Showing papers on "Electrical impedance published in 1969"

Microstrip lines for microwave integrated circuits

Abstract: Microstrips, transmission lines of metallic layers deposited on a dielectric substrate, are very useful for the microwave and millimeter wave hybrid integrated circuits required for solid-state radio systems because of their simplicity and planar structure. To design hybrid integrated circuits with microstrips requires computation or measurement of the impedance, the attenuation, the guide wavelength, and the unloaded Q of the line. These parameters can be obtained from the effective dielectric constant and the characteristic impedance of the corresponding air line. This paper gives the exact design data for all line parameters for the most important cases. We report the impedance and attenuation measurements performed on microstrips. Satisfactory agreement is obtained with theoretical results based on conformal mapping with logarithmic derivatives of theta functions and expressions involving the partial derivatives of the impedance with respect to independent line parameters.

Surface Waves in Piezoelectrics

Abstract: The effect of various electromagnetic boundary conditions on the propagation of surface waves in piezo‐electrics is considered. Basic for the analysis is the introduction of an electric ``surface impedance'' which relates the electric potential to the normal component of electric displacement in the surface. An analytic expression for this impedance is found in the case of weak piezoelectric coupling which permits the calculation of the phase velocity for arbitrary values of the impedance. It is also shown that within the weak coupling approximation the surface impedance contains the information on material parameters necessary for calculating the power transferred to surface waves from an impressed electric current.

Ekg amplifying electrode pickup

Abstract: An amplifying electrode pickup for an electrocardiograph (EKG.) device consisting broadly of an impedance converter integrated amplifier circuit potted in a metal shell. The integrated circuit is biased by a nanoamp electrical current. The EKG. signal is sensed by a small sensor plate or disc positioned in a boot or cover and is electrically insulated from the shell. The circuit has a very high input impedance to minimize the effect of skin contact resistance changes, and a very low output impedance to minimize noise pickup by the signal line between the electrode and the EKG. electronics. Electronic circuitry in the potted metal shell also includes a diode voltage clamp and decoupling RC circuits. A multiconductor cable provides shielding, conducts power to the electrode, and transmits the signal from the electrode through an integral coaxial cable. Because of the low (nanoamp) biasing current, signal traces of numerous separate electrodes can be simultaneously recorded without exceeding the maximum permissible current through the human body as established by the American Heart Association.

The piezoelectric crystal unit—Definitions and methods of measurement

Abstract: The properties of a piezoelectric crystal unit as a circuit element are characterized and defined, in terms of a general equivalent circuit that is valid at any frequency up to and including the lower UHF ranges but reduces to the conventional equivalent circuit if the parameters are properly redefined. The characteristic values such as resonance frequency and resistance, parallel resonance frequency and resistance, etc., for a crystal unit with or without other reactive elements in series and/or parallel are tabulated and their significance is illustrated with the aid of the crystal impedance and admittance diagrams. These diagrams are also used in deriving and describing the methods to be followed when determining the crystal equivalent circuit parameters by impedance bridge measurements. Techniques are developed for use with various types of impedance and admittance bridges and the relations required to determine the resonance resistance R 1 , resonance frequency f s , and quality factor Q 0 of the motional arm, and the reactance X- 0 of the parallel capacitance from the measured quantitites are listed. The effects of transmission lines of various lengths between the plane of measurement in the bridge and the crystal unit are fully considered. The nature and magnitude of the sources of measurement errors, exclusive of errors in bridge calibration, are examined.

Nonlinearity of Cardiac Pacemaker Electrodes

Abstract: Nonlinear properties of electrodes immersed in saline were studied in the time domain and frequency domain. Three electrode materials were tested: platinum-iridium, Elgiloy, and stainless steel. For time domain measurements, current pulses of 1.0 to 2.0 ms duration and varying amplitudes were applied to the electrodes. Frequency domain measurements of polarization impedance were made with an impedance bridge, utilizing sinusoidal currents of varying amplitudes at frequencies between 0.1 and 10 kHz.

Combining network providing compensated tuning voltage for varactor

Abstract: A control circuit for an indirect frequency synthesizer which combines a plurality of control functions into a single compensated tuning voltage for the varactor control element of an associated voltage controlled oscillator. The combining circuit includes a resistor network for summing phase control and modulating signals, and a variable resistance circuit for generating a coarse steering signal. The summing network is resistively connected to the variable resistance circuit to form a variable impedance resistor divider operative to attenuate the combined phase control and modulating signals in a manner inversely related to the magnitude of the coarse steering signal and to combine the attenuated control signals with the coarse steering signal and to combine the attenuated control signals with the coarse steering voltage to provide the varactor tuning signal. More specifically, the attenuation provided by the impedance divider is operative to substantially compensate for the variation in voltage versus frequency sensitivity of the varactor with changes in the coarse steering voltage.

Fundamentals of Network Analysis

Abstract: Equivalent circuits for electronic devices will be shown to consist of simple current or voltage generators, together with impedances or admittances. In Chapter 1, we found that such devices could only operate correctly if they were connected to suitable load and bias circuits consisting of impedances or admittances. In addition, any signal to be amplified was supplied from an a.c. current or voltage source together with its associated impedance or admittance.

