Small Current Variations Research Articles

Electrochemical stripping analysis from micro-counter electrode

Electrochemical stripping analysis (anodic, cathodic, or adsorptive) is usually based on the pre-concentration of a target analyte on the working electrode surface and then measuring its quantity via its direct quantitative electrochemical transformation (with the electrode refreshed afterwards). In this work, we demonstrate a new approach to carry out electrochemical stripping analysis of non-adsorbing species, thus not based on the analyte being directly pre-concentrated on the working electrode (WE), but on the signal obtained indirectly from the counter electrode (CE) where metal ions are reduced and then electrochemically stripped. Different from the CE with large surface area in classical electrochemical measurements, an ultramicroelectrode is chosen here as CE to purposely exploit the polarization effect. The concept is based on oxidizing the analyte on WE in one compartment of the electrochemical cell while reducing Cu2+ on CE from another compartment connected with an ionic bridge or a less common metal “bridge”. The deposited Cu on CE is then analyzed by stripping in another three-electrode cell, and the charge shows good linear relationship with the concentration of analyte in the former cell. As the stripping current response (peak) is much clearer than the small current variations corresponding to the direct oxidation of the analyte, it improves the resolution of raw signal. Besides, it may also reduce the background signal from blank solution by “filtering” the non-Faradaic charge. Like in classical electrochemical stripping analysis, one may also prolong the oxidation time in exchange for higher sensitivity of analysis. This work extends the applications of stripping analysis and offers a new angle of electroanalysis by capturing signals from counter electrode.

Series DC Arc Fault Detection Method for PV Systems Employing Differential Power Processing Structure

Arc fault detection is an important process for ensuring the safety of PV and grid-connected inverters and is essential for producing PV systems in real applications. However, it is difficult to detect series dc arc faults using conventional fuses because these faults produce only small current variations. In addition, the arc fault detection devices have limited performance, because they focused on arc fault detection between PV arrays and inverter. Moreover, they require the additional current and voltage sensors to implement the arc fault detection algorithm. This article proposes an arc fault detection algorithm employing differential power processing (DPP) structure. The proposed algorithm only uses intrinsic voltage sensors of DPP and inverter, which can improve the cost-effectiveness of PV systems. In addition, the proposed algorithm can integrate the functionality of maximum power processing for each PV panel and arc fault detection. The voltage relationship between DPP and inverter is analyzed to detect the arc fault condition according to the DPP voltage sensing type. The performance of DPP units and its voltage relationship are verified with the control hardware-in-the-loop system. The arc fault detection performance is verified with the prototype PV system.

Design 5.0 µm Gap Aluminium Interdigitated Electrode for Sensitive pH Detection

The aim of the research study to design high sensitive biosensor for medical applications. IDE pattern was designed using AutoCAD software with 5 µm ginger gap. The fabrication process was done using a conventional photolithography process and standard CMOS process. The fabricated electrode was physically characterized using a low power microscope (LPM) and a high power microscope (HPM). The electrically validated through I-V measurements and chemically tested with different pH buffer solutions. Al IDE was well fabricated with 0.1 µm tolerance between the design mask and fabricated IDEs. Electrical measurements confirmed that IDE was well fabricated without any shortage and results of similar IDE samples were confirmed that the repeatability of the device. The extremely small current variations in nano ampere range were quantitatively detected using an extra small volume of 2 µl for different pH buffer solutions. It is confirmed that IDEs are sensitive in both alkali and hydroxyl ions medium.

Development of Voltage Amplifier Electronic Reader for Multiplex Detection of Two Electrode Electrical Biosensors

Amperometric electrical biosensors have small current variations at nano to micro range. There are limited number of electrical based two electrode electronic readers for biosensors are commercial available because of the amplification and noise issues at nano to micro ampere current range. The electronic reader focused on design a voltage amplifier circuit to capture and amplify three different range of current as nano, micro and mili ampere and convert it to detectable voltage range as an output voltage signal. Current input as nano, micro and mili current were flown through 10 K Ω, 10 Ω and 10 m Ω resistors, respectively to convert different current inputs to the similar range in micro voltage. Then, MAX 4238 op-amp IC was used to amplify micro voltage to mili voltage. Arduino Uno circuit was act as the process and control circuit to read the output voltage from the amplifier circuit. Arduino Uno circuit will convert analog signal to digital signal and then the output voltage value is display in the LCD screen. The Proteus 8 Pro software was used to design, simulate and calibrate the amplifier circuit and Arduino Uno circuit. While, Arduino software was used to create a programming code and to upload in Arduino Uno circuit. Start your abstract here.

