Showing papers on "Electrical impedance published in 1970"

Measurement of the Intrinsic Properties of Materials by Time-Domain Techniques

Abstract: In this paper a method is presented for determining the complex permittivity and permeability of linear materials in the frequency domain by a single time-domain measurement; typically, the frequency band extends from VHF through X band. The technique described involves placing an unknown sample in a microwave TEM-mode fixture and exciting the sample with a subnanosecond baseband pulse. The fixture is used to facilitate the measurement of the forward- and back-scattered energy, s21(t) and s11(t), respectively. It is shown in this paper that the forward- and back-scattered time-domain "signatures" are uniquely related to the intrinsic properties of the materials, namely, e* and ?*. By appropriately interpreting s21(t) and s11(t), one is able to determine the real and imaginary parts of ? and ? as a function of frequency. Experimental results are presented describing several familiar materials.

Elastomeric graded acoustic impedance coupling device

Abstract: An ultrasonic probe has a solid, flexible, elastic, graded acoustical impedance coupling device having fine geometrical and naturally shaped, metal and glass component powders, with their characteristic acoustic impedance values, disposed in graded varying concentrations in solid, elastomeric silicones, polyurethane, or the like low acoustic impedance, solid elastomers, providing a shaped, composite matrix coupling or a delay line. The graded matrix of component fine shaped powder in an elastomer provides a proximate matching impedance adjacent to the interface with the flat piezoelectric transducer at one device end, and a similar matching impedance near the interface to the inspected workpiece at the other device end, with intermediate low-loss graded impedance values inbetween. When a lens is employed, an effective tapered impedance can be obtained at the interface with the test article by graduating the solid concentrations primarily at the workpiece end. The elasticity of the device provides close conformation with the inspected workpiece surface, and reduces the acoustic reflection due to surface roughness and irregularities.

Simulation of AC System Impedance in HVDC System Studies

Abstract: In some studies of HVDC system design, ac system impedance is represented by its inductance at power frequency. However, for several studies better simulation of the impedance- frequency characteristic (from power frequency to a few kilohertz) of the ac system is important. This paper presents a simple approach to calculating an approximate equivalent network consisting of parallel LCR branches and having an impedance-frequency characteristic similar to that given for the ac system. For given typical ac system impedance diagrams (usually obtained from ac system models and simulators), simulation of an ac system by corresponding equivalent networks during studies of certain HVDC problems would provide a more accurate means of designing HVDC systems.

Alternating Current Distribution Between Planar Conductors

Abstract: The general theory for the vector potential produced by a sinusoidal current of finite cross section has been developed in a preceding paper.1 In the present work, this theory is applied to a coil between a number of plates of finite electrical conductivities and permeabilities. Linear, isotropic, and homogeneous media are assumed throughout. The Green's function solution is first obtained, and the principle of superposition is then used to effect the desired result. A number of physically observable phenomena, such as the impedance, the power loss due to the presence of the conductors, and the time‐averaged electromagnetic force on the conductors are subsequently calculated from the vector potential. The treatment is sufficiently general to allow the solution of a number of difficult electromagnetic induction problems, while each of the expressions obtained for the physically observable phenomena is in terms of an infinite integral that may readily be evaluated on a computer. In all cases for which exper...

SWITCHING AND MEMORY IN ZnSe–Ge HETEROJUNCTIONS

Abstract: Heterojunctions of nZnSe–pGe switched from a high impedance to low in 100 nsec when a threshold voltage is exceeded. Resetting occurs in the opposite bias direction in 10 nsec after sufficient current is applied. Either state is maintained with all bias removed for a minimum of two weeks.

Evaluation of specific cerebral impedance and cerebral current density

Abstract: Determinations of physiological impedance are usually made for relatively large samples of tissues.18 More recent work has indicated the desirability for determinations of specific impedance for very small volumes. Several investigators have designed electrode systems that confine measurements to within a few mm of a specific lo~at ion .~*~,9*~7 Measurements of the specific impedance of cerebral cortex and cerebral white matter were made by Freygang and Landau6 with two microelectrodes that sampled the voltage drop across cerebral tissue due to the passage of an external current. R a n ~ k , ~ using four in-line electrodes, also measured various neural impedances. Typical currents were in the 0.1-0.5 microampere range. These currents gave no indication of neural excitability. This project was initiated to investigate methods for determination of specific cerebral impedance and cerebral current density during the application of diffuse electrical currents such as those used for electroanesthesia. The four-electrode method uses a separate source of low level current that is isolated from and independent of the anesthesia current supply. A two-electrode method capable of measuring specific impedance and current density was also investigated.

