Dielectric Impedance Studies of Poly(vinyl butyral)-Cenosphere Composite Films

In the current study, amino silane functionalized cenosphere particles was used as a reinforcing filler in poly(vinyl butyral) matrix and were made by melt blending. The changes observed in the dielectric performance of the composite films with varying weight percentage of cenosphere particle in the matrix were investigated. The dielectric property and impedance spectroscopy were evaluated as a function of applied frequency in the range of 50 Hz to 5 MHz. It is observed that, because of orientation polarization of the PVB polymer, the permittivity and impedance decrease, whereas conductivity increases. Tangent loss graph indicates that the property of the matrix is associated with geometrical fill factor and the lowest quality factor. Therefore, above 10 kHz, these composites can be considered as dielectric loss-less material. (C) 2013 Society of Plastics Engineers

Frequency and Temperature-Independent Electrical Transport Properties of 2BaO-0.5Na(2)O-2.5Nb(2)O(5)-4.5B(2)O(3) Glass-Ceramics

The temperature (300-973K) and frequency (100Hz-10MHz) response of the dielectric and impedance characteristics of 2BaO-0.5Na(2)O-2.5Nb(2)O(5)-4.5B(2)O(3) glasses and glass nanocrystal composites were studied. The dielectric constant of the glass was found to be almost independent of frequency (100Hz-10MHz) and temperature (300-600K). The temperature coefficient of dielectric constant was 8 +/- 3ppm/K in the 300-600K temperature range. The relaxation and conduction phenomena were rationalized using modulus formalism and universal AC conductivity exponential power law, respectively. The observed relaxation behavior was found to be thermally activated. The complex impedance data were fitted using the least square method. Dispersion of Barium Sodium Niobate (BNN) phase at nanoscale in a glass matrix resulted in the formation of space charge around crystal-glass interface, leading to a high value of effective dielectric constant especially for the samples heat-treated at higher temperatures. The fabricated glass nanocrystal composites exhibited P versus E hysteresis loops at room temperature and the remnant polarization (P-r) increased with the increase in crystallite size.

Dendritic atrophy constricts functional maps in resonance and impedance properties of hippocampal model neurons

A gradient in the density of hyperpolarization-activated cyclic-nucleotide gated (HCN) channels is necessary for the emergence of several functional maps within hippocampal pyramidal neurons. Here, we systematically analyzed the impact of dendritic atrophy on nine such functional maps, related to input resistance and local/transfer impedance properties, using conductance-based models of hippocampal pyramidal neurons. We introduced progressive dendritic atrophy in a CA1 pyramidal neuron reconstruction through a pruning algorithm, measured all functional maps in each pruned reconstruction, and arrived at functional forms for the dependence of underlying measurements on dendritic length. We found that, across frequencies, atrophied neurons responded with higher efficiency to incoming inputs, and the transfer of signals across the dendritic tree was more effective in an atrophied reconstruction. Importantly, despite the presence of identical HCN-channel density gradients, spatial gradients in input resistance, local/transfer resonance frequencies and impedance profiles were significantly constricted in reconstructions with dendrite atrophy, where these physiological measurements across dendritic locations converged to similar values. These results revealed that, in atrophied dendritic structures, the presence of an ion channel density gradient alone was insufficient to sustain homologous functional maps along the same neuronal topograph. We assessed the biophysical basis for these conclusions and found that this atrophy-induced constriction of functional maps was mediated by an enhanced spatial spread of the influence of an HCN-channel cluster in atrophied trees. These results demonstrated that the influence fields of ion channel conductances need to be localized for channel gradients to express themselves as homologous functional maps, suggesting that ion channel gradients are necessary but not sufficient for the emergence of functional maps within single neurons.

