Showing papers on "Electrical impedance published in 1998"

Method and system for heating solid tissue

Abstract: Methods for heating tissue by delivering radio frequency energy through tissue electrodes comprise controlling energy delivery so that an abrupt increase in impedance between the electrodes and the tissue is observed, typically in the form of an abrupt decrease in power delivered to the electrodes. The power at which the impedance increases and/or the time required to induce such an increase in impedance, are relied on to determine acceptable ranges to achieve a maximum sustainable delivery of radio frequency energy to the tissue consistent with complete, rapid, and uniform heating of the tissue.

Liquid-crystal adaptive lenses with modal control.

Abstract: We report on a novel approach to the realization of nematic liquid-crystal (LC) phase correctors to form spherical and cylindrical wave fronts. A LC cell with a distributed reactive electrical impedance was driven by an ac voltage applied to the cell boundary to yield the desired spatial distribution of the refractive index. The two-dimensional function of the phase delay introduced into the light beam depends on the frequency of the ac control voltage, the geometry of the boundary electrode surrounding the LC cell, and the electrical parameters of the cell. We realized a cylindrical adaptive lens with a clear aperture of 15 mm x 4mm and a spherical adaptive lens with circular aperture of 6.5 mm. Both devices are capable of focusing collimated light in the range infinity...0.5 m.

High frequency surgical apparatus with tracking of impedance measurement

Abstract: The HF surgical instrument (21) with a HF generator (11), is connectable with at least one active electrode (12) output (13) and at least one neutral electrode (14) - output (15), at which at least one part neutral electrode (14a) of a neutral electrode pair (14a,14b) can be connected. The individual electrodes (14a,14b) of which are connected at an auxiliary voltage with a marked lower frequency than the HF. A monitoring circuit from the auxiliary voltage and the auxiliary current flowing between the part neutral electrodes produces an impedance signal (19) representative for the impedance between the part neutral electrodes. With the exceeding of the first fixed upper alarm threshold (17) and/or a lower second upper alarm threshold (20) matchable to the actual value of the impedance signal, for the impedance signal (19) delivers a HF generator blocking signal (22) and/or an alarm signal (23). The matching of the second alarm threshold (20) is carried out by pressing a SET push button (24).

Conducted electromagnetic emissions in induction motor drive systems. II. Frequency domain models

Abstract: For pt.I see ibid., vol.13, no.4, p.757-67 (1998). Predicting conducted emissions in pulsewidth modulation (PWM) inverter induction motor drive systems requires various frequency-dependent effects to be considered. A frequency domain method has advantages in such cases compared to a time domain approach. Based on the modal analysis presented in Part I, this paper develops frequency domain models to evaluate the spectra of the conducted emissions directly. The common and differential mode excitation sources are modeled in the frequency domain and related to the switching functions of the PWM inverter. Network models are established where the induction motor is represented using its frequency-dependent impedance characteristics, which can be obtained from measurements. The influences of system unbalances and of transmission-line effects due to long cables are investigated. Predicted emission spectra are compared with laboratory measurements and those derived from the time domain simulation. It is found that the agreement is good. The proposed method allows emission spectra to be predicted without recourse to specialist circuit simulators.

Qualitative impedance-based health monitoring of civil infrastructures

Abstract: This paper presents a qualitative health monitoring technique to be used in real-time damage evaluation of civil infrastructures such as bridge joints. The basic principle of the technique is to monitor the structural mechanical impedance which will be changed by the presence of structural damage. The mechanical impedance variations are monitored by measuring the electrical impedance of a bonded piezoelectric actuator/sensor patch. This mechanical-electrical impedance relation is due to the electromechanical coupling property of piezoelectric materials. This health monitoring technique can be easily adapted to existing structures, since only a small PZT patch is needed, giving the structure the ability to constantly monitor its own structural integrity. This impedance-based method operates at high frequencies (above 50 kHz), which enables it to detect incipient-type damage and is not confused by normal operating conditions, vibrations, changes in the structure or changes in the host external body. This health monitoring technique has been applied successfully to a variety of light structures. However, the usefulness of the technique for massive structures needs to be verified experimentally. For this purpose, a 500 lb quarter-scale deck truss bridge joint was built and used in this experimental investigation. The localized sensing area is still observed, but the impedance variations due to incipient damage are slightly different. Nevertheless, by converting the impedance measurements into a scalar damage index, the real-time implementation of the impedance-based technique has been proven feasible.

