Showing papers on "Electrical impedance published in 1976"

A New Load-Pull Characterization Method for Microwave Power Transistors

Abstract: A novel method for microwave power transistor load-pull characterization is presented. The method provides an equivalent load-pull measurement technique without using an output impedance tuner. In this method, both input and output ports of a test transistor are simultaneously driven by external signals at the same specified frequency. Results of its application to a medium-power GaAs FET are given.

Electrosurgical safety circuit and method of using same

Abstract: An improved electrosurgical safety circuit where the currents in the active and patient leads are monitored, the monitored currents being respectively rectified and then subtracted from one another. Whenever the active current exceeds the patient or return current by an amount corresponding to a dynamically variable threshold, an appropriate measure is taken such as the sounding of an alarm and/or the de-energization of the electrosurgical generator. The dynamic threshold varies in accordance with the level of the signal applied to the patient and compensates for leakage current through stray capacitance from the active lead to ground. The patient lead is substantially grounded at radio frequencies through a frequency sensitive network. The frequency sensitive network may include a capacitor, the value of which is such as to provide the foregoing frequency response. Since as small a capacitor as possible must be used to provide a high impedance at low frequencies, and since the radio frequency voltage across the capacitor must be kept low to thereby keep the voltage patient low at radio frequencies, a further network is employed to enable the use of a small capacitor while at the same time decreasing the effective voltage thereacross whereby protection of the patient is enhanced.

Position Sensing by Charge Division

Abstract: A summary of a comprehensive analysis of theoretical and practical aspects of position sensing by charge division from resistive electrodes is presented. Properties of transformer decoupling of the resistive electrode from detection bias voltage are analyzed and compared to the usual capacitive decoupling methods. Optimization and limitation of signal shaping is discussed as a function of diffusion time constant, signal rise times, and noise.

RF Impedance of United States and European Power Lines

Abstract: Impedance measurements were made of 86 commercial 50-Hz AC power distribution systems throughout the LF-HF (0.02-30 MHz) spectrum in six European countries. The impedances are those presented to devices/appliances connected to the ac power source. The European results are presented in graphic and tabular form and are compared to impedances of U.S. power lines.

The input admittance of the rectangular cavity-backed slot antenna

Abstract: The input admittance of the rectangular cavity-backed slot antenna is investigated. The slot is assumed narrow so that the voltage distribution in its aperture is sinusoidal. Equations which represent the input admittance of this slot, backed by a rectangular cavity in which a single propagating wave is assumed to exist, are given. Calculations based on these representations are compared to available measured data. As the depth of the cavity increased the resonant frequency decreased and the bandwidth became narrower. Input admittance curves as a function of electrical slot length are also presented for several size cavities.

A highly efficient method for calculating transmission line transients

Abstract: A highly efficient method for digital calculation of transients on transmission lines with frequency-dependent effects is presented. The most time consuming part of calculating the transmission line transients in time-domain techniques such as traveling-wave methods is numerical evaluation of real-time convolution for including the frequency-dependent effects of the transmission lines. In the new method developed in the paper, a time response of a frequency-dependent parameter is simulated with linear curves. Then, the convolution in time-domain is evaluated by a sum of very few multiplications of the time response and a traveling-wave variable in which the effect of the frequency dependent parameter is to be included. Computation time required for the convolution is reduced to much less than one tenth, and the total computation time of a transient calculation is easily reduced by half compared with conventional methods for calculating transmission line transients.

Dielectric coated wire antennas

Abstract: An electrically thin dielectric insulating shell on an antenna composed of electrically thin circular cylindrical wires is examined. A moment method solution is obtained, and the insulating shell is modeled by equivalent volume polarization currents. These polarization currents are related in a simple manner to the surface charge density on the wire antenna. In this way the insulating shell causes no new unknowns to be introduced, and the size of the impedance matrix is the same as for the uninsulated wires. The insulation is accounted for entirely through a modification of the symmetric impedance matrix. This modification influences the current distribution, impedance, efficiency, field patterns, and scattering properties. The theory is compared with measurement for dielectric coated antennas in air.

