Showing papers on "Electrical impedance published in 2001"

Micromachined impedance spectroscopy flow cytometer for cell analysis and particle sizing

Abstract: A new cytological tool, based on the micro Coulter particle counter (μCPC) principle, aimed at diagnostic applications for cell counting and separation in haematology, oncology or toxicology is described. The device measures the spectral impedance of individual cells or particles and allows screening rates over 100 samples s−1 on a single-cell basis. This analyzer is intended to drive a sorting actuator producing a subsequent cell separation. Size reduction and integration of functions are essential in achieving precise measurements and high throughput. 3D finite element simulations are presented to compare various electrode geometries and their influence on cell parameters estimation. The device is based on a glass-polyimide microfluidic chip with integrated channels and electrodes microfabricated at the length scale of the particles to be investigated (1–20 μm). A laminar liquid flow carries the suspended particles through the measurement area. Each particle’s impedance signal is recorded by a differential pair of microelectrodes using the cell surrounding media as a reference. The micromachined chip and processing electronic circuit allow simultaneous impedance measurements at multiple frequencies, ranging from 100 kHz to 15 MHz. In this paper, we describe the microfabrication and characterisation of an on-chip flow-cytometer as the first building block of a complete cell-sorting device. We then discuss the signal conditioning technique and finally impedance measurements of cells and particles of different sizes and types to demonstrate the differentiation of subpopulations in a mixed sample.

Electro-Mechanical Impedance Method for Crack Detection in Thin Plates

Abstract: This paper describes the utilization of Electro-Mechanical (E/M) impedance method for structural health monitoring of thin plates. The method allows the direct identification of structural dynamics by obtaining its E/M impedance or admittance signatures. The analytical model for two-dimensions structure was developed and verified with experiments. Good matching of experimental results and calculated spectra was obtained for axial and flexural components. The ability of the method to identify the presence of damage was investigated by performing an experiment where the damage in the form of crack was simulated with An EDM slit placed at various distances from the sensor. It was found that the crack presence dramatically modifies the E/M impedance spectrum and this modification decreases as the distance between the sensor and the crack increases. Several overall-statistics damage metrics, which may be used for on-line structural heath monitoring, were investigated. Among these candidate damage metrics, the α-th power of the correlation coefficient deviation, CCD α , 3 < α < 7, used in the high frequency band 300-450 kHz, was found to be most successful. Careful selection of the high frequency band and proper choice of the appropriate damage metric were found to be essential for successful damage detection and structural health monitoring.

Design and application of a wireless, passive, resonant-circuit environmental monitoring sensor

Abstract: A wireless, passive, remote query sensor platform is presented capable of monitoring the complex permittivity of a surrounding medium, temperature, humidity, and pressure. The sensor is a planar two-dimensional inductor–capacitor circuit, of scaleable-size, that resonates at a characteristic frequency the value of which is dependent upon the parameters of interest. The resonant frequency of the sensor is detected remotely with one or a pair of loop antennas by measuring the impedance or voltage spectrum of the antenna(s), with the environmental parameters of interest then calculated from the measured resonant frequency. The wireless, remote query nature of the platform enables the LC sensor to monitor the environmental conditions from within sealed opaque containers. The paper describes the operational principles, design criteria, illustrative applications, and performance limitations of the sensor platform.

Kinetic Characterization of Single Particles of LiCoO2 by AC Impedance and Potential Step Methods

Abstract: This is the first report of impedance technique run on single particle electrodes with the aim of clarifying its electronic and ionic transport properties. Measurements were successfully conducted on a particle of 15 μm diam resulting in impedance magnitude on the order of MΩ. The impedance spectra exhibited (i) one semicircle in the high frequency region, (ii) Warburg impedance in low frequencies, and finally, (iii) a limiting capacitance in the very low frequencies. The spectra were analyzed using a modified Randles-Ershler circuit, so that the reaction kinetics could be precisely evaluated. The charge transfer resistance decreased as the potential increased, whereas the double layer capacitance was almost invariant with the potential. Thus, the apparent chemical diffusion coefficient of lithium ions was determined to be to as function of electrode potential. These results are in agreement with those obtained by potential step chronoamperometry technique. © 2001 The Electrochemical Society. All rights reserved.

