Showing papers on "Electrical impedance published in 1986"

Application of Kramers‐Kronig Transforms in the Analysis of Electrochemical Impedance Data II . Transformations in the Complex Plane

Abstract: Algorithms have been developed to apply the Kramers-Kronig transforms in the analysis of experimental electrochemical impedance data. The application of these algorithms is illustrated by transforming calculated impedance data for an electrical equivalent circuit, by transforming experimental data for TiO/sub 2-/coated carbon steel in HCl/KCl solution at 25/sup 0/C, and by analyzing data for an aluminum alloy in 4M KOH at 60/sup 0/C. These transforms, coupled with statistical techniques, provide a powerful means of evaluating the validity of impedance data with respect to spurious errors that are present in either the real or imaginary component, and with respect to system stability.

Quantification of membrane properties of trigeminal root ganglion neurons in guinea pigs.

Abstract: Passive and active (voltage- and time-dependent) membrane properties of trigeminal root ganglion neurons of decerebrate guinea pigs have been determined using frequency-domain analyses of small-amplitude perturbations of membrane voltage. The complex impedance functions of trigeminal ganglion neurons were computed from the ratios of the fast Fourier transforms of the intracellularly recorded voltage response from the neuron and of the input current, which had a defined oscillatory waveform. The impedance magnitude functions and corresponding impedance locus diagrams were fitted with various membrane models such that the passive and active properties were quantified. The complex impedances of less than one-quarter of the 105 neurons which were investigated extensively could be described by the complex impedance function for a simple RC-electrical circuit. In such neurons, the voltage responses to constant-current pulses, using conventional bridge-balance techniques, could be fitted with single exponential curves, also suggesting passive membrane behavior. A nonlinear least-squares fit of the complex impedance function for the simple model to the experimentally observed complex impedance yielded estimates of the resistance of the electrode, and of input capacitance (range, 56 to 490 pF) and input resistance (range, 0.8 to 30 M omega) of the neurons. The majority of trigeminal ganglion neurons were characterized by a resonance in the 50- to 250-Hz bandwidth of their impedance magnitude functions. Such neurons when injected with "large" hyperpolarizing current pulses using bridge-balance techniques showed membrane voltage responses that "sagged" (time-dependent rectification). Also, repetitive firing commonly occurred with depolarizing current pulses; this characteristic of neurons with resonance in their impedance magnitude functions was not observed in neurons with "purely" passive membrane behavior. A nonlinear least-squares fit of a five-parameter impedance fitting function based on a membrane model to the impedance locus diagram of a neuron with resonance yielded estimates of its membrane properties: input capacitance, the time-invariant part of the conductance, the conductance activated by the small oscillatory input current, and the relaxation time constant for this conductance. The ranges of the estimates for input capacitance and input resistance were comparable to the ranges of corresponding properties derived for neurons exhibiting "purely" passive behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Measurement of Eardrum Acoustic Impedance

Abstract: In this paper we describe a system which we have developed to measure cat ear canal specific acoustic impedance Z sp , magnitude and phase, as a function of frequency, for frequencies between 200 Hz and 33 kHz, and impedance magnitudes between 4.0 to 4.0×l05 rayles (MKS). The object to be measured is placed at the end of a 3.5 mm diameter sound delivery tube. After a simple calibration procedure, which determines the Thevenin parameters for the acoustic source transducer, the impedance may be calculated from the pressure measured at the orifice of the delivery tube with the unknown load in place. This procedure allows for a fast but accurate measure of a specific acoustic impedance. The system has been tested by measuring the impedance of a long cavity and comparing this response to the exact solution of the linearized Navier Stokes equations (acoustic equations including viscosity and thermal conduction). We have used this system to measure the impedance of the normal cat tympanic membrane in more than 30 cats. Healthy animals were found to have a real input impedance of ρc between 0.3 to 20.0 kHz. When the scala vestibuli was drained, the real part of the impedance dropped to less than ρc/10 for frequencies less than 3.0 kHz. Above 3 kHz, the impedance for the drained cochlea is best described by an open circuited transmission line.

