Showing papers on "Electrical impedance published in 1999"

Impedance-Based Structural Health Monitoring for Temperature Varying Applications

Abstract: A new structural health monitoring technique capable of in-service, on-line incipient damage detection has been proposed by the Center for Intelligent Material Systems and Structures, Physical changes in a structure cause changes in the mechanical impedance. Due to the electromechanical coupling in piezoelectric materials, this change causes a change in the electrical impedance of the piezoelectric sensor. Hence, by monitoring the electrical impedance and comparing this to a baseline measurement, we can determine when structural damage has either occurred or is imminent. However, in almost all practical health monitoring applications, the structure being monitored is constantly undergoing change due to the effect of external boundary conditions. One of the important factors that leads to this change is the temperature variations. In this paper, temperature effects on the electrical impedance of piezoelectric materials and the structures have been investigated. A computer algorithm was developed which incorporates temperature compensation into our health monitoring applications. Three experimental investigations were performed successfully under the temperature varying condition, in the range of 25 to 75°C, including a bolted pipe structure, composite reinforced aluminum and precision part such as gears. It was found that, by this compensation procedure, the impedance based health monitoring tehcnique is able to detect damage in the incipient stage, even with the presence of significant temperature variation.

Method and apparatus for measuring complex impedance of cells and batteries

Abstract: A periodic time-varying current with smallest period 1/f1 excites a cell/battery (10) and provides a timing reference. Linear circuitry (35, 55) produces two signals, one proportional to the excitation current, the other proportional to the responding time-varying voltage. These signals are processed with identical frequency-limiting filters (40, 60) to attenuate higher-order harmonics and noise. Using the timing reference for synchronization, a microprocessor/microcontroller (20) commands analog to digital converters (45, 65) to sample the frequency-limited current and voltage signals at equally-space times over a period and accepts the digitized samples as inputs. The digital samples are averaged over multiple periods and employed to calculate averaged Fourier coefficients of in-phase and quadrature components of frequency-limited current and voltage at frequency f1. By numerically combining these Fourier coefficients, the microprocessor/microcontroller (20) determines real and imaginary parts of the cell/battery's (10) complex impedance at frequency f1.

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 criterion. 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 paper 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.

Method and apparatus for determining battery properties from complex impedance/admittance

Abstract: A device includes a microprocessor or microcontroller and measures real and imaginary parts of complex immittance of a cell or battery at n discrete frequencies, where n is an integer number equal to or greater than 2. The device determines cell/battery properties by evaluating components of an equivalent circuit model comprising 2n frequency-independent elements. Equating real and imaginary parts of measured immittance to values appropriate to the model at the n measurement frequencies defines a system of 2n nonlinear equations. Introducing 2n intermediate variables permits solving these equations and leads to values for the 2n model elements. A table of element values contains virtually the same information as the spectrum of complex immittance over a wide frequency range but provides this information in a more concise form that is easier to store, analyze, and manipulate. Thus, the 2n element values may themselves comprise the desired result. If desired, however, a predetermined relationship between one or more of the elements and an additional electrical, chemical, or physical property of the cell/battery may be further invoked to determine the additional property.

AC impedance and state-of-charge analysis of a sealed lithium-ion rechargeable battery

Abstract: A 7.2V, 1.25 Ah sealed lithium-ion rechargeable battery has been studied for estimating its state-of-charge (SOC) by AC impedance. The dispersion of impedance data over the frequency range between 100 kHz and 25 mHz comprises an inductive part and two capacitive parts. As the inductive behaviour of the battery is attributed to the porous nature of the electrodes, only the capacitive components have been examined. The data obtained at several SOC values of the battery have been analyzed by a non-linear least-squares fitting procedure. The presence of two depressed semicircles in the capacitive region of the Nyquist plots necessitated the use of an electrical equivalent circuit containing constant phase elements instead of capacitances. The impedance parameters corresponding to the low-frequency semicircle have been found useful for predicting the SOC of the battery, mainly because the magnitude of these parameters and their variations are more significant than those of the high-frequency semicircle. The frequency maximum (f(max)) of the semicircle, the resistive component (Z') corresponding to f(max), the phase angle (phi) in the 5.0 Hz-0.1 Hz frequency range, the equivalent series resistance (R-s) and the equivalent series capacitance (C-s) have been identified as suitable parameters for predicting the SOC values of the lithium-ion battery.

