Showing papers on "Electrical impedance published in 2004"

Antenna miniaturization and bandwidth enhancement using a reactive impedance substrate

Abstract: The concept of a novel reactive impedance surface (RIS) as a substrate for planar antennas, that can miniaturize the size and significantly enhance both the bandwidth and the radiation characteristics of an antenna is introduced. Using the exact image formulation for the fields of elementary sources above impedance surfaces, it is shown that a purely reactive impedance plane with a specific surface reactance can minimize the interaction between the elementary source and its image in the RIS substrate. An RIS can be tuned anywhere between perfectly electric and magnetic conductor (PEC and PMC) surfaces offering a property to achieve the optimal bandwidth and miniaturization factor. It is demonstrated that RIS can provide performance superior to PMC when used as substrate for antennas. The RIS substrate is designed utilizing two-dimensional periodic printed metallic patches on a metal-backed high dielectric material. A simplified circuit model describing the physical phenomenon of the periodic surface is developed for simple analysis and design of the RIS substrate. Also a finite-difference time-domain (FDTD) full-wave analysis in conjunction with periodic boundary conditions and perfectly matched layer walls is applied to provide comprehensive study and analysis of complex antennas on such substrates. Examples of different planar antennas including dipole and patch antennas on RIS are considered, and their characteristics are compared with those obtained from the same antennas over PEC and PMC. The simulations compare very well with measured results obtained from a prototype /spl lambda//10 miniaturized patch antenna fabricated on an RIS substrate. This antenna shows measured relative bandwidth, gain, and radiation efficiency of BW=6.7, G=4.5 dBi, and e/sub r/=90, respectively, which constitutes the highest bandwidth, gain, and efficiency for such a small size thin planar antenna.

Dielectric spectroscopy in a micromachined flow cytometer: theoretical and practical considerations

Abstract: We propose a model to determine the influence of different cell properties, such as size, membrane capacitance and cytoplasm conductivity, on the impedance spectrum as measured in a microfabricated cytometer. A dielectric sphere of equivalent complex permittivity is used as a simplified model to describe a biological cell. The measurement takes place between a pair of facing microelectrodes in a microchannel filled with a saline solution. The model incorporates various cell parameters, such as dielectric properties, size and position in the channel. A 3D finite element model is used to evaluate the magnitude of the electric field in the channel and the resultant changes in charge densities at the measurement electrode boundaries as a cell flows past. The charge density is integrated on the electrode surface to determine the displacement current and the channel impedance for the computed frequency range. The complete impedance model combines the finite element model, the electrode-electrolyte interface impedance and stray impedance, which are measured from a real device. The modeled dielectric complex spectra for various cell parameters are discussed and a measurement strategy for cell discrimination with such a system is proposed. We finally discuss the amount of noise and measurement fluctuations of the sensor.

Improving Accessibility of the Impedance-Based Structural Health Monitoring Method:

Abstract: This paper presents current research on impedance-based structural health monitoring technique. The basic principle behind this technique is to apply high-frequency structural excitations (typically higher than 30 kHz) through the 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. Three examples, including a bolted joint, gas pipeline, and composite structure, are presented to illustrate the effectiveness of this health monitoring technique to a wide variety of practical field applications. Although many proof-of-concept experiments have been performed using the impedance methods, the impedance-measuring device (HP4194A) is still bulky and expensive. Therefore, an operational amplifier-based turnkey device that can measure and record the electric impedance of a PZT has been developed. The ...

System and method for dual-band antenna matching

Abstract: A dual-band antenna matching system and a method for dual-band impedance matching are provided. The method comprises: accepting a frequency-dependent impedance from an antenna; and, selectively supplying a conjugate impedance match for the antenna at either a first and a second communication band, or a third and a fourth communication band. More specifically, the method comprises: tuning a first tuning circuit to a first frequency; and, simultaneously tuning a second tuning circuit to a second frequency. In response, a conjugate match is supplied to the antenna in the first communication band in response to the first frequency. Simultaneously, the antenna is matched in the second communication band in response to the second frequency. When the first tuning circuit is tuned to a third frequency, and the second tuning circuit is tuned to a fourth frequency, then conjugate matches are supplied for the third and fourth communication bands, responsive to the third and fourth frequencies, respectively.