Domain size correlated magnetic properties and electrical impedance of size dependent nickel ferrite nanoparticles

We report here the investigations on the size dependent variation of magnetic properties of nickel ferrite nanoparticles. Nickel ferrite nanoparticles of different sizes (14 to 22 nm) were prepared by the sol-gel route at different annealing temperatures. They are characterized by TGA-DTA, XRD, SEM, TEM and Raman spectroscopy techniques for the confirmation of the temperature of phase formation, thermal stability, crystallinity, morphology and structural status of the nickel ferrite nanoparticles. The magnetization studies revealed that the saturation magnetization (M-s), retentivity (M-r) increase, while coercivity (H-c) and anisotropy (K-eff) decrease as the particle size increases. The observed value of M-s is found to be relatively higher for a particle size of 22 nm. In addition, we have estimated the magnetic domain size using magnetic data and correlated to the average particle size. The calculated magnetic domain size is closely matching with the particle size estimated from XRD. Impedance spectroscopy was employed to study the samples in an equivalent circuit to understand their transport phenomena. It shows that nickel ferrite nanoparticles exhibit a non-Debye behavior with increasing particle size due to the influence of increasing disorders, surface effects, grain size and grain boundaries, etc. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Photochemical Deposition of Co-Ac Catalyst on ZnO Nanorods for Solar Water Oxidation

The preparation of ZnO nanorod films decorated with cobalt-acetate (CoAc) electrocatalyst and its activity for photoelectrolysis of water have been demonstrated. The photochemically prepared CoAc catalyst is chemically and morphologically similar to the electrochemically prepared CoAc catalyst. The on-set potential of oxygen evolution reaction is lower on CoAc-ZnO photoanode in relation to bare ZnO photoanode. There is a three to four fold increase in photooxidation current of OER due to the presence of CoAc co-catalyst on ZnO. Thus, the photochemically prepared CoAc on ZnO is an alternative and efficient co-catalyst for photoelectrochemical oxygen evolution reaction. The enhancement in photocatalytic activity of ZnO by the CoAc catalyst photochemically deposited from acetate buffer solution is significantly greater than the cobalt-phosphate (CoPi) co-catalyst deposited from phosphate buffer solution. (C) The Author(s) 2015. Published by ECS. All rights reserved.

A Gold Sensors Array for Imaging The Real Tissue Phantom in Electrical Impedance Tomography

Surface electrodes in Electrical Impedance Tomography (EIT) phantoms usually reduce the SNR of the boundary potential data due to their design and development errors. A novel gold sensors array with high geometric precision is developed for EIT phantoms to improve the resistivity image quality. Gold thin films are deposited on a flexible FR4 sheet using electro-deposition process to make a sixteen electrode array with electrodes of identical geometry. A real tissue gold electrode phantom is developed with chicken tissue paste and the fat cylinders as the inhomogeneity. Boundary data are collected using a USB based high speed data acquisition system in a LabVIEW platform for different inhomogeneity positions. Resistivity images are reconstructed using EIDORS and compared with identical stainless steel electrode systems. Image contrast parameters are calculated from the resistivity matrix and the reconstructed images are evaluated for both the phantoms. Image contrast and image resolution of resistivity images are improved with gold electrode array.

A Physical Model for Inception and Propagation of Upward Lightning Leader from a 1200 kV AC Power Transmission Line

UHV power transmission lines have high probability of shielding failure due to their higher height, larger exposure area and high operating voltage. Lightning upward leader inception and propagation is an integral part of lightning shielding failure analysis and need to be studied in detail. In this paper a model for lightning attachment has been proposed based on the present knowledge of lightning physics. Leader inception is modeled based on the corona charge present near the conductor region and the propagation model is based on the correlation between the lightning induced voltage on the conductor and the drop along the upward leader channel. The inception model developed is compared with previous inception models and the results obtained using the present and previous models are comparable. Lightning striking distances (final jump) for various return stroke current were computed for different conductor heights. The computed striking distance values showed good correlation with the values calculated using the equation proposed by the IEEE working group for the applicable conductor heights of up to 8 m. The model is applied to a 1200 kV AC power transmission line and inception of the upward leader is analyzed for this configuration.

Impedance spectroscopic studies on microwave synthesized NaPO3-V2O5 glasses containing SO42- ions

Impedance spectroscopic studies on modified phospho-vanadate glasses containing SO42- ions have been carried out over wide range of frequency. Modulated DSC studies suggest that the addition of alkali salt makes the glass less rigid and more fragile. The frequency dependent impedance data has been used to calculate d.c conductivity and activation energies. These values are comparable with the other ionic liquids. The conductivity and relaxation phenomenon was rationalized using universal a.c conductivity power law and modulus formalism. The activation energies for relaxation mechanism was also determined using imaginary parts of electrical modulus peaks which were close to those of the d.c conductivity implying the involvement of similar energy barriers in both the processes. Kohlrausch-William-Watts (KWW) stretched exponent beta, is temperature insensitive and power law (s) exponent is temperature dependent. The enhanced conductivity in these glasses is attributed to the depolymerised structure in which migration of Na+ ions proceeds in an expanded network comprising SO42- ions in the interstitials. The effect of structure on activation energy is well supported by abinitio DFT computations. (C) 2015 Elsevier B.V. All rights reserved.

