Showing papers on "Electrical impedance published in 2008"

The use of electrochemical impedance spectroscopy for biosensing

Abstract: This review introduces the basic concepts and terms associated with impedance and techniques of measuring impedance. The focus of this review is on the application of this transduction method for sensing purposes. Examples of its use in combination with enzymes, antibodies, DNA and with cells will be described. Important fields of application include immune and nucleic acid analysis. Special attention is devoted to the various electrode design and amplification schemes developed for sensitivity enhancement. Electrolyte insulator semiconductor (EIS) structures will be treated separately.

Simple and Accurate Analytical Model of Planar Grids and High-Impedance Surfaces Comprising Metal Strips or Patches

Abstract: Simple analytical formulas are introduced 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.

Joint-space impedance control for tendon-driven manipulators

Abstract: A system and method for controlling tendon-driven manipulators that provide a closed-loop control of joint torques or joint impedances without inducing dynamic coupling between joints. The method includes calculating tendon reference positions or motor commands by projecting a torque error into tendon position space using a single linear operation. The method calculates this torque error using sensed tendon tensions and a reference torque and internal tension. The method can be used to control joint impedance by calculating the reference torque based on a joint position error. The method limits minimum and maximum tendon tensions by projecting the torque error into the tendon tension space and then projecting ii back into joint space.

A Real-Time Voltage Instability Identification Algorithm Based on Local Phasor Measurements

Abstract: This paper proposes a new voltage instability risk indicator based on local phasor measurements at fast sampling rate. The effectiveness of the indicator is analyzed at EHV load and ldquotransitrdquo buses. The risk criterion is based on the real-time computation of the Thevenin equivalent impedance of the classic electrical circuit given by an equivalent generator connected to an equivalent load impedance through an equivalent connecting impedance. The main contribution of the paper is the innovating algorithm utilized on the real-time adaptive identification of the Thevenin voltage and impedance equivalents. The algorithm performance is shown through a detailed sensitivity analysis. The paper presents important numerical results from the actual Italian EHV network.

Six-DOF Impedance Control of Dual-Arm Cooperative Manipulators

Abstract: In this paper, the problem of impedance control of dual-arm cooperative manipulators is studied. A general impedance control scheme is adopted, which encompasses a centralized impedance control strategy, aimed at conferring a compliant behavior at the object level, and a decentralized impedance control, enforced at the end-effector level, aimed at avoiding large internal loading of the object. Remarkably, the mechanical impedance behavior is defined in terms of geometrically consistent stiffness. The overall control scheme is based on a two-loop arrangement, where a simple proportional integral derivative inner motion loop is adopted for each manipulator, while an outer loop, using force and moment measurements at the robots wrists, is aimed at imposing the desired impedance behaviors. The developed control scheme is experimentally tested on a dual-arm setup composed of two 6-DOF industrial manipulators carrying a common object. The experimental investigation concerns the four different controller configurations that can be achieved by activating/deactivating the single impedance controllers.

Slip-enhanced electrokinetic energy conversion in nanofluidic channels

Abstract: We investigate theoretically the influence of hydrodynamic slip at the surface of a nanofluidic channel on the efficiency with which electrokinetic phenomena can be used to convert hydrostatic energy to electrical power. Slip is introduced by applying the Navier boundary condition to the pressure-driven and the electro-osmotic components of the fluid velocity. A strong enhancement in the efficiency is predicted for increasing slip length due to the resulting decrease in the fluidic impedance and increase in the streaming conductance. These effects are moderated by a decrease in the electrical impedance, which promotes dissipation. The maximum efficiency approaches 100% as the slip length diverges, and a potentially practical 40% efficiency is expected for a moderate 30 nm slip length in a 10 nm high channel. Recently reported slip lengths for carbon nanotube filters suggest that efficiencies above 70% and high power densities might be achieved in a graphitic system.

Electro-Mechanical Impedance-Based Wireless Structural Health Monitoring Using PCA-Data Compression and k-means Clustering Algorithms:

Abstract: This article presents a practical method for an electro-mechanical impedance-based wireless structural health monitoring (SHM), which incorporates the principal component analysis (PCA)-based data ...