Electrical impedance tomography

Abstract: Methods and apparatus for obtaining a representation of the distribution of electrical impedance within a multiphase flow with an electrically continuous or discontinuous principle flow (3) contained within an electrically conductive solid ring electrode (1), comprising providing a plurality of mutually spaced electrical contacts (2) mounted at the outside wall of the ring and electrically contacted with the ring, applying currents or voltages (4) to the ring from the electrical contacts (2), generating a more homogeneous electric field distribution within the material (3), measuring voltage or current (5) distribution along the ring from other electrical contacts (2), relatively intensifying the imaging sensitivity at the central area of the sensing domain using a π/2 angle sensing strategy and reconstructing the representation of the impedance distribution using CG method with an error processing strategy.

Multiple antenna impedance optimization

Abstract: A multiple antenna mobile communication device, such as a cellular telephone, having multiple radios and multiple antennas located in close proximity to each other uses a parallel tuning circuit to optimize the isolation between the antennas. The parallel tuning circuit can include multiple impedance matching circuits to match the impedance in multiple frequency bands or isolating antennas.

A high-impedance ground plane applied to a cellphone handset geometry

Abstract: A high-impedance electromagnetic surface is a new type of metallic structure exhibiting high surface impedance and the suppression of propagating surface currents at a particular frequency band. We experimentally characterize such a high-impedance surface designed near 2.4 GHz. We describe an antenna built on such a surface, integrated into a printed circuit board that was designed for the form factor of a portable handset. Measurement shows high radiation efficiency near 2.4 GHz.

dc-Electrical Degradation of the BT-Based Material for Multilayer Ceramic Capacitor with Ni internal Electrode: Impedance Analysis and Microstructure

Abstract: The impedance of a BaTiO3 (BT)-based multilayer ceramic capacitor with a nickel internal electrode (Ni-MLCC) was investigated by measuring the frequency domain at various temperatures. All the obtained impedance data could be successfully fitted to a 4-RC section electrical equivalent network. The 4-RC section electrical equivalent network was successfully correlated to the microstructure: the core, the shell, the grain boundary, and the ceramic/internal electrode interface regions. Based on this electrical equivalent network, the electrical properties including the Curie-Weiss law, the current-voltage characteristics, and dc electrical degradation, were well explained. A model for the degradation behavior for BT-based Ni-MLCC with thin active layer thickness was proposed.

Sensitive micro magnetic sensor family utilizing magneto-impedance (MI) and stress-impedance (SI) effects for intelligent measurements and controls

Abstract: Recent development in the field of highly sensitive, quick response and small power consumption micro magnetic sensor family (MI sensors and SI sensors) utilizing the magneto-impedance (MI) and stress-impedance (SI) effects mainly in amorphous wires is summarized. The MI and SI sensors are constituted with CMOS inverter IC and MI and SI heads magnetized with the sharp pulse current generating the skin effect, which realize the application specified integrated circuits (ASIC) sensors. Various pocketable or handy micro sensors have been developed, such as the handy terrestrial field sensor and the electronic compass for automobiles using the amorphous zero-magnetostrictive (FeCoSiB) wire MI chips combined with the CMOS IC circuit. Highly sensitive micro stress (strain) sensors and micro acceleration sensors are also developed using the amorphous magnetostrictive (CoSiB) wire SI elements combined with the CMOS IC circuit. Various small oscillatory motions in human bodies, such as the finger tip blood vessel pulsation (FTP) and the mechano-encephalogram, and road bridge oscillation during car passing are sensitively detected using the SI acceleration sensor.

