Showing papers on "Electrical impedance published in 2007"
TL;DR: It is proposed that the spatial summation of LFP and MUA is determined by the size of these signals' generators and the nature of neural events underlying them, rather than by biophysical properties of gray matter.
435 citations
TL;DR: In this paper, over 150 journal papers were reviewed with respect to AC impedance modeling and validation in solid oxide fuel cell (SOFC) diagnosis, and the challenges currently faced by AC impedance modelling and validation were identified and possible directions and approaches in addressing these challenges were suggested.
357 citations
TL;DR: This letter presents an improved backward/ forward sweep algorithm for three-phase load-flow analysis of radial distribution systems and shows that the algorithm is accurate and computationally efficient in comparing with two other commonly used methods.
Abstract: This letter presents an improved backward/ forward sweep algorithm for three-phase load-flow analysis of radial distribution systems. In the backward sweep, Kirchhoff's Current Law and Kirchhoff's Voltage Law are used to calculate the upstream bus voltage of each line or a transformer branch. Then, the linear proportional principle is adopted to find the ratios of the real and imaginary components of the specified voltage to those of the calculated voltage at the substation bus. In the forward sweep, the voltage at each downstream bus is then updated by the real and imaginary components of the calculated bus voltage multiplying with the corresponding ratio. The procedure stops after the mismatch of the calculated and the specified voltages at the substation is less than a convergence tolerance. The proposed algorithm is tested with three IEEE benchmark distribution systems. Results show that the algorithm is accurate and computationally efficient in comparing with two other commonly used methods
291 citations
TL;DR: In this article, different types of commercially available double layer capacitors (EDLCs) were analyzed in accelerated ageing tests by impedance spectroscopy and the characteristic change of the impedance parameters was discussed and an ageing model for EDLCs was developed.
265 citations
TL;DR: An experimental study is presented to demonstrate how this technique can be used to detect structural damage in real time and a modified frequency-domain autoregressive model with exogenous inputs (ARX) is described.
Abstract: This paper presents an overview and recent advances in impedance-based structural health monitoring. The basic principle behind this technique is to apply high-frequency structural excitations (typically greater than 30 kHz) through surface-bonded piezoelectric transducers, and measure the impedance of structures by monitoring the current and voltage applied to the piezoelectric transducers. Changes in impedance indicate changes in the structure, which in turn can indicate that damage has occurred. An experimental study is presented to demonstrate how this technique can be used to detect structural damage in real time. Signal processing methods that address damage classifications and data compression issues associated with the use of the impedance methods are also summarized. Finally, a modified frequency-domain autoregressive model with exogenous inputs (ARX) is described. The frequency-domain ARX model, constructed by measured impedance data, is used to diagnose structural damage with levels of statistical confidence.
198 citations
TL;DR: In this paper, the authors presented the design and control of two three-level Z-source inverters, whose output voltage can be stepped down or up using only a single LC impedance network connected between the dc input source and either a neutral-point-clamped (NPC) or dc-link cascaded inverter circuitry.
Abstract: Three-level Z-source inverters are recent single-stage topological solutions proposed for buck-boost energy conversion with all favorable advantages of three-level switching retained. Despite their effectiveness in achieving voltage buck-boost conversion, existing three-level Z-source inverters use two LC impedance networks and two isolated dc sources, which can significantly increase the overall system cost and require a more complex modulator for balancing the network inductive voltage boosting. Offering a number of less costly alternatives, this letter presents the design and control of two three-level Z-source inverters, whose output voltage can be stepped down or up using only a single LC impedance network connected between the dc input source and either a neutral-point-clamped (NPC) or dc-link cascaded inverter circuitry. Through careful design of their modulation scheme, both inverters can function with the minimum of six device commutations per half carrier cycle (similar to that needed by a traditional buck three-level NPC inverter), while producing the correct volt-sec average and inductive voltage boosting at their ac output terminals. Physically, the designed modulation scheme can conveniently be implemented using a generic "alternative phase opposition disposition" carrier-based modulator with the appropriate triplen offset and time advance/delay added. The designed inverters, having a reduced passive component count, are lastly tested in simulation and experimentally using a laboratory prototype with the captured results presented in a later section of the letter
198 citations
TL;DR: In this paper, a solid oxide fuel cell was investigated based on differences in impedance spectra due to a change of operating parameters and the result was used to separate the anode and cathode contributions and to identify various types of processes.
