Showing papers on "Electrical impedance published in 1983"

Impedance measurement of individual skin surface electrodes.

Abstract: The methods for the individual determination of skin surface electrode impedances are briefly discussed. A measurement technique is described with which it is possible to measure two skin surface electrodes simultaneously, but individually, at the same frequency. The design of a small, portable, battery-operated meter using this principle is described with block diagrams. Results are presented from the study of bilateral g.s.r. waves, the site dependence of the skin impedance, the differences between 10Hz and 1000 Hz data, and tissue segment impedance.

Fault current limiter using a superconducting coil

Abstract: A novel circuit, consisting of solid-state diodes and a biased superconducting coil, for limiting the fault currents in three phase ac systems is presented. A modification of the basic circuit results in a solid-state ac breaker with current limiting features. The operating characteristics of the fault current limiter and the ac breaker are analyzed. An optimization procedure for sizing the superconducting coil is derived.

Accurate fault impedance locating algorithm

Abstract: Fault resistances affect the accuracy of short-circuit location, when distance to the fault is determined by means of measuring reactance at one end of the transmission line. This is because the current which flows through the fault resistance is slightly shifted in phase with respect to the current measured at the end of the line in question, due to the effect of the prefault load current. As a result, the fault resistance is recognised as an apparent impedance with both resistive and reactive components. The latter produces an error in the fault location, as it affects the measured reactance. The paper presents a simple algorithm which compensates for the error, and makes it possible to locate short circuits accurately; even if fault resistances are comparatively high.

The synthesis of surface reactance using an artificial dielectric

Abstract: A thin artificial dielectric layer consisting of a rectangular array of closely spaced, thin conductive cylinders (pins), was constructed above a perfectly conducting ground plane. The reactance of the surface was measured at 4.8 GHz for a variety of pin heights and dielectric embedding material by measuring the height-gain profile of a transverse magnetic (TM) surface wave launched across it. Design equations using the theories of artifical dielectrics and propagation in anisotropic media are given. These can be used to predict the surface reactance providing a correction factor accounting for fringing fields at the tops of the pins is included. Using an embedding dielectric tends to reduce this fringing effect.

Variable frequency current control device for discharge lamps

Abstract: A control circuit for starting and operating a gas discharge lamp comprising a variable frequency waveform generator coupled to the discharge lamp via a non-resonant coupling network that includes a reactance type ballast impedance. The lamp current is monitored to automatically vary the frequency of the variable frequency generator as a function of the lamp current so as to vary the reactance of the ballast impedance in a sense to regulate or limit the lamp current.

Measurement and Modeling of the Apparent Characteristic Impedance of Microstrip

Abstract: Voltage and current cannot be defined uniquely for microstrip except at zero frequency, and therefore microstrip has not been rigorously incorporated into circuit theory. However, in engineering practice, micro-strip exhibits an apparent characteristic impedance, denoted here by ZA, that can be measured. Three methods of measuring ZA were devised and used in measuring three impedance levels of microstrip. These methods are described and experimental results presented. The measurements of ZA were found to be consistent with the power-current characteristic impedance definition of the approximate longitudinal-section electric (LSE) model of nricrostrip. Simple approximate formulas for representing ZA are also discussed.

Large-signal modeling of GaAs MESFET operation

Abstract: A numerical modeling technique is described which allows the accurate large-signal characterization of highly doped (>1023m-3) GaAs MESFET's. A rigourous two-dimensional numerical analysis is used to extract the FET terminal currents. Specially formulated finite difference equations are used to produce stable, accurate, and efficient solutions. By embedding the device in a simple circuit model, a two, terminal time domain response is obtained which is Fourier analyzed to produce a "device surface". The technique is applied to the analysis and design of a Ku -band monolithic microwave Oscillator, using a 0.5-µm gate length MESFET. A simple equivalent circuit model is proposed which predicts an output of 4 dBm at 16.2 GHz for this oscillator.

Approximate computation of the acoustic impedance from seismic data

Abstract: The approximate computation of the acoustic impedance from seismic data is usually based on the recursive formula h 1 + Ck ktl = ‘k Gtegrated seismic pulse multiplied with twice the impedance in the top layer. For impedance values less than 0.2 in absolute value this is also equal to the acoustic impedance function (minus the acoustic impedance in the top layer) convolved with the seismic pulse. where h, is the acoustic impedance in layer number k and ck is the pressure reflection coefficient for the interface between layer k and k + 1. The above formula is derived from a discrete layered earth model. When we consider a continuous earth model and discretize the results, we obtain the recursive formula The computation of the acoustic impedance from band-limited seismic data corresponds to an exponential transformation of the integrated seismic trace. On a band-limited acoustic impedance section with well-separated reflectors and low noise level the direction of change in the acoustic impedance can be correctly identified.