Eddy current gauge for monitoring displacement using printed circuit coil

Abstract: A proximity detection system for non-contact displacement and proximity measurement of static or dynamic metallic or conductive surfaces is provided wherein the measurement is obtained by monitoring the change in impedance of a flat, generally spiral-wound, printed circuit coil which is excited by a constant current, constant frequency source. The change in impedance, which is detected as a corresponding change in voltage across the coil, is related to the eddy current losses in the distant conductive material target. The arrangement provides for considerable linear displacement range with increased accuracies, stability, and sensitivity over the entire range.

Uhf tuning circuit utilizing a varactor diode

Abstract: In the UHF tuning portion of a television receiver, a varactor tuned circuit is coupled to the gate electrode of a field effect transistor (FET) through an impedance transformation network comprising a series connected capacitor and shunt connected inductor. In order to increase the signal power transferred between the tuned circuit and the FET at the lower end of the UHF range, the values of the capacitor and inductor are selected so that the relatively low value of equivalent parallel impedance exhibited by the tuned circuit at the lower end of the UHF range is impedance transformed to a value approximately equal to the value of the impedance exhibited at the gate of the FET. A second impedance transformation network, similar to the first, is coupled between the drain of the FET and a second varactor tuned circuit to further increase the signal power transferred between the FET and the second tuned circuit at the lower end of the UHF band. The values of the capacitor and inductor comprising the impedance transformation networks are also selected so that the signal power gain of the UHF tuning portion at the upper end of the UHF range is not substantially degraded. Because of the impedance transformation networks, resonant points below the lowest frequency in the UHF band are established.

The prediction of the impedance of the thorax to defibrillating current.

Abstract: In this paper a technique for predicting thoracic impedance to defibrillator pulses is described The impedance to low-current (10 mA) high-frequency (10-500kHz) sinusoidal current is used as an indicator of the impedance of the thorax to high-current, damped sinusoidal waveform pulses Results from 71 dogs to which defibrillator shocks of 4 to 220 A peak current were applied show that thoracic impedance can be predicted by this method This information indicates that it is possible to design a defibrillator that can automatically measure chest impedance prior to a defibrillation shock and deliver a predetermined peak current to the subject

Expressions for Wavelength and Impedance of a Slotline

Abstract: Closed-form approximate expressions for slot wavelength and characteristic impedance for a slotline are presented. These expressions have an accuracy of about 2 percent for substrate permittivity ranging between 9.7 and 20.

Method of and apparatus for automatic measurement of impedance or other parameters with microprocessor calculation techniques

Abstract: This disclosure is concerned with a new technique for automatically measuring impedance (though the process is also applicable to other parameters and characteristics as well) wherein a series of voltages are sequentially presented to a common detector and analog-to-digital converter, the numerical values of which voltages are of themselves meaningless, but from which, with the aid of microprocessor calculating equipment, ratios may be calculated that indicate impedance (or other parameters).

Relations for Analysis and Design of Surface-Wave Resonators

Abstract: Analysis and design relations are presented for elec- trical resonators formed from an interdigital transducer on a piezo- electric substrate, with arrays of many metal reflecting elements on both sides of the transducer to create surface-wave resonance. The "image" point of view is used for analyzing the arrays. Simple expressions are obtained for predicting the stop-band width of an array, the stop-band attenuation of an array, and the apparent point of reflection from the array, in terms of r = ZJZ, the ratio of the surface-wave impedance in the metalized regions to that in the unmetalized regions. The attenuation relation also provides a con- venient means for measuring r. Simple means are presented for including the array dissipation loss in the calculation of its input impedance, and such loss is found to be major significance. Equivalent circuits are presented for surface-wave resonators, along with equations for the reactance or susceptance slope param- eters and resonance Q's at the frequencies of series and parallel resonance. Several experimental resonators were fabricated, and the measured results agree well with the theory. Our experimental results show that for an array of metal reflecting strips if the outer ends of the strips are shorted together r 1.