Use of plasma tube impedance variations to frequency stabilize a CO 2 laser

Abstract: A method for stabilizing the frequency of a single- J - value CO 2 laser to the center of its output power versus frequency curve based upon the variation of the impedance of the plasma tube with the optical power extracted is described. Frequency modulation of the laser produces an ac component of voltage drop across the plasma tube, which is synchronously detected to generate a frequency-error signal.

Characteristic Impedance and Phase Velocity of a Dielectric-Supported Air Strip Transmission Line with Side Walls

Abstract: The characteristic impedance and phase velocity of a dielectric-supported air strip transmission line with side walls and with center conductors having zero thickness have been obtained by means of the variational method. Green's functions are used for setting up the variational expression. Using a 22-term expansion for the charge distribution on the center conductors, the Rayleigh-Ritz method is then applied in the calculation of the characteristic impedance and phase velocity of the strip transmission line. Design curves are presented and a correction factor is derived that can be applied when the thickness of the center conductors is not zero. The design curves are quite general and apply equally well to any isotropic dielectric material that is used as a support, regardless of its dielectric constant. The experimental data presented verifies the theoretical results.

A Compact Broad-Band Thin-Film Lumped-Element L-Band Circulator

Abstract: Impedance matrices including magnetic losses are developed for a number of lumped-element ferrite-loaded symmetrical three-port junctions. The scattering matrix eigenvalues corresponding to these matrices are determined as functions of frequency and circuit parameters and are used to analyze these three-ports with emphasis on their properties as circulators. A very compact broad-band thin-film lumped-element circulator is derived from the idealized equivalent circuit. An experimental model approximately represented by this circuit is shown to have a 20-dB isolation bandwidth of greater than 30 percent with an insertion loss of less than 0.6 decibel. A switchable circulator which requires no magnetic-field switching is treated using this same analytical approach. It is suggested that this type of analysis together with additional experimental refinement of equivalent circuits will lead eventually to a computerized design of lumped-element circulators.

Rheoplethysmographic device and method of operation

Abstract: A rheoplethysmographic device (inductance plethysmograph) comprising a high frequency electric generator of which the voltage is applied to a subject by means of a pair of injection electrodes, characterised by the fact that the injection electrodes are placed in series with at least one current setting impedance interposed between the subject and the generator, at least one pair of collector electrodes being placed on the subject within the zone subjected to voltage by the injection electrodes, the voltage collected between the electrodes of each pair and that collected between one pair of points of a current setting impedance being subsequently led after amplification to a differential device and then to an indicating device for measurement, control recording or transmission, the position of the said pair of points being such that the voltage received between them substantially balances the mean voltage between the corresponding pair of collector electrodes so that after amplification of each of the said voltages and passage through the differential device, the output voltage varies about zero.

Impedance of a Short Dipole Antenna in a Warm Isotropic Plasma

Abstract: The impedance of a short dipole antenna with a finite radius is considered using the Vlasov theory of the plasma rather than the simpler hydrodynamic theory. Analytic and numerical computations are presented for the longitudinal portion of the impedance. The results of this paper are compared with similar calculations for spherical antennas and filamental dipole antennas.

The impedance properties of dielectric-covered narrow radiating slots in the broad face of a rectangular waveguide

Abstract: An extension of Oliner's theory is used to predict the impedance of slots with dielectric coatings. Theoretical curves are presented which show the change in impedance as a function of dielectric constant, dielectric losses, and dielectric thickness. The effect of a dielectric or plasma upon the resonant frequency is also included. The agreement with experimental dielectric-covered slot data justifies the extension of Oliner's theory.

Acoustic impedance matching system

Abstract: A transducer assembly incorporating a stratified medium for conducting acoustic waves from an acoustic source of relatively high impedance, such as a piezoelectric crystal, to a gaseous environment of relatively low impedance, the stratified medium including typically at least one layer of a foam structured low density plastic material, whereby uniform variations in impedance are provided progressively from the source through the layers of the stratified medium into the gaseous environment to effect an impedance match.

