Showing papers on "Electrical impedance published in 1968"

The Pinning Potential and High‐Frequency Studies of Type‐II Superconductors

Abstract: The electrical impedance of type‐II superconductors as a function of frequency is discussed in terms of a ``pinning potential.'' Many flux‐pinning properties of the mixed state at any frequency can be treated in terms of such a potential and a simple phenomenological extension of the Bardeen‐Stephen flux‐flow theory. The form of the potential can be determined by various dc and high‐frequency experiments. There is a critical frequency above which the impedance for subcritical currents becomes the impedance of the ``ideal'' mixed state. Much below this frequency the impedance is zero. This critical frequency is given by ω0=2πCρnα/φ01/2Hc2H1/2. At microwave frequencies, almost all effects of flux pinning are absent, and the properties of the ``ideal'' mixed state are observed even in the most strongly pinned material. Such measurements have been used to determine the effective mass of the flux tube.

An Accurate Calculation of Uniform Microstrip Transmission Lines

Abstract: An analytical program for calculating the field distribution about a microstrip transmission line bounded by a shielding wall is used to calculate the impedance, velocity, and attenuation parameters. The program input parameters are the dimensions of the strip and shielding wall and the relative dielectric constant of the substrate material. The field distribution about the strip is integrated to find the charge density on the strip and walls with and without the dielectric substrate. From these two calculations, the relative velocity and impedance can be calculated.

A large signal analysis of IMPATT diodes

Abstract: This paper presents results on RF power output and efficiency of IMPATT oscillators obtained from a large-signal model of these devices. The results are obtained from a closed-form solution of the nonlinear equations describing a Read-type IMPATT diode. The closed-form solution is obtained by assuming a short transit time through the drift region compared to the RF period. The solution is used to obtain the large-signal diode impedance. The analysis shows that the power output of an IMPATT diode depends strongly on the series load resistance presented to the active part of the diode and that the change in diode reactance with increasing bias current also depends on the series resistance. Plots of power output as a function of frequency, bias current, and load resistance are presented. Frequency tuning of the oscillator through current variation is also discussed. Experimental results are presented and compared with the theoretical ones wherever possible. The results lead to an improved understanding of such oscillators and are extremely useful in optimizing their performance and determining their limitations.

Solid-state constant power ballast for electric discharge device

Abstract: 1,255,043. Supply systems for discharge lamps. WESTINGHOUSE ELECTRIC CORP. 9 April, 1969 [29 April, 1968], No. 18136/69. Heading H2H. [Also in Division G3] The current through a discharge lamp 10 is maintained at a desired average value by alternately supplying the lamp from a D.C. source 11 until the current reaches a predetermined value and then using the energy stored in an inductor 14 to pass current through the lamp (via a diode 18) for a predetermined fixed time, these alternate cycles producing a triangular shaped current waveform giving the desired average current, Fig. 2 (not shown). The lamp current is detected by a resistor R1 whose output signal is used to control a Schmitt trigger circuit formed by transistors Q2, Q3 and determining the ON/OFF times of a switching transistor Q1 controlling the supply to members 10, 14. During warm-up of the lamp, these ON/OFF times are controlled by a current peak detecting circuit R2, R4, D2, C1 which causes the control circuit to operate in a variable pulse-frequency mode. When steady-state lamp operation has been reached the voltage developed across a capacitor C2 is increased to exceed that across capacitor C1 and cause control to pass to an average-current-detecting circuit R10, R11, D6, C2, which thereafter operates the transistor Q1 at a fixed mark/space ratio corresponding to the desired average current. This current is automatically varied, to maintain constant power with supply voltage variations, by a network R12, R13, C3, D5 which controls the Schmitt trigger circuit to vary the mark/space ratio of transistor Q1 in accordance with supply voltage variations as sensed by the capacitor C3. The described control circuit also automatically compensates for variation of the lamp voltage with ageing to maintain constant lamp power, the theoretical basis of this aspect of the invention being discussed. Operation of the circuit on an A.C. supply is envisaged together with various modifications such as replacing resistor R1 by an impedance or a current transformer and obtaining the predetermined OFF time of transistor Q1 by time delay means other than the circuit C2, R11.

Variable impedance switching regulator

Abstract: A DC step-up voltage regulator with a series arrangement of a raw DC source and an energy storing inductor which are alternately connected to a low impedance circuit to build up the inductor current and to an output circuit which includes a capacitor which is charged by the current flow from the inductor. A control circuit varies the amount of inductor current buildup needed to hold the output voltage constant and also provides periodic and constant time intervals of sufficient duration to discharge the inductor current into the capacitor.

