiconductor switches in such a way that the resulting demagnetizing field is rotating and follows a predetermined amplitude variation in accordance with one or more profiles stored in the memory of the microprocessor.

Abstract: This invention relates to the field of degaussing devices and has particular applicability to such devices which are used to remove magnetic bias from digital recording heads in mass storage devices. It provides for a device which employs a microcontroller integrated circuit capable of hardware multiply and a digital to analog converter to produce a decaying sinewave signal. The rest of the general requirements for a functional degauss circuit are generally shown. The height and frequency of this sinewave signal can be modified under software control using this invention.

Abstract: Prior art magnetic chuck control systems do not utilize state of the art components and do not sufficiently isolate the power output from control circuits. The instant invention discloses a magnetic chuck control system employing solid state circuitry including a power output circuit (24) adapted to apply a DC voltage to an object such as a magnetic chuck (12) or the like so as to magnetize the same. The power output circuit employs a triac reversing circuit and is interfaced with a digital control circuit (26) and a digital-to-analog converter circuit (30) so as to apply alternating polarity voltage signals of successively reduced magnitude to the chuck during a demagnetizing operation. All high voltage is confined to the power output circuit so as to provide significant safety protection to the operator.

Abstract: A dual-function circuit is provided which may be used to both magnetically bias and alternately, quickly degauss a magnetic device. The circuit may be magnetically coupled or directly connected electrically to a magnetic device, such as a magnetostrictive transducer, to magnetically bias the device by applying a d.c. current and alternately apply a selectively damped a.c. current to the device to degauss the device. The circuit is of particular value in many systems which use magnetostrictive transducers for ultrasonic transmission in different propagation modes over very short time periods.

Abstract: A machine having a conveyor for carrying a workpiece to be magnetized therethrough. It includes two demagnetizing magnets arranged at a mutual angle of 90.degree. and both at 45.degree. to the direction of travel on the conveyor. The magnets are arranged respectively above and below the conveyor, and hence above and below the workpiece on the conveyor, and are spaced apart in the direction of travel of the conveyor. The conveyor, structurally, includes a stationary base, and endless belts carrying paddles, the paddles engaging the workpieces and moving them along the base. The workpieces "float, " capable of moving to any position according to the condition of magnetism in them and the position and shape of the demagnetizing magnets, and upon encountering the field of the demagnetizing magnet that is disposed above the workpieces, the workpieces are capable of being attracted up to that demagnetizing magnet, off of the base of the conveyor.

Abstract: A demagnetizing power source for producing an attenuation alternating field to demagnetize a magnetized substance. This power source is provided with a memory circuit for sending actuating signals to a polarity changing-over circuit to change over the polarity of direct current supplied from a rectifying circuit to an exciting coil. In the memory circuit are stored a plurality of preset demagnetizing patterns. The polarity changing-over circuit changes over alternatively the polarity and gradually decreases the change-over cycle according to the selected demagnetizing pattern.

Abstract: Apparatus is disclosed for bulk erasing magnetic tapes spirally wound on a carrier. A pair of magnetic structures are spaced apart by an air gap of sufficient width to receive the tape carrier. Circuitry is provided for producing a rotating magnetic field in the air gap substantially parallel with the tape. Preferably, the magnetic structures take the form of multi-legged iron cores. The cores are mounted so that corresponding legs on opposing cores have the same magnetic polarity. A phase shifter circuit is adapted to supply currents 90.degree. out of phase with one another to selected pairs of legs in the cores to create a rotating magnetic field in the air gap.

Abstract: An electronic current control device for energizing and de-energizing an electromagnet, such as a magnetic chuck, includes a DC power source preferably in the form of a phase-controlled SCR power unit. A conduction angle control signal is routed to positive or negative gates in the power unit to determine polarity and amplitude of direct current through the electromagnet windings. In the "on" mode an analog current feedback loop maintains a predetermined magnetizing level of current through the windings. In the demagnetize mode, a digital system decreases the current amplitude stepwise while alternating the polarity. When the sensed current attains the selected peak level for a given step, a digital count is decremented. The polarity is reversed according to the odd or even count, and a new peak reference level is established corresponding to the digital count.

Abstract: A demagnetizer for removing residual magnetism in vehicles includes a single coil which is adapted to surround a portion or the whole of the body of a vehicle. A direct current and alternating current are supplied to the single coil simultaneously to produce a d.c. magnetic field and an a.c. magnetic field. The direction and magnitude of the d.c. magnetic field are so arranged, that the d.c. magnetic field cancels the external magnetic field. The magnitude of the a.c. magnetic field is varied within a predetermined range periodically to remove the residual magnetism.

