Resistor-capacitor Circuit Research Articles

The functional sequence of hydrogen in electronic conduction of sol–gel derived Al-doped ZnO films as determined via impedance spectroscopy

Sol–gel derived Al-doped ZnO (AZO) films were annealed under various degrees of hydrogen reduction treatments. Three sequential equivalent circuits were obtained by simulating the impedance spectra of the AZO films. By interpreting the equivalent circuit elements, the functional sequence of hydrogen in AZO films was disclosed. Hydrogen destroys the energetic barriers at grain boundaries and releases free electrons, which are shown by the presence of a parallel resistor–capacitor circuit, a constant phase element and a short Warburg element in equivalent circuits.

Moisture Evaluator: a direct measure of fingertip skin hydration during object manipulation

The mechanical properties of the fingertip skin are very important when studying dexterous manipulation. These properties are strongly influenced by the level of skin hydration. Currently, there is no device capable of measuring skin moisture during object manipulation. Skin moisture levels during object manipulation were measured using the Moisture Evaluator, a probe consisting of gold-covered electrodes connected to a resistor-capacitor circuit. In vivo calibration was performed by comparison with measurements obtained using a Corneometer at two normal force levels (0.2 and 2 N). Measurements from the Moisture Evaluator were well correlated with those from the Corneometer. A new device for evaluating skin moisture at the fingertip has been designed and validated.

Ventricular fibrillation time constant for swine

The strength–duration curve for cardiac excitation can be modeled by a parallel resistor–capacitor circuit that has a time constant. Experiments on six pigs were performed by delivering current from the X26 Taser dart at a distance from the heart to cause ventricular fibrillation (VF). The X26 Taser is an electromuscular incapacitation device (EMD), which generates about 50 kV and delivers a pulse train of about 15–19 pulses s−1 with a pulse duration of about 150 µs and peak current about 2 A. Similarly a continuous 60 Hz alternating current of the amplitude required to cause VF was delivered from the same distance. The average current and duration of the current pulse were estimated in both sets of experiments. The strength–duration equation was solved to yield an average time constant of 2.87 ms ± 1.90 (SD). Results obtained may help in the development of safety standards for future electromuscular incapacitation devices (EMDs) without requiring additional animal tests.

M3EDM: MEMS-enabled micro-electro-discharge machining

This paper reports a photolithography compatible micro-electro-discharge machining technique that is performed with microelectrode actuators driven by hydrodynamic force. The movable planar electrodes suspended by the anchors are microfabricated directly on the workpiece. The electrode structures with fixed–fixed and cantilever configurations are defined by patterning 18 µm thick copper foil laminated on the workpiece through an intermediate photoresist layer and released by sacrificial etching of the resist layer. All the patterning and sacrificial etching steps are performed using dry-film photoresists towards achieving high scalability of the machining technique to large-area applications. The parasitic capacitance of the electrode structure is used to form a resistance–capacitance circuit for the generation of pulsed spark discharge between the electrode and the workpiece. The suspended electrodes are actuated towards the workpiece using the downflow of dielectric machining fluid, initiating and sustaining the machining process. Micromachining of stainless steel is experimentally demonstrated with a machining voltage of 90 V and continuous flow of the fluid at a velocity of 3.4–3.9 m s−1, providing a removal depth of 20 µm with an average surface roughness of 520 nm. The experimental results of the electrode actuation are shown to agree well with the theoretical estimations.

Functional Mechanisms Shaping Lateral Geniculate Responses to Artificial and Natural Stimuli

Functional models of the early visual system should predict responses not only to simple artificial stimuli but also to sequences of complex natural scenes. An ideal testbed for such models is the lateral geniculate nucleus (LGN). Mechanisms shaping LGN responses include the linear receptive field and two fast adaptation processes, sensitive to luminance and contrast. We propose a compact functional model for these mechanisms that operates on sequences of arbitrary images. With the same parameters that fit the firing rate responses to simple stimuli, it predicts the bulk of the firing rate responses to complex stimuli, including natural scenes. Further improvements could result by adding a spiking mechanism, possibly one capable of bursts, but not by adding mechanisms of slow adaptation. We conclude that up to the LGN the responses to natural scenes can be largely explained through insights gained with simple artificial stimuli.