Universal active filter using current conveyors

Abstract: A universal second-order active filter network employing CCII-type current conveyors is reported. The circuit offers wide bandwidth, high input impedance and independent control of ?0, Q and voltage gain with separate grounded resistors. The circuit also uses grounded capacitors and is therefore ideal for integration.

Eddy current surface mapping system for flaw detection

Abstract: A system and method for nondestructive testing of a part using eddy current impedance measuring techniques. An eddy current probe is positioned above the surface of the part for measuring an induced eddy current signal and generating an electrical signal representative thereof. A first and second movement signal is generated representative of a first and second scan direction of the probe. Relative movement is effected between the probe and the part, whereby the probe scans the part for producing electrical signals varying as a function of eddy current signal. The electrical signals are converted to mutually perpendicular drive signals representative of the eddy current signature at a corresponding location of the part. The first and second movement signals are combined with the mutually perpendicular drive signals of and second composite signal which varies as a function of the movement of the probe and eddy current signal. The first and second composite signals are applied to a display means for generating a three-dimensional image representative of irregularities in the part.

A Printed-Circuit Hybrid-Ring Directional Coupler for Arbitrary Power Divisions

Abstract: A directional coupler in the form of a hybrid ring particularly suited for printed circuits is described. The maximum power-split ratio between the two output ports of a printed-circuit conventional hybrid-ring coupler is limited by the highest impedance line that can be realized [1]. The hybrid-ring directional coupler described in this paper allows a larger power-split ratio for the same impedance lines, and thereby increases the range of the power-split ratio that can be realized for printed circuits. A theoretical analysis was conducted using the scattering matrix, and experimental verification of the theoretical results was achieved in a stripline configuration at Ku-band.

Application of Impedance Spectroscopy to Materials Science

Abstract: In this article the term "impedance spectroscopy" is used to describe any technique in which data, equivalent to the real and imaginary parts of a complex electrical quantity, are measured as a function of frequency. The frequency range involved here is from about 1 04 to about 106 Hz. The complex electrical quantity may be impedance, conductance, permittivity, electric modulus, etc . Although the most widely used data acquisition technique is single-point detection in the frequency domain, measurement methods based on injection of multiple frequencies, Fourier trans­ formation from the time domain, and analysis of noise spectra are not excluded. The results, however, will always be presented and discussed in the frequency domain. In recent years, acquisition of impedance spectra has been dramatically simplified, first by automatic phase-sensitive detectors, and second by direct digital sampling of signals . For the deter­ mination of bulk properties, such as ionic conductivity, two point measure­ ments are adequate; but for s tudies of interfacial phenomena three elec­ trode measurements are usually made, often via a potentiostat, which allows the de bias at the electrode/electrolyte interface to be independently varied. Depending on the relative values of the sample and lead impedances compared with the input impedance of the measuring system, varymg amounts of care may have to be taken to avoid spurious effects.

Protection system for preventing defibrillation with incorrect or improperly connected electrodes

Abstract: A protection circuit for a defibrillator that prevents a defibrillator pulse from being generated if the impedance between the defibrillator's electrode leads is not characteristic of the impedance between a pair of defibrillator electrodes properly connected to the defibrillator. The impedance measuring circuit applies a current to the electrode leads and the resulting voltage is measured to provide an indication of the electrode's impedance. The current is applied between the electrodes at about 33 kHz to approximate the impedance between a pair of defibrillator electrodes during a defibrillation pulse. The output of the measurement circuit is converted to an 8 bit word by an analog-to-digital converter and read by a microprocessor which compares the measured impedance to various impedance values in order to either generate an enable signal for the defibrillator or display messages indicative of open or short circuited electrode leads or a patient monitoring electrode connected to the electrode leads. the impedance measurement circuit operates in either of two ranges which are selected by the microprocessor on the basis of the measured impedance values.