Abstract: A process for demagnetizing components by subjecting them to the influences of the alternating magnetic field of a coil supplied by an oscillator circuit which includes a capacitor also includes providing a voltage supply to the oscillator at the resonant frequency and thereafter reducing the intensity of the alternating field acting on the components. This can be done in several ways, such as by varying the frequency of the supply voltage or by varying the capacitance connected in circuit with the coil. The process may also be used for calibrating permanent magnets.

Abstract: A demagnetizing apparatus for removing residual magnetism in the body of an automobile which is equipped with a magnetic bearing indicator. A first and a second coil are wound around a substantially flat frame of a non-magnetic material to produce respectively a fixed d.c. magnetic field and a controllable a.c. magnetic field in orthogonal directions with each other and along flat surfaces of the substantially flat frame. The substantially flat frame with coils is positioned adjacent to but spaced from a body portion such as a roof, door or floor of the automobile, so that the d.c. magnetic field produced by the first coil cancel the external magnetic field caused by the terrestrial magnetism. The a.c. magnetic field is controlled to be intensified and weakened alternately thereby to remove the residual magnetism of the body portion without being influenced by the external magnetic field.

Abstract: A method for the protective magnetization of vessels by using magnetic loops (11).The field strength of the magnetic field surrounding the vessel is detected by means of a Hall generator (12) and the current through the magnetic loop (11) is controlled in dependence on the field strength thus detected.

Abstract: In the electromagnet control apparatus described herein, demagnetization of the electromagnet and a workpiece held thereby, following a period of holding, is effected by stepwise adjustment of the phase setting of a power control means such as a triggerable, semi-conductor switching device, thereby controlling the average AC voltage applied to a full wave bridge through which the electromagnet is energized. Reversing switch means are interposed between the bridge and the electromagnet for reversing the direction of the energizing current at each successive step.

Abstract: A pair of demagnetizing coils, or more than two, and the article to be demagnetized is put in the coils. The demagnetizing is done by reversing the polarity in a series of steps in a cycle, and the current reduced in successive steps, to a point at or near zero. The cycle can be varied as to time period, and the number of steps within a cycle varied. The applied initial voltage can be adjusted or predetermined as to maximum value, with corresponding current values, and the number of steps predetermined within the cycle independently of the maximum voltage. The apparatus can be set in manual mode, wherein the cycle timer period and number of steps can be independently set, and to automatic mode, wherein the cycle time and number of steps are directly correlated.

Abstract: A method for demagnetizing an automobile is disclosed in which the terrestrial magnetism is detected by a direction-detecting sensor and the running direction of the automobile is indicated in response to a signal produced from the direction-detecting sensor. The distortion of the magnetic field caused by the permanent magnetism of the magnetic materials of the whole body of the automobile is erased by placing the automobile in an AC magnetic field which gradually increases from zero to a predetermined intensity and then gradually decreases to zero, and thereafter the direction-detecting sensor is mounted at the magnetic center of the automobile.

Abstract: A magnetic chuck control system employing solid state circuitry including a power output circuit adapted to apply a DC voltage to an object such as a magnetic chuck or the like so as to magnetize the same. The power output circuit employs a triac reversing circuit and is interfaced with a digital control circuit and a digital-to-analog converter circuit so as to apply alternating polarity voltage signals of successively reduced magnitude to the chuck during a demagnetizing operation. All high voltage is confined to the power output circuit so as to provide significant safety protection to the operator.

Abstract: A circuit for controlling operation of an electromagnet includes a source of voltage connectable to the electromagnet to produce current flow in one direction and develop a magnetic force therein. A dissipating circuit is connectable to the electromagnet to form a closed loop and has impedance means for dissipating stored energy with gate means between the closed loop and the source producing current flow from the source through the closed loop when the residual potential drops to the potential of source and produce reverse current flow through the magnet. The circuit also has a reverse current limiting means in parallel with the impedance means and includes a manually variable resistor to adjust the limit of reverse current flow.

Abstract: One or more additional helical coil windings (each situated within a space between adjacent ones of a plurality of paced ferromagnetic shielding cans of graduated size and (each one of which encloses all cans smaller than itself), are oriented coaxial with the helical coil winding of the maser itself (situated within the innermost can). This permits optimum degaussing to be achieved with small degaussing current.

Abstract: An automatic electronic head demagnetizer is built into a standard cassette housing. The cassette housing is provided with a resiliently mounted pressure pad which forms part of an electrical switch connected to circuitry inside the cassette housing. When the cassette housing is inserted into a conventional cassette tape recorder or playback machine and the "play" button thereof is depressed, the machine head moves into engagement with the pressure pad, pushing the latter into the cassette housing. As a result, the pressure pad, which is electrically conductive, makes electrical contact with another switch component inside the cassette housing, thereby closing an electrical switch in the housing. This activates the control circuit for the demagnetizing inductor. In response to such activation, a demagnetizing field is established and then caused to decay from an initial maximum amplitude towards zero, whereas the frequency of the demagnetizing field is caused to increase from zero.