DC Series Arc Fault Detection Algorithm for Distributed Energy Resources Using Arc Fault Impedance Modeling

Arc fault detection is important technology to guarantee the safety of power systems and is therefore essential for producing practical power systems for real-world applications. However, fuses and arc fault detection devices (AFDD) struggle to detect series arc faults in DC systems, because the series arc fault induces small current variation between the normal and abnormal conditions. In addition, switching noise from the grid-connected inverter makes detecting arc fault conditions even more difficult. This paper proposes arc fault detection algorithm based on the relative comparison of current variability in terms of frequency spectrum and time series. The operational principle of the proposed algorithm is analyzed to detect the arc fault condition. In addition, the investigation of arc fault impedance using the small-signal modeling can obtain the resonant frequency of arc fault condition at low frequency range. From the impedance model, the frequency analysis range can be designed to avoid the switching noise of inverter. The performance of proposed arc fault detection algorithm is verified with a 3.8 kW grid-connected PV system and arc fault generator.

Small-signal model for the single-electron transistor: part I

A simple small-signal model of the single-electron transistor is presented. The terminal voltage variations are considered to be sufficiently small to result in small current variations that can be expressed using linearized relations. The derivation of such relations and the development of an equivalent circuit to represent them are presented. Two-port analysis of the small-signal circuit of the single-electron transistor is proposed and explained using various parameters such as impedance parameters, admittance parameters, and hybrid parameters. The variation of the magnitude of these parameters is plotted with respect to frequency. The transconductance and drain resistances and their frequency variation are also discussed. The effect of parasitic capacitance on the proposed small-signal model is also analyzed.

Design, fabrication and characterization of 1.0 μm Gap Al based interdigitated electrode for biosensors

Interdigitated electrode (IDE) based electrical biosensors are promising in the medical application field. The aim of the research study is design, fabricate and characterize of low cost, high sensitive biosensor for medical applications. IDE pattern was designed using AutoCAD software with 1 μm finger gap. Fabrication process was done using conventional photolithography process and standard CMOS process. Fabricated electrode was physically characterized using SEM images, electrically validated through I–V measurements and chemically tested with different pH buffer solutions. Al IDE was well fabricated with 0.1 μm tolerance between design mask and fabricated IDEs. Electrical measurements confirmed that IDE was well fabricated without any shortage and results of similar IDE samples were confirmed that the repeatability of the device. The extremely small current variations in nano ampere range were quantitatively detected using extra small volume of 1 μl for different pH buffer solutions. It is confirmed that IDEs are sensitive in both alkali and hydroxyl ions medium.

1-D nanoporous anodic alumina rugate filters by means of small current variations for real-time sensing applications.

A rugate filter based on nanoporous anodic alumina was fabricated using an innovative sinusoidal current profile with small current variation. The resulting structure consisted of highly parallel pores with modulations of the pore diameter along the pore axis and with no branching. The effect of the period time and the pore widening post-treatment was studied. From reflectance measurements, it was seen that the position of the reflection band can be tuned by adjusting the period time and the width by pore-widening post-treatments. We tested one of the rugate filters by infiltrating the structure with EtOH and water in order to evaluate its sensing capabilities. This method allows the fabrication of complex in-depth modulated nanoporous anodic alumina structures that open up the possibility of new kinds of alumina-based optical sensing devices.

Visualization of Oxygen Consumption of Single Living Cells by Scanning Electrochemical Microscopy: The Influence of the Faradaic Tip Reaction