Input impedance of a short dipole antenna in a warm anisotropic plasma, 1, Kinetic theory

Abstract: A theory is presented for the input impedance of a short, cylindrical dipole antenna immersed in a warm anisotropic plasma which is described by the kinetic theory (Boltzmann equation). The plasma is assumed to be homogeneous with collisions included. The input impedance is based on the induced EMF technique and a quasistatic approximation. The dipole is assumed to have a triangular current distribution along its axis. For a dipole oriented parallel to the static magnetic field, the input impedance is derived as a one-dimensional integral suitable for numerical integration. Under certain conditions, this integral can be evaluated giving analytical formulas valid near the second and third electron cyclotron harmonics. The results show new contributions to the input impedance due to the excitation of cyclotron harmonic waves which propagate near the harmonics of the electron cyclotron frequency. These harmonic effects are not predicted by either the cold or hydrodynamic theories.

Controlled impedance connector

Abstract: A controlled impedance connector for providing a high density controlled impedance interface between a computer backplane and printed circuit (PC) logic card circuitry having signal carrying conductors and a ground surface imbedded in a dielectric medium at selected spacings to achieve a desired characteristic impedance. A common ground surface is provided for a plurality of signal conductors which are in a selected geometrical relationship with the ground surface. Another embodiment of the invention uses a plurality of microstrips embedded in a dielectric medium and dielectrically separated from a common ground surface to achieve the desired characteristic impedance.

Automatic ac biasing of a magnetoresistive element

Abstract: Two magnetoresistive (MR) elements are connected with two matched impedance elements in a bridge arrangement for sensing magnetic flux manifesting information recorded on magnetic media. An alternating current (AC) bias is applied to the bridge's input, and short-term variations in the bridge output signal envelope are detected as representing recorded information. Long-term (average) variations in the signal envelope are also detected and used to adjust the AC bias to maintain a constant average envelope. Additional bridge inputs may be connected in parallel with the first, and the additional bridges' outputs used to derive additional information signals without any additional AC bias adjustment circuits.

Interpretation of AC Impedance Measurements in Solids

Abstract: In order to use solid materials most effectively in solid electrolyte applications, they need to be characterized as fully as is practical. Here, one useful method of electrical response characterization will be discussed: measurement of the response when a small-signal sinusoidal potential difference is applied across a sample. A great deal more can be learned from the frequency and temperature dependence of the resulting impedance than from ordinary DC or single-frequency AC conductance measurements alone.

High‐voltage probe system with subnanosecond rise time

Abstract: A high‐voltage probe measuring system with an overall rise time of less than 50 psec and a peak voltage capability of 20 kV has been developed. Probe perturbations at the 50 Ω impedance level are minimized by maintaining a moderately high input impedance, in conjunction with the absorption of internal reflection waves by means of a lossy distributed transmission line. System long‐term stability and constructional reproducibility have been investigated.

Determination of the interaction impedance of coupled cavity slow wave structures

Abstract: The interaction impedance of coupled cavity slow wave structures can be measured by perturbing the resonances of a shorted length of the structure using a dielectric rod. An analysis of this procedure is presented. The analysis retains radial as well as axial electric fields and all significant space harmonics. The results obtained are easily programmed formulas for calculating total interaction impedance or Pierce impedance using the experimental data.

Telephone range extender with gain

Abstract: A telephone Range Extender with Gain (REG) is disclosed for extending the range of loop lengths over which telephone service can be provided. This is accomplished by providing voice frequency gain, a higher voltage talking battery, and supervisory and signaling circuitry for increasing the level of supervisory and signaling currents at the central office end. The range extender requires no adjustment for loops of different lengths. A π configuration negative impedance amplifier includes an adjustable gain circuit responsive to the resistance of the connected loop to automatically adjust the gain of the amplifier to the length of the loop. At the same time, an impedance matching circuit is transformer-coupled to the loop. The frequency shaping of the negative resistance amplifier and the impedance matching network, when reflected through the transformer, provides acceptable impedance matching for a wide range of loop lengths and wire gauges. For stability, the gain of the amplifier is forced to a low value when the central office termination becomes an open circuit.