Power system protective relaying by time-coordinated sampling and calculation

Abstract: A method of controlling the operation of a breaker in a transmission line by first monitoring the current and if the current exceeds a prescribed limit, measuring a sampling of the voltage on the line when the current is at zero and dividing this value by the maximum current on the line to obtain a first quantity which is added to a second quantity obtained by measuring a sampling of the voltage when the current is at its maximum value and dividing this voltage by the maximum current. The previous calculations will provide a measure of impedance since the voltage when the current is zero is equal to Vm sin phi while the voltage when the current is at maximum is equal to Vm cosine phi and impedance in a rectangular coordinate representation is: z R jX Vm cosine phi /Im + j(Vmsin phi /Im). This apparent impedance is then compared against relay characteristics which are implemented in a programmed general purpose computer and in the event the apparent impedance lies within the relay characteristic zone, the associated breaker is tripped.

A High‐Sensitivity Superconducting Detector

Abstract: Weakly connected superconductors can function as very low power sensors by utilizing the coherence properties of superconductors. One configuration which has produced significant success incorporates a superconducting point contact and a small resistance element in a low‐inductance superconducting circuit. When the critical supercurrent (ic) of the point contact is of the order of φ0/L, (φ0=h/2e, L=inductance of the ring), that circuit exhibits coherent quantum behavior. Used as a parametric amplifier, it has been used to measure ultralow voltages, limited by the thermal noise fluctuations in the resistance element R. The voltage sensitivity is approximated by 8kTR/φ0, where k is Boltzmann's constant and T the absolute temperature of the resistance R. We have measured 4×10−16 V across 1.7×10−10 Ω at 4.2°K with a signal‐to‐noise ratio approaching 10. The operation of this sensor follows from the Josephson oscillation of voltage‐biased superconducting point contacts. A dc voltage V0 across the resistance of...

Frequency selectivity using positive impedance converter-type networks

Abstract: It is shown that positive impedance converter-type networks may be used to realize a driving-point impedance that is ideally a frequency dependent negative resistor. This concept may be used to realize new types of inductorless selective networks. A simple resonant circuit application is discussed.

A Transformer-Ratio-Arm Bridge for Measuring Large Capacitors Above 100 Volts

Abstract: A high-voltage bridge suitable for measuring capacitance ratios up to a million to one is described. The high ratio is realized by cascading a two-stage current transformer to a bridge based on the current comparator principle. Circuits that compensate for the lead impedances of large capacitors are presented. The bridge is direct reading in the capacitance ratio and the dissipation factor and the uncertainties for both components are less than 10 parts per million (ppm).

Alternating current switching apparatus with improved electrical contact protection and alternating current load circuits embodying same

Abstract: A SWITCHING APPARATUS FOR AN ALTERNATING LOAD CIRCUIT IS PROVIDED WITH A BIDIRECTIONAL OR BILATERAL SEMICONDUCTOR TRIODE DEVICE OF THE THYRISTOR TYPE CONNECTED FOR CONDUCTION IN SHUNT WITH THE CONTACTS OF AN ELECTROMECHANICAL SWITCH FOR ARC SUPPRESSION, AND HAS A GATE CIRCUIT COMPRISED IN WHOLE OR IN PART BY REACTIVE PASSIVE ELEMENTS WHICH EXHIBIT IMPEDANCE CHARACTERISTICS TO RENDER THE SOLID STATE TRIODE DEVICE CONDUCTIVE IN RESPONSE TO ARCING CONDITIONS AT THE SWITCH CONTACTS BUT WHICH PRECLUDE SUCH A RESPONSE DUE TO CIRCUIT TRANSIENTS. THE SOLID STATE TRIODE DEVICE IS ALSO SUBSTANTIALLY INSTANTANEOUSLY RESPONSIVE TO RELATIVELY LARGE DV/DT CHARACTERISTICS OR EXTREME EXCESSES (EXCEEDING THE BREAKOVER VOLTAGE OF SOLID STATE DEVICE) OF ARCING VOLTAGE APPEARING ACROSS THE SWITCH CONTACTS.

Current stabilizer circuit for thermionic electron emission device

Abstract: A current stabilizer circuit for a thermionic electron emission device is described in which the cathode heating winding of a power supply transformer is connected to the high-voltage winding through a heating current control circuit. The control circuit senses changes in the emission current of an X-ray tube or other electron emission device having a thermionic cathode, and produces a control signal which is applied to a variable impedance means connected in series with the cathode filament to vary the heating current in order to maintain such emission current substantially constant. The control circuit may operate by series regulation or by pulse duration modulation of the cathode heating current to change the average heating current and temperature of the cathode and thereby vary its electron emission in order to stabilize the emission current in spite of changes in the power supply voltage which tend to vary such emission current.