Broadband impedance matching probe

Abstract: A probe for testing integrated circuits at microwave frequencies employs a tapered coaxial transmission line to transform the impedance at the probe tips (12) to the impedance of the test instruments. Mechanically resilient probe tip structures (12) allow reliable probing of non-planar circuits and the elastic probe body allows large overprobing without damage to the test circuit. Novel insulator structures (13) for the coaxial line allow easy and accurate assembly and high performance.

A Kalman filter approach to track fast impedance changes in electrical impedance tomography

Abstract: In electrical impedance tomography (EIT), an estimate for the cross-sectional impedance distribution is obtained from the body by using current and voltage measurements made from the boundary. All well-known reconstruction algorithms use a full set of independent current patterns for each reconstruction. In some applications, the impedance changes may be so fast that information on the time evolution of the impedance distribution is either lost or severely blurred. Here, the authors propose an algorithm for EIT reconstruction that is able to track fast changes in the impedance distribution. The method is based on the formulation of EIT as a state-estimation problem and the recursive estimation of the state with the aid of the Kalman filter. The performance of the proposed method is evaluated with a simulation of human thorax in a situation in which the impedances of the ventricles change rapidly. The authors show that with optimal current patterns and proper parameterization, the proposed approach yields significant enhancement of the temporal resolution over the conventional reconstruction strategy.

Differential signal transmission circuit

Abstract: Differential signal transmission circuit for transmitting a high speed signal through a differential transmission line with: a CMOS (complementary metal oxide semiconductor) differential driver for receiving a transmitted from an LSI for high speed signal and passing the signal to a differential transmission cable; and an impedance matching circuit provided between an output of the CMOS differential driver and ground to reduce an output impedance of the CMOS differential driver; wherein said impedance matching circuit comprises a series termination circuit which is provided between the output of the CMOS differential driver and the differential transmission cable, and a pair of parallel resistors, which are provided between the output of the CMOS differential driver and mass which, with the sum of the resistance of series termination circuit and an overall impedance is adjusted at the output of the CMOS differential driver to a characteristic impedance of the differential transmission cable, and wherein the total impedance at the output of the CMOS differential driver is set by the parallel resistors.

Self-excited induction generator with excellent voltage and frequency control

Abstract: A capacitor-excited induction generator used with a hydraulic turbine in a stand-alone generating system can provide a high quality voltage and frequency control not matched by other small generating units. This is achieved without a turbine governor by using a controllable additional impedance on the load side. The control is achieved using a static converter. The analysis of the system and the design of the power and control system are presented. Measurements from an experimental unit are provided to verify the predicted performance.

Investigation of the electrical properties of SnO2 varistor system using impedance spectroscopy

Abstract: The electrical properties of tin oxide varistors doped with CoO, Nb2O5, and Cr2O3, were investigated using the impedance spectroscopy technique with the temperature ranging from 25 to 400 °C. The impedance data, represented by means of Nyquist diagrams, show two time constants with different activation energies, one at low frequencies and the other at high frequencies. These activation energies were associated with the adsorption and reaction of O2 species at the grain boundary interface. The Arrhenius plots show two slopes with a turnover at 200 °C for both the higher and lower frequency time constants. This behavior can be related with the decrease of minor charge carrier density. The barrier formation mechanism was associated with the presence of CrSn⋅ at the surface, which promotes the adsorption of the O′ and O″ species which are in turn proposed as being responsible for the barrier formation.