Abstract: Many processes contribute to the overall impedance of an electrochemical cell, and these may be difficult to separate in the impedance spectrum. Here, we present an investigation of a solid oxide fuel cell based on differences in impedance spectra due to a change of operating parameters and present the result as the derivative of the impedance with respect to ln(f). The method is used to separate the anode and cathode contributions and to identify various types of processes.
191 citations
TL;DR: This study investigates multiple levels of impedance-matching methods for piezoelectric energy harvesting in order to enhance the conversion of mechanical to electrical energy.
Abstract: This study investigates multiple levels of impedance-matching methods for piezoelectric energy harvesting in order to enhance the conversion of mechanical to electrical energy. First, the transduction rate was improved by using a high piezoelectric voltage constant (g) ceramic material having a magnitude of g33 = 40 times 10-3 V m/N. Second, a transducer structure, cymbal, was optimized and fabricated to match the mechanical impedance of vibration source to that of the piezoelectric transducer. The cymbal transducer was found to exhibit ~40 times higher effective strain coefficient than the piezoelectric ceramics. Third, the electrical impedance matching for the energy harvesting circuit was considered to allow the transfer of generated power to a storage media. It was found that, by using the 10-layer ceramics instead of the single layer, the output current can be increased by 10 times, and the output load can be reduced by 40 times. Furthermore, by using the multilayer ceramics the output power was found to increase by 100%. A direct current (DC)-DC buck converter was fabricated to transfer the accumulated electrical energy in a capacitor to a lower output load. The converter was optimized such that it required less than 5 mW for operation.
177 citations
TL;DR: In this paper, an alternative model for fitting electrochemical impedance spectra of protective coatings is proposed, which describes broadening of the semicircle in the complex plane, in the absence of corrosion reactions.
170 citations
TL;DR: An imaging system capable of magnification, subwavelength-resolution and impedance matching, which minimizes reflection losses is developed, which is based on available materials and existing fabrication technologies.
Abstract: We propose an approach to optical imaging beyond the diffraction limit, based on transformation optics in concentric circular cylinder domains. The resulting systems allow image magnification and minimize reflection losses due to the impedance matching at the input or output boundaries. While perfect impedance matching at both surfaces can be obtained only in a system with radius-dependent magnetic permeability, we demonstrate that comparable performance can be achieved in an optimized nonmagnetic design.
164 citations
TL;DR: In this paper, the global impedance response has a quasi-constant phase element (CPE) character, but with a CPE coefficient alpha that is a function of both dimensionless frequency K and dimensionless current density J, and for small values of K, alpha approached unity, whereas, for larger values of J, alpha reached values near 0.78.
Abstract: Geometry-induced current and potential distributions modify the global impedance response of a disk electrode subject to faradaic reactions. The problem was treated for both linear and Tafel kinetic regimes. The apparent capacity of a disk electrode embedded in an insulating plane was shown to vary considerably with frequency. At frequencies above the characteristic frequency for the faradaic reaction, the global impedance response has a quasi-constant-phase element (CPE) character, but with a CPE coefficient alpha that is a function of both dimensionless frequency K and dimensionless current density J. For small values of J, alpha approached unity, whereas, for larger values of J, alpha reached values near 0.78. The calculated values of alpha are typical of those obtained in impedance measurements on disk electrodes. For determining the interfacial capacitance, the influence of current and potential distributions on the impedance response cannot be neglected, even if the apparent CPE exponent alpha has values close to unity. Several methods taken from the literature were tested to determine their suitability for extracting interfacial capacitance values from impedance data on disk electrodes. The best results were obtained using a formula which accounted for both ohmic and charge-transfer resistances.