A high-accuracy impedance spectrometer for measuring sediments with low polarizability

Abstract: Spectral impedance measurements are receiving increased attention with regard to the characterization of soils, sediments and rocks, particularly in terms of the internal rock structure, the mineralogical composition and the chemistry of fluids contained in porous rocks. In fluid-saturated, porous sedimentary rocks, which are of particular relevance for many hydrological and environmental problems, the polarization processes that give rise to an observed phase shift between input current and output voltage signals are caused by the interaction of the electrolyte in the pores of the rock with electrically charged mineral surfaces. However, this phase response is relatively weak, typically smaller than 10 mrad and sometimes even of the order of only 1 mrad. In order to reliably measure such phase responses in the relevant frequency range, a high-accuracy impedance spectrometer is required. This system must allow phase measurements between 1 mHz and 1 kHz with a phase accuracy better than 0.1 mrad. In this paper, we present a new impedance spectrometer which meets these requirements. It is based on the four-point measurement method and offers a measurement range from 1 mHz to 45 kHz. Furthermore, we present design information for the sample holder and the electrodes, and methods for performing numerical corrections to reduce measurement errors. The overall accuracy of the setup was validated using water and sand with well-defined polarizable objects.

Impedance matching and emission properties of optical antennas in a nanophotonic circuit

Abstract: An experimentally realizable prototype nanophotonic circuit consisting of a receiving and an emitting nano antenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between nanophotonic circuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the transmitting nano antenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nano antenna impedance to the transmission line characteristic impedance by variations of the antenna length and width realizable by modern microfabrication techniques. The radiation efficiency of the transmitting antenna also depends on its geometry but is independent of the degree of impedance matching. Our systems approach to nanophotonics provides the basis for realizing general nanophotonic circuits and a large variety of derived novel devices.

High-Frequency Modeling of Power Transformers for Use in Frequency Response Analysis (FRA)

Abstract: This paper presents an advanced model of the frequency response of a three-phase power transformer for use in conjunction with diagnostic measurements by the method of frequency response analysis (FRA). The model includes high- frequency behavior of the laminated core and the insulation through taking into account the frequency dependencies of the complex permittivity of insulation materials (paper, pressboard, and oil) and of the anisotropic complex permeability of magnetic core and conductors. A lumped parameter circuit model is used to simulate the frequency response of open-circuit impedance, short-circuit impedance, and impedance between primary and secondary windings, in which the characteristics of circuit elements are calculated by means of the finite-element method. The effect of correct representation of each circuit element on the FRA response is analyzed and discussed in comparison to measurement results on a real transformer.

A GSM/EDGE/WCDMA Adaptive Series-LC Matching Network Using RF-MEMS Switches

Abstract: To preserve link quality of mobile phones, under fluctuating user conditions, an adaptively controlled series-LC matching circuit is presented for multi-band and multi-mode operation. Following a bottom-up approach, we discuss the design of an RF-MEMS unit cell for the construction of a 5-bit switched capacitor array. To reduce dielectric charging of the RF-MEMS devices their average biasing voltage is minimized by applying a bipolar waveform with a small high/low duty-cycle obtained from a high-voltage driver IC. RF-MEMS capacitive switches are applied because of their high linearity, low loss, large tuning range, and easy control in the discrete domain. Application specific RF-MEMS pull-in and pull-out voltage requirements are derived. An impedance phase detector is used to feed mismatch information to an up-down counter providing robust iterative control. The measured MEMS array capacitance tuning ratio is almost a factor 10. Module insertion loss is 0.5 dB at low-band and high-band. Harmonic distortion is less than -85ndBc at 35 dBm output power and the EVM, measured in EDGE-mode, is less than 1% at 27 dBm . The adaptively controlled module, connected to a planar inverted-F antenna, shows desired impedance correction. For extreme hand-effects the maximum module impedance correction at 900 MHz is -75jOmega.