Line security system

Abstract: A system for insuring the security of electrical transmission lines extending between a monitor station and a remote station utilizes a voltage source at the monitor station which impresses an AC voltage signal on the transmission lines At the remote station, the AC voltage signal is rectified and the rectified signal is applied to a current regulator which provides a quiescent pulsed direct current of constant level to the transmission lines The current regulator is arranged to provide a higher alarm current when an intruder is detected at the remote station At the monitoring station, a shorted line fault detector provides a signal when a reversal in the direction of normal current flow occurs in the transmission lines, an open line fault detector provides a signal when a drop in current below the quiescent current level is detected, and an alarm current fault detector provides a signal when a rise in current above the quiescent current level is detected The impressed voltage is periodically reduced in amplitude to a level which barely sustains the minimum quiescent current level to test line impedance

Circuit for supplying direct current to a telephone line

Abstract: Two PNP transistors are coupled between the positive pole of a direct current source and one side of a telephone line, and two NPN transistors are coupled between the negative pole of the direct current source and the other side of the telephone line. The transistors are provided with circuits to control the direct current supplied to the telephone line. The transistors present a high impedance to voice frequency and alternating current signals on the telephone line, and thus provide the desired current without large inductors.

Network parameters of a waveguide broad wall-slot radiator

Abstract: It is found from experimental investigation that the equivalent network of a thin displaced longitudinal slot in the broad wall of a rectangular waveguide changes from a parallel element to a series element a back to parallel element again as the length of the slot is increased from about ㎻/2 to about 3㎻/2. In the paper, analytical experssions for the immitance variations in the series and shunt forms of representations have deen found. The electric-field distribution in th aperture plance of the slot is replaced by suitable magnetic-curent distribution. The field distribution in the aperture plane of a slot, representable as a shunt element, is an even function and produces a discontinuity in modal current. The analytical expression for the complex admittance in the shunt form of equivalent network has been found from the reaction of the magnetic field due to the slot with the magnetic current exciting the slot and the discontinuity in modal current. A slot, whose equivalent network is a series element, has an odd distribution of electric field in its aperture plane, and such a slot produces a discontinuity in modal voltage. The analytical expression for the impedance in the series form of equivalent network is found from the power radiated by, and power stored in the vicinity of, the radiating slot and the discontinuity in modal voltage. The analytical expression for the impedance in the series form of equivalent network is found from the power radiated by, and power stored in the vicinity, of the radiating slot and the discontinuity in modal volage. The theoretical results are in good agreement with experimental observations.

Circuit arrangement for the ignition and alternating current supply of a gas and/or vapor discharge lamp

Abstract: An ignition circuit for a discharge lamp comprising a ballast impedance in series with the lamp across the AC supply terminals. A capacitor and an SCR connected in series across the lamp electrodes. A diode connected anti-parallel to the SCR. A zener diode between the SCR anode and gate electrodes. The series circuit, including the ballast impedance, the capacitor, and the SCR and diode connected in anti-parallel, is under critically damped.

Automatic impedance matching system for RF sputtering

Abstract: A previously described' “L” type matching network used for rf sputtering is shown here as part of Fig. 1. The purpose of the network is to transform the complex impedance of a sputtering system to a purely resistive value of 50 Ω. This makes possible the use of a transmission line with a characteristic impedance of 50 for the conveyance of rf power to the system. The rf power is conveniently monitored by a power meter in the transmission line. Since the power meter is capable of measuring both forward and reflected power, the voltage standing wave ratio (VSWR) on the transmission line can be computed. The VSWR will be unity when the matching network is adjusted so that the transmission line is terminated in its characteristic impedance. Practically, it is difficult to achieve a VSWR of unity (zero reflected power), so the network is adjusted to approach that optimum state as nearly as possible.