TL;DR: In this paper, a power harvester has been designed and fabricated in a CMOS 0.18-process that operates at the UHF band of 920 MHz, and the circuit employs an impedance transformation circuit to boost the input RF signal that leads to the improvement of the circuit performance.
Abstract: This paper presents a guideline to design and optimize a power harvester circuit for an RF identification transponder. A power harvester has been designed and fabricated in a CMOS 0.18- process that operates at the UHF band of 920 MHz. The circuit employs an impedance transformation circuit to boost the input RF signal that leads to the improvement of the circuit performance. The power harvester has been optimized to achieve maximum sensitivity by characterizing both the impedance transformation network and the rectifier circuit and choosing the optimum values for the circuit parameters. The measurement results show sensitivity of 14.1 dBm for dc output voltage of 1 V and the output current of 2 mum that corresponds to the output power of 2 muW.
Patent•
[...]
TL;DR: In this article, a low-loss interface for connecting an integrated circuit such as a monolithic microwave integrated circuit to an energy transmission device such as the waveguide is disclosed, which is a pin attached to a matching network that matches the impedance of the energy produced at the circuit to the impedance required by a waveguide without the use of a dielectric material.
Abstract: In general, in accordance with an exemplary aspect of the present invention, a low-loss interface for connecting an integrated circuit such as a monolithic microwave integrated circuit to an energy transmission device such as a waveguide is disclosed. In one exemplary embodiment, the interface comprises a pin attached to a matching network that matches the impedance of the energy produced at the circuit to the impedance required by the waveguide without the use of a dielectric material.
TL;DR: In this article, the axial preloading of a piezoelectric bimorph vibrating in the flexural mode was studied for a power harvester to effectively scavenge energy from ambient mechanical vibrations/noise with varying frequency spectra.
Abstract: We study the technique to adjust the performance of a piezoelectric bimorph vibrating in the flexural mode through axial preloads, which is useful for a power harvester to effectively scavenge energy from ambient mechanical vibrations/noise with varying-frequency spectra. The external circuit connected to the bimorph is simplified as an impedance in the analysis. Analytical solutions are derived. The analyses show that resonance happens when the natural frequency of the bimorph is adjusted adjacent to the external driving frequency by preloading, and the output power density can be raised many more times in that case. The mechanism for an axial preload to improve the bimorph performance at varying-frequency vibrations is examined in detail.
TL;DR: In this paper, a new method for designing the microstrip branch-line couplers with predetermined compact size and bandwidth is proposed, which can be easily fabricated on the printed circuit board without any lumped element.
Abstract: A new method for designing the microstrip branch- line couplers with predetermined compact size and bandwidth is proposed in this paper. With the proposed approach, the size of the quarter-wavelength transmission line in the branch-line coupler can be reduced greatly. In addition, the proposed couplers can be easily fabricated on the printed circuit board without any lumped element. A chart concludes the relationship between bandwidth and size reduction rate. It shows that open stubs with low impedance perform better than those with high impedance; moreover, the more open stubs with low impedance utilized, the broader the bandwidth will be. Furthermore, the measured frequency responses show good agreement with the theoretical results.
TL;DR: In this article, the influence of geometry-induced current and potential distributions on the impedance response of an ideally polarized disk electrode was calculated using a coherent notation for local and global impedance which accounts for global, local, local interfacial, and both global and local ohmic impedances.
Abstract: Two numerical methods were used to calculate the influence of geometry-induced current and potential distributions on the impedance response of an ideally polarized disk electrode. A coherent notation is proposed for local and global impedance which accounts for global, local, local interfacial, and both global and local ohmic impedances. The local and ohmic impedances are shown to provide insight into the frequency dispersion associated with the geometry of disk electrodes. The high-frequency global impedance response has the appearance of a constant-phase element CPE but can be considered to be only an apparent CPE because the CPE exponent is a function of frequency.
TL;DR: In this article, simple analytical formulas for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays or square patches over ground planes are introduced.
Abstract: This paper introduces simple analytical formulas for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied.
TL;DR: A microfluidic device to capture physically single cells within microstructures inside a channel and to measure the impedance of a single HeLa cell using impedance spectroscopy is presented.
