Showing papers on "Electrical impedance published in 2000"

Polarization Resistance Method for Determination of Instantaneous Corrosion Rates

Abstract: The polarization resistance method for the determination of instantaneous corrosion rates of metals were reviewed. The assumptions in electrode kinetics that govern the connection between the slope of steady-state applied electrochemical potential-applied current density (Eapp-iapp) measurements (i.e., the polarization resistance) and the corrosion rate were restated. Electrochemical impedance, as well as statistical and spectral electrochemical noise methods for obtaining polarization resistance, also were discussed. Traditional sources of error such as high excitation voltage amplitudes, insufficiently slow voltage ramp rates, high alternating current (AC) frequencies, inadequate polarization hold periods, high solution resistance, presence of parallel reduction-oxidation reactions, and nonuniform current and potential distributions were examined with the goal of defining some of the conditions and circumstances where these complicating factors are important. Other complicating factors such as ...

Influence of the boundaries in the impedance of porous film electrodes

Abstract: This paper presents an enhanced model for the impedance of porous film electrodes. The impedance of a transmission line with two transport channels, a crosswise element and arbitrary terminal loads is solved analytically. The local impedances at the boundaries represent a frequency-dependent response of the blocking of ionic and electronic charge carriers at the two faces of the electrode region. A general expression is found that contains, as particular cases, a number of models of impedance for porous electrodes used in the literature. Some examples of the generalised transmission line illustrate the use of the model in the interpretation of experimental data. First, a polarisable electrode showing low-frequency dispersion of the constant phase element (CPE) type is analysed, and diagnosis criteria are derived to recognise whether the dispersion is caused by the boundary or the inner surface. Secondly, the manifestation in the impedance of the failure of a porous electrode due to direct charge transfer between the substrate and a redox couple in solution is investigated.

Method and apparatus for monitoring and controlling tissue temperature and lesion formation in radio-frequency ablation procedures

Abstract: Impedance and capacitance-related parameters are monitored in the electrical circuit of a tissue-ablation apparatus wherein RF electrical power is administered at predetermined frequencies Tissue temperature has been found to correlate well with low-frequency impedance, or with the resistive component of impedance at any frequency Therefore, one or both of these parameters are calculated and tracked during the ablation procedure to estimate tissue temperature Similarly, tissue lesion formation has been found to correlate well with changes in the capacitive component of tissue impedance Thus, this parameter can be used to track tissue lesion formation during the ablation procedure The ratio of tissue-to-blood interface with the ablation electrode is estimated by measuring impedance at a very low frequency and a very high frequency The difference between these two values divided by the high-frequency value is taken to be a measure of such ratio Alternatively, other electrical parameters indicative of changes in the capacitive component of the system may be measured and the ratio is calculated as a function of these changes with respect to a baseline value

An Integrated Health Monitoring Technique Using Structural Impedance Sensors

Abstract: This paper presents an integrated methodology to detect and locate structural damage. Two different damage detection schemes are combined in this methodology, which involves utilizing the electromechanical coupling property of piezoelectric materials and tracking the changes in the frequency response function data, respectively. Physical changes in the structure cause changes in mechanical impedance. Due to the electromechanical coupling in piezoelectric materials, this change in structural mechanical impedance causes a change in the electrical impedance of the piezoelectric sensor. Hence, by monitoring the electrical impedance one can qualitatively determine when structural damage has occurred or is imminent. Based on the fact that damage produces local dynamic changes, this technique utilizes a high frequency structural excitation (typically greater than 30 kHz) through the surface-bonded piezoelectric sensor/actuators. As a second step, a newly developed model-based technique, using a wave propagation ...

Automatic activation of electrosurgical generator bipolar output

Abstract: An automatic circuit that controls a surgical instrument having a pair of bipolar electrodes. The circuit comprises means for measuring the current between the pair of electrodes, an impedance detection circuit in electrical communication with the current measuring means, a comparator in electrical communication with the impedance detection circuit and a controller electrically connected to the comparator. The impedance detection circuit calculates the impedance between the electrodes based on the measured current and generates a first signal indicative of the calculated impedance. The comparator processes the first signal and generates an activation signal if the calculated impedance falls within a predetermined range of impedance values and generates a deactivation signal if the calculated impedance exceeds a deactivation threshold. The controller receives the activation and deactivation signals and transmits a first control signal to a radiofrequency energy output stage to activate the electrodes in response to the activation signal and transmits a second control signal to the radiofrequency output stage to deactivate the electrodes in response to the deactivation signal.