Analog telemetry system for biomedical implant

Abstract: An analog data transmission circuit for a biomedical implant employs a linear amplifier to modulate the impedance of a resonant circuit tuned to an externally generated constant carrier frequency. The resonant circuit comprises a tuned coil in circuit with a linear modulating switch and a digital modulating switch. The digital switch is gated by the digital data output from digital control circuitry within the implant. The linear amplifier output drives the linear modulation switch. The switches are preferably matched pairs of MOSFET's of opposite polarity having complementary parasitic diodes which form a phantom diode bridge. The bridge acts as a full wave rectifier and boosts the bias voltage on the sources of the FET pair forming the linear modulation switch such that the radiated amplitude is independent of the distance of the programming head. A timed power-up circuit supplies power to the amplifier and starts a square wave calibration period in response to the approach of the programming head. For ICEG transmission, a charge dump circuit depolarizes the lead before it is coupled to the amplifier.

Ballast circuit for multiple parallel negative impedance loads

Abstract: A current-balancing transformer is provided to supply plural parallel-connected electrical loads, especially loads such as gas discharge lamps which exhibit negative impedance and/or non-linear impedance over at least a part of their normal operating range. The current-balancing transformer forces current sharing among the loads so that each of the parallel-connected loads is supplied operating current.

Determination of Synchronous Machine Electrical Characteristics by Test

Abstract: A method of obtaining synchronous machine d and q axis impedances by test as function of frequency of d, q components is presented. The test involves running the machine at reduced speeds, with a line-to-line short circuit between phases, and temporarily applying excitation to produce line-to-line short circuit current at fundamental frequency corresponding to the particular running speed. Records of line-to-line voltages and short circuit current, along with measurement of rotor angle, are processed to yield d and q components of voltages, currents and flux linkages which turn out to be periodic functions of the fundamental frequency plus harmonics. Straight forward Fourier analysis yields the complex values of operational inductances or impedances L d (j2?), L q (j2?), Z d (j2?) or Z g (j2?) where ?is equal to the speed of the machine at which the tests are conducted.

Multilayered printed circuit board with controlled 100 ohm impedance

Abstract: A printed circuit board of six planar layers has the layers separated by a dielectric of epoxy glass. The two central layer planes form a ground plane and a voltage plane. The two external planes and the internal planes involve series of microstrip signal lines of specially calculated widths and dielectric separations to provide an essentially 100 ohm characteristic impedance for the signal lines in reference to the ground and voltage planes.

Integrated oscillator and microstrip antenna system

Abstract: A three-element active device is physically and electrically integrated (e.g., by soldering) onto shaped conductive areas in a thin conformable microstrip structure which includes a microstrip antenna radiator. Two of the elements of the active device are connected to microstrip reactance structures which form a series-resonant partial oscillator circuit. The third (output) element of the active device is connected directly to the microstrip antenna radiator via a microstrip transmission line which, together, directly provide the r.f. load impedance for the thus completed oscillator circuit. Quarter wavelength r.f. microstrip segments are also provided to facilitate the feeding of d.c. bias to the active device without disturbing the r.f. circuitry. The oscillator load impedance to be provided by the microstrip radiator is predetermined in accordance with conventional device-line or loadpull impedance measurements so as to maximize the power output of the active device.

Electronic hybrid having synthesized impedance circuitry

Abstract: An electronic hybrid circuit for coupling a two-wire communication path to a four-wire communication path includes amplifier circuits having a reactive feedback path such that the output impedance of each amplifier is approximately zero ohms at d.c. and is a predetermined value at audio frequencies. The amplifiers are arranged to provide battery and voice signal injection on the two-wire path.