Abstract: This work presents a microfluidic device to capture physically single cells within microstructures inside a channel and to measure the impedance of a single HeLa cell (human cervical epithelioid carcinoma) using impedance spectroscopy. The device includes a glass substrate with electrodes and a PDMS channel with micro pillars. The commercial software CFD–ACE+ is used to study the flow of the microstructures in the channel. According to simulation results, the probability of cell capture by three micro pillars is about 10%. An equivalent circuit model of the device is established and fits closely to the experimental results. The circuit can be modeled electrically as cell impedance in parallel with dielectric capacitance and in series with a pair of electrode resistors. The system is operated at low frequency between 1 and 100 kHz. In this study, experiments show that the HeLa cell is successfully captured by the micro pillars and its impedance is measured by impedance spectroscopy. The magnitude of the HeLa cell impedance declines at all operation voltages with frequency because the HeLa cell is capacitive. Additionally, increasing the operation voltage reduces the magnitude of the HeLa cell because a strong electric field may promote the exchange of ions between the cytoplasm and the isotonic solution. Below an operating voltage of 0.9 V, the system impedance response is characteristic of a parallel circuit at under 30 kHz and of a series circuit at between 30 and 100 kHz. The phase of the HeLa cell impedance is characteristic of a series circuit when the operation voltage exceeds 0.8 V because the cell impedance becomes significant.
TL;DR: It is demonstrated that the MLS technique can give multi-frequency (broad-band) measurement in a short time period and good agreement is shown between the MLS data and both circuit simulations and conventional AC single frequency measurements.
Abstract: A novel impedance spectroscopy technique has been developed for high speed single biological particle analysis. A microfluidic cytometer is used to measure the impedance of single micrometre sized latex particles at high speed across a range of frequencies. The setup uses a technique based on maximum length sequence (MLS) analysis, where the time-dependent response of the system is measured in the time domain and transformed into the impulse response using fast M-sequence transform (FMT). Finally fast Fourier transform (FFT) is applied to the impulse response to give the transfer-function of the system in the frequency domain. It is demonstrated that the MLS technique can give multi-frequency (broad-band) measurement in a short time period (ms). The impedance spectra of polystyrene micro-beads are measured at 512 evenly distributed frequencies over a range from 976.5625 Hz to 500 kHz. The spectral information for each bead is obtained in approximately 1 ms. Good agreement is shown between the MLS data and both circuit simulations and conventional AC single frequency measurements.
TL;DR: A general approach to analytically solve the electric field distributions for two different designs of cytometers: parallel facing electrodes and coplanar electrodes, using the Schwarz-Christoffel Mapping method is presented.
Abstract: Microfabricated impedance cytometers have been developed to measure the electrical impedance of single biological particles at high speed. A general approach to analytically solve the electric field distributions for two different designs of cytometers: parallel facing electrodes and coplanar electrodes, using the Schwarz–Christoffel Mapping method is presented. Compared to previous analytical solutions, our derivations are more systematic and solutions are more straightforward. The solutions have been validated by comparison with numerical simulations performed using the finite element method. The influences on the electric field distribution due to the variations in the geometry of the devices have been discussed. A simple method is used to determine the impedance sensitivity of the system and to compare the two electrode designs. For identical geometrical parameters, we conclude that the parallel electrodes design is more sensitive than the coplanar electrodes.
04 Jun 2007
TL;DR: In this article, an on-line software method for impedance estimation of the energized impedances such as power system grid is presented. The proposed method is based on producing a perturbation on the output of the power converter that is in the form of periodical injection of one or two voltage harmonic signals.
Abstract: The paper presents an on-line software method for impedance estimation of the energized impedances such as power system grid. The proposed method is based on producing a perturbation on the output of the power converter that is in the form of periodical injection of one or two voltage harmonic signals. The single harmonic injection uses a 600 Hz signal and the double harmonic injection uses a 400 Hz and 600 Hz signals, respectively. During the perturbation, the current response(s) at the same frequency as the injected signal(s) is/are measured. The value of the grid impedance is estimated using two different signal processing algorithms. The DFT technique is used for the single harmonic injection and the statistic technique is used for the double harmonic injection. The grid impedance estimation is used for compliance with the anti-islanding requirements of the German standard (VDE0126) and for robust control of the distributed power generation systems (DPGS). Selected results are presented to confirm the performances of the proposed method.