Experimental and Numerical Studies of Thermally Induced Acoustic Waves in an Enclosure

The behaviors of thermally induced acoustic waves generated by the rapid heating of a bounding solid wall in a closed cylindrical tube are investigated experimentally. The induced flow and pressure fields due to rapid heating are also numerically simulated. In the experiments, a resistance-capacitance circuit is used to generate a rapid temperature increase in a thin nickel foil located at one end of the closed cylindrical tube. The thermally generated pressure (acoustic) waves undergo repeated reflections at the two ends of the tube and gradually decay. The time-dependent pressure variation in the tube and the voltage and temperature histories at the foil are recorded by a fast-response measurement system. The characteristics of the generation, propagation, and decay of the acoustic waves are measured by two different transducers (Bruel & Kjaer model 4193 and Endevco model 8507C-1). To simulate the experiments numerically, the compressible unsteady axisymmetric Navier-Stokes equations are solved by a highly accurate algorithm. Both the experimental and numerical studies predict similar pressure wave shapes and profiles. The measured decay rate of the acoustic waves is found to be somewhat faster than the numerically predicted rate.

Extended charge banking model of dual path shocks for implantable cardioverter defibrillators

BackgroundSingle path defibrillation shock methods have been improved through the use of the Charge Banking Model of defibrillation, which predicts the response of the heart to shocks as a simple resistor-capacitor (RC) circuit. While dual path defibrillation configurations have significantly reduced defibrillation thresholds, improvements to dual path defibrillation techniques have been limited to experimental observations without a practical model to aid in improving dual path defibrillation techniques.MethodsThe Charge Banking Model has been extended into a new Extended Charge Banking Model of defibrillation that represents small sections of the heart as separate RC circuits, uses a weighting factor based on published defibrillation shock field gradient measures, and implements a critical mass criteria to predict the relative efficacy of single and dual path defibrillation shocks.ResultsThe new model reproduced the results from several published experimental protocols that demonstrated the relative efficacy of dual path defibrillation shocks. The model predicts that time between phases or pulses of dual path defibrillation shock configurations should be minimized to maximize shock efficacy.DiscussionThrough this approach the Extended Charge Banking Model predictions may be used to improve dual path and multi-pulse defibrillation techniques, which have been shown experimentally to lower defibrillation thresholds substantially. The new model may be a useful tool to help in further improving dual path and multiple pulse defibrillation techniques by predicting optimal pulse durations and shock timing parameters.

Modeling Ion Diffusion Current in Nanochannel Using Infinitesimal Distribution Resistor–Capacitor Circuits

A theoretical model that considers both the diffusion and electrical osmosis fluxes to estimate the diffusion current through a nanochannel is proposed. The equivalent impedance of a nanochannel is modeled as a series connection of finite resistor–capacitor (RC) circuits. The impedances of the electrical double layer and buffer solution in each infinitesimal RC circuit are represented using a capacitor and a resistor, respectively. The diffusion-induced current in the proposed model is position dependent due to the electrical double layer effect. Computer simulations and experiments using a nanoporous anodic aluminum oxide (AAO) thin film as the filter to separate electrolysis with an ion concentration gradient were conducted. Electrochemical impedance spectroscopy (EIS) was performed to measure the impedance of the porous AAO thin film in the frequency domain such that the capacitor and resistor can be estimated accordingly. A high degree of coincidence between the theoretical and experimental data is observed.

The electrochemical behavior of nitinol in simulated physiological solutions

The electrochemical behavior of nitinol in simulated human bile and phosphate-buffered saline (PBS) was examined using electrochemical impedance spectroscopy. In addition, cyclic potentiodynamic polarization tests were performed in the simulated bile and salt-only bile, and the results compared with those obtained previously in PBS. The potentiodynamic tests showed that electropolishing was effective in providing nitinol with a high resistance to pitting corrosion in the bile solutions, as found in PBS. Differences between the breakdown potential and the corrosion potential indicated that mechanically polished nitinol should be more susceptible to pitting corrosion in simulated bile than in the salt-only bile and PBS. The impedance spectra showed near-capacitive behavior in both PBS and simulated bile, and the data could be fitted by a parallel resistance-capacitance (as a constant phase element) circuit associated with the passive oxide film. The thickness of the oxide was determined from the capacitive component and found to be consistent with surface analytical results reported in the literature. Resistivities obtained from resistance values indicated that compositional features of the oxide were similar for PBS and simulated bile.