Methods to study the ionic conductivity of polymeric electrolytes using a.c. impedance spectroscopy

Abstract: Composite polymeric electrolytes of PEO-LiClO4-Al2O3 and PEO-LiClO4-EC were prepared and the ionic conductivity by a.c. impedance was calculated using four different methods, and three kinds of representations of a.c. impedance spectra were adopted. The first is based on the Nyquist impedance plot of the imaginary part (Z″) versus the real part (Z′) of the complex impedance. The second and the third correspond to the plots of imaginary impedance Z″ as a function of frequency (f), and the absolute value (|Z|) and phase angle (θ) as a function of f, respectively. It was found that the values of the ionic conductivity calculated using the three representations of a.c. impedance spectra are basically identical.

Measurement of network harmonic impedances: practical implementation issues and their solutions

Abstract: Determination of network harmonic impedances using pre- and post-disturbance steady-state waveforms is a well-known technique. Due to practical constraints, however, it is not quite straightforward to implement the technique for real-life applications. Using an actual utility case as an example, this paper presents practical implementation issues involved and their solutions. Improvements are made to the technique by applying /spl alpha/-/spl beta/-0 transformation on three-phase measurements. The usefulness of the improved technique is demonstrated with simulation and field measurement results. Since the technique only requires steady-state data, it can be easily implemented with many common power quality meters. One of the applications of the technique is to determine the existence of resonance conditions for shunt capacitor applications.

Dielectric spectroscopy of Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

Abstract: Complex impedance spectroscopic data were acquired on single crystals of the morphotropic phase boundary composition of 068Pb(Mg1/3Nb2/3)O3-032PbTiO3 over a wide range of temperatures (25–525 °C) and frequencies 1 kHz–1 MHz This study takes advantage of plotting ac data simultaneously in the form of impedance and modulus spectroscopic plots This permits the easy interpretation of microscopic processes responsible for the measured ac response Frequency explicit plots of imaginary components of impedance and modulus exhibit Debye-like peak shapes The data for ac conductivity were computed from the impedance data and the activation energy for conduction at different frequencies was determined Cole–Cole diagrams were plotted and these indicate the presence of a single relaxation process The relaxation times determined from these plots followed an Arrhenius law, and the activation energy for relaxation was found to be 12 eV The ac conductivity data was found to obey Jonscher’s universal power law and

Impedance feedback control for scanning electrochemical microscopy.

Abstract: A new constant-distance imaging method based on the relationship between tip impedance and tip-substrate separation has been developed for the scanning electrochemical microscope. The tip impedance is monitored by application of a high-frequency ac voltage bias between the tip and auxiliary electrode. The high-frequency ac current is easily separated from the dc-level faradaic electrochemistry with a simple RC filter, which allows impedance measurements during feedback or generation/collection experiments. By employing a piezo-based feedback controller, we are able to maintain the impedance at a constant value and, thus, maintain a constant tip-substrate separation. Application of the method to feedback and generation/collection experiments with tip electrodes as small as 2 microm is presented.

A modeling method of a high impedance fault in a distribution system using two series time-varying resistances in EMTP

Abstract: More reliable algorithms for detecting a high impedance fault (HIF) require the voltage and current data at a relaying point instead of a faulted branch when HIF occurs. Thus, an accurate modeling method of HIF is essential for the development of a reliable detecting algorithm. The data should contain the complex characteristics of HIF such as buildup and shoulder as well as nonlinearity and asymmetry. This paper presents a modeling method of the above-mentioned HIF characteristics. Among the experiment data on a 22.9 (kV) distribution system conducted by Korea Electric Power Corporation (KEPCO), experiment data showing all the above characteristics is chosen in this paper. Two series time-varying resistances (TVRs) controlled by transient analysis of control systems (TACS) in EMTP are employed for modeling. One TVR is used for nonlinearity and asymmetry from the voltage-current characteristic for one cycle in the steady state after HIF, and then the other TVR for buildup and shoulder from the waveforms in the transient state after HIF. The comparison of the modeling results with the experiment data shows close correspondence. With the developed HIF model, the voltage and current at the relaying point are obtained with various load condition and fault condition such as fault distance and inception angle.