TL;DR: A differential ac readout concept for FET microarrays, which enables a stable operation of the sensor against many of these side-parameters, reliable readout and a possibility for a quick screening of large sensor arrays.
TL;DR: In this article, a new electrode model involving the fractal structure of activated carbon used as electrode material was proposed for an electric double layer capacitor (EDLC), where the branch pore structure of three sizes of cylindrical pores were related to macro, meso, and micro pore sizes.
TL;DR: The present computer simulation results suggest that MAT-MI can reconstruct conductivity images of biological tissue with high spatial resolution and high contrast and in the present simulation study, a two-layer spherical model is used.
Abstract: We have conducted computer simulation and experimental studies on magnetoacoustic-tomography with magnetic induction (MAT-MI) for electrical impedance imaging. In MAT-MI, the object to be imaged is placed in a static magnetic field, while pulsed magnetic stimulation is applied in order to induce eddy current in the object. In the static magnetic field, the Lorentz force acts upon the eddy current and causes acoustic vibrations in the object. The propagated acoustic wave is then measured around the object to reconstruct the electrical impedance distribution. In the present simulation study, a two-layer spherical model is used. Parameters of the model such as sample size, conductivity values, strength of the static and pulsed magnetic field, are set to simulate features of biological tissue samples and feasible experimental constraints. In the forward simulation, the electrical potential and current density are solved using Poisson's equation, and the acoustic pressure is calculated as the forward solution. The electrical impedance distribution is then reconstructed from the simulated pressure distribution surrounding the sample. The present computer simulation results suggest that MAT-MI can reconstruct conductivity images of biological tissue with high spatial resolution and high contrast. The feasibility of MAT-MI in providing high spatial resolution images containing impedance-related information has also been demonstrated in a phantom experiment
TL;DR: In this article, an accurate fault-location algorithm has been obtained for the line-to-line fault as an extension of the author's previous work for line to ground fault location.
Abstract: From a direct three-phase circuit analysis, an accurate fault-location algorithm has been obtained for the line-to-line fault as an extension of the author's previous work for line-to-ground fault location. Robustness of the proposed algorithm to load impedance uncertainty is enhanced by the introduction of impedance compensation using voltage and current measurements. Simulation results show a high degree of accuracy and robustness to load uncertainty.
TL;DR: In this paper, an experimental and statistical investigation was conducted to show the influence of external loading on EM admittance signatures of PZT transducers, and it was observed that the susceptance signature is a better indicator than conductance signature for detecting in situ stress in the host structure.
Abstract: Damage detection using electromechanical (EM) impedance in structural health monitoring (SHM) of engineering structures is rapidly emerging as a useful technique. In the EM impedance method, piezoceramic (PZT) transducers are either surface bonded to or embedded inside the host structure and are subjected to electric actuation. The EM admittance signatures of the PZT transducers, which consist of real and imaginary parts, serve as indicators to predict the health/integrity of the host structure. However, in real life, structural components such as slabs, beams and columns are constantly subjected to some form of external loading. The EM admittance signature obtained for such a constantly loaded structure is different from that obtained when damages are present in the structure. This paper presents an experimental and statistical investigation to show the influence of loading on EM admittance signatures. It is also observed that the susceptance signature is a better indicator than the conductance signature for detecting in situ stress in the host structure. This observation is further supported by a statistical analysis. This paper is expected to be useful for the non-destructive evaluation of engineering structures with external loading.
TL;DR: In this paper, the influence of geometry-induced current and potential distributions on the impedance response of a blocking disk electrode with a local constant phase element behavior was calculated and the results were shown to provide insight into the frequency dispersion associated with the geometry of disk electrodes.