Precision Slotted-Line Impedance Measurements Using Computer Simulation for Data Correction

Abstract: A precision slotted-line measurement system is described that provides rapid impedance measurements over a wide dynamic range for both active and passive devices Phase accuracy of 01° at 70 GHz and magnitude accuracy of 05 percent are obtainable for high VSWR measurements Phase-locked sources used for both the slotted-line drive and the receiver local oscillator provide greater than 70 dB of dynamic range for an incident power level of -50 dBm at the unknown A micrometer positioner for the slotted-line probe provides an order of magnitude improvement in probe-position accuracy over that obtainable using the conventional slotted-line scale and micrometer A computer program simulates the slotted line and its associated connector by several sections of lossy transmission line together with appropriate discontinuity capacitance and contact loss This form of model has the advantage that frequency dependence is implicitly included Impedance measurement is simple and rapid The only data required are the frequency, the position of an unknown null, either the width of the minimum or the VSWR, and the desired reference plane extension The corrected data may be plotted directly on a Smith chart Printout is in a convenient format for data evaluation

Impedance and admittance matrices of distributed three-layer N-ports

Abstract: The port impedance and admittance matrices of threelayer structures of linear, passive, isotropic materials are defined and their properties briefly investigated. Discrete equivalent circuit representations are given, together with two examples.

Generalized theory of static power frequency changers

Abstract: The thesis is concerned with static frequency changers, using solid-state switching devices, capable of directly (i.e. without an intermediate dc link) converting polyphase ac power of a given frequency to single or polyphase power of a chosen frequency. The thesis consists of two parts. The first part, comprising five chapters, is devoted to the study of ideal frequency changers operated from ac Sources having zero internal impedance. The second part, comprising two chapters, considers sources with finite internal impedances . Chapter 1 introduces the basic concepts of static frequency conversion, outlines the basic mathematical models representing static frequency changers and defines the output and input performance indicators. Chapter 2 presents a detailed investigation of that class of three-pulse frequency changers which will be studied in the thesis. A large portion of the chapter is devoted to the study of output waveform generation. The mathematical tools of the investigation, existence matrices and modulating functions, are introduced and defined. Analytical expressions for output waveforms corresponding to various practical modulating functions are derived and the related performance indicators are computed. Assuming a given desired output performance, criteria for an optimal modulating function are established. It is proved that only one system can generate an output waveform conforming to the postulated prerequisites. This system is termed the "Unrestricted" Frequency Changer. Expressions for the input current waves are also derived in this chapter and the corresponding input performance indicators are determined . The concept of a new frequency changer having the unique property of providing unity input power factor, regardless of the load, is introduced. This system is termed the "Unity Power Factor" Frequency Changer. In Chapter 3 the previous results are extended to systems having pulse numbers which are integral multiples of three. Chapter 4 is devoted to the study of output voltage control. Three basic methods are analysed and detailed quantitative data for output voltage and input current waves, and the related performance indicators, are presented in graphical form. In Chapter 5 special aspects of static frequency changing are investigated. It is shown that the input displacement factor is variable. The concept of the "Controlled Displacement Factor" Frequency Changer is introduced It is proven that the naturally commutated cycloconvertor is theoretically equivalent to a particular "Controlled Displacement Factor" Frequency Changer. Chapter 6 presents a detailed analysis of the "Unrestricted" Frequency Changer, operated from an ac source with finite internal impedance. The basic conditions are defined and an outline is given of the techniques of symmetrical components used for the analysis. The input current, input terminal voltage and output voltage waveforms are expressed in terms of the input terminal impedance and the positive, negative and zero sequence components of the output currents. The equivalent sequence impedances and the output impedance matrix are derived . The output voltage unbalance is computed under various conditions and presented in graphical form. The relationships between the amplitudes of the unwanted components in the output waveform and the resonant frequency of the input terminal circuit are also graphically presented. The results obtained are verified by computer simulations. In Chapter 7 a similar analysis of the "Unity Power Factor" Frequency Changer is carried out . The computed data are also graphically presented. Again, the results are verified by appropriate computer simulations.

Broad-Band Equivalent-Circuit Determination of Gunn Diodes

Abstract: A method has been developed for the direct broad-band measurement of the impedance of a Gunn diode operating at a bias voltage exceeding threshold. This method is based upon determination of an equivalent-circuit model for the diode mount and package, which is found to be valid over the 1- to 20-GHz range. Using this circuit, the low-field diode equivalent circuit is found and takes the form of a parallel RC circuit as expected from the theory. An unusual result is that the low-field capacitance is found to be strongly dependent on the bias voltage; this dependence is presumed due to the free-carrier contribution to the effective dielectric constant. Some direct broad-band measurements are reported for an active Gunn diode biased beyond threshold. These measurements provide additional insight into the conditions under which significant parametric action may occur in a Gunn diode.