Modeling of a Cantilever-Based Near-Field Scanning Microwave Microscope

Abstract: We present a detailed modeling and characterization of our scalable microwave nanoprobe, which is a micro-fabricated cantilever-based scanning microwave probe with separated excitation and sensing electrodes. Using finite-element analysis, the tip-sample interaction is modeled as small impedance changes between the tip electrode and the ground at our working frequencies near 1GHz. The equivalent lumped elements of the cantilever can be determined by transmission line simulation of the matching network, which routes the cantilever signals to 50 Ohm feed lines. In the microwave electronics, the background common-mode signal is cancelled before the amplifier stage so that high sensitivity (below 1 atto-Farad capacitance changes) is obtained. Experimental characterization of the microwave probes was performed on ion-implanted Si wafers and patterned semiconductor samples. Pure electrical or topographical signals can be realized using different reflection modes of the probe.

Novel Modified UWB Planar Monopole Antenna With Variable Frequency Band-Notch Function

Abstract: A novel modified microstrip-fed ultrawideband (UWB) planar monopole antenna with variable frequency band-notch characteristic is presented. By inserting two slots in the both sides of microstrip feedline on the ground plane, much wider impedance bandwidth can be produced. A modified H-shaped conductor-backed plane with variable dimensions is used in order to generate the frequency band-stop performance and control its characteristics such as band-notch frequency and its bandwidth. The designed antenna has a small size of 22 x 22 mm2 and operates over the frequency band between 3.1 and 14 GHz for VSWR < 2 while showing the band rejection performance in the frequency band of 5.1 to 5.9 GHz.

Studies of structural, thermal and electrical behavior of polymer nanocomposite electrolytes

Abstract: Structural, thermal and electrical behavior of polymer-clay nanocomposite electrolytes consisting of polymer (polyethylene oxide (PEO)) and NaI as salt with different concentrations of organically modified Na + montmorillonite (DMMT) filler have been investigated. The formation of nanocomposites and changes in the structural properties of the materials were investigated by X-ray diffraction (XRD) analysis. Complex impedance analysis shows the existence of bulk and material-electrode interface properties of the composites. The relative dielectric constant (er) decreases with increase in frequency in the low frequency region whereas frequency independent behavior is observed in the high frequency region. The electrical modulus representation shows a loss feature in the imaginary component. The relaxation associated with this feature shows a stretched exponential decay. Studies of frequency dependence of dielectric and modulus formalism suggest that the ionic and polymer segmental motion are strongly coupled manifeasting as peak in the modulus (M") spectra with no corresponding feature in dielectric spectra. The frequency dependence of ac (alternating current) conductivity obeys Jon- scher power law feature in the high frequency region, where as the low frequency dispersion indicating the presence of electrode polarization effect in the materials.

Fractional Electrical Impedances in Botanical Elements

Abstract: Fractional calculus (FC) is no longer considered solely from a mathematical viewpoint, and is now applied in many emerging scientific areas, such as electricity, magnetism, mechanics, fluid dynamics, and medicine. In the field of dynamical systems, significant work has been carried out proving the importance of fractional order mathematical models. This article studies the electrical impedance of vegetables and fruits from a FC perspective. From this line of thought, several experiments are developed for measuring the impedance of botanical elements. The results are analyzed using Bode and polar diagrams, which lead to electrical circuit models revealing fractional-order behaviour.

Experimental investigation of dielectric barrier discharge plasma actuators driven by repetitive high-voltage nanosecond pulses with dc or low frequency sinusoidal bias

Abstract: Experimental studies were conducted of a flow induced in an initially quiescent room air by a single asymmetric dielectric barrier discharge driven by voltage waveforms consisting of repetitive nanosecond high-voltage pulses superimposed on dc or alternating sinusoidal or square-wave bias voltage. To characterize the pulses and to optimize their matching to the plasma, a numerical code for short pulse calculations with an arbitrary impedance load was developed. A new approach for nonintrusive diagnostics of plasma actuator induced flows in quiescent gas was proposed, consisting of three elements coupled together: the schlieren technique, burst mode of plasma actuator operation, and two-dimensional numerical fluid modeling. The force and heating rate calculated by a plasma model was used as an input to two-dimensional viscous flow solver to predict the time-dependent dielectric barrier discharge induced flow field. This approach allowed us to restore the entire two-dimensional unsteady plasma induced flow ...