Method and system for controlling radio frequency radiation in microelectronic packages using heat dissipation structures

Abstract: A method and apparatus are disclosed for attenuating RF noise produced by electronic systems by providing low RF impedance shorting of heat dissipating structures, such as heat sinks, to PCB reference planes. The RF impedance shorting path uses existing package pins with dedicated electrical paths through the package to the bottom surface of the heat sink. Such an arrangement provides very low RF impedance because of the minimal length and resistance of the shorting path, and also provides minimal disruption of the PCB design rules and tolerances by using existing package leads.

Controlled electroporation and mass transfer across cell membranes

Abstract: Electroporation is performed in a controlled manner in either individual or multiple biological cells or biological tissue by monitoring the electrical impedance, defined herein as the ratio of current to voltage in the electroporation cell. The impedance detects the onset of electroporation in the biological cell(s), and this information is used to control the intensity and duration of the voltage to assure that electroporation has occurred without destroying the cell(s). This is applicable to electroporation in general. In addition, a particular method and apparatus are disclosed in which electroporation and/or mass transfer across a cell membrane are accomplished by securing a cell across an opening in a barrier between two chambers such that the cell closes the opening. The barrier is either electrically insulating, impermeable to the solute, or both, depending on whether pore formation, diffusive transport of the solute across the membrane, or both are sought. Electroporation is achieved by applying a voltage between the two chambers, and diffusive transport is achieved either by a difference in solute concentration between the liquids surrounding the cell and the cell interior or by a differential in concentration between the two chambers themselves. Electric current and diffusive transport are restricted to a flow path that passes through the opening.

Computer Simulations of the Impedance Response of Lithium Rechargeable Batteries

Abstract: A mathematical model is developed to simulate the impedance response of a wide range of lithium rechargeable battery systems. The mathematical model is a macroscopic model of a full‐cell sandwich utilizing porous electrode theory to treat the electrode region and concentrated solution theory for transport processes in solution. Insertion processes are described with charge‐transfer kinetic expressions and solid‐phase diffusion of lithium into the active electrode material. The impedance model assumes steady‐state conditions and a linear response with the perturbation applied about the open‐circuit condition for the battery. The simulated impedance response of a specific system, the lithium‐polymer cell , is analyzed in more detail to illustrate several features of the impedance behavior. Particular attention is paid to the measurement of solid‐phase lithium‐ion diffusion coefficients in the insertion electrodes using impedance techniques. A number of complications that can lead to errors in diffusion‐coefficient measurements based on impedance techniques are discussed. © 2000 The Electrochemical Society. All rights reserved.

A micropower dry-electrode ECG preamplifier

Abstract: This paper describes the development of a very low-power preamplifier intended for use in pasteless-electrode recording of the human electrocardiogram. The expected input signal range is 100 /spl mu/V-10 mV from a lead-II electrode configuration. The amplifier provides a gain of 43 dB in a 3-dB bandwidth of 0.05 Hz-2 kHz with a defined high input impedance of 75 M/spl Omega/. It uses a driven common electrode to enhance rejection of common-mode interfering signals, including low-frequency motion artifact, achieving a common-mode rejection ratio (CMRR) of better than 80 dB over its entire bandwidth. The gain and phase characteristics meet the recommendations of the American Heart Association, ensuring low distortion of the output ECG signal and making it suitable for clinical monitoring. The amplifier has a power consumption of 30 /spl mu/W operating from a 3.3-V battery and is intended for use in small, lightweight, portable electrocardiographic equipment and heart-rate monitoring instrumentation.

Silicon equivalent ptc circuit

Abstract: A series current regulator with an on-silicon temperature sensor (102) formed over current battery protection device (100) The protection device (100) regulates current in a pass element (101) linearly while sensing the junction temperature of the pass element (101) If the temperature of the pass element (101) reaches a predetermined threshold, the on-silicon temperature sensor (102) actuates a switch (104) which causes the pass element (101) to go into a high impedance mode The protection device offers advantages over positive temperature coefficient (PTC) and further includes faster trip time and lower leakage current

Non-linear light-emitting load current control

Abstract: A sensor circuit for detecting a current supplied to a non-linear light-emitting diode (LED) and for producing a current reading dependent on temperature. The sensor circuit comprises first and second serially interconnected resistors also connected in series with the LED, and a temperature-dependent impedance connected in parallel with one of the first and second resistors. At least a portion of the current through the LED flows through the sensor circuit to enable the first and second serially interconnected resistors and said temperature-dependent impedance to produce a variable voltage signal representative of the current through the LED and dependent on temperature.