Magnetic resonance imaging interference immune device

Abstract: A voltage compensation unit reduces the effects of induced voltages upon a device having a single wire line. The single wire line has balanced characteristic impedance. The voltage compensation unit includes a tunable compensation circuit connected to the wire line. The tunable compensation circuit applies supplemental impedance to the wire line. The supplemental impedance causes the characteristic impedance of the wire line to become unbalanced, thereby reducing the effects of induced voltages caused by changing magnetic fields.

An RF electronically controlled impedance tuning network design and its application to an antenna input impedance automatic matching system

Abstract: A novel design is proposed for an electronically tunable impedance unit. The prototypes include lumped elements, but no electromechanical control methods. The devices can tune many different complex impedances at minimum manufacture costs. Two antenna input impedance automatic matching systems are also presented, based on the tuning network. One includes a simplified version of the generic tuner, which can achieve good matching levels between the antenna and the power module with low losses. In a more complete version, an application specific integrated circuit control unit is developed including a complex search algorithm. In order to obtain a good matching level, both systems require a control module to select the proper tuner impedance configuration. The measurements and results of both constructed prototypes are presented. The designs were carried on terrestrial trunked radio mobile stations in the 380-400-MHz frequency band and supported high power levels (greater than 40 dBm).

Electromagnetic compatibility handbook

Abstract: EMI Sources Decibel and Approximations Electrical Length Fast Bode Magnitude Plotting Skin Depth, Wire Impedance, and Nonideal Resistors Nonideal Capacitors and Inductors Passive Filters Cable Modeling Transient Behaviour in the Time Domain Air Breakdown Transient Behaviour in the Frequency Domain Spectra of Periodic and Aperiodic Signals Transmission Lines and Matching Passive Contact Probes Inductance, Magnetic Coupling, and Transformers Magnetic Materials and a Few Devices Baluns and Balanced Circuits Cable Shielding and Crosstalk Radiated Emissions and Susceptibility Conducted Emissions and Susceptibility Plane Wave Shielding Electric Field Shielding Magnetic Field Shielding Additional Shielding Concepts Test Chambers Floating Metal and Guard Electrodes Electrostatic Discharge Grounding Circuit Board Layout for EMC Antenna Appendix A-Summary of the Three Major Coordinate Systems Appendix B-Definitions for Common and Uncommon Functions Appendix C-Conversion, Unit and Notation Tables Appendix D-Helpful Mathematical Relationships References

Development of an equivalent circuit model of a fuel cell to evaluate the effects of inverter ripple current

Abstract: In this paper an impedance model of the proton exchange membrane fuel cell stack (PEMFCS) is proposed The proposed study employs an equivalent circuit of the PEMFCS derived by frequency response analysis (FRA) technique An equivalent circuit for the fuel cell stack is developed to evaluate the effects of ripple currents generated by the power-conditioning unit The calculated results are then verified by means of experiments on three commercially available fuel cells: Avista Labs SR-12 (500 W), Ballard Nexa (12 kW) and BCS-Tech (300 W) PEMFC system The relationship between ripple current and fuel cell performance: such as power loss and fuel consumption is investigated Experimental results show that the ripple current can contribute up to 10% reduction in the available output power

A model of force and impedance in human arm movements

Abstract: This paper describes a simple computational model of joint torque and impedance in human arm movements that can be used to simulate three-dimensional movements of the (redundant) arm or leg and to design the control of robots and human-machine interfaces. This model, based on recent physiological findings, assumes that (1) the central nervous system learns the force and impedance to perform a task successfully in a given stable or unstable dynamic environment and (2) stiffness is linearly related to the magnitude of the joint torque and increased to compensate for environment instability. Comparison with existing data shows that this simple model is able to predict impedance geometry well.

Simulation of microelectrode impedance changes due to cell growth

Abstract: Observation of impedance changes caused by cell growth on microelectrodes provides information about cell coverage and other important quantities, such as the cell-electrode gap. In this paper, we use finite-element simulations to calculate the impedance changes caused by cell growth on electrodes comparable in size to the cell. Parameters describing the impedance of the electrode without cells are derived from measurement. The results show that the impedance magnitude is expected to increase by at least 100% for partial cell coverage. We also report the frequency dependence of the magnitude and phase of the impedance and compare the simulation results with a lumped-element model. The simulation results are important for the design and modeling of arrays of cell-sized electrodes and also for the interpretation of experiments.