System, apparatus, method and sensors for monitoring structures

Abstract: A system, apparatus and method for monitoring structures is provided. The system includes a measurement acquisition unit having a first connection point for receiving a sensor unit and a second connection point that is electrically isolated from the first connection point when invoking the sensor unit. A measurement sensor for detecting moisture includes a pair of spaced apart conductors; and an impedance circuit in parallel with the conductors and having a finite impedance such that an impedance of the measurement sensor greater than the finite impedance indicates an impaired connection. A termination module includes a base attachable to a measurement sensor, and the impedance circuit. A moisture content measurement sensor includes: a pair of conductors in electrically insulating material; and electrically conductive probe supports attached to the conductors for receiving probes and forming electrical connections between conductors and probes. Eyelet rivets may be used as probe supports.

Chip Impedance Matching for UHF RFID Tag Antenna Design

Abstract: Passive UHF RFID tag consists of a microchip attached directly to an antenna. Proper impedance match between the antenna and the chip is crucial in RFID tag design. It directly influences RFID system performance characteristics such as the range of a tag. It is known that an RFID microchip is a nonlinear load whose complex impedance in each state varies with the frequency and the input power. This paper illustrates a proper calculation of the tag power reflection coefficient for maximum power transfer by taking into account of the changing chip impedance versus frequency.

Modeling and design methodology for metal-insulator-metal plasmonic Bragg reflectors

Abstract: In this paper, we present a modeling and design methodology based on characteristic impedance for plasmonic waveguides with Metal-Insulator-Metal (MIM) configuration. Finite-Difference Time-Domain (FDTD) simulations indicate that the impedance matching results in negligible reflection at discontinuities in MIM heterostructures. Leveraging the MIM impedance model, we present a general Transfer Matrix Method model for MIM Bragg reflectors and validate our model against FDTD simulations. We show that both periodically stacked dielectric layers of different thickness or different material can achieve the same performance in terms of propagation loss and minimum transmission at the central bandgap frequency in the case of a finite number of periods.

Frequency-difference electrical impedance tomography (fdEIT): algorithm development and feasibility study.

Abstract: Frequency-difference electrical impedance tomography (fdEIT) has been proposed to deal with technical difficulties of a conventional static EIT imaging method caused by unknown boundary geometry, uncertainty in electrode positions and other systematic measurement artifacts. In fdEIT, we try to produce images showing changes of a complex conductivity distribution with respect to frequency. Simultaneously injecting currents with at least two frequencies, we find differences of measured boundary voltages between those frequencies. In most previous studies, real parts of frequency-difference voltage data were used to reconstruct conductivity changes and imaginary parts to reconstruct permittivity changes. This conventional approach neglects the interplay of conductivity and permittivity upon measured boundary voltage data. In this paper, we propose an improved fdEIT image reconstruction algorithm that properly handles the interaction. It uses weighted frequency differences of complex voltage data and a complex sensitivity matrix to reconstruct frequency-difference images of complex conductivity distributions. We found that there are two major sources of image contrast in fdEIT. The first is a contrast in complex conductivity values between an anomaly and background. The second is a frequency dependence of a complex conductivity distribution to be imaged. We note that even for the case where conductivity and permittivity do not change with frequency, the fdEIT algorithm may show a contrast in frequency-difference images of complex conductivity distributions. On the other hand, even if conductivity and permittivity values significantly change with frequency, there is an example where we cannot find any contrast. The performance of the proposed method is demonstrated by using computer simulations to validate its feasibility in future experimental studies.

Optimal Single-Port Matching Impedance for Capacity Maximization in Compact MIMO Arrays

Abstract: A complete multiple-input multiple-output (MIMO) system model with compact arrays at both link ends containing arbitrary matching networks is presented based on a Z-parameter approach. The complete channel matrix including the coupling effect is also presented. Utilizing this system model, the optimum single-port matching impedance for capacity maximization is derived for a 2 times 2 MIMO system with coupling at the receivers only. A closed-form result for the optimum matching impedance in high signal-to-noise ratio scenarios is given and proved to be equal to the input impedance of the receive end. Simulation of ideal dipoles verifies our analytical results and demonstrates the superiority of the optimum matching to other matching conditions in improving MIMO system performance. Experimental data for monopoles is also presented to further confirm our numerical findings and validate the accuracy of our derivation.