Electrical Impedance of the Human Body

Abstract: : The object of this report is to establish the theoretical range of radio frequency impedance of the human body in the 1 - 30 MHz range. The report defines whole body rf impedance, summarized available specific tissue impedance data, and predicts likely values of total body impedance for various electrode sizes and locations from known specific tissue data and skin impedance. The report also discusses the relation of body impedance to electrode impedance, skin impedance and specific body impedance.

The Characteristic Impedance and Coupling Coefficient of Coupled Rectangular Strips in a Waveguide

Abstract: The effect of both the ground planes and sidewalls on the characteristic impedance and coupling coefficient of two coupled strip-Iines are investigated. Numerical results are given that should aid in the design of miniature directional couplers where the sidewalls are close enough to the strips to have a large effect. It is shown, for example, that the coupling coefficient can be varied as a function of distance to enhance the bandwidth, while the impedance can he maintained constant to improve the directivity.

Negative resistance antenna amplifier arrangement

Abstract: An oscillator circuit is kept at a predetermined stable-operating point below the onset of oscillations by high-resistance feedback in the emitter circuit. The tuned circuit of the oscillator has one winding of a transformer whose second winding is connected either in series between the antenna and the receiver, or in parallel with the receiver. The impedance seen looking into the second winding is a negative resistance.

Starting arrangement for solid-state commutated motor

Abstract: A circuit comprising a solid-state commutating means in an oscillatory circuit for a direct current motor. The circuit includes photosensitive means actuated by electric light means gated by the rotor and connected to modify the feedback as the amount of illumination striking the photosensitive means varies in response to the gating. The change in feedback controls the current in the circuit to provide proper starting and running currents. In particular the solid-state commutating means may be in the form of a circuit similar to a flip-flop with separate stator coils in series with the active elements of the flip-flop and with feedback resistors connecting the output of one part of the flip-flop to the input of the other. The photosensitive means include photoconductive cells connected to change the effective impedance of the feedback resistors and means may be included so that, after the motor has gotten started, the amount of current through the electric light may be reduced to a value too low to cause incandescence or the current may even be turned off entirely.

Computer memory storage device

Abstract: A flip-flop circuit is formed with a pair of active electronicswitching elements. Connected in circuit with at least one of these switching elements as an impedance coupler is a passive storage element. A digital signal to be stored is written into the passive storage element, thereby changing its effective impedance in the circuit. The readout signal is obtained from the electronic-switching elements by providing power to such active switching elements in response to a readout address, the electronic-switching elements assuming a conductive or nonconductive state in accordance with the effective circuit impedance of the associated passive storage element.

Electronic metering system

Abstract: A quantum radiometer is provided for use with different photovoltaic cells in probes, each with a different wavelength filter. Temperature compensating, calibrating and scaling resistors mounted in a given probe comprise a voltage divider connected to the output of a low input impedance amplifier. The cell in the probe is connected directly to the input of the amplifier. A switch converts the arrangement of the resistors in the voltage divider to change the output from radiant power (watts) to photocurrent (optical amperes or photons/second). A digital display unit connected to the output of the voltage divider provides numerical display with a fixed radix point and a constant scaling factor. A variable exponent for the scaling factor is changed automatically as the gain of the amplifiers is altered to (1) provide in the display a nonzero digit in the most significant position and (2) prevent a carry out of the most significant digit position. Offset current may be introduced at the voltage divider, such as to introduce a conversion constant.

Very low frequency subminiature active antenna

Abstract: A subminiature active antenna includes two non-magnetic conductive plane elements in spaced parallel relationship separated by a distance of the order of the principal dimension of the plane elements. A conductive member connected to a first plane element, extends at right angles through the second plane element, and is connected to a capacitance multiplier circuit grounded to the second plane member. The capacitance multiplier circuit has an input impedance of phase and amplitude substantially matching the conjugate aggregate impedance presented to it by the antenna members which are thus caused to appear to a received wave field as a much larger capacitance and consequently develop a greater useful signal.

Admittance Probe Method of Measuring Time Resolved Plasma Electron Temperatures

Abstract: It is shown that the plasma electron temperature in electron volts is given by the product of the ion saturation current and the probe‐to‐plasma resistance at the floating potential. An ac capacitance bridge circuit is described which will measure this resistance with a response time that approaches the ion transit time across the sheath. The method is demonstrated by a measurement of electron temperature in the Wisconsin toroidal octupole.

Minimization of backscattering of a loop by impedance loading--Theory and experiment

Abstract: A study on the minimization of the backscattering of a conducting loop by the impedance loading method is presented. A conducting circular loop loaded symmetrically with two identical lumped impedances is assumed to be illuminated by a plane electromagnetic wave at normal incidence. The induced current on and the backscattered field by the loaded loop are determined. The optimum impedance loading for zero backscattering is obtained. The optimum reactive loading for minimum backscattering is also studied. An experiment was conducted to verify the theory.