High frequency conductivity of the high-mobility two-dimensional electron gas

Abstract: We measure the real and imaginary conductivity sigma(k = 0,omega) of a high-mobility two-dimensional electron gas (2DEG) system at frequencies below and above the momentum scattering rate. The imaginary part of the 2DEG impedance is observed to be inductive, consistent with the Drude model. Using this kinetic inductance, we construct a transmission line by capacitively coupling the 2DEG to an Al Schottky barrier gate separated by 5000 A from the 2DEG. The measured wave velocity and temperature-dependent damping of this transmission line are in good agreement with a simple Drude model. Exciting these modes is equivalent to exciting a 2D plasma mode strongly modified by the interaction between the 2DEG and the gate.

Cell/tissue analysis via controlled electroporation

Abstract: An electrical current is created across an electrically conductive medium comprising a cell which may be part of a tissue of a living organism. A first electrical parameter which may be current, voltage, or electrical impedance is measured. A second electrical parameter which may be current, voltage or a combination of both is then adjusted and/or analyzed. Adjustments are carried out to facilitate analysis and/or obtain a desired degree of electroporation. Analysis is carried out to determine characteristics of the cell membrane and/or tissue.

Method and apparatus for linear amplification of a radio frequency signal

Abstract: A method and apparatus is provided that amplitude modulates a modulated radio frequency (RF) signal (411) by modulating the supply voltage of a power amplifier (410). The method and apparatus further provide an impedance modulator (412) that reduces output signal (415) errors in response to an error signal generated by a feedback circuit (416) that includes a quadrature modulator (506), a limiter (520), a comparator (502), and a quadrature downconverter (510). Intermodulation distortion generated in the feedback circuit (416) by delay mismatches between amplitude and phase feedback paths, and non-linear effects of AM/PM conversion in a limiter (520), are suppressed by placing limiter (520) and quadrature downconverter (510) in a forward path of the overall amplifier loop.

The Foster reactance theorem for antennas and radiation Q

Abstract: The calculation of antenna Q has been an interesting and a controversial topic for years. We first give a rigorous study of antenna Q by introducing a complete description of the complex power balance relation for an antenna system. Using the complex Poynting theorem, we have shown that the antenna is essentially equivalent to a one port lossy network. The Foster reactance theorem is usually stated for a lossless network. The main purpose of this paper is to determine whether the Foster reactance theorem holds for antennas. By making use of a complex frequency domain version of the Poynting theorem, we have shown that the Foster reactance theorem is valid for an antenna. Finally, the Foster reactance theorem for the antenna has been applied to demonstrate the widely held assumption Q/spl ap/1/B, provided Q/spl Gt/1, where B stands for the fractional bandwidth of an arbitrary antenna.

Conformal strip excitation of dielectric resonator antenna

Abstract: A new excitation scheme that employs a conducting conformal strip is proposed for dielectric resonator antenna (DRA) excitation. The new excitation scheme is successfully demonstrated by using a hemispherical DRA whose exact Green function is found using the mode-matching method. The moment method is used to solve the unknown strip current from which the input impedance is obtained. Novel recurrence formulas were obtained so that the impedance integrals are evaluated analytically. This solves the singularity problem of the Green function and substantially reduces the computation time. An experiment was carried out to verify the theory. The co- and cross-polarized field patterns are also shown. In addition, an experimental technique which deals with the problem of an air gap between the DRA and the ground plane is presented.

An electrochemical impedance measurement technique employing Fourier transform

Abstract: We describe a novel technique for measuring electrochemical impedance, in which the electrode potential is ramped to a desired bias potential and a small potential step is applied to the working electrode after a short time delay. Fourier transform of the first derivative of the current signal thus obtained provides ac currents in the frequency domain, which allows the computation of impedances of the electrode/electrolyte interface in the whole frequency range. A home-built data acquisition system for these measurements and the results obtained therefrom were used for the measurements. The advantage of the technique includes an extremely short time of less than 1 ms for impedance measurements in the whole frequency region while equilibrium conditions of the electrochemical system are being maintained before and after the measurements, among many others. This technique is expected to revolutionize electrochemical measurements and to find important applications such as in situ measurements during battery cycling, corrosion testing, and other electrochemical experiments.

Tunable impedance surface

Abstract: A tuneable impedance surface for steering and/or focusing a radio frequency beam. The tunable surface comprises a ground plane; a plurality of elements disposed a distance from the ground plane, the distance being less than a wavelength of the radio frequency beam; and a capacitor arrangement for controllably varying the capacitance of at least selected ones of adjacent elements. A method of tuning the high impedance surface allows the surface to mimic, for example, a parabolic reflector or a diffraction grating.