External control of dissipation in a nanometer-scale radiofrequency mechanical resonator

Abstract: We demonstrate a technique by which the quality factor of a magnetically-actuated mechanical resonator is controlled by an external electrical circuit. Modulation of this parameter is achieved by local variation of the electrical impedance presented to the resonator at its resonance frequency. We describe a theory that explains this result as arising from eddy currents in the external electrical circuit, which are driven by electromotive forces generated through motion of the resonator in the applied magnetic field. The theory is in good agreement with the induced variation in quality factor that we observe.

Method and apparatus for an optimized circuit for an electrostatic radio frequency identification tag

Abstract: A radio frequency identification (RFID) tag (100), optimized for electrostatic applications, includes a first antenna element (112), a second antenna element (114) and an RFID circuit (116). The first antenna element is electrically isolated from the second antenna element. The RFID circuit has a first pad (230) and a second pad (232) with an input capacitance between them. The first and second pads of the RFID circuit are coupled, respectively, to the first and second antenna elements. The RFID circuit includes a load modulation circuit (222) coupled to at least one of the first or second pads to produce a load modulated signal on at least one of the first or second pads that varies from a first amplitude to a second amplitude. The load modulation circuit has a modulation impedance and a predetermined voltage threshold that an input signal must exceed before the modulated signal is produced.

Reducing simultaneous switching noise and EMI on ground/power planes by dissipative edge termination

Abstract: Power and ground planes are required to have low impedance over a wide range of frequencies. Parallel ground and power planes in multilayer printed-circuit boards exhibit multiple resonances, which increase the impedance and also the radiation from the edge of the board. Resistive termination along the board edges reduces the resonance peaks. Simple and straightforward design expressions, simulated self and transfer impedances, as well as measured impedance plots are presented for power-ground planes.

A new model for the FDTD analysis of the shielding performances of thin composite structures

Abstract: A new model is proposed for the transient analysis of the electromagnetic field penetration through air-embedded conductive structures realized by thin multilayered composite panels. A magnetic field controlled formulation is developed in the frequency-domain to express the tangential components of the electric field on the external faces of the composite slab as a function of the tangential components of the magnetic field by means of the surface and transfer impedances of the thin panel coated on a perfect magnetic medium. The corresponding time-domain model is obtained by applying the inverse Fourier transform to the field quantities; an efficient piecewise linear convolution procedure is developed for the numerical calculation of the resulting convolution integrals. The model is implemented in one-dimensional (1-D) and two-dimensional (2-D) FDTD codes and applied to the analysis of different shielding configurations, both in the frequency and in the time domain.

Cancellation system for frequency reuse in microwave communications

Abstract: Substantial improvements in frequency reuse in microwave communications systems is achieved by canceling co-channel interference and transmitter leakage Interferometric beam-narrowing reduces beamwidth without reducing peak magnitude of the beam pattern Frequency-dependent beam-shaping compensates for frequency-dependent distortions of the beam pattern thereby improving bandwidth A spatial demultiplexing technique utilizes spatial gain distributions of received signals to separate signals, even from co-located transmit sources, and uses microwave lensing to enhance received spatial gain distributions Predetermined cross-polarization interference is used to separate differently-polarized receive signals A reference branch provides a cancellation signal to a receiver to cancel transmitter leakage signals An error signal controls an impedance-compensation circuit that is responsive to changes in antenna impedance but not to receive signals A dc bias magnetic field applied to a magnetic permeable material adjusts non-linear distortion in a cancellation circuit for canceling distortion in a transmitter leakage signal Discreet impedance elements approximate a circuit having distributed impedance

In Vivo and In Situ Ischemic Tissue Characterization Using Electrical Impedance Spectroscopya

Abstract: The investigation of processes of ischemia in different organ tissues is very important for the development of methods of protection and preservation during surgical procedures. Electrical impedance spectroscopy was used to distinguish between different tissues and their degree of ischemia. We describe mathematical methods used to adjust experimental data to Cole-Cole models for one-circle and two-circle impedance loci and a study of the main parameters for representing the behavior of ischemia in time. In vivo and in situ postmortem measurements of different tissues from pigs are shown in the 100 Hz to 1 MHz range. The Cole parameters that best characterize the ischemia are R0 and fc.