Current limiting device for limiting short circuit current in energy transfer systems

Abstract: An electrically normal conducting impedance winding is connected in series with one of two inductively interlinked windings of a current limiting device and has an inductivity which is such that approximately the same electric voltage drop occurs at the impedance winding as does at the other of the windings when the current limiting device is operated at a current which is smaller than or equal to the limiting current. The series connection of the impedance winding and the one of the windings of the current limiting device is connected in parallel with the other of the windings of the current limiting device. The two windings, one of which is connected in series with the impedance winding and the other of which is connected in parallel with the series connection, have mutually opposed and substantially equal ampere turns. The one of the windings at least partially comprises superconducting material and has a critical field intensity which is exceeded when the limit value of the current is exceeded and the winding becomes electrically normal conducting.

Short cylindrical antennas with enhanced radiation or high directivity

Abstract: The feasibility of enhancing the radiated power or improving the directivity of a short cylindrical antenna by double impedance loading is investigated. An approximate solution for the current on a doubly loaded short antenna is developed, and typical current dlstributions, impedances, and radiation patterns of antennas appropriately loaded to implement enhanced radiation or high directivity are presented. Significant improvements in radiated power or directivity can be achieved with optimum impedance loadings. Theoretical predictions are verified by the results of an experimental study.

Characterization of Packaged Microwave Diodes in Reduced-Height Waveguide

Abstract: A technique for the measurement of package parasitic and equivalent-circuit parameters of microwave semiconductor devices at the frequency of operation is presented. In this method a two-port coupling circuit is found which transforms the impedance measured in rectangular waveguide to the terminals of the equivalent circuit used to represent the semiconductor device. This approach combines known properties of radial transmission lines and of impedance measurement in the TE/sub 10/-mode full-height waveguide to obtain an analytical referencing technique for a diode mounted across a reduced-height waveguide. Application of this technique is illustrated by measurements of several varactor diodes.

Apparatus for monitoring speed utilizing a tuned circuit whose phase changes in proportional to speed

Abstract: A motion detector system using a pulse tachometer comprising a wheel of non-magnetic, non-conductive material such as fiber or Teflon having a plurality of equally spaced magnetically distinct pins in the periphery which move into proximity of a pick-up coil of a tuned circuit to vary the impedance therein. Varying the impedance effects a circuit phase-shift which is compared with a predetermined reference phase of voltage and current in said circuit to provide an indication of any movement of the wheel and a measurement of the speed of movement in a measured time interval.

Electrical impedance cephalography, electrode guarding, and analog studies*

Abstract: In the registration of the electrical impedance cephalogram (EIC) or rheoencephalogram (REG), one applies electrodes superficially to the surface of the scalp. From this fact arises a major difficulty: what is desired is not the impedance fluctuations in the scalp and superficial tissues, but rather the impedance fluctuations occurring more deeply, in the brain and contained vascular tissues themselves. A prime problem in electrical impedance cephalography is therefore an evaluation of techniques and selection of those that are least contaminated by the impedance fluctuations of the scalp.

Physical displacement measuring system utilizing impedance changing the frequency of an oscillatory circuit

Abstract: An analog data transmission system having as the transmitting means an oscillator with a tuned circuit and means to vary the tuning of this circuit by an incremental value by a switching means operating repetitively, the entire system including a receiving means having a frequency discriminator followed by a voltage sensitive readout device which measures the difference between the two alternate frequencies of the oscillator caused by the switching.

Crystal band pass filter circuit

Abstract: A band pass filter circuit including at least two stages of crystal filtering preceding each of a pair of integrated amplifier circuits. All of the crystal filters have the same resonant frequencies, and an impedance coupling network is provided between each of the crystals and its associated utilization circuit to minimize the effects of reflected impedance variation. Also a de-Qing network is provided between each pair of the crystal filters to prevent undesired ringing of the crystal.