Impedance measurements of bodily matter

Abstract: A method and apparatus for generating an impedance spectrum which is characteristic of a sample of bodily matter in a resonant circuit and which may be used to analyse the sample.

Radio frequency coil for open magnetic resonance imaging system

Abstract: A quadrature coil suitable for use with an open frame MRI system provides crossing pairs of arrays of parallel conductor elements, respectively. Compact configuration is provided through use of an isolating circuit for incorporating parasitic capacitances at the resonance frequency of the coil into a blocking parallel resonance. Termination of the parallel conductor elements may be accomplished by equal impedance node connectors formed from branching pairs of conductors or a triangular least resistance connection form. RF shields are provided by pairs of conductive sheets containing eddy current reducing slots aligned with the parallel conductors elements of the coil.

Microfabricated AC impedance sensor

Abstract: A microfabricated instrument for detecting and identifying cells and other particles based on alternating current (AC) impedance measurements. The microfabricated AC impedance sensor includes two critical elements: 1) a microfluidic chip, preferably of glass substrates, having at least one microchannel therein and with electrodes patterned on both substrates, and 2) electrical circuits that connect to the electrodes on the microfluidic chip and detect signals associated with particles traveling down the microchannels. These circuits enable multiple AC impedance measurements of individual particles at high throughput rates with sufficient resolution to identify different particle and cell types as appropriate for environmental detection and clinical diagnostic applications.

Filter structures for integrated circuit interfaces

Abstract: A method of optimizing the frequency response of an interconnect system of the type which conveys high frequency signals between bond pads of separate integrated circuits (ICs) mounted on a printed circuit board (PCB) through inductive conductors, such as bond wires and package legs, and a trace on the surface of the PCB. To improve the interconnect system, capacitance is added to the trace and inductance is added to the conductors, with the added trace capacitance and conductor inductance being appropriately sized relative to one another and to various other interconnect system impedances to optimize the interconnect system impedance matching frequency response.

High bandwidth passive integrated circuit tester probe card assembly

Abstract: Described herein is a probe card assembly providing signal paths for conveying high frequency signals between bond pads of an integrated circuit (IC) and an IC tester. The frequency response of the probe card assembly is optimized by appropriately distributing, adjusting and impedance matching resistive, capacitive and inductive impedance values along the signal paths so that the interconnect system behaves as an appropriately tuned Butterworth or Chebyshev filter.

Fiber-edge electrooptic/magnetooptic probe for spectral-domain analysis of electromagnetic field

Abstract: We propose a new class of an electromagnetic-held probing scheme for microwave planar circuit diagnosis. The measurement principle is based on the electrooptic/magnetooptic effects of crystals glued at optical fiber facets. We have combined the concept of those fiber-edge probes with a fiber-optic RF spectrum analyzing system containing a continuous-wave semiconductor laser source, a fast photodetector, and an RF spectrum analyzer to realize a highly sensitive measurement equipment of local impedance. Electromagnetic-field intensity on a microstrip transmission line has been measured in the frequency domain, where voltage and current amplitudes have been independently investigated with sensitivities of 16 mV/Hz-1/2 and 0.33 mA/Hz-1/2, respectively. In addition, it has been shown that the former value can be improved to be 0.7 mV/Hz-1/2 or smaller by the resonant cavity enhancement effect.

Impedance characteristics of planar bow-tie-like monopole antennas

Abstract: The impedance characteristics of planar bow-tie-like monopole antennas have been studied experimentally. The planar bow-tie-like monopole antenna achieves a broad bandwidth, typically of >75%. A modified formula is suggested to accurately evaluate the frequency corresponding to the lower edge of the impedance bandwidth.

Digital fault location for parallel double-circuit multi-terminal transmission lines

Abstract: Two new methods are proposed for fault point location in parallel double-circuit multi-terminal transmission lines by using voltages and currents information from CCVTs and CTs at all terminal. These algorithms take advantage of the fact that the sum of currents flowing into a fault section equals the sum of the currents at all terminals. Algorithm 1 employs an impedance calculation and algorithm 2 employs the current diversion ratio method. Computer simulations are carried out and applications of the proposed methods are discussed. Both algorithms can be applied to all types of fault such as phase-to-ground and phase-to-phase faults. As one equation can be used for all types of fault, classification of fault types and selection of faulted phase are not required. Phase components of the line impedance are used directly, so compensation of unbalanced line impedance is not required.