Power semiconductor device

Abstract: PROBLEM TO BE SOLVED: To reliably make overcurrent protection of a power transistor, by suppressing the dispersion in the maximum value of a load current. SOLUTION: A power PNP transistor 18 is fixed onto and electrically connected to a surface 16 of a metal radiating plate 15 through a platelike resistor 17. Further, a controlling integrated circuit device 20 is fixed onto the surface 16 through an electrically insulating paste 19, and the resistor 17, the transistor 18 and the device 20 are connected using thin metal wires 42 to 44. A load current Io from an input terminal flows from the emitter to the collector of the transistor 18, and further flows through the resistor 17 in a thickness direction to reach the plate 15. The device 20 detects a voltage across the resistor 17 corresponding to the current Io between the plate 15 and the surface of the resistor 17 on the side of the transistor 18. When such voltage becomes high, the device 20 excessively changes the impedance of the transistor 18 to suppress an overcurrent.

Ratiometric autotuning algorithm for RF plasma generator

Abstract: An RF plasma system employs frequency tuning to change the frequency of an RF generator (14) within a frequency range to match the impedance of a plasma chamber (18). Forward power and reflected power magnitudes are obtained from a bidirectional sensor (16). The ratio of reflected power to forward power is obtained for one frequency, and then the frequency is changed. The tuning algorithm compares the ratio of reflected to forward power at the new frequency with the ratio obtained earlier. If the new ratio is smaller, the frequency is changed again in the same direction, but if larger, then the frequency is changed in the other direction. These steps are iterated until the ratio of reflected to forward power reaches a minimum. The tuning algorithm can be implemented in hardware or in software.

Two and Three-Electrode Impedance Studies on 18650 Li-Ion Cells

Abstract: Two and three electrode impedance measurements were made on 18650 Li-ion cells at different QB temperatures ranging from 35 C to {minus}40 C. The ohmic resistance of the cell is nearly constant the temperature range studied although the total cell impedance increases by an order of magnitude in the same temperature range. In contrast to what is commonly believed, we show from our three-electrode impedance results that, the increase in cell impedance comes mostly from the cathode and not from the anode. Further, the anode and cathode contribute to both the impedance loops (in the NyQuist plot).

Exact treatment of the dispersion and beam interaction impedance of a thin tape helix surrounded by a radially stratified dielectric

Abstract: An exact dispersion relation is obtained for electromagnetic waves propagating on a thin metallic tape helix of arbitrary width, supported by a radially stratified dielectric layer and enclosed by a metallic shell. By expanding the surface currents on the tape in a series of Chebyshev polynomials, the unquantifiable assumptions made in all previously published analyzes of the tape helix regarding the forms of the surface current on the tape, or the electric fields at the radius of the tape, are avoided. The power flow and interaction impedance are exactly computed. The dispersion relation is solved numerically for slow waves and the resulting phase velocity and interaction impedance are compared to those computed using the frequently made assumptions of constant current along the tape and zero current across the tape. It is found that for wide tapes significant errors are made in both the phase velocity and interaction impedance when neglecting the transverse variation of the longitudinal current and neglecting the transverse current. For narrow tapes, the two approaches agree to good accuracy. Plots of the surface currents for wide and narrow tapes are presented. The longitudinal current shows a significant variation across the tape. An example is given showing the existence of an optimum tape width, at which the on-axis interaction impedance is maximized. It is separately shown how an approximate, but useful model of metallic vanes may be incorporated in the analysis by the modification of certain boundary conditions. In all cases, computations of phase velocity and impedance across a wide frequency band take well under a minute on a modern workstation.