Computation of power released during corona treatment on polymeric insulators under ac and dc excitation

With increasing energy demand, it necessitates to generate and transmit the electrical power with minimal losses. High voltage power transmission is the most economical way of transmitting bulk power over long distances. Transmission insulator is one of the main components used as a mechanical support and to electrically isolate the conductor from the tower. Corona from the hardware and conductors can significantly affect the performance of the polymeric insulators. In the present investigation a methodology is presented to evaluate the corona performance of the polymeric shed material under different environment conditions for both ac and dc excitation. The results of the comprehensive analysis on various polymeric samples and the power released from the corona electrode for both the ac and dc excitation are presented. Some interesting results obtained from the chemical analysis confirmed the presence of nitric acid species on the treated sample which in long term will affect the strength of the insulator, also the morphological changes were found to be varying for different experimental conditions. (C) 2015 The Authors. Published by Elsevier Ltd.

High Performance Modulation of High-Frequency AC Link Inverter

Inverters with high voltage conversion ratio are used in systems with sources such as batteries, photovoltaic (PV) modules or fuel cells. Transformers are often used in such inverters to provide the required voltage conversion ratio and isolation. In this paper, a compact high-frequency (HF) transformer interfaced AC link inverter with lossless snubber is discussed. A high performance synchronized modulation scheme is proposed for this inverter. This modulation addresses the issue of over-voltage spikes due to transformer leakage inductance and it is shown that the circuit can operate safely even when the turn-on delay, such as dead-time, is not used in the HF rectifier section. The problem of spurious turn-on in the HF inverter switches is also mitigated by the proposed modulation method. The circuit performance is validated experimentally with a $900W$ prototype inverter.

On the Equivalence of Acoustic Impedance and Squeeze Film Impedance in Micromechanical Resonators

In this work, we address the issue of modeling squeeze film damping in nontrivial geometries that are not amenable to analytical solutions. The design and analysis of microelectromechanical systems (MEMS) resonators, especially those that use platelike two-dimensional structures, require structural dynamic response over the entire range of frequencies of interest. This response calculation typically involves the analysis of squeeze film effects and acoustic radiation losses. The acoustic analysis of vibrating plates is a very well understood problem that is routinely carried out using the equivalent electrical circuits that employ lumped parameters (LP) for acoustic impedance. Here, we present a method to use the same circuit with the same elements to account for the squeeze film effects as well by establishing an equivalence between the parameters of the two domains through a rescaled equivalent relationship between the acoustic impedance and the squeeze film impedance. Our analysis is based on a simple observation that the squeeze film impedance rescaled by a factor of jx, where x is the frequency of oscillation, qualitatively mimics the acoustic impedance over a large frequency range. We present a method to curvefit the numerically simulated stiffness and damping coefficients which are obtained using finite element analysis (FEA) analysis. A significant advantage of the proposed method is that it is applicable to any trivial/nontrivial geometry. It requires very limited finite element method (FEM) runs within the frequency range of interest, hence reducing the computational cost, yet modeling the behavior in the entire range accurately. We demonstrate the method using one trivial and one nontrivial geometry.

A Simple Hysteretic Energy Harvesting Method for Nonneutral AC Switches in Load Automation

This paper presents a simple hysteretic method to obtain the energy required to operate the gate-drive, sensors, and other circuits within nonneutral ac switches intended for use in load automated buildings. The proposed method features a switch-mode low part-count self-powered MOSFET ac switch that achieves efficiency and load current THD figures comparable to those of an externally gate-driven switch built using similar MOSFETS. The fundamental operation of the method is explained in detail, followed by the modifications required for practical implementation. Certain design rules that allow the method to accommodate a wide range of single-phase loads from 10 VA to 1 kVA are discussed, along with an efficiency enhancement feature based on inherent MOSFET characteristics. The limitations and side effects of the method are also mentioned according to their levels of severity. Finally, experimental results obtained using a prototype sensor switch are presented, along with a performance comparison of the prototype with an externally gate-driven MOSFET switch.