Experimental investigation of the input-impedance characteristics of an antenna in a rectangular waveguide

Abstract: The input impedance of a monopole antenna in a rectangular waveguide is investigated experimentally. It is found that theoretical results based on the assumption of a sinusoidal current distribution are in good agreement for monopole lengths up to about 0.6 of the guide height and about 1/4 λ0. For longer monopoles, a more accurate theory should be sought.

Computer-Aided Small-Signal Characterization of IMPATT Diodes

Abstract: This paper is a discussion of IMPATT wafer small-signal characteristics in the frequency range of 2.0-8.0 GHz. These characteristics have been obtained by computer conversion of reflection phase-gain data. The data handling technique which allows establishment of the desired reference plane and the reduction of the admittance data into the desired equivalent circuit is presented. A calibration procedure using reference impedances consistent with the diode geometry is discussed. The validity of the microwave measurement technique and the data handling process is demonstrated by comparison of the values of junction capacitance determined at microwave frequencies with junction capacitance measurements at 30 MHz. Representative plots are given for wafer conductance and susceptance as a function of frequency with current density as a parameter. In addition, typical values obtained for the circuit elements are presented. These data illustrate the capability of determining package inductance, series resistance as a function of bias voltage, and, with the diode in avalanche, the parallel G, L, and C of the wafer admittance. The diode equivalent circuit was studied as a function of current density to compare results with the existing analytical small-signal theories. This procedure permits the separation of the wafer elements from the parasitic elements of the package. Data obtained from these measurements are extremely useful for ascertaining wafer design parameters and assisting in circuit design.

Modulated impedance feeding system for log-periodic antennas

Abstract: A modulated impedance feeding system for log-periodic antennas including loading elements, a transmission line to couple energy to or from the elements, and impedance-modulating means for matching the image impedances of the transmission line and the loading elements in the regions of local reflections to realize essentially frequency independent performance A log-periodic monopole array and a cavity backed slot array are provided, fed with a modulated impedance meandering line according to the invention A log-periodically scaled directional coupler feed line for antenna arrays is provided, including in one embodiment thereof a coupler fed, log-periodic resonant V array

A general method for obtaining impedance and coupling characteristics of practical microstrip and triplate transmission line configurations

Abstract: In order to design an interconnection system for nanosecond-risetime logic circuitry, it is necessary to obtain a balance between impedance variations, propagation velocities, and crosstalk levels so as to achieve the best system speed as well as system speed control. To accomplish this, it is necessary to relate the electrical material properties and physical dimensions of the connections to characteristic impedances, propagation velocities, and crosstalk coupling coefficients. Two practical transmission line configurations: the microstrip line, which is coated for physical protection, and the offset or unsymmetrical triplate line, are being fabricated by mass production techniques. Because of the close control required and the many factors affecting impedance and coupling, these configurations require accurate means for predicting their characteristics. An improved "subintervals" technique and a series approximating the Green's function have been combinedto yield a single practical computer algorithm. Excellent agreement has been obtained in comparing the results of computations with large scale-model transmission line measurements. The method is quite general because dimensions, conductor shapes, and dielectric properties may vary widely.

Method and apparatus for detecting short circuits in the machining gap in an edm process

Abstract: A method and apparatus for accurately determining the presence and magnitude of a short circuit condition in an electrodischarge machining (EDM) process. An electrically conductive tool and an electrically conductive workpiece are connected to a pulseproducing power supply and positioned in a dielectric medium to form a machining gap therebetween. The machining gap is placed in an impedance-measuring circuit as the impedance to be measured. The impedance-measuring circuit checks the gap condition by measuring the impedance of the machining gap between pulses from the power supply. In the embodiment disclosed, changes in gap impedance between output pulses are detected by a modified wheatstone bridge. During the time between pulses, a voltage less than the ionization voltage is applied to the bridge. If there is no short circuit condition, the bridge is balanced; and the bridge output is zero. A short circuit condition will cause an imbalance in the bridge producing a resultant error signal on the bridge output. This output is fed back within the power supply causing a change in its output parameters which will tend to alleviate the short circuit condition.

Skin Effect in Multiple and Polyphase Conductors

Abstract: The modal theory of current flow, previously successful in predicting skin-effect behavior of single isolated conductors, is generalized to apply to any number of parallel conductors arbitrarily arranged in space and excited electrically by arbitrary currents. The distribution of current density within each conductor is found in terms of a summation of the modal functions, and the terminal parameters of the system of conductors are given as an impedance matrix relating the total conductor currents to the voltage drops in the various conductors. Sequence impedances, losses, and other electrical properties are then calculable from the basic impedance matrix.

A gas discharge lamp circuit employing a transistorized oscillator

Abstract: An oscillator circuit for starting and operating gas-filled tubes having a starting mode which provides a signal of high voltage and very high frequency followed by an operating mode after the tube ionizes whereby the voltage and frequency are considerably reduced, but current through the tube is increased. In the operating mode, the impedance of the secondary is substantially the ohmic resistance of the tube so that overall efficiency is very high.