In vitro modulation of endogenous rhythms by AC electric fields: Syncing with clinical brain stimulation

Humans are exposed to an increasing prevalence of weak and strong AC electric fields, as part of daily life in the modern world. Further, electric fields are being deployed to modulate brain function for research and clinical applications. A single electric field pulse, applied via transcranial electrical or magnetic stimulation, can transiently excite or disrupt activity in neural circuits. In contrast, extended exposure to steady electric fields or pulse trains can result in long-term effects on neural activity including potentiation or depression. In addition, it has been demonstrated that brain stimulation with electric fields can improve cognitive performance in normal subjects (Marshall et al. 2006). The impact of electric fields on brain function has motivated the development of therapies to treat a wide range of psychiatric and neurological diseases using transcranial electrical or magnetic stimulation (Wassermann & Lisanby, 2001), as well as deep brain stimulation with implanted electrodes. The mechanisms by which electric fields affect brain function have not been fully elaborated. A recent report in The Journal of Physiology by Deans et al. (2007) presents new data on the interaction of AC electric fields down to a cellular level as well as with neuronal population dynamics. The report reveals a frequency-specific ability of AC electric fields to rhythmically polarize pyramidal neurons of the CA3 region of the hippocampus and demonstrates the ability of AC fields to alter pharmacologically induced endogenous oscillations in the hippocampus. These data have important implications for understanding the effect of environmental AC fields and therapeutic stimulation on the activity of neuronal ensembles. A central finding of this study is that an AC electric field, applied in vitro to a brain slice set to oscillate in the gamma frequency range through bath application of kainate, shifts the ongoing oscillation to centre on the applied field frequency or a subharmonic of that frequency. This review of Deans et al. (2007) is intended to elucidate the connection between their work and other recent in vitro findings concerning electric fields in the brain with some recent clinical findings pertaining to cognitive function and electric fields.

Electrical properties of electrodeposited polyaniline nanotubes

The electrical properties of polyaniline nanotubes-aluminum like Schottky diode are described. Polyaniline nanotubes (PANI) were deposited on aluminum thin films using the polarographic technique. The nanotubes were characterized by scanning electron microscopy (SEM) and UV-Vis absorption spectra. The electrical properties of the heterojunction PANI-Al were examined. The current density–voltage (J × V) profile has shown a behavior typical of Schottky diode, with ideality factor (n) of 6.76 and ϕb of 0.70 eV. Impedance spectroscopy data apparently shows that the resistance dominated the AC behavior of the PANI-Al system. The equivalent circuit is composed from a resistor in series with a parallel resistor–capacitor circuit. The results indicate that polyaniline nanotubes may be interesting to the development of electro-optical devices with 2D structure.

Characteristic Frequency of Carbon Black Filled Rubber

Due to the high electrical conductivity of carbon black (CB) particles, the presence of CB improves the conductivity of filled rubbers. The impedance spectra of CB filled rubber were simulated using an infinite resistor‐capacitor (RC) circuit by considering the tunneling conduction mechanism for the CB contact regions. The calculated results had a similar appearance to the experimental results, i.e., the Cole‐Cole plot was a semi‐circle and a peak appeared in a plot of the imaginary component of complex impedance with respect to the frequency from which the characteristic frequency was obtained. For a simple RC circuit in parallel connection, the logarithm of the characteristic frequency should be a linear function of the 1/3 power of the average number of primary particles per aggregate. A slight deviation from the line found in the simulations was attributed to the network contribution. Additionally, low CB loading had little effect on the characteristic frequency, in accordance with the experimental data, while high loading had a marked effect. Furthermore, the calculations showed that the characteristic frequency was affected not only by the distribution of individual CB aggregates, but also by the percentage of agglomerates at high CB loading.

Complex impedance spectra analysis of SnO2-glaze composites

SnO2-glaze composites were prepared by Sb-doped SnO2 and SiO2−CaO−Al2O3−B2O3 glaze. The composites changed from an electrical insulator to a conductor as the SnO2 content increased from Owt% to 90 wt%. The complex impedance spectra of the fabricated composites were investigated in the frequency range of 100Hz-40 MHz and three kinds of typical shape of complex impedance spectra were recorded and analyzed. The spectrum is quite close to the model of conduction via nonohmic contacting when the SnO2 content is relatively low. In high loading region, the spectrum shows the conduction pattern through ohmic contact chains. In the moderate loading region, the model is a mixture of the above two models. Equivalent circuit of the composite changes from resistor-capacitor circuit to resistor-inductor circuit as the content of SnO2 increases.