The respiration activity of an individual living cell is an indicator of its metabolic vitality. Closely positioned microelectrodes have been suggested for determination of the respiration activity by monitoring the local oxygen concentration. Although first attempts for visualization of the oxygen consumption rate of single living cells by means of scanning electrochemical microscopy (SECM) were already described in 1998, evaluation of the respiratory activity of individual cells remains challenging and the complexity is often underestimated. In particular, the dimensions of the cell itself lead to limitations of conventionally used constant-height mode SECM investigations. Apart from convolution of the oxygen reduction current at the SECM tip with topographic effects, constant-height mode experiments require working distances comparable or below the height of the cell body, thus increasing the risk of tip crash. Attempts to overcome these restrictions include among others positioning of the tip to distances outside the feedback range, embedding of the cells into cavities, or efforts to subtract topographic contributions after cell death. Moreover, as living cells are irregular in dimension, the tip-to-cell distance varies with the tip position. Therefore, constant-distance mode (cd-mode) SECM techniques are inherently advantageous for this purpose. In particular, coupling SECM with scanning probe techniques, such as atomic force microscopy (AFM) and scanning ion conductance microscopy (SICM) as well as shearforce and impedance-based techniques, led to efficient strategies to control the tip-to-sample separation. Recently, we described a shearforce-based cd method (4D SF/ CD-SECM) that is able to work at various tip-to-sample separations. It can hence detect complete diffusion profiles in the surroundings of sources or sinks of redox-active species. Although SECM distance control systems are available, the detection of the respiration activity of single living cells remains challenging. Owing to the small rate of oxygen consumption by a single cell, only small current variations ontop of a high background current are measured. Even more importantly, a biological cell acts as an immiscible liquid– liquid interface in a SECM experiment. Lipophilic redox mediators are known to undergo transmembrane diffusion processes and can be utilized to investigate intracellular redox activity. However, concentration changes in the vicinity of the cellular membrane, for example by the tip reaction, may induce local concentration gradients and cause a diffusional exchange of redox species over the lipid bilayer in a socalled SECM-induced transfer (SECM-IT) mode. The high solubility of oxygen in lipids promotes this transmembrane diffusion and oxygen can easily cross the cell membrane. This diffusion process superimposes the detection of cell respiration. As a result, in most reports addressing detection of cell metabolism based on the detection of variations in the local oxygen concentration, the positioned microelectrode does not act as a passive observer but actively influences the oxygen concentration inside the gap between tip and cell, resulting in imaging artifacts that have not previously been addressed. Even though mentioned occasionally, this effect was neglected in SECM investigations of respiration activity at living cells. Herein, we address the influence of the oxygen reduction rate at the SECM tip on imaging the respiration activity at living cells. We provide strategies to avoid limitations resulting from a strong tip reaction using a potential pulse profile at the tip with a time dependent data acquisition in the shearforce-based cd-mode of SECM. Commonly, the detection of the local oxygen concentration in close proximity to the cell body is performed by means of a variation of the generator-collector mode of SECM with the tip being continuously polarized at oxygen reduction potential. The tip competes with the respiring living cell for the available oxygen inside the gap between SECM tip and cell surface. Crossing the cell body during a SECM line scan should therefore lead to a decrease of the tip current owing to a locally lowered oxygen concentration caused by cell [*] Dr. M. Nebel, S. Gr tzke, Prof. Dr. W. Schuhmann Lehrstuhl f r Analytische Chemie, Elektroanalytik & Sensorik and Center for Electrochemical Sciences, CES Ruhr-Universit t Bochum Universit tsstrasse 150, 44780 Bochum (Germany) E-mail: wolfgang.schuhmann@rub.de

Design Tradeoffs Between Constant Power Speed Range, Uncontrolled Generator Operation, and Rated Current of IPM Motor Drives

A closed-form approximate formulation is proposed to establish a relationship between the uncontrolled generator (UCG) operation of interior permanent-magnet (IPM) motors at high speed and the constant power speed range (CPSR) and drive current capabilities. High-saliency IPM motors of the PM-assisted synchronous reluctance type are mainly considered in the analysis, since they are proved to have the most favorable ratio between flux weakening capability and UCG voltage. The results of the analysis show the tight relationship between the uncontrolled overvoltage and the CPSR of the drive. Moreover, where the uncontrolled voltage is higher, the relationship between the CPSR and the motor current amplitude becomes stiffer: For small current variations, a large reduction of the speed range can occur. The analysis is validated experimentally on two motors of very different size (500 W and 1 MW).

Investigation of Improvement of Dynamic Switching Operation for Wavelength Switch With Super-Structure-Grating (SSG)-DBR-LD, Delayed-Interference Signal-Wavelength Converter (DISC), and Bandpass Filter

We demonstrate dynamic wavelength switching operation using a super-structure grating (SSG)-DBR-LD and a semiconductor optical amplifier (SOA)-delayed-interference signal-wavelength converter (DISC) for optical packet switch and buffering systems. The wavelength conversion-type optical switch has the advantage of lowering packet blocking probability and reducing numbers of the required SOAs in the DISC-type wavelength converter. However, we confirmed that large optical spikes occur at the timing of wavelength switching due to the optical chirping. By detuning the center wavelength of a bandpass filter to suppress optical chirped wavelength component, we could reduce the intensity of the spikes. We also observed the alternate wavelength switching operation with small optical spikes with fixed detuning of the bandpass filter and the fixed optical phase bias of the Mach-Zehnder Delayed Interferometer (MZDI) by setting the small current variation of the SSG-DBR-LD for wavelength switching. Error free performance was also achieved under back-to-back and 50 km single mode fiber transmission.