Abstract: A compact hand-held demagnetizing device is used for demagnetizing a magnetic recording and reproducing head. It comprises a handle portion and a demagnetizing head. The handle portion contains a circuit for generating a decreasing alternating current for exciting a drive coil for the demagnetizing head. Means is provided to indicate the time when the demagnetizing operation is initiated or when the demagnetizing operation can be initiated and when the demagnetizing operation is completed.

Abstract: An apparatus for converting three-phase electrical energy into direct current includes Scott-connected transformers with oppositely biased SCRs connected in parallel to two of three input terminals. The SCRs are controlled so that they fire in alternate and rotating sequence between the two input terminals. The secondary output voltages of four terminals are rectified so that the common rectified output voltage is a substantially DC voltage with a minimum ripple. The secondary output terminals are aligned in a common plane and are connected to deformable, tapered leads. The rectifiers are connected between the deformable leads and to a common slotted, conductive plate which is connected to a welding electrode. A center tap from each of the secondary windings is connected to another welding electrode. The deformable tapered leads and the slotted conductive plate provide an equal resistive path for pairs of rectifiers for each secondary output to equalize the current flow through the two sets of diodes.

Abstract: A magnetizable iron core is surrounded by a magnetizing solenoid coil which can be energized by 60 hertz regular house power. An article of magnetizable material to be magnetized is placed adjacent the core and the solenoid coil is energized. A normally closed dwell switch in series with the solenoid coil is activated by the magnetization of the iron core to move to an open condition to interrupt flow to the solenoid after first permitting current to flow in said solenoid coil momentarily. Upon sucn interruption of current flow to the solenoid, the article is magnetized. To demagnetize an article, it is put in contact with the iron core, and means is provided to override the dwell switch. The solenoid coil is continuously energized. The article to be demagnetized is then moved away from the iron core. The resulting decreasing alternating current field completely demagnetizes the article.

Abstract: Demagnetizing methods and apparatus are provided in which a pipe, tube, rod, bar or other elongated part to be demagnetized is moved through the coil assembly to which pulses of current are applied to produce magnetic field pulses of alternating polarity and of substantially constant durations and magnitudes with a substantially constant repetition rate, each current pulse being effective to produce by the end thereof a reversal of the magnetic field in all portions of the part positioned within the confines of the coil assembly and immediately adjacent thereto, the part being moved longitudinally through the coil assembly at a velocity sufficiently low as to effect demagnetization of all portions of the part. The duration of each current pulse is at least 50 milliseconds and most preferably on the order of 0.5 seconds and the velocity of movement is preferably less than two feet per second.

Abstract: A demagnetizer for a magnetic head for a recording/reproducing device. The demagnetizer includes an electromagnet for producing an alternating magnetic field which gradually decreases in intensity. The demagnetizer is mounted in a case formed in the shape of a tape cassette. The electromagnet is resiliently held within the case adjacent to the opening for the magnetic head to be demagnetized. The electromagnet is energized by an oscillating drive circuit, the output of which is controlled by a capacitor.

Abstract: A magnetic tape sensing head demagnetizer disclosed has a housing with a hollow handle portion and a clear plastic probe portion projecting outwardly from the handle portion. A coil within the handle portion receives the inner end of a core which has an outer probe end that is received by the probe portion to protect it during demagnetizing of a tape sensing head as an AC voltage provides a pulsating flux to the core. A bulb received within the handle portion of the housing shines light through the probe portion thereof to provide illumination during the demagnetizing. Closing of a normally open switch energizes the coil with the AC voltage and concomitantly applies a portion of the voltage across the coil to the bulb to provide the illumination.

Abstract: This invention is concerned with a portable demagnetizer which includes a demagnetizing head supported within a hand held housing. Also contained within the housing is a variable control for applying voltages of decreasing step-less magnitude to the demagnetizing head; and means are also provided to apply a step-less alternating current power to the demagnetization head while voltages of decreasing magnitude are applied to the demagnetizing head. The housing is provided with a control means on the outside thereof so that the demagnetizer may be hand held and varied at the same time by a single individual user, particularly because of a minimum of parts and the use of step-less decreasing voltage magnitudes and the use of step-less alternating current power, which is applied to the demagnetizing head. Similar results can be achieved by slowly moving the work away from the alternating field.