The first and the final fifty nanoseconds of a fast focus discharge

Abstract: Conventional plasma focus devices of different capacitor bank energy (kilojoules to megajoules) show very similar discharge behavior with respect to breakdown, compression, and pinch data. The use of SPEED 1—a plasma focus driven by a fast high impedance bank (voltage 200 kV, initial current rise >5×101 2 A/sec, bank impedance 160 mΩ),—allowed the investigation of a 400 nsec discharge in a parameter range not previously accessible. Considerable improvement of current and neutron efficiency (30 A/J; 106/J) has been achieved as compared with values (≤20 A/J; 2×105/J) of conventional slow devices of equal energy (20 kJ). Exceptional compression dynamics (current derivative spike >101 3 A/sec FWHM 10 nsec) is observed from electric signals. This is due to the current stabilizing effect of the high bank impedance and especially to improved current sheath structure (reduced thickness, enhanced conductivity). Current density and conductivity of the sheath depend on ignition parameters at breakdown (voltage, current rise), the low values of which are possibly responsible for the similarity of the discharge behavior of conventional devices. Conclusions on further improvements are drawn.

Class-E resonant regulated DC/DC power converters: analysis of operation, and experimental results at 1.5 MHZ

Abstract: We present analytical results, design considerations and experimental results at 1.5 MHZ, for a novel, resonant, high-frequency de/de converter. The circuit works virtually without dynamic losses at several-MHz switching frequency. The analysis gives the permissible area of the equivalent load impedance for lossless operation, presents a model for regulation by narrow-band frequency control, and characterizes the output full-wave rectifier. Experimental data from a 1.5-MHz, 40-W converter verify the results of the theoretical analysis. The measured efficiency was 85%.

Alternating current limiting apparatus

Abstract: An alternating current limiting apparatus is disclosed which includes first, second, and third circuit. The first circuit is formed of a winding means such as transformer, autotransformer, or reactor and a capacitor serially connected to the winding means and is connected between two different kinds of power systems. The second circuit is formed of a series combination of a closing device composed of, e.g. a gap, mechanical or semiconductor switch, or a non-linear resistive element, and a resistor. The second circuit is connected across the output terminals of the winding means. The third circuit is formed of a reactor and a second resistor serially connected to the reactor. The third circuit is connected in parallel with the first circuit. The closing device is normally kept in its open state to form a series resonance circuit of the transformer and the capacitor, thereby directly interconnecting the systems with null impedance therebetween. Upon a system fault, the closing device is closed to switch the impedance as seen from the primary side of the winding means over to a small value to detune the series resonance, thereby forming a parallel resonance circuit between the combination of the small impedance with the capacitor and the third circuit including the reactor to enlarge the total impedance between the systems so that an overcurrent therebetween due to the fault may be suppressed.

Controlled turn-on thyristors

Abstract: In a one or more amplified stage thyristor design it is possible to control the peak current level of all but the final stage with impedance built into the p-base zone. This impedance reduces both the current and the duty cycle of the protected amplifying stage effectively protecting it from undesirable temperature rises during turn-on. A further bonus and perhaps equally important is the fact that the amplifying stage and its current control impedance can be used to reduce and essentially fix the voltage level at which the following stage turns on. This results in a lower voltage, lower stress turn-on of the following stage, and a device essentially protected from di/dt turn-on failure. This paper describes several aspects of controlled turn-on in the context of a 2.6- and 6-kV light triggered thyristor. In particular we discuss selection of the resistor value, the problem of unwanted current control resistor modulation by device current as well as some factors affecting the proper wattage of such resistors. We also discuss the role current control resistors can play in controlling avalanche current from known locations on the device.

Apparatus for detecting ferromagnetic material

Abstract: A convertor is used having an impedance responsive to the magnetic field intensity of the earth. The convertor may be coupled to a detector for monitoring the impedance of the convertor and generating a call signal responsive to the change in impedance. Generally, the impedance is primarily inductance and the detector is an oscillator using the convertor in a resonant circuit with a frequency monitor coupled to the detector. The convertor is an open magnetic structure having a non-linear BH curve biased by the earth's magnetic field. The open magnetic structure is a core of a highly permeable material which approaches saturation under the influence of the earth's magnetic field, with the axis of the core at least partially aligned with the magnetic flux lines of the earth's magnetic field, and a coil wound around the axis of the core.