Frequency-dependent electrical transport in carbon nanotubes

Abstract: Carbon nanotubes exhibit exceptional dc electrical transport but relatively little is known about their ac behavior. We discover, in the ac impedance spectra of nanotubes, an intrinsic resonance at a fixed ultrasonic frequency of 37.6 kHz. In the 100 Hz to 8 MHz frequency range the overall impedance shows a negative capacitance associated with the dynamical response of the metal-nanotube contact. These effects could be used to compensate capacitance in electronic circuits or to fabricate nanotube-based transducers.

Suppressing interference in AC measurements of cells, batteries and other electrical elements

Abstract: The disclosed invention relates to measuring an ac dynamic parameter (e.g., impedance, admittance, resistance, reactance, conductance, susceptance) of an electrochemical cell/battery or other electrical element under conditions of possible interference from potential sources such as ac magnetic fields and/or ac currents at the powerline frequency and its harmonics. More generally, it relates to evaluating a signal component at a known frequency f1 under conditions of possible hum, noise, or other spurious interference at one or more other known frequencies. A microprocessor or microcontroller commands A/D circuitry to sample a band-limited signal at M evenly spaced times per period 1/f1 distributed over an integer number N of such periods and calculates time-averaged Fourier coefficients from these samples. The frequency response of the calculated Fourier coefficients displays perfect nulls at evenly spaced frequencies either side of frequency f1. By choosing N according to algorithms disclosed herein, null responses are made to coincide with the one or more frequencies of potential hum, noise, or other spurious interference.

Analysis of the impedance spectra of short conductive fiber-reinforced composites

Abstract: The presence of small amounts of short conductive fibers in a composite of finite matrix conductivity results in the subdivision of the one matrix impedance arc into two separate low and high frequency arcs in the complex impedance plane These features are attributable to a “frequency-switchable” interfacial impedance on the fiber surfaces, rendering them insulating at DC and low AC frequencies, but conducting at intermediate frequencies A combination of physical simulations (single wires in tap water) and pixel-based computer modeling was employed to investigate the roles of fiber pull-out, debonding, and orientation on the impedance response of fiber-reinforced composites The ratio of the low frequency arc size to the overall DC resistance (γ-parameter) is sensitive to pull-out and/or debonding, especially when a fiber just barely makes contact with the matrix The γ-parameter is also quite sensitive to fiber orientation with respect to the direction of the applied field Ramifications for the characterization of cement, ceramic, and polymer matrix composites are discussed

Output driver circuit with well-controlled output impedance

Abstract: An output driver circuit for driving a signal onto a signal line. The output driver circuit comprises at least one driver circuit and a passive network. The passive network is configured to limit the variation in the output impedance of the output driver circuit. The output driver circuit thus provides an output impedance that closely matches the loaded impedance of the signal line at all times so as to minimize secondary reflections on the signal line.

Real-Time Spectrum Analysis in Microstrip Technology

Abstract: We report on a time-domain analog to the spatial far-field Fraunhofer diffraction using microstrip lines with chirped distributed Bragg coupling between the fundamental microstrip mode and the same but counter-propagating mode. The chirping of the microstrip impedance yields to linear group delays within the reflected bandwidth. Under the condition of a temporal equivalent of the spatial Fraunhofer inequality, the distortion of a frequency-limited pulse results in an output reflected signal whose complex envelope is, except a phase factor, proportional to the Fourier Transform of the input pulse envelope. This has important temporal applications and, in particular, the devices designed in this paper work as real-time energy spectral density analyzers.

Power plane SPICE models and simulated performance for materials and geometries

Abstract: A SPICE model for power plane simulation has been developed. It is based on the geometries and materials of the power planes and uses a unit cell composed of RLC elements, transmission line elements or the HSPICE W-element. Simulated resonances in the frequency domain and delays in the time domain are consistent with results calculated from physical dimensions. SPICE model simulations compare well with hardware measurements in both the frequency and time domains. The role of dielectric thickness, dielectric constant and parallel pairs of power planes is demonstrated through simulation. The spreading inductance of power planes is defined, discussed and measured. Power plane performance in terms of impedance, resonances, damping and spreading inductance is optimized by the use of a thin dielectric layer between conductive planes.