Stabilization of a tungsten ⟨310⟩ cold field emitter

Cold-field-emission current from a tungsten ⟨310⟩ emitter in a scanning electron microscope (SEM) gun, evacuated by an ion pump and a supplementary nonevaporative getter pump, was stabilized. It was verified that the probe current from a local (310) crystal plane exhibits different time variations in comparison to that of total current. As for the probe current under a pressure of 2×10−9 Pa, a stable plateau region—which lasted about 4 h—appeared just after flashing of the emitter. By observing emission patterns, it was verified that these different emission characteristics are originated from the anisotropy of current decay in accordance with crystal planes. With low-temperature “mild flashings” at 700 °C, the plateau region was extended to 12 h, which is long enough for practical SEM application. The superior properties of the plateau region, namely, high current, low noise, and small current variation, will enhance the performance and usability of electron microscopes.

Innovative Amorphous Silicon Balanced Ultraviolet Photodiode

An innovative balanced photodiode structure made in amorphous silicon/amorphous silicon carbide, suitable for detecting small current variations on a large background signal, is presented and characterized. The structure is a three-terminal device, constituted by two series-connected n-i-p photosensors, where the output signal is the difference between the currents flowing through the two diodes. The layer thickness and optical properties of the thin-film materials and the geometry of the structure have been optimized for the detection of ultraviolet radiation. Common mode rejection ratio (CMRR) values ranging between 30 dB at 254 nm and 42 dB at 365 nm have been measured, independent on the bias voltage. The decrease of the CMRR at lower wavelengths has been ascribed to differences in the surfaces of the two diodes exposed to the light.

Widely Vernier tunable external cavity laser including a sampled fiber Bragg grating with digital wavelength selection

We demonstrate an easy and efficient step tunable sampled fiber Bragg grating (SFBG) external cavity laser. A small current variation applied to a single electrode induces a step tuning of 15 nm based on the Vernier effect between an SFBG with a comb-like reflectivity and a two-section semiconductor laser diode. Thanks to the low current variation of less than 3 mA in the phase section, the output power remains constant within 0.6 dB at 6 dBm. The side-mode suppression ratio is greater than 40 dB over the whole tuning range.

Calculation of damping torque of power systems compensated with TCSC

AbstractThe thyristor‐controlled series capacitor (TCSC) is being developed to improve the transmission capability of power systems. The TCSC is thought to compensate transmission line reactance without causing subsynchronous resonance (SSR). However, in order to evaluate its effect quantitatively, we must calculate the frequency response of the generator damping torque. Simulations need a long computing time, and it is hard to choose the frequency freely. In this paper, we propose a method of analytically calculating the damping torque. First, when a generator rotor oscillates at some frequency, two voltage components appear. We analytically calculate the damping torque from small current variations due to the voltage components. The damping characteristic changes depending on the method of firing thyristors. The best characteristic is obtained when triggering with reference to the fundamental wave of TCSC voltage or current is used. By choosing an appropriate firing angle, we can drastically reduce negative damping by the TCSC. The damping characteristic is closely related to the system impedance. The fact that the TCSC has large resistance in the 0 to 60 Hz range helps significantly in improving the characteristic. Lastly, numerical simulations of SSR are used to examine the validity of our investigation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(1): 39–49, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10068

Response of X- and K-band cross section of the sea surface to small current variations

The modulation of the energy of centimetre waves on the sea surface by slowly varying currents is studied. An energy balance is used that contains effects of refraction, input of energy by wind, dissipation, and nonlinear triad interactions. This model predicts modulation factors on the order of 100 to 1000. The nonlinearity of the model makes it possible to find these large values, which, under certain circumstances, are also encountered in experiments.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A method for the dynamic continuous estimation of excitability changes of single fiber terminals in the central nervous system

A method is presented allowing direct and continuous estimation of the excitability changes of single fiber terminal arborizations within the central nervous system. In essence, the method measures the current required to maintain a preset antidronic firing probability of the unit under study. This implies operation in a closed loop system controlled by a computer. With this technique one can accurately determine input-output curves of single units requiring relatively small current variations (0.15–2.1 μA) to change from zero to maximal probability of response. The method also allows measurement of the excitability changes produced by conditioning volleys to sensory nerves.