Ionic and electronic impedance imaging using atomic force microscopy

Abstract: Localized alternating current (ac) impedance measurements are acquired directly through a conductive atomic force microscope (AFM) tip. Both a spectroscopy mode (where full impedance spectra are obtained at fixed locations on a sample surface) and an imaging mode (where single frequency impedance maps are acquired across a sample) are used to characterize Au/Si3N4 test structures, ZnO varistors, and Nafion membrane (an ion conductor). Both modulus and phase information are acquired simultaneously. The use of an ac technique permits the study of electrochemical systems and ion conductors in addition to electronic systems. The capabilities and limitations of the AFM impedance imaging technique are discussed in detail.

Impedance measurements and modeling of a transition-edge-sensor calorimeter

Abstract: We describe a method for measuring the complex impedance of transition-edge-sensor (TES) calorimeters. Using this technique, we measured the impedance of a Mo/Au superconducting transition-edge-sensor calorimeter. The impedance data are in good agreement with our linear calorimeter model. From these measurements, we obtained measurements of unprecedented accuracy of the heat capacity and the gradient of resistance with respect to temperature and current of a TES calorimeter throughout the phase transition. The measurements probe the internal state of the superconductor in the phase transition and are useful for characterizing the calorimeter.

Off-diagonal impedance in amorphous wires and its application to linear magnetic sensors

Abstract: We investigated the magnetic-field behavior of the off-diagonal impedance in Co-based amorphous wires under sinusoidal (50 MHz) and pulsed (5 ns rise time) current excitations. For comparison, we measured the field characteristics of the diagonal impedance as well. In general, when an alternating current is applied to a magnetic wire, the voltage signal is generated not only across the wire but also in a pickup coil wound on it. These voltages are related to the diagonal and off-diagonal impedances, respectively. We demonstrate that these impedances have a different behavior as functions of axial magnetic field: the diagonal impedance is symmetrical, whereas the off-diagonal one is antisymmetrical with a near-linear portion within a certain field interval. For the off-diagonal response, the dc bias current is necessary to eliminate circular domains. In the case of the sinusoidal excitation without a dc bias current, the off-diagonal response is very small and irregular. In contrast, the pulsed excitation, combining both high- and low-frequency harmonics, produces the off-diagonal voltage response without additional biasing. This behavior is ideal for a practical sensor circuit design. We discuss the principles of operation of a linear magnetic sensor based on a complementary metal-oxide-semiconductor transistor circuit.

Off-diagonal impedance in amorphous wires and application to linear magnetic sensors

Abstract: The magnetic-field behaviour of the off-diagonal impedance in Co-based amorphous wires is investigated under the condition of sinusoidal (50 MHz) and pulsed (5 ns rising time) current excitations. For comparison, the field characteristics of the diagonal impedance are measured as well. In general, when an alternating current is applied to a magnetic wire the voltage signal is generated not only across the wire but also in the coil mounted on it. These voltages are related with the diagonal and off-diagonal impedances, respectively. It is demonstrated that these impedances have a different behaviour as a function of axial magnetic field: the former is symmetrical and the latter is antisymmetrical with a near linear portion within a certain field interval. In the case of the off-diagonal response, the dc bias current eliminating circular domains is necessary. The pulsed excitation that combines both high and low frequency harmonics produces the off-diagonal voltage response without additional bias current or field. This suits ideal for a practical sensor circuit design. The principles of operation of a linear magnetic sensor based on C-MOS transistor circuit are discussed.

Microstrip "wiggly-line" bandpass filters with multispurious rejection

Abstract: A method to achieve the rejection of multiple spurious passbands in parallel-coupled-line microstrip bandpass filters is proposed. As it was previously demonstrated by the authors, using a continuous perturbation of the width of the coupled-lines following a sinusoidal law, the wave impedance can be modulated so that the first undesired harmonic passband of the filter is rejected, while the desired passband is maintained virtually unaltered. In this letter, the scope of the method is extended to reject multiple spurious passbands by employing different periods in each coupled-line section tuned to the different bands to be rejected. Simulated and measured data show that for an order-seven bandpass filter prototype, a rejection level exceeding 30 dB is obtained in the first four spurious passbands, while the desired pass-band is kept almost unaltered.