Improved system and method for determining tissue contact of an implantable medical device within a body

Abstract: An improved system for monitoring the status of an IMD such as medical electrical lead during an implant procedure is provided. The system includes a signal generator for supplying a first signal such as a constant current or voltage to the IMD. A resulting voltage or current signal is generated, respectively, and may be sensed as an indication of the impedance of a portion of the body that is proximal to one or more electrodes carried by the lead. This impedance indication is converted to an audible signal having a frequency that is proportional to the amplitude of the impedance indication. The pitch of the audible signal therefore rises when measured impedance increases, and drops as the impedance decreases. These pitch changes allow a user to determine positional information associated with the IMD, including the degree of lead tissue contact and extent of fixation of a device to tissue.

Single output stage power amplification for multimode applications

Abstract: The present invention eliminates the need for complex impedance networks or parallel amplification stages for multi-mode mobile terminals. A wideband power amplifier is configured to amplify signals in different frequency bands corresponding to different operating modes. The supply voltage of the wideband power amplifier is adjusted in light of the load impedance of radiating circuitry to achieve a desired output power for the respective operating modes.

Eddy current loss measuring sensor, thickness measuring system, thickness measuring method, and recorded medium

Abstract: A thickness measuring system comprises: an eddy current loss measuring sensor having an exciting coil for receiving a high frequency current to excite a high frequency magnetic field to excite an eddy current in a conductive film, and a receiving coil for outputting the high frequency current which is influenced by an eddy current loss caused by the eddy current; an impedance analyzer for measuring the variation in impedance of the eddy current loss measuring sensor, the variation in current value of the high frequency current or the variation in phase of the high frequency current on the basis of the high frequency current outputted from the receiving coil; an optical displacement sensor for measuring the distance between the conductive film and the eddy current loss measuring sensor; and a control computer including a thickness calculating part for calculating the thickness of the conductive film on the basis of various measured results of the impedance analyzer and optical displacement sensor, and the eddy current loss measuring sensor further has a ferrite member surrounding the exciting coil and the ferrite member has an opening in the bottom surface portion thereof for allowing the exciting coil to be exposed.

Validation and evaluation of electrochemical impedance spectra of systems with states that change with time

Abstract: The influence of hindered water removal from a polymer electrolyte fuel cell under constant load was investigated using electrochemical impedance spectroscopy. The cathodic gas outlet of the cell was closed and impedance measurements were performed at periodic time intervals. Under the experimental conditions, the investigated system is far from steady-state conditions. It is shown that enhanced mathematical techniques are required for evaluation of the impedance data obtained. These techniques, the time course interpolation as well as the Z-HIT refinement, lead to quasi-causal spectra which are well interpreted by means of the porous electrode model.

Broadband Time-Domain Impedance Models

Abstract: The modeling of a set of impedance values given either experimentally or heuristically for implementation as a time-domain impedance-equivalent boundary condition (TDIBC) is discussed. It is shown that impedance as defined by the reflection of plane harmonic waves when extended for broadband time-domain applications can correspond to mathematically feasible but physically unacceptable noncausal reflection processes. Given a set of impedance data on a finite, positive, and real frequency range, it is possible to construct causal time-domain models that render efficient implementation of TDIBC for broadband reflections. However, these models defined by measurement of harmonic waves may not be valid for the reflection of impulses, for which measurement of transient reflections is warranted.

Harmonic matching network for a saturated amplifier

Abstract: Systems and methods for increasing the efficiency of direct current (DC) power to radio frequency (RF) power include a harmonic matching network that inhibits harmonic current flow for a number of harmonic frequencies The matching network includes a number of sections, where each section generates an impedance that resonates with the output capacitance at a harmonic frequency Each section of the matching network also creates a high impedance to the amplifier at the respective odd harmonic frequency