Figures of merit to characterize the importance of on-chip inductance

Abstract: A closed form solution for the output signal of a CMOS inverter driving an RLC transmission line is presented. This solution is based on the alpha power law for deep submicrometer technologies. Two figures of merit are presented that are useful for determining if a section of interconnect should be modeled as either an RLC or an RC impedance. The damping factor of a lumped RLC circuit is shown to be a useful figure of merit. The second useful figure of merit considered in this paper is the ratio of the rise time of the input signal at the driver of an interconnect line to the time of flight of the signals across the line, AS/X circuit simulations of an RLC transmission line and a five section RC II circuit based on a 0.25 /spl mu/m IBM CMOS technology are used to quantify and determine the relative accuracy of an RC model. One primary result of this study is evidence demonstrating that a range for the length of the interconnect exists for which inductance effects are prominent. Furthermore, it is shown that under certain conditions, inductance effects are negligible despite the length of the section of interconnect.

Direct drive backlight system

Abstract: A power conversion circuit drives a cold cathode fluorescent lamp (CCFL) while requiring minimal number of external components. The circuit includes a controller, a direct drive network responsive to control inputs from the controller and coupled to receive a power signal, and a secondary network coupled to the CCFL. The direct drive network is low Q circuit comprising a plurality of switching transistors and a primary winding of a transformer such that an impedance of the direct drive network consists essentially of an inductance of the primary winding and capacitance of the direct drive network consists essentially of parasitic capacitance reflected from the secondary winding. The Q of the direct drive network is less than about 0.5 so that a square wave voltage signal is provided across the primary winding of the transformer. However, the inductance of the transformer is sufficiently high such that the voltage across a secondary winding of the transformer is sinusoidal. The secondary network comprises the secondary winding of the transformer coupled to the CCFL through a connector to provide a sinusoidal current to the CCFL. The controller controls the current passing through the CCFL by pulse width modulating the control inputs to the direct drive network.

Harmonic cancellation by mixing nonlinear single-phase and three-phase loads

Abstract: The voltage on the distribution line is, in most cases, distorted even at no load of the transformer. This is due to the "background" distortion on the medium-voltage line caused by the large number of single-phase nonlinear loads, such as PCs, TVs, VCRs, etc. This paper proposes a method to mix single-phase and three-phase nonlinear loads and reduce the harmonic currents significantly. The dependence of the phase angle of the harmonic currents as a function of the short-circuit impedance is investigated using SABER for the three-phase and the single-phase diode rectifier both with and without DC-link inductance. The phase angle of the fifth harmonic current of a three-phase diode rectifier is always in counterphase with the fifth harmonic current of a single-phase diode rectifier. This leads to the conclusion that adding three-phase rectifier load can actually improve the power quality at the transformer. This is also validated by a number of on-site measurements in several applications of three-phase adjustable-speed drives.

Apparatus and method for starting a fluorescent lamp

Abstract: A power conversion circuit drives a cold cathode fluorescent lamp (CCFL) while requiring minimal number of external components. The circuit includes a controller, a direct drive network responsive to control inputs from the controller and coupled to receive a power signal, and a secondary network coupled to the CCFL. The direct drive network is low Q circuit comprising a plurality of switching transistors and a primary winding of a transformer such that an impedance of the direct drive network consists essentially of an inductance of the primary winding and capacitance of the direct drive network consists essentially of parasitic capacitance reflected from the secondary winding. The Q of the direct drive network is less than about 0.5 so that a square wave voltage signal is provided across the primary winding of the transformer. However, the inductance of the transformer is sufficiently high such that the voltage across a secondary winding of the transformer is sinusoidal. The secondary network comprises the secondary winding of the transformer coupled to the CCFL through a connector to provide a sinusoidal current to the CCFL. The controller controls the current passing through the CCFL by pulse width modulating the control inputs to the direct drive network.