Saturable reactor-type power supply

Abstract: Power supply of the saturable reactor type is disclosed The improvement is the inclusion of a variable impedance network, such as a pair of opposed semiconductor controlled rectifiers, in series with the current winding of the saturable reactor Also included is an electronic circuit for changing the impedance of the variable impedance circuit, such as a control circuit for monitoring an operating parameter and for enabling or disabling the firing of the semiconductor controlled rectifiers in response to a change in the operating parameter A preferred embodiment of the power supply also includes a transformer and a rectifier for supplying high-voltage, direct current to a sputtering apparatus

A CMOS monolithic 3½-digit A/D converter

Abstract: A 3 1/2-digit A/D converter, combining linear and digital circuits on a CMOS monolithic integrated chip, providing auto-polarity, auto-zero, auto-calibration, high input impedance and low power dissipation, will be described.

Sensitivity compensated fire detector

Abstract: A fire detector of the ionization type is characterized by sensitivity compensating circuitry. The detector includes an ionization chamber in series circuit with a reference impedance to form a voltage divider, and circuitry for sensing the voltage at the juncture between the ionization chamber and reference impedance and for generating a current flow which changes in value with changes in the voltage. The sensitivity compensating circuitry monitors the current flow, and for slowly occurring changes corresponding to slow changes in the juncture voltage adjusts the current flow to and maintains the flow at a quiescent value. The compensating circuitry responds relatively slowly to changes in current flow, and therefore does not significantly affect the current flow in response to a rapid change in juncture voltage. Thus, upon the occurrence of products of combustion within the ionization chamber, a relatively rapid change occurs in the juncture voltage to cause at least a predetermined change in the current flow, in response to which an alarm is generated.

Combined controlled oscillator and frequency multiplier

Abstract: A voltage controlled oscillator which, for example, may be utilized in a phase locked loop, includes an odd number (n) of cascaded COS-MOS inverter stages with a feedback path coupling the output of the last stage to the input of the first stage to form a ring configuration. The ring configuration oscillates at a frequency f 1 determined by the transconductances of the inverter stages and the shunt capacitances between the stages. Signals comprising impulses of current having frequency components at f 1 and 2f 1 flow through the power supply inputs of each of the stages as they successively are switched from one state to another. A frequency selective impedance path is coupled between a source of power supply voltage and the power supply inputs of each of the stages to develop a second signal having a frequency f 2 equal to a multiple nf 1 or 2nf 1 . The voltage applied to the commonly connected power supply inputs may be controlled to control f 1 and, consequently, f 2 .

Loop type standard magnetic field generator

Abstract: In a loop type standard magnetic field generator comprising loop within which a transmission line having an inner conductor and an outer conductor is coaxially provided and an oscillator for feeding a signal to the loop through the transmission line, the magnetic field strength at a given point is obtained, irrespective of the signal frequency, from the indicated value of an indicator connected to the loop via the transmission line and an element connected thereto, by choosing the length of the transmission line and/or the impedance of the element so that the frequency characteristic of the ratio of the indicated value of the indicator to the electric current flowing through the loop is cancelled by the frequency characteristic of the ratio of the electric current flowing through the loop to the magnetic field strength at the given point to thereby make the frequency characteristic of the indicated value of the indicator and the magnetic field strength constant.

The effect of a progressive decrease in the circulating blood volume of the dog on the transthoracic impedance.

Abstract: The correlations between the haemodynamic and transthoracic electrical impedance changes resulting from a progressive reduction in the circulating blood volume were studied in four intact mongrel dogs artificially ventilated with a mixture of halothane in nitrous oxide-oxygen. The cardiac output of the dogs was measured by both the electrical impedance and the fibre optic dye dilution techniques. It was found that significant correlations existed between the blood loss and the arterial blood pressure, the maximum first derivative of the transthoracic impedance, the Heather Index, the transthoracic impedance, the maximum rate of change of aortic pressure and the cardiac stroke work. There was also a good correlation between the dye and impedance cardiac output values, the impedance value always being higher than the corresponding dye value. The correlation between the Heather Index and the PEP/LVET ratio and 1 /PEP2 varied markedly from dog to dog.