Abstract: Numerical methods were used to calculate the influence of geometry-induced current and potential distributions on the impedance response of a blocking disk electrode with a local constant-phase element behavior. While the calculated global impedance is purely capacitive, the local impedance has high-frequency inductive loops that were observed in experiments conducted on a stainless steel electrode in 0.05 M NaCI + 0.005 M Na 2 SO 4 electrolyte. The calculated global impedance responses are in good agreement with experimental results obtained using both the steel electrode and a glassy-carbon disk in KCl electrolytes of differing concentrations. The computed local and both local and global ohmic impedances are shown to provide insight into the frequency dispersion associated with the geometry of disk electrodes.
TL;DR: In this article, the applicability of closed form expressions for the ground impedance and ground admittance of buried horizontal wires (bare and insulated) for lightning or switching transient analyses based on transmission line (TL) theory is investigated.
Abstract: The paper investigates the applicability of some closed form expressions for the ground impedance and ground admittance of buried horizontal wires (bare and insulated) for lightning or switching transient analyses based on transmission line (TL) theory. In view of the frequency contents that typically characterize such transients, the behavior of the ground impedance and admittance is studied for a wide frequency range up to 10 MHz. Low frequency approximation of the ground impedance is not always appropriate for transient analysis. Sensitivity analyses show that, unlike overhead wires, the ground impedance for buried wires is little sensitive to the ground conductivity. On the other hand, the ground admittance varies strongly with the ground conductivity. The paper also discusses the results of transient analysis of buried cables performed by means of electromagnetic transient programs (EMTP) that neglect the ground admittance. The limits of such an approximation are discussed in order to evaluate the applicability of EMTP-like programs to the transient analysis of buried conductors. Transient pulse propagation in time domain based on finite difference time domain (FDTD) method of solution of TL equations is also discussed for a future inclusion of non-linear phenomena, like soil ionization and arcing/breakdown mechanisms, in the soil. The analysis presented could be useful in estimating surge propagation characteristics of buried wires for appropriate insulation coordination and transient protection.
Patent•
07 Aug 2007
TL;DR: In this paper, an electrosurgical system and method is described, which consists of a generator and a microprocessor adapted to generate at least one tissue parameter based as a function of the initial impedance, impedance drop, the impedance minimum and the first impedance rise.
Abstract: An electrosurgical system and method are disclosed. The system includes an electrosurgical generator adapted to supply electrosurgical energy to tissue. The generator is further adapted to supply an electrical signal having at least one substantially constant value to tissue to determine initial tissue impedance response. The generator includes sensor circuitry adapted to continuously monitor initial tissue impedance response, wherein the initial tissue impedance response includes one of an initial impedance, an impedance drop, an impedance minimum and a first impedance rise. The generator also includes a microprocessor adapted to generate at least one tissue parameter based as a function of the initial impedance, the impedance drop, the impedance minimum and the first impedance rise. The system also includes an electrosurgical instrument including at least one active electrode adapted to apply electrosurgical energy to tissue for treatment.
TL;DR: In this paper, the authors used maximum length sequences (MLS) for periodic excitation signal in a microfluidic impedance cytometer, which allowed multi-frequency single cell impedance measurements to be made in a short time period.
Abstract: Measurements of the dielectric (or impedance) properties of cells can be used as a general characterization and diagnostic tool. In this paper, we describe a novel impedance spectroscopy technique for the analysis of single biological cells in suspension. The technique uses maximum length sequences (MLS) for periodic excitation signal in a microfluidic impedance cytometer. The method allows multi-frequency single cell impedance measurements to be made in a short time period (ms). Spectral information is obtained in the frequency domain by applying a fast M-sequence transform (FMT) and fast Fourier transform (FFT) to the time domain response. Theoretically, the impedance is determined from the transfer function of the system when the MLS is a current excitation. The order of the MLS and sampling rate of A/D conversion are two factors that determine the bandwidth and spectral accuracy of the technique. Experimentally, the applicability of the technique is demonstrated by characterizing the impedance spectrum of red blood cells (RBCs) in a microfluidic cytometer. The impedance is measured within 1 ms at 512 discrete frequencies, evenly distributed in the range from 976.56 Hz to 500 kHz. The measured spectrum shows good agreement with simulations.