An apparatus for controlling the generation of electric fields

Abstract: An apparatus (60) according to the present invention includes a voltage generator (1) for generating brief voltage pulses for the impression of voltage on electrodes (6, 15, 16, 24) included in the apparatus, and a measurement unit (50) which is coupled to the electrodes. These are designed to be secured at or inserted in tissue in a restricted region of a human or an animal in order therebetween to form electric fields in the tissue. The measurement unit (50) is disposed to determine the impedance between the electrodes which is substantially determined by the electric properties of the tissue which is located between the electrodes. A registration and calculator device (10) forms a control unit which, based on the impedance determined by the measurement unit, controls the output voltage of the voltage generator such that the electric field which is formed in the tissue always has a predetermined value. The treatment with the electric field realizes a perforation of cell membranes in the tissue which thereby permits the passage of substances fed to the body (e.g. cytostatic or genetic material).

Radio-frequency impedance measurements using a tunnel-diode oscillator (TDO) technique

Abstract: A resonant method based on a tunnel-diode oscillator (TDO) for precision measurements of relative impedance changes in materials, is described. The system consists of an effective self-resonant LC-tank circuit driven by a forward-biased tunnel diode operating in its negative resistance region. Samples under investigation are placed in the core of an inductive coil and impedance changes are determined directly from the measured shift in resonance frequency. A customized low temperature insert is used to integrate this experiment with a commercial Model 6000 Physical Property Measurement System (Quantum Design). Test measurements on a manganese-based perovskite sample exhibiting colossal magneto-resistance (CMR) indicate that this method is well suited to study the magneto-impedance in these materials.

Measurement and control of current/voltage waveforms of microwave transistors using a harmonic load-pull system for the optimum design of high efficiency power amplifiers

Abstract: One of the most important requirements that RF and microwave power amplifiers designed for radiocommunication systems must meet is an optimum power added efficiency (PAE) or an optimal combination of PAE and linearity. A harmonic active load-pull system which allows the control of the first three harmonic frequencies of the signal coming out of the transistor under test is a very useful tool to aid in designing optimized power amplifiers. In this paper, we present an active load-pull system coupled to a vectorial "nonlinear network" analyzer. For the first time, optimized current/voltage waveforms for maximum PAE of microwave field effect transistors (FET's) have been measured. They confirm the theory on high efficiency microwave power amplifiers. The proposed load-pull setup is based on the use of three separated active loops to synthesize load impedances at harmonics. The measurement of absolute complex power waves is performed with a broadband data acquisition unit. A specific phase calibration of the set-up allows the determination of the phase relationships between harmonic components. Therefore, voltage and current waveforms can be extracted. The measurement results of a 600 gate periphery GaAs FET (Thomson Foundry) exhibiting a PAE of 84% at 1.8 GHz are given. Such results were obtained by optimizing the load impedances at the first three harmonic components of the signal coming out of the transistor. Optimum conditions correspond to a class F operation mode of the FET (i.e., square wave output voltage and pulse shaped output current). A comparison between measured and simulated current/voltage waveforms is also presented.

Elastic impedance estimation for inversion of far offset seismic sections

Abstract: A computer-implemented method, and system implementing the method, of performing impedance inversion of seismic survey data are disclosed. Sonic and density well logs are used to generate an elastic impedance model, at selected angles of incidence or offset range, using an expression for elastic impedance that depends upon the measured or estimated compressional velocity, shear velocity, and density of the subsurface layers in the survey region. The elastic impedance expression also includes a reference density value, and is dependent upon the ray parameter (or angle of incidence). This elastic impedance model is used, for example by way of a pseudo-density log, in estimating the input wavelet, and in carrying out an impedance inversion of the seismic survey over the entire survey region, for at least two angles of incidence. Low-frequency components of the elastic impedance, at the selected angles of incidence, are merged with the corresponding impedance inversion sections, to produce a merged impedance model at the selected angles of incidence. Rock properties, such as Poisson's ratio, are then retrieved from a comparison, such as a ratio, of the impedance traces at the varying angles of incidence for common midpoints.