Adaptive multi-mode resonant piezoelectric shunt damping

Abstract: Multiple-modes of structural vibration can be suppressed through the connection of an electrical impedance to the terminals of a bonded piezoelectric transducer. The so-called resonant shunts, one commonly used class of shunt impedances, provide good nominal damping performance but they are highly sensitive to variations in transducer capacitance and structural resonance frequencies. This paper introduces a new technique for the online adaptation of multi-mode resonant shunts. By minimizing the relative phase difference between a vibration reference signal and the shunt current, circuit component values can be optimally tuned online. Experiments on a cantilever beam validate the proposed technique and demonstrate the simplicity of implementation. The adaptive law converges quickly and maintains optimal performance in the presence of environmental uncertainties.

Analytical drain thermal noise current model valid for deep submicron MOSFETs

Abstract: In this paper, a physics-based MOSFET drain thermal noise current model valid for deep submicron channel lengths was derived and verified with experiments. It is found that the well-known /spl mu/Q/sub inv//L/sup 2/ formula, previously derived for long channels, remains valid for short channels. Carrier heating in the gradual channel region was taken into account implicitly with the form of diffusion noise source and then impedance field method taking velocity saturation effect was used to calculate the external drain thermal noise current. The derived model was verified by experimental noise for devices with channel lengths down to 0.18 /spl mu/m. Excellent agreement between measured and modeled drain thermal noise was obtained for the entire V/sub GS/ and V/sub DS/ bias regions.

Design of parallel-coupled microstrip filters with suppression of spurious resonances using substrate suspension

Abstract: Substrate suspension is used to suppress the spurious response of microstrip bandpass filters at twice the passband frequency (2f/sub o/). It is known that a proper height of substrate suspension can be used to equalize the even- and odd-mode phase velocities for coupled microstrip lines. In this paper, this property is applied to design the coupled stages of a parallel-coupled line filter so that the spurious response at 2f/sub o/ can be completely suppressed. The individual image impedance for each coupled stage is changed accordingly. Required filter design formulas are derived for a series of coupled stages having different image impedances. Several filters made on a substrate of relative high dielectric constant are designed and fabricated. The measured results show that a rejection level of better than -40 dB to the spurious resonance at 2f/sub o/ can be obtained.

A simple and accurate model for microstrip structures with slotted ground plane

Abstract: A simple and accurate circuit model for microstrip filtering structures with slotted ground plane is presented. The unit cell model consists of a series inductance and shunt capacitance for the microstrip line, an ideal transmission line characterized by its impedance and electrical length for the slot, and an ideal transformer to model coupling to the slot. The coupling mechanism to the slots resonances and subsequent emergence of transmission gaps is explained for different positions of the microstrip line. Excellent agreement with measurement is demonstrated over the broad bandwidth of dc to 20 GHz.

Multi-path transthoracic defibrillation and cardioversion

Abstract: External electromagnetic stimulation of the interior of the body by applying three or more electrodes to the exterior of the patient to establish at least two electrical paths across the interior of the patient, determining impedance information representative of an impedance distribution across the interior of the body, delivering an electromagnetic waveform across each of the at least two electrical paths, wherein at least one parameter of the waveform is selected using the impedance information to produce a selected current density distribution at one or more locations within the interior of the body.

Microfluidic devices for methods development

Abstract: Microfluidic devices with multiple fluid process regions for subjecting similar samples to different process conditions in parallel are provided. One or more common fluid inputs may be provided to minimize the number of external fluid supply components. Solid materials such as chromatographic separation media or catalyst media is preferably provided in each fluid process region. Solid materials may be supplied to the devices in the form of slurry, with particles retained by porous elements or frits. Different fluid process regions may having different effective lengths, different solid material types or amounts, or may receive different ratios of common fluids supplied to the device. The flow resistances of dissimilar fluid process regions may be balanced passively with the addition of impedance elements in series with each fluid process region.

An impedance model to improve the higher frequency limit of electrical measurements on the capacitor cell made from electrodes of finite resistances

Abstract: capacitors are highly affected above 100 kHz due to the presence of the electrodes resistance and leads inductance. An impedance model has been used to improve the higher frequency limit of the dielectric measurements on the isotropic liquids and anisotropic liquid crystal materials filled in parallel plate capacitors made from the electrodes having finite resistance (specially indium tin oxide coated electrodes). By using this model it has been possible to extend the upper frequency limit of the correct measurement of capacitance and conductance (and hence e′ and e″) at least by a decade of the frequency.