Impedance Characteristics of Electric Dipoles Over a Conducting Half‐Space

Abstract: The input resistance of a Hertzian electric dipole located over a homogeneous conducting half-space is considered. It is shown that the functional dependence of the input resistance on the ‘loss tangent’ of the half-space is consistent with electrostatic concepts, provided the frequency is sufficiently low. On the other hand, at the higher frequencies, the results are compatible with the surface impedance formulations based on the compensation theorem. The results have possible application to remote sensing of planetary surfaces from an elevated source.

Isolator comprising tuned lumped element circulator

Abstract: The present invention relates to an isolator having a low forward direction loss over a very wide frequency range and a sufficiently high backward loss in a desired frequency range, and having a very compact configuration and a simple construction. The isolator according to the present invention comprises a lumped element type circulator which is operative in the desired frequency range, a resonant circuit having its impedance characteristics to be at low impedance in said frequency range and to be at high impedance outside of said frequency range and being connected between outer conductor of the lumped element type circulator and a ground conductor, and an absorbing resistor connected between one of the terminals of the circulator and the outer conductor or the ground conductor.

Impedance measuring network

Abstract: A circuit is connected to an ultrasonic transducer being fed by a constant current or constant voltage power supply. By rectifying, differentiating, and amplifying the transducer coil voltage an output signal that is a function of the transducer and load impedance is provided that can be displayed so as to determine the operating condition of the ultrasonic apparatus.

Phase coherent and amplitude stable frequency shift oscillator apparatus

Abstract: A phase coherent and amplitude stable frequency shift oscillator apparatus comprising a negative impedance converter, biased into an unstable oscillatory condition, in combination with a pair of impedances respectively coupled to the input terminals thereof for determining the frequency of oscillation. One of the impedances includes a series resistive-reactive impedance circuit and the other includes a parallel resistive-reactive impedance circuit. Means are provided for changing the value of the resistive components of the impedances in order to alter the output frequency of the oscillator apparatus and a level limiting and buffering means is provided for stabilizing the oscillatory operation and buffering the output obtained from the apparatus.

Circuit impedance measuring device employing clamp on magnetic current sensor

Abstract: This disclosure relates to an electrical component impedance measuring device that is capable of measuring the impedance of an electrical component permanently connected in an electrical circuit. It comprises a source of electrical energy with means coupled to this source for connecting the electrical component in circuit with the source. A split-magnetic core having an opening position therein is supported by means that position a lead from the electrical component through this opening with the lead carrying current that flows only through the electrical component whose impedance is to be measured. Means are coupled to the core for sensing and measuring the flux in this core.

Microstrip High-Power High-Efficiency Avalanche-Diode Oscillator

Abstract: A simple microstrip oscillator circuit has been designed and operated satisfactorily with high-power high-efficiency avalanche diodes. The power output obtained from a single diode chip is ahout 100 watts at 1 GHz with efficiencies of 25 to 30 percent. Mechanical tuning capability of a few hundred megahertz and a combined power output from series-connected diodes have been demonstrated using the circuit. An essential part of the circuit is a low-pass filter tuning section which enables the circuit to support high-order harmonics including the transit-time frequency and prevents them from getting to the load. Probe measurements of the electric field show strong second as well as third harmonics inside the circuit.

High frequency battery charger employing an inverter

Abstract: A charger designed to be within a specified weight limitation employs a method and circuit for rapid-charging which circuit employs an inverter for changing a direct current voltage to an alternating-current voltage having a substantially square wave form and a relatively high frequency in the order of 10,000 Hertz, and a rectifying circuit connected to the output of the inverter, for changing the high frequency alternating-current voltage to direct-current voltage for application to the battery to be charged. At least one unilateral impedance element is in the current path through the rectifying circuit with the element briefly providing a discharge path for the battery at the end of each period of forward conduction through the element.

Cylindrical Antenna in Uniaxial Resonant Plasmas

Abstract: The current distribution and the input admittance of a cylindrical antenna immersed in two types of uniaxial resonant plasmas are treated in this paper as boundary value problems. It is first indicated that the Hallen type integral equation approach is not suitable, since it does not describe the actual physical phenomenon closely. The method used here is based on the concept of multiple reflections of current waves between the two terminals of a solid antenna, and simple approximate solutions for thin antennas are obtained by using the newly developed extension of the Wiener-Hopf technique.

Line shapes in the radio-frequency size effect of metals

Abstract: Thin metal plate surface impedance during excitation by HF electromagnetic field as function of magnetic field, calculating line shapes

Equivalent Circuit of a Superconducting Bolometer

Abstract: The theory of superconducting bolometer operation is presented and a small‐signal equivalent circuit developed. This circuit contains a portion that represents dynamic thermal effects and a portion resulting from superconductive phenomena. It is shown that the incremental impedance is greater than the dc resistance even for the limit of zero‐frequency modulation. A peaking phenomenon is predicted in the incremental impedance versus temperature for this circuit. The characteristic parameters of a tin superconducting bolometer are presented to indicate the usefulness of incremental impedance measurements in determining these parameters.