Impedance-measuring transformer bridge with automatic digital balancing circuit

Abstract: The present invention relates to automatic electrical bridgebalancing circuits and, more particularly, to bridge circuits, preferably of the transformer bridge type, employing alternatingcurrent digital servo controls for effecting rapid balancing of unknown impedance elements, such as capacitances.

Ac/dc electrode and power supply system for a glass furnace

Abstract: 1281424 Supply systems for glass melting furnaces H L PENBERTHY 8 June 1970 27659/70 Heading H2H [Also in Division H5] Protection of the electrodes 18, 20 in a glass melting furnace 10 is ensured by arranging by means of a differential impedance device that the alternating current applied to the electrodes from a source 22 has a direct current component superimposed thereon. The direct current component is derived from the A.C. supply 22 by a thyristor 28 connected in anti parallel with a diode 26 thus modifying a half cycle of the source relative to the preceding half cycle. Alternatively the diode 26 may be in parallel with a variable impedance device or a resistor which may be constituted by the resistance of the leads 37, 38. Three phase arrangements are disclosed wherein the electrodes are connected to the three phases and in which an auxiliary electrode connected to the neutral of the A.C. supply may be provided. In other embodiments the electrodes may be associated with an adjacent auxiliary electrode.

Electric control circuits for electromagnetic devices

Abstract: AN ELECTRIC CONTROL CIRCUIT FOR AN ELECTROMAGNETIC DEVICE SUCH AS CLUTCH OR A BRAKE INCLUDES A FIRST MEANS FOR ENERGISING THE COIL OF THE DEVICE TO OPERATE THE DEVICE AND A SECOND MEANS FOR SUBSEQUENTLY PROVIDING A REVERSE CURRENT FLOW THROUGH THE COIL WHEREBY RAPIDLY TO REDUCE THE ENERGISATION OF THE COIL. THE FIRST MEANS INCLUDES AN ENERGISING CIRCUIT FOR THE COIL HAVING A CAPACITOR AND A FIRST CONTROLLED IMPEDANCE DEVICE WHICH IS OPERABLE BY A CONTROL SIGNAL TO ENERGISE THE COIL AND CHARGE THE CAPACITOR. THE SECOND MEANS INCLUDES A DISCHARGE CIRCUIT FOR THE CAPACITOR AND COMPRISES THE COIL AND A SECOND CONTROLLED IMPEDIANCE DEVICE WHICH OPERATES ONLY WHEN THE FIRST CONTROLLED IMPEDANCE DEVICE IS RENDERED INOPERATIVE. WHEN IT IS REQUIRED TO REDUCE THE ENERGISATION OF THE COIL, THE FIRST CONTROLLED IMPEDANCE DEVICE IS RENDERED INOPERATIVE WHEREUPON THE SECOND CONTROLLED IMPEDANCE DEVICE AUTOMATICALLY OPERATES TO DISCHARGE THE CAPACITOR THROUGH THE COIL TO PROVIDE THE REVERSE CURRENT FLOW THERETHROUGH.

Temperature compensated oscillator using temperature controlled continual switching of frequency determining impedance

Abstract: Method of and device for compensating the temperature variation in the oscillation frequency of an oscillator wherein an impedance element, for example, a capacitor coupled to the oscillator is switched between two levels of its value, whereby the temperature variation is compensated for on an average.

An Accurate Calculation of Uniform Microstrip Transmission Lines

Abstract: An analytical program for calculating the field distribution about a microstrip transmission line bounded by a shielding wall is used to calculate the impedance, velocity, and attenuation parameters. The program input parameters are the dimensions of the strip and shielding wall and the relative dielectric constant of the substrate material. The field distribution about the strip is integrated to find the charge density on the strip and walls with and without the dielectric substrate. From these two calculations, the relative velocity and impedance can be calculated.

Negative impedance boosting

Abstract: Linearized and feedback-stabilized negative impedance circuits having only R, C, and solid state components, powered in series at intervals along a cable pair, offer new possibilities in bilateral transmission. After discussing the basic negative impedance boosting units and the transmission characteristics they impart to a line (computed, with experimental confirmation), this paper describes a field test of two 32-mile telephone lines, largely 22-gauge, each having an insertion loss of only 3 dB at 1,000 Hz. It also shows means for broadening bandwidth and almost eliminating delay distortion over negative impedance boosted lines. Treatment of this sort adapts them to unusual uses. Examples include converting rectangular to raised-cosine pulses in transmission, without pulse-forming circuitry, and the bilateral two-wire transmission of carrier or pulse signals in both directions simultaneously, without frequency separation.