Memory performance prediction for high-performance microprocessors at deep submicrometer technologies

The desire for large size, high-speed, and low-power on-chip memory necessitates early and accurate estimates of memory performance. A new performance model as well as an early cache design tool and predictor of access and cycle time for cache stack (PRACTICS) has been developed for on-chip static random access memory (SRAM) cache design that includes both delay and dynamic-power models. Efficient models for distributed interconnect delays, verified by Cadence simulations, are introduced, and their necessity is demonstrated. In the delay model, the access time is estimated by decomposing each component into several equivalent lumped resistance-capacitance (RC) circuits and using an appropriate order pi model to approximate the distributed wire delays of each stage. The dynamic-power model calculates the charging power dissipation of the load capacitances using the same equivalent lumped RC circuits. The delay model has been validated with an Intel 18-Mb SRAM at the 180-nm node, achieving accuracy to within 10% of the measured results. The dynamic-power model has been validated with an International Business Machines Corporation (IBM) 18-Mb SRAM at the 180-nm node, to within 13% of the measured power consumption. Detailed comparisons between PRACTICS and cache access and cycle time model (CACTI) in both validation cases indicate that an improved wire delay, appropriate circuit structures, and technology dependent parameters are necessary to accurately predict large cache memory performance at deep submicrometer technology nodes. PRACTICS is used to analyze the access time and power consumption in terms of cache sizes and various degrees of associativity for architectural studies. In addition, the PRACTICS simulation results show that repeater insertion reduces the access time significantly, with a small overhead in dynamic-power consumption for large size cache design at deep submicrometer technology

AC impedance analysis and EMI shielding effectiveness of conductive SBR composites

Flexible conductive polymer composites were prepared using styrene–butadiene rubber (SBR) as a matrix and conductive carbon black as filler. The filler loading was varied from 10 to 60 phr. The complex AC impedance and electromagnetic interference shielding effectiveness (EMI SE) of the composites were measured at the microwave frequencies of 7.8–12.4 GHz. The effect of variation in filler concentration and measurement frequency on the AC impedance and EMI SE of the composites were investigated. Equivalent circuits describing the conduction behavior of the composites were determined by means of Nyquist plots. The complex electric modulus of the composites was also determined. Increase in the filler loading increased the capacitive nature of the materials. The composites were better defined by a parallel resistor–capacitor circuit in series with a resistor. The EMI SE was found to pass through a maximum with increase in frequency. However, with the increase in filler loading and sample thickness of the material, the EMI SE was found to increase continuously. POLYM. ENG. SCI., 46:1342–1349, 2006. © 2006 Society of Plastics Engineers.

Time and frequency response characteristics of bacteriorhodopsin-based photodetectors

The time and frequency response behavior of a new class of photodetectors based on a light-sensitive protein, known as bacteriorhodopsin (bR), is described. Each bR-based detector consists of an indium tin oxide (ITO) electrode/bR thin film/indium tin oxide (ITO) electrode structure. The response of the photodetector to square-wave and transient pulse illumination are both simulated using an equivalent resistor-capacitor (RC) circuit and experimentally observed. The investigative study demonstrates that the physical dimensions of the sensor surface, load resistance and capacitance, and the illumination conditions all have an impact on the transient response and gain-bandwidth characteristics. It is observed that changing the sensing area of the detector only affects the amplitude of the response, but not the bandwidth. Increasing the load resistance produces a higher gain, but reduces bandwidth. Increasing the load capacitance has the effect of dramatically reducing both gain and bandwidth. The observations and conclusions derived from this research provide design guidelines for developing hybrid photoelectric sensors and imaging arrays using bacteriorhodopsin thin films.

Violation of Kirchhoff's Laws for a Coherent RC Circuit

What is the complex impedance of a fully coherent quantum resistance-capacitance (RC) circuit at gigahertz frequencies in which a resistor and a capacitor are connected in series? While Kirchhoff's laws predict addition of capacitor and resistor impedances, we report on observation of a different behavior. The resistance, here associated with charge relaxation, differs from the usual transport resistance given by the Landauer formula. In particular, for a single-mode conductor, the charge-relaxation resistance is half the resistance quantum, regardless of the transmission of the mode. The new mesoscopic effect reported here is relevant for the dynamical regime of all quantum devices.