Efficient integral equation formulations for admittance or impedance representation of planar waveguide junctions

Abstract: In this paper we describe very efficient impedance and admittance Integral Equation (IE) formulations for the study of passive microwave devices composed of cascaded uniform waveguide sections. The formulation leads directly to reduced multimode matrix representations that only involve a small number of accessible, or interacting, modes. In addition to theoretical results, a performance comparison is also discussed which clearly demonstrates the improvement achieved.

Disk-loaded monopoles with parallel strip elements

Abstract: Design considerations and experimental performance data are presented for disk-loaded folded monopoles in which the vertical elements consist of flat parallel strips separated by a dielectric. The presence of the dielectric and the flat strip geometry permit control of resonance frequency, susceptance slope, and impedance step-up ratio over ranges suitable for the design of electrically small antennas with a broad double-tuned response. Graphs are presented giving the impedance step-up ratio due to folding for various strip dimensions derived from static calculations. Experimental results are shown for antennas with heights in the range of one-eighth to one-tenth wavelength.

Impedance matching device

Abstract: An impedance matching device includes a variable capacitor constituted by a non-linear dielectric thin film and an upper electrode disposed on a lower electrode formed on a substrate. The non-linear dielectric thin film is formed by a deposition, screen-printing, electroplating, or other technique, and changes its relative dielectric constant according to applied voltage. Therefore, the capacity of the variable capacitor is controlled and the impedance is matched, by simply controlling the applied voltage across the non-linear dielectric thin film. Consequently, the arrangement makes it possible to cut down the impedance matching device in size and cost, compared to an arrangement incorporating a capacitor and a coil for adjustment, effects a much simpler matching operation, and facilitates a manufacturing process.

High impedance fault detection on distribution systems

Abstract: The detection of high impedance faults on electrical distribution systems has been one of the most persistent and difficult problems facing the electric utility industry. Recent advances in digital technology have enabled practical solutions for the detection of a high percentage of these previously undetectable faults. This paper reviews several mechanical and electrical methods of detecting high impedance faults. The issues and application of this technology are also discussed.

Body fluids monitor

Abstract: Method and apparatus are described for determining volumes of body fluids in a subject using bioelectrical response spectroscopy. The human body is represented using an electrical circuit. Intra-cellular water is represented by a resistor in series with a capacitor; extra-cellular water is represented by a resistor in series with two parallel inductors. The parallel inductors represent the resistance due to vascular fluids. An alternating, low amperage, multi-frequency signal is applied to determine a subject's impedance and resistance. From these data, statistical regression is used to determine a 1% impedance where the subject's impedance changes by no more than 1% over a 25 kHz interval. Circuit components of the human body circuit are determined based on the 1% impedance. Equations for calculating total body water, extra-cellular water, total blood volume, and plasma volume are developed based on the circuit components.

Harmonic impedance measurement using three-phase transients

Abstract: In this paper, a technique is presented for measuring the harmonic impedances of an unbalanced three-phase distribution feeder. The technique uses transients in bus voltages and feeder currents generated by several close-trip operations of the shunt capacitor bank. The work is based on the assumption that the impedance of the feeder does not change over time during which the switching operations are performed. Mathematical development of the technique is verified with the laboratory and the field tests. The technique provided good measurements of the harmonic impedances up to 1.5 kHz for the given capacitor sizes. Statistical indices were developed to assess the accuracy of the estimated impedance values.

Apparatus for controlling the impedance of high speed signals on a printed circuit board

Abstract: The present invention relates to the placement of signal traces on a two-sided printed circuit board such that impedance of the traces is controlled and so that the number of power and ground pins required on an integrated circuit are minimized.