Radio-frequency impedance measurements using a tunnel-diode oscillator technique

Abstract: A resonant method based on a tunnel-diode oscillator for precision measurements of relative impedance changes in materials is described. The system consists of an effective self-resonant LC tank circuit driven by a forward-biased tunnel diode operating in its negative resistance region. Samples under investigation are placed in the core of an inductive coil and impedance changes are determined directly from the measured shift in resonance frequency. A customized low temperature insert is used to integrate this experiment with a commercial Model 6000 Physical Property Measurement System (Quantum Design). Test measurements on a manganese-based perovskite sample exhibiting colossal magnetoresistance indicate that this method is well suited to study the magnetoimpedance in these materials.

Electric cautery device

Abstract: PROBLEM TO BE SOLVED: To supply optimum power to viable tissues at all times in a treating process, to perform lowly invasive treatment to the tissues in a short time and to satisfy the request to QOL of a patient. SOLUTION: This electric cautery device 11 is provided with an impedance monitoring means 26 for monitoring impedance of the viable tissue which is a load, a high frequency power generation means provided with a waveform generation means 21 and a variable DC power source circuit means 23 and a main control means 20 for controlling the entire device. In this case, a measurement current for measuring the impedance of a cauterization part is made to flow for a prescribed period immediately before making a high frequency current for treatment flow, the tissue impedance during the prescribed period is detected, load characteristics of the electric cautery device 11 are automatically switched so as to match the tissue impedance at the time of starting cauterization and rated load resistance intrinsic to the device at all times corresponding to a level of the detected tissue impedance and output power as being set is supplied.

Assessment and calibration of a low-frequency system for electrical impedance tomography (EIT), optimized for use in imaging brain function in ambulant human subjects.

Abstract: An EIT system has been produced that has been optimized for imaging impedance changes with scalp electrodes during brain activity in ambulant subjects. It can record from 225 Hz to 65 kHz, has a small headbox on a lead 10 m long, and has software programmable electrode selection. In calibration experiments in a small cylindrical tank filled with potassium chloride solution and samples of cucumber, noise was less than 1% with averaging, and acceptable images were produced at frequencies down to 1800 Hz. This suggests that EIT can be performed at low frequencies, which are likely to give larger signals during brain activity. Future work will include trials in humans and improvement of the current source and isolation.

System and method for edge termination of parallel conductive planes in an electrical interconnecting apparatus

Abstract: A system and method are presented for stabilizing the electrical impedance of a structure (e.g., an electrical interconnecting apparatus) including a pair of parallel planar conductors separated by a dielectric layer. The structure may be, for example, a PCB, a component of a semiconductor device package, or formed upon a surface of an integrated circuit substrate. An electrical resistance connected between the planar conductors about a periphery of the structure serves to stabilize the electrical impedance of the structure, thereby reducing an amount of electromagnetic energy radiated from the structure. The electrical resistance may be multiple discrete electrical resistances dispersed about the periphery of the structure, and the structure need not be rectangular. For example, a portion of the periphery of the structure may define a curve. A general method for stabilizing the electrical impedance of the structure includes selecting a spacing distance. A grid is generated by superimposing two orthogonal sets of parallel lines upon one another, wherein the parallel lines within each set are separated by the spacing distance. The grid is dimensioned such that it completely covers the structure when overlayed upon the structure. The characteristic impedance of the structure may then be estimated using a physical dimension of the grid. The value of the electrical resistance may then be computed using the estimated characteristic impedance of the structure. The grid may also be used to determine the location of the discrete electrical resistances.

Drive level dependence of the resonant frequency in BAW quartz resonators and his modeling

Abstract: The influence of the excitation current on the resonant frequency and its mathematical description makes necessary the introduction of a nonlinear impedance characteristic of the piezoelectric resonator. This influence was modeled by the nonlinear electrical equivalent circuit; the equivalent series resistance and equivalent motional capacitance are taken to be functions of the amplitude of the excitation current by means of the relations derived in the work. The equivalent circuit was analyzed by the method of equivalent linearization. The relationships between the amplitudes of voltage applied on the AT-cut resonator and the first current harmonics or phase-frequency dependence of the excited resonator, respectively, are derived. Amplitude jumps and dynamic temperature change phenomena are discussed.