Electronic telephone interface circuit

Abstract: An electronic telephone interface circuit having a simplified, inductorless electronic gyrator circuit which also functions as an amplifying impedance convertor, and further having passive current and voltage limiting protection devices and an extremely fast active current limiting circuit The system is particularly suitable for coupling a high impedance electronic system to a telephone communications system, and is adapted to permit the interface circuit and the electronic system to be powered solely from the telephone system

Waves Guided by Conductive Strips Above a Periodically Perforated Ground Plane

Abstract: This paper considers the propagation of waves along an array of conductive strips situated above a periodically perforated conductive plane. Each conductor has zero thickness and finite sheet resistance, and the dielectric is homogeneous. The surface current density on the conductors is approximated by a finite number of current elements having rooftop spatial dependence. The transverse electric field is expressed in terms of the current, and the electric field boundary condition is satisfied in an integral sense over the conductors. This generates a matrix equation whose solution gives the dispersion curve relating the propagation constant to frequency, as well as the current distribution. The simulation results are used to obtain equivalent transmission-line parameters applicable to printed circuit boards found in high-performance computers. A characteristic impedance is defined and it is shown that, with proper interpretation, the uniform transmission-line equations for propagation constant and characteristic impedance apply to such computer packages. The coupling between adjacent strips is caculated, and the effect of finite resistivity discussed.

Remote control of open circuit voltage in a welding power supply

Abstract: A three-phase thyristor (42, 43) controlled welding output supply requiring only a single firing pulse of short duration per phase per half cycle is shown. Once a firing pulse has been provided (122), a holding impedance (40) connected between the output electrodes (32, 34) is provided to the neutral terminal (18) of a wye wound secondary (17) to provide a path for holding current independently of the load presented by the arc. An improved firing control circuit includes in addition to the normal firing capacitor (82), a negative phase angle impedance (86, 87, 88) attached to one end of a conventional breakdown device (117) used to fire a master thyristor gate (119). Stepped up voltage (60) is provided to the control circuit for greater noise immunity. Also shown is a remote control (151) for controlling a reversible motor (150) to drive through a slip clutch (140), the main voltage controlling variable impedance (80).

The Newton-Raphson Load Flow Applied to AC/DC Systems with Commutation Impedance

Abstract: Existing conditions in industrial ac-dc power systems may result in significant commutation resistances. If the resistance to reactance ratio of the commutation impedance is high, significant errors can result in load-flow studies which neglect the resistive portion. A method is presented for inclusion of a resistance-inductance fed bridge rectifier in a Newton-Raphson (N-R) load flow program. Polar form of the power flow equations is assumed. An example problem is provided for comparison.

High input impedance current conveyor filters

Abstract: Two new active RC canonic band pass filters are presented. The new configurations offer a very high input impedance and employ single grounded resistors for independent adjustments of ω0, Q and gain.

The Use of Complex Plane Plots in Studying the Electrical Response of Rocks

Abstract: Laboratory measurements have been made of the impedance of saturated samples of Berea Sandstone and Spirit River Formation sandstone throughout the frequency range of 5Hz to 13MHz. When the data from a saturated sample are presented as a complex impedance plot the frequency dispersion produces a “non-ideal” distribution of points in the form of a depressed and slightly distorted semicircle and an inclined straight line. It is possible to separate the low frequency electrode response from the bulk sample response, thereby isolating the effect of polarization at the sample/electrode interface. The frequency response of the sample can be modelled by an equivalent circuit proposed by RAISTRICK et al. (1976) which includes a frequency dependent admittance term. Different samples and varying levels of water saturation cause changes in the complex impedance plots which can be related to this admittance term. The form of this term and its significance with respect to rock properties needs further investigation.

Radio frequency network having plural electrically interconnected field effect transistor cells

Abstract: A radio frequency network is provided having a plurality of field effect transistor cells, each one of such cells having a reactive element, and coupling means for electrically interconnecting the plurality of field effect transistor cells, such coupling means having an impedance in accordance with the reactance of the reactive elements of the cells to provide such radio frequency network with a predetermined characteristic impedance related to the impedance of an input circuit which feeds radio frequency energy to an input one of the plurality of cells. With such arrangement the coupling means and the plurality of field effect transistor cells provide the radio frequency network with a predetermined characteristic impedance which is related to the impedance of the input circuit.

Impedance Measurement of the Electrical Structure of Skeletal Muscle

Abstract: The sections in this article are: 1 Methods and Techniques 1.1 Microelectrode Techniques 1.2 Analysis of Sinusoidal Data 1.3 Impedance Analysis With Fourier Techniques 1.4 Instrumentation Noise 1.5 Manipulation of Impedance Data 1.6 Theory and Curve Fitting 1.7 Electrical Models of the T System 1.8 Necessity for Morphometry 2 Results of Impedance Measurements 2.1 Impedance Measurements of Normal Frog Fibers 2.2 Other Preparations of Skeletal Muscle 2.3 Impedance Measurements of Muscle Fibers in Various Conditions 2.4 Comparison With Other Results 3 Discussion 3.1 Impedance Measurements of Nonlinearities 3.2 Other Methods