Transient and steady-state short-circuit currents in rectifiers for DC traction supply

Abstract: This paper presents some significant extension and analytical formalization of the knowledge on transient and steady-state short-circuit currents in DC traction systems. Electrical supply substations (ESSs) in modern metrorail and railway DC systems are equipped with 6- and 12-pulse diode bridge rectifiers. Large existing plants are equipped with 6-pulse converters, but the 12-pulse option is preferred in the design of new plants in the parallel configuration. Such a converter presents a good compromise between number and voltage/current rating of semiconductor devices, complexity and rating of transformers, DC-side voltage ripple, and AC-side current harmonic content. In this paper, the author considers the features of 6- and 12-pulse conversion units in terms of transient and steady-state short-circuit currents on zero fault impedance, accurate determination of the transient DC short-circuit current is important for correct rating and tuning of protection devices and power equipment (high-speed circuit breakers, isolator switches, switchgears, DC-busbars, etc.). An analytical solution of the short-circuit behavior is given for zero fault impedance currents: phase currents of the transformer, transient short-circuit DC current, approximate expression of the DC short-circuit current, and accurate expression of the steady-state DC short-circuit current. The general calculation method used in the paper is extensible to any conversion unit with a double secondary transformer.

Grazing behavior of scatter and propagation above any rough surface

Abstract: At grazing, propagation and scatter become inextricably connected For sufficiently low source/observer heights, free-space inverse-distance propagation no longer applies and plane-wave descriptions of scatter give way to surface-wave modes Concepts like surface radar cross section must be reinterpreted; lack of awareness of these facts in attempts to correlate measurements with grazing-angle laws has led to contradictions When plane-wave depictions hold, a regime is entered where backscatter follows a grazing angle-to-the-fourth power dependence for surfaces of any roughness scales for both polarizations and for perfectly conducting as well as impedance boundaries above penetrable media Propagation is described in terms of a roughness-modified effective impedance/admittance that approaches a constant at grazing for all roughness profiles These facts are first explored with numerical examples, after which we establish universal laws that confirm these suspicions We derive expressions for the first Taylor-series expansion terms for scatter and impedance/admittance versus grazing angle Statistics are neither required nor excluded-the laws hold for single arbitrary deterministic profiles as well as averages over ensembles of random surface samples Proofs of these claims are based on two-dimensional (2-D) fields over one-dimensional (1-D) impedance/admittance boundaries

Voltage current sensor with high matching directivity

Abstract: A technique for measuring the current, voltage and phase of a Radio Frequency (RF) power wave to an RF load, accounts for the finite length of the voltage and current pickups, and corrects for effects of standing wave components of voltage and current. Voltage and current are computed as complex functions of the voltage pickup signal and the current pickup signal, based on coefficients precalibrated for the predetermined radio frequency. Alternatively, a corrected current value can based on the corrected voltage value and complex load impedance. The correction coefficients can be obtained, for each of a plurality of calibrating radio frequencies within an RF range, from voltage and current pickup signals under conditions of (a) open circuit load, (b) short circuit load, (c) fixed known impedance load; and (d) one of voltage and current being applied at a precise input level to a known load from an RF calibration source.

Blood vessel cross-sectional area detector and compliance measurement device and method

Abstract: Impedance catheter (14) has two outer electrodes (34, 35), and two central electrodes (36, 37). A signal processor (16) comprises an instrumentation amplifier (38) connected between voltage electrodes (36, 37), to sense the voltage developed thereon by the output current of current source (32). A DC output voltage is determined based on the potential difference of voltage electrodes (36, 37), which is converted into an impedance value. The cross-sectional area A is derived from the impedance value.

Portable fluid screening device and method

Abstract: This invention relates to a fluid screening device (10), comprising: an impedance sensor (22) including a cavity for holding a fluid to be screened, an impedance of the impedance sensor being affected by conditions of the fluid; an impedance measuring circuit (38) for measuring the impedance of the impedance sensor with respect to at least one frequency; a processsor (34) for processsing impendance data taken by the impedance measuring circuit (38) for purposes of determining a condition of the fluid; and a connector (25) which operatively couples the impedance sensor (22) to the impedance measuring circuit (38); the connector (25) allowing the impedance sensor (22) to be selectively detached from the impedance measuring circuit (38)