Stability of grid-connected PV inverters with large grid impedance variation

Abstract: Photovoltaic (PV) inverters used in dispersed power generation of houses in the range of 1-5 kW are currently available from several manufacturers. However large grid impedance variation is challenging the control and the grid filter design in terms of stability. In fact the PV systems are well suited for loads connected in a great distance to the transformer (long wires) and the situation becomes even more difficult in low-developed remote areas characterized by low power transformers and long distribution wires with high grid impedance. Hence a theoretical analysis is needed because the grid impedance variation leads to dynamic and stability problems both in the low frequency range (around the current controller bandwidth frequency) as well as in the high frequency range (around the LCL-filter resonance frequency). In the low frequency range the possible variation of the impedance challenges the design of resonant controllers adopted to mitigate the effect of the grid harmonic distortion on the grid current. In the high frequency range the grid impedance influence the frequency characteristic of the filter and the design of passive or active damping (to ensure stability) becomes more difficult. In this paper both topics are addressed and discussed with simulation and experimental results.

Analog tunable matching network using integrated thin-film BST capacitors

Abstract: This paper presents an electronically tunable impedance transformer and matching network for RF applications, utilizing thin-film barium strontium titanate (BST) tunable capacitors in an integrated-passive network on sapphire. The impedance transformer can be electronically varied from a 4:1 to 2:1 transformation in a 50 ohm environment. A slight modification of this circuit is shown to provide a match for a highly-reactive integrated antenna allowing the antenna to be used with improved efficiency from 420MHz to 500MHz. ACPR measurements are presented on the latter network showing ACPR1 of >50 dBc at 27 dBm drive power.

Measurement of noise source impedance of SMPS using a two probes approach

Abstract: A novel approach to determine common-mode (CM) and differential-mode (DM) noise source impedances of a low-power switched mode power supply (SMPS) has been developed using a two current probes approach. The proposed approach allows measurement of noise source impedance of a SMPS without interrupting its normal operation. With proper setup calibration, the proposed approach can derive an equivalent circuit model, consisting of resistive and reactive components, to represent the noise source impedance with reasonable accuracy. Once the equivalent circuit model of the noise source impedance is obtained through the measurement, the most effective filter configuration and suitable component values for the built-in power line electromagnetic interference (EMI) filter of the SMPS could be designed with ease.

Acousto-electric tomography

Abstract: Although the electric impedance of biological tissues is highly sensitive to their physiological and pathological status, pure electrical impedance tomography (EIT) has very poor spatial resolution. We invented acousto-electric tomography (AET) to image the electric impedance properties of biological tissues with high spatial resolution. AET is based on acousto-electric modulation, which is the localized variation in conductivity produced by a focused ultrasonic wave. It combines the contrast advantage of EIT and the resolution advantage of ultrasound imaging. The spatial resolution of AET is primarily defined by the size of the ultrasonic focal spot. Therefore, the resolution is much better than that of EIT, and it is scalable with the acoustic parameters. The contrast of AET is determined by the combination of three factors: the electric impedance, the media dependent modulation coefficient, and the acoustic properties. Unlike EIT, AET forms images directly without resorting to inverse algorithms. And unlike traditional ultrasonography, AET is free of speckles.

Extraction of high frequency power cable characteristics from S-parameter measurements

Abstract: A technique is developed for extraction of the wave propagation properties of power cables from S-parameter measurements. The method extracts the complex propagation constant and the characteristic impedance, as well as the LCRG telegrapher's equation parameters. The extraction process is developed after clarifying the effect of the connection between the measurement port and the power cable. It is concluded that treating the connection solely as a characteristic impedance change could lead to considerable errors in the parameter extraction. Furthermore, the method corrects for electrical lengths, which are not accounted for by the standard network analyzer calibration. The extraction is demonstrated for a medium voltage cross linked polyethylene (XLPE) cable over the frequency range 300 kHz to 300 MHz. The results are compared to a time domain short pulse propagation method for cable characterization. Both measurement methods are evaluated against a cable model.