Transfer function technique for impedance and absorption measurements in an impedance tube using a single microphone

Abstract: Using a periodic pseudorandom sequence as the noise source, it is possible to implement the two‐microphone transfer function technique for impedance and absorption measurement in an impedance tube with a single microphone, thereby eliminating the elaborate calibrating procedure and any error associated with phase‐mismatching. Results obtained by the proposed procedure compared well with those obtained by the standard standing‐wave‐ratio method.

Characteristic Impedance of Integrated Circuit Bond Wires (Short Paper)

Abstract: In microwave circuit analysis, bond wires are frequently modeled as lumped elements or sections of microstrip. These models are insufficient since part of the wire is suspended above the substrate. This paper shows numerical results that provide the line impedance and effective dielectric constant for a round wire above a grounded dielectric substrate.

Uniform intensity led driver circuit

Abstract: A unique driver circuit for providing constant average current through a driven element or elements having varying impedance first samples the impedance at the drive terminal in order to determine impedance of the driven elements. For increasing impedance of the driven elements, the duty cycle of the driving signal is increased, thereby resulting in a near-constant average current through the driven elements when the number of driven elements in series is changed.

Inductive impedance of a spirally wound Li/MoS2 cell

Abstract: The impedance of cylindrical lithium molybdenum disulfide cells has been measured in the frequency range of 1 kHz to 10 MHz. In this frequency range, it is shown that the inductance associated with the spiral geometry of the cell electrodes contributes significantly to the cell impedance. It is also shown that the resistive component of the impedance at high frequency is attributable in part to damping of induced currents in the can and central mandrel of the cell, and to radial ion flow between electrodes in the spiral winding.

Circuit layout for an infrared room surveillance detector

Abstract: A circuit layout operating in the current mode for an infrared room surveillance detector includes a high impedance operational amplifier connected directly to a pyroelement used as an infrared sensor. This results in a high sensitivity detector circuit with a low noise component in the detector output signal and maintaining a high impedance detector circuit. The detector circuit has a constant amplification over a relatively broad frequency range. The reaction resistor of the operational amplifier is chosen to have a high impedance, preferably in a range higher than 1011 Ohm. It is advantageous to take the reference voltage required for the evaluation of the detector output signal from the operational amplifier, so that aside from the simplified circuit layout, no further structural parts capable of increasing the interference sensitivity of the detector circuit are required. To further increase the electromagnetic compatibility, the threshold value comparator stage may also be located in the detector housing.

Method for calculating the properties of coupled-cavity slow-wave structures from their dimensions

Abstract: In the development of computer models of coupled-cavity travelling wave tubes, it is necessary to have some means of calculating the properties of the slow-wave structure. Direct calculation is difficult because of the complexity of the shapes involved. One possible method makes use of the equivalent circuit representation of the slow-wave structure. In the paper it is shown that the parameters of the equivalent circuit can be calculated from the dimensions of the structure. Once these parameters are known, it is very quick and easy to compute the phase change per cavity and the interaction impedance at any frequency. The results obtained by this method are compared with those of experiment and it is shown that useful accuracy can be obtained.

Temperature control in which the control parameter is the degree of imperfection in the impedance matching

Abstract: A temperature control system is disclosed for controlling heating current to a heater having an impedance which varies substantially with temperature. The change in impedance of the heater changes the degree of mismatch between the power transmission system and the heater resulting in a change in the voltage which is reflected back to the power transmission system. The reflected voltage is monitored and its magnitude compared to a reference source and the power to the heater is controlled in response to this comparison.

Wideband transmission line signal combiner/divider

Abstract: RF signals may be split or combined across a wide band of frequencies with low insertion losses, large isolation between input ports, and low voltage standing wave ratio by means of coaxial transmission line sections interconnected in a bridge configuration. Even mode impedances between the cable shield and the common ground plane may be eliminated by placing ferrite sleeves on each line section. Impedance transformations introduced by the splitter/combiner are counteracted by a coaxial line impedance transformer.

Nonvolatile reprogrammable electronic potentiometer.

