Papers by Keyword: Impedance

Abstract: The composition of the surface and electrical properties of silicon oxide nanocomposites of porous silicon were investigated by FTIR spectroscopy in the range of 400 – 4000 cm^-1 and by impedance spectroscopy in the frequency range of 25 Hz – 1 MHz. It was revealed the different dispersion of electrical capacitance in different frequency bands and the complex relaxation processes that affect the electrical transport properties of nanocomposites. The correlations between the IR absorption spectra of silicon oxide composites and processes of charge transfer was defined. On the basis of analysis of spectra of thermal stimulated depolarization it was shown that oxidation of the surface of porous silicon nanocrystals gives rise to changing the density of states in different energy ranges.

Abstract: We consider the control problem for two-dimensional model of the electromagnetic field, which describes the scattering TM-polarized electromagnetic waves in an infinite homogeneous medium containing permeable dielectric obstacle with a covered for masking boundary. The role of control function is played by index of refraction of the dielectric obstacle. We prove the solvability of the control problem, derive the optimality system, which describes the necessary conditions of an extremum and develop an efficient numerical algorithm for the solution of the control problem.

Abstract: Electrochemical behavior of carbon steel in 1 M acetic acid (CH₃COOH) containing tetramethyl ammonium bromide (TMB) as the cationic inhibitor was investigated by potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The aim of this study is to evaluate the inhibition efficiency of cationic inhibitor for carbon steel corrosion. The electrochemical analysis revealed that inhibition efficiency significantly increased with the increasing of inhibitor concentration. Polarization study indicated that TMB acted as a mixed type inhibitor, which inhibited both cathodic and anodic reactions. The changes of impedance parameters by different inhibitor concentration showed a better protection due to formation of a thin film onto the steel surface. This study suggests that TMB is able to inhibit corrosion process of carbon steel in acidic medium with significant inhibition efficiency.

Abstract: The cloaking problem is considered for a 2-D wave scattering model in an unbounded homogenous medium containing an impenetrable covered (cloaked) boundary. The control is a surface impedance which enters the boundary condition as a coefficient. The problem is reduced to the inverse extremal problem of choosing the surface impedance. The solvability of the original scattering problem for 2-D Helmholtz equation and of the extremal problem is proved. Optimality system describing the necessary extremum conditions is derived. The algorithm for numerical solving of the control problem based on the optimality system and boundary element method is designed.

Abstract: We consider the control problem for two-dimensional model of the electromagnetic field which describes the scattering E-polarized electromagnetic waves in an infinite homogeneous medium containing permeable dielectric obstacle with a partially covered (for masking) boundary. The role of control function is played by surface conductivity entering the impedance boundary condition on the covered part of the boundary and the index of refraction of the dielectric obstacle. We prove the solvability of the control problem, derive the optimality system which describes the necessary conditions of an extremum and develop an efficient numerical algorithm for the solution of the control problem.

Abstract: Films of starch/PEO blends were prepared via solution casting technique and their properties with different amount of ammonium nitrate, NH₄NO₃ were compared. The measurement of conductivity at room temperature were carried out using impedance spectroscopy. The highest conductivity calculated is found to be 2.81±0.46 x 10^-7Scm^-1 with addition of 35wt% NH₄NO_{3 .}

Abstract: To analysis the low voltage ride through tests results carried out in Inner Mongolia, the impedance model of low voltage ride through test equipment ability with the wind turbine is established. The grid current variation caused by series or parallel impedance switching is analyzed theoretically. Results show that grid current will become larger while the parallel impedance of low voltage test equipment is smaller. Consequently, suggestion is proposed to take optimal configuration of impedance in the equipment to reduce effect on grid current, which can ensure the smooth running of low voltage ride through test.

Abstract: The amino functionalized magnesium phyllosilicate clay (AC) intercalated over PVA-Nafion hybrid nanocomposite membranes were prepared by sol-gel method. The free standing membranes were obtained by solution recasting. The composition of clay materials such as AC and montmorillonite (MMT) was varied between 2-10 wt.% with respect to PVA-Nafion content. The molecular interactions and surface morphology of nanocomposite membranes were investigated by FT-IR and SEM analyses respectively. The thermal and mechanical stabilities of nanocomposite membranes were studied using TGA and Nanoindentation techniques. For 6 wt. % AC/PVA-Nafion, TGA results showed no appreciable mass change up to 380 °C and hardness calculated from nanoindentation studies was nearly 30 % higher than the other compositions. An improved conductivity was obtained for 6 wt. % AC/PVA-Nafion (1.4×10^-2 S/cm) compared to pure Nafion (1.2×10^-2 S/cm) and PVA-Nafion and MMT/PVA-Nafion composite membranes. From these studies, we observed that 6 wt. % AC/PVA-Nafion membrane possessed a good conductivity with higher thermal and mechanical stabilities.

Abstract: It is generally believed that materials with high imaginary permeability and high imaginary permittivity are effective absorbers. For specific samples, however, the adjustment of input impedance is still necessary for the sample property optimization. By analyzing the relation between the diffraction rate and the input impedance, a method of absorption maximization for slab sample are presented in this sample. Medium choosing and volume rate controlling is the key of this method.

Abstract: Wet gel electrodes are widely used for ECG/EEG monitoring, their low impedance results in high-quality signals. But they have important drawbacks too, such as time-consuming electrode set-up for EEG followed by a painful removal, skin irritation by the gel and signal degradation due to gel drying. Hence various dry electrode types are investigated, such as hard metal electrodes with low impedance but limited patient comfort/safety. We focus on flexible conductive polymer-based electrodes to combine low impedance, user comfort and safety. The composition of the conductive polymers is optimized to improve various properties such as conductivity, which directly affects signal quality and sensitivity to motion artifacts, and mechanical properties of the electrodes, important with respect to patient comfort. Electrode impedance and ECG/EEG signal recordings are evaluated using various polymer compositions and compared to wet gel electrode results. Additive optimization to improve processability of the conductive formulations is performed by dedicated flow studies, and will result in a high electrode fabrication yield. Very promising results are obtained regarding impedance, EEG/ECG signal quality and user comfort.