High-performance current differencing transconductance amplifier and its application in precision current-mode rectification

Abstract: A CMOS-based circuit for realization of high-performance current differencing transconductance amplifier (CDTA) is demonstrated. The proposed circuit offers the advantages of a wide frequency bandwidth and very small input terminal impedance. The results of circuit simulations and an application example are given to illustrate the advantages of the proposed circuit for precise high-frequency signal rectification.

An Electrical Circuit for Modeling the Dynamic Response of Li-Ion Polymer Batteries

Abstract: An equivalent electrical circuit model based on parameters taken from ac impedance measurements obtained from a Li-ion polymer battery is simulated in a Matlab/Simulink environment The model representation contains relevant parameters, including ohmic resistance, slow migration of Li-ions through the surface layers, faradaic charge transfer process, solid-state diffusion of Li-ions, and charge accumulation (intercalation capacitance) within the host material The model also takes into account the non-homogeneous distribution properties (eg, particle size, pore geometry) of the electrode which account for deviation from the ideal finite space Warburg behavior The simulated and experimental results are compared and demonstrate that the impedance model can accurately predict the discharge power performance and transient and dynamic behavior of the Li-ion polymer batteries

Real-time monitoring primary cardiomyocyte adhesion based on electrochemical impedance spectroscopy and electrical cell-substrate impedance sensing.

Abstract: The cell−substrate distance is a direct indicator of cell adhesion to extracellular matrix which is indispensable in cell culture. A real-time monitoring approach can provide a detailed profile of cell adhesion, so that enables the detecting of adhesion-related cell behavior. In this work, we report a novel real-time impedance-based method to record the adhesion profile of cardiomyocyte, overcoming its inscrutability due to the primary culture. Microfabricated biosensors are applied in cardiomyocyte culture after characterizing the cell-free system. Cyclic frequency scanning data of cell-related impedance are generated and automatically fit into the equivalent circuit model, which is established using electrochemical impedance spectroscopy. The data are displayed as the alteration of normalized cell−substrate distance and the essential parameters for manual electric cell−substrate impedance sensing calibration of absolute distance. The time course displays a significant decline in the equivalent cell−subs...

Effective Radii of On-Chip Decoupling Capacitors

Abstract: Decoupling capacitors are widely used to reduce power supply noise. On-chip decoupling capacitors have traditionally been allocated into the white space available on a die or placed inside the rows in standard cell circuit blocks. The efficacy of on-chip decoupling capacitors depends upon the impedance of the power/ground lines connecting the capacitors to the current loads and power supplies. A design methodology for placing on-chip decoupling capacitors is presented in this paper. A maximum effective radius is shown to exist for each on-chip decoupling capacitor. Beyond this effective distance, a decoupling capacitor is ineffective. Depending upon the parasitic impedance of the power distribution system, the maximum voltage drop seen at the current load is caused either by the first droop (determined by the rise time) or by the second droop (determined by the transition time). Two criteria to estimate the minimum required on-chip decoupling capacitance are developed based on the critical parasitic impedance. In order to provide the required charge drawn by the load, the decoupling capacitor has to be charged before the next switching cycle. For an on-chip decoupling capacitor to be effective, both effective radii criteria should be simultaneously satisfied.

Three-dimensional hydrodynamic focusing in a microfluidic Coulter counter

Abstract: Electrical impedance-based particle detection or Coulter counting, offers a lab-on-chip compatible method for flow cytometry. Developments in this area will produce devices with greater portability, lower cost, and lower power requirements than fluorescence-based flow cytometry. Because conventional Coulter apertures are prone to clogging, hydrodynamic focusing improves the device by creating fluid-walled channels with variable width to increase sensitivity without the associated risk of blocking the channel. We describe a device that focuses the sample in three dimensions, creating a narrow sample stream on the floor of the channel for close interaction with sensing electrodes. The key to this design is a stepped outlet channel fabricated in a single layer with soft lithography. In contrast to previous impedance-based designs, the new design requires minimal alignment with the substrate. Three-dimensional focusing maximizes the sensitivity of the device to cell-size particles within much larger channels. Impedance-based particle sensing experiments within this device show an increase in percentage conductivity change by a factor of 2.5 over devices that only focus the sample in the horizontal direction.