Abstract: A variable impedance circuit for use in an external circuit whereby the impedance may be altered by the external circuit has a plurality of two terminal impedance elements (12) connected in series. A node (42, 43, 55) is provided between each pair of impedance elements in the series chain (40). The first impedance element (13) and the last impedance element (15) in the series chain (40) are connected to terminals (14, 16), at least one of which is accessible for connection to the external circuit. Each of the nodes (42, 43, 55) may be connected to a terminal (18) which is also accessible for connection to the external circuit. An electrically reprogrammed read-only memory (25) stores the identity of the nde connected such that the identity of this node is retained when power is removed from the variable impedance circuit. When power is returned to the circuit, the node which was previously connected to the terminal is automatically reconnected.

Dual-frequency modified C/V technique

Abstract: A technique is presented which allows the carrier density profile to be obtained from very leaky Schottky-barrier devices. Measurements of the impedance as a function, of applied reverse voltage for two frequencies are combined to yield the depletion layer capacitance, along with expressions for the parasitic series and shunt resistances. The technique is easily extendable to MOS devices.

Impedance matched, high-power, rf antenna for ion cyclotron resonance heating of a plasma

Abstract: A resonant double loop radio frequency (rf) antenna for radiating high-power rf energy into a magnetically confined plasma. An inductive element in the form of a large current strap, forming the radiating element, is connected between two variable capacitors to form a resonant circuit. A real input impedance results from tapping into the resonant circuit along the inductive element, generally near the midpoint thereof. The impedance can be matched to the source impedance by adjusting the separate capacitors for a given tap arrangement or by keeping the two capacitances fixed and adjustng the tap position. This results in a substantial reduction in the voltage and current in the transmission system to the antenna compared to unmatched antennas. Because the complete circuit loop consisting of the two capacitors and the inductive element is resonant, current flows in the same direction along the entire length of the radiating element and is approximately equal in each branch of the circuit. Unidirectional current flow permits excitation of low order poloidal modes which penetrate more deeply into the plasma.

Impedance of a horizontal coil above a conducting half-space

Abstract: The induction of eddy currents by a circular, air-cooled coil of rectangular cross section, carrying a low-frequency alternating current and with its axis parallel to the surface of a homogeneous conducting half-space is considered. An exact, closed-form expression for the coil impedance is derived. The calculations are in excellent agreement with experiment and agree with an independent calculation of coil impedance which is valid in the limit of small skin depth.

Staggered ground-plane microstrip transmission line

Abstract: A microstrip transmission line comprises a plurality of signal-carrying lines disposed along a dielectric ribbon and separated by a predetermined spacing. Ground-plane conductors are disposed on the opposite side of the ribbon in staggered relation to the signal-carrying lines such that the ground-plane conductors occupy spaces corresponding to the gaps between adjacent signal-carrying lines. This arrangement lowers the capacitance and raises the impedance of the transmission line while maintaining high signal line density.

Impedance of metal-solid electrolyte interfaces☆

Abstract: High frequency impedance measurements using a reflectometer measuring the impedance of a body disposed between two electrodes, by means of two bidirectional couplers connected by controlled variable attenuators to a mixer circuit determining the modulus and the phase of the coefficient of the reflection due to the load, independently of the power level of the generator.

High frequency impedance measuring apparatus using two bidirectional couplers

Abstract: High frequency impedance measurements using a reflectometer measuring the impedance of a body disposed between two electrodes, by means of two bidirectional couplers connected by controlled variable attenuators to a mixer circuit determining the modulus and the phase of the coefficient of the reflection due to the load, independently of the power level of the generator.

Dual band antenna having separate matched inputs for each band

Abstract: This dual input antenna system has a first input which provides an impedance match over a first range of frequencies and a second input which provides an impedance match over a second range of frequencies. This effectively enables a narrow band antenna to operate and provide a matched condition at two separate frequency ranges. First and second longitudinal radiating elements are connected at respective ends by an approximate 1/2 wavelength transmission line. The other end of each radiating element is connected by transmission lines to a receive filter and transmit filter, respectively. The receive and transmit filters provide a substantial reactance outside of the respective passbands. The wavelengths of the first and second transmission lines are selected to transform the reactance of each filter into a value which will provide a match condition for the other transmission line at the respective frequency ranges.