α , γ, and normal, abnormal glow discharge modes in radio-frequency capacitively coupled discharges at atmospheric pressure

Discharge modes, α and γ, of a radio-frequency helium capacitively coupled discharge at atmospheric pressure were investigated with the discharge gap distance between electrodes varied from 1 to 5mm. As similarly observed in other experiments, the α and γ mode and the α–γ mode transition were observed with large drops in the voltage (310–179V) and the phase angle between the voltage and current (54°–18°), and a contraction of the plasma volume (8.5–0.17cm3, at 3mm gap distance). The discharge voltage where the α–γ mode transition occurred versus the gap distance showed a similar behavior with the Paschen curve for a gas breakdown. Depending on the gap distance, normal and abnormal glow regimes were observed in the αmode. At 1 and 2mm, the α mode remained in the abnormal glow discharge until the α–γ mode transition occurred as the discharge current increases. At 3mm, however, the α mode was excited as a normal glow discharge with a constant current density (17mA∕cm2) but it became an abnormal glow discharge as the current increased. At 4mm, the α mode was sustained as a normal glow discharge, then the transition to the γ mode occurred. Using a simple resistor-capacitor circuit model and a α sheath breakdown model, the discharge modes and the mode transition properties were studied.

Study of grain boundary contribution and enhancement of magnetoresistance in La0.67Ca0.33MnO3/V2O5 composites

Electrical transport (90–300 K) and magnetic (5–375 K) properties of the La0.67Ca0.33MnO3 + x% V2O5 (x = 0, 2, 5, 15 and 30) type magnetic–nonmagnetic composite system show appreciable grain boundary contribution. These composites, except for the one with x = 30%, show metal–insulator transitions at T = Tp which decrease with increasing V2O5 concentration. The high temperature (T > Tp) semiconducting part of the resistivity (ρ) data follow a small polaron hopping conduction mechanism. The magnetoresistance (MR) in this system increases with increasing V2O5 content, showing a maximum value (25% at 93 K and field H = 1.15 T) for the sample with x = 15%. Spin polarization is considered to be responsible for such an increase of MR. Neither thermoelectric power (between 90 and 300 K) nor magnetization data indicate any noticeable change of the Curie temperature (TC) with change of x, suggesting that V2O5 remains at the grain boundary. The complex impedance (Z*) of the composite system, measured over a frequency range of 0.01 kHz–13 MHz, at 300 K shows strong frequency dependence and the impedance plane plots (Z′–Z″) are semicircular for different V2O5 content. An equivalent resistor–capacitor circuit (Rg (Rgb Cgb)) has been proposed to explain the impedance results in this composite system.

The porous media model for the hydraulic system of a conifer tree: Linking sap flux data to transpiration rate

Linking sap flow in tree boles to plant transpiration continues to be a fundamental and practical research problem in physiological ecology and forest hydrology. Many models have been proposed to describe water movement within trees with varying degrees of success. The prevailing resistance–capacitance ( RC)-circuit models have the advantage of being easy to implement. However, RC models are ordinary differential equation (ODE) models that reduce the spatial–temporal dynamics of a tree hydraulic system to the temporal variation of simplified quantities; thus, the RC parameterization is more empirical and open to various interpretations. For coniferous trees, a reasonable alternative to RC circuit models is a porous media (PM) model, which is a partial differential equation (PDE) model that describes the spatial–temporal dynamics. The model more closely represents the physical elements of the conifer hydraulic system but also requires a direct estimation of its properties. Our proposed PM model is original in that it formulates a theoretical link between measured quantities (i.e., sap flux density and tree structure) and model parameters, obtained during nighttime, which permits direct numerical conversion of sap flow to transpiration rate during daytime. In addition to fully simulating the PDE, we propose an alternative method to transform the PDE into a set of ODEs, to significantly reduce computational demands. Although the ODE results are noisy, the transpiration pattern produced by the ODE, once filtered, is similar to that of the PDE. We demonstrate that measurements of the sap flux in multiple positions below and within the crown can be used to compute the height-dependent transpiration rate; but if rates of bulk crown transpiration are of primary interest, readily obtainable measurements at two heights, at the base of the tree and below the crown, are sufficient for the computation.