Electrical switching in benzidine-DDQ under pressure

The effect of pressure on non-ohmic conduction and electrical switching in the charge transfer complex benzidine-DDQ has been studied up to a pressure of 7·66 GPa at a temperature of 300K. Pulsed I-V measurements reveal heating contribution to non-ohmicity and switching. At high electric fields (∼ 3 × 103 V/cm), the sample switches from high resistance OFF state of several kiloohms to low resistance ON state of several ohms. Temperature dependence of conductivity of ON state show semiconducting behaviour with very low activation energy.

Thin film amorphous semiconductor microwave switches

Microwave switches operating in the X band were designed and fabricated using amorphous chalcogenide semiconductors of composition GexTeyAsz. Threshold devices were shown to operate as microwave modulators at modulation frequencies of up to 100 MHz. No delay time was observed at the highest frequency although the modulation efficiency decreased above 10 MHz owing to the finite recovery time which was approximately 0.3 × 10−8s. The devices can also be used as variolossers, the insertion loss being 0.5 dB in the OFF state and increasing on switching from 5 dB at 1 mA device current to 18 dB at 100 mA.The behaviour of the threshold switches can be explained in terms of the formation of a conducting filament in the ON state with a constant current density of 2 × 104Acm−2 that is shunted by the device capacitance. The OFF state conductivity σ varies as ωn (0.5 < n < 1) which is characteristic of hopping in localized states. However, there was evidence of a decrease in n or a saturation of the conductivity at high frequencies.As a result of phase separation memory switches require no holding current in the ON state and may be used as novel latching semiconductor phase-shifters.

Principle of a Dual Current Source Converter for AC Motor Drives

The principle of operation of a dual current source converter is briefly explained. The combination of two single current source converters (SCSC) to form a ``dual (duplex) current source converter'' (DCSC) is proposed. The DCSC is shown to have the following merits: 1) it retains all the advantages of the SCSC; 2) it reduces the harmonic content of the current waveform considerably; and 3) since the load current is shared equally between two current source converters, ratings of the individual components employed in the circuit are considerably lowered. A DCSC can be an attractive choice for sophisticated large horsepower drives where a good performance of the drive rather than cost is a prime factor. An open-loop control scheme employing the DCSC for an ac motor drive has been successfully implemented in the laboratory. Oscillograms of the improved load current waveforms are shown.

Characterization, electrical percolation and magnetization studies of polystyrene/multiwall carbon nanotube composite films

Polystyrene/multiwall carbon nanotube composite films are prepared with loading up to 7 weight percent (wt%) of multiwall carbon nanotubes by solution processing and casting technique. In the formation of these composite films, iron filled carbon nanotubes with high aspect ratio (similar to 4000) were used. Scanning electron microscopy study shows that the nanotubes are uniformly dispersed within the polymer matrix. At high magnification, bending of carbon nanotubes is noticed which can be attributed to their elastic properties. The electrical conductivity measurements show that the percolation threshold is rather low at 0.21 wt%. Hysteresis loop measurements on the bulk multiwall carbon nanotube and composite samples are done at 10, 150 and 300 K and the coercivity values are found to be largest at all the temperatures, for 1 wt% composite sample. (C) 2010 Elsevier B.V. All rights reserved.

A Resonant Integrator Based PLL and AC Current Controller for Single Phase Grid Connected PWM-VSI

Grid connected PWM-VSIs are being increasingly used for applications such as Distributed Generation (DG), power quality, UPS etc. Appropriate control strategies for grid synchronisation and line current regulation are required to establish such a grid interconnection and power transfer. Control of three phase VSIs is widely reported in iterature. Conventionally, dq control in Synchronous Reference Frame(SRF) is employed for both PLL and line current control where PI-controllers are used to track the DC references. Single phase systems do not have defined direct (d) and quadrature (q) axis components that are required for SRF transformation. Thus, references are AC in nature and hence usage of PI controllers cannot yield zero steady state errors. Resonant controllers have the ability to track AC references accurately. In this work, a resonant controller based single phase PLL and current control technique are being employed for tracking grid frequency and the AC current reference respectively. A single phase full bridge converter is being operated as a STATCOM for performance evaluation of the control scheme.

Synthesis and electrical properties of the (PVA)(0.7)(Kl)(0.3)center dot xH(2)SO(4) (0 <= x <= 5) polymer electrolytes and their performance in a primary Zn/MnO2 battery

Solid acid polymer electrolytes (SAPE) were synthesised using polyvinyl alcohol, potassium iodide and sulphuric acid in different molar ratios by solution cast technique. The temperature dependent nature of electrical conductivity and the impedance of the polymer electrolytes were determined along with the associated activation energy. The electrical conductivity at room temperature was found to be strongly depended on the amorphous nature of the polymers and H2SO4 concentration. The ac (100 Hz to 10 MHz) and dc conductivities of the polymer electrolytes with different H2SO4 concentrations were analyzed. A maximum dc conductivity of 1.05 x 10(-3) S cm(-1) has been achieved at ambient temperature for electrolytes containing 5 M H2SO4. The frequency and temperature dependent dielectric and electrical modulus properties of the SAPE were studied. The charge transport in the present polymer electrolyte was obtained using Wagner's polarization technique, which demonstrated the charge transport to be mainly due to ions. Using these solid acid polymer electrolytes novel Zn/SAPE/MnO2 solid state batteries were fabricated and their discharge capacity was calculated. An open circuit voltage of 1.758V was obtained for 5 M H2SO4 based Zn/SAPE/MnO2 battery. (C) 2010 Elsevier Ltd. All rights reserved.

Electrical transport in magnesium aluminate

The conductivity of MgAl2O4 has been measured at 1273, 1473 and 1673 K as a function of the partial pressure of oxygen ranging from 105 to 10−14 Pa. The MgAl2O4 pellet, sandwiched between two platinum electrodes, was equilibrated with a flowing stream of either Ar + O2, CO + CO2 or Ar + H2 + H2O mixture of known composition. The gas mixture established a known oxygen partial pressure. All measurements were made at a frequency of 1 kHz. These measurements indicate pressure independent ionic conductivity in the range 1 to 10−14 Pa at 1273 K, 10−1 to 10−12 Pa at 1473 K and 10−1 to 10−4 Pa at 1673 K. The activation energy for ionic conduction is 1·48 eV, close to that for self-diffusion of Mg2+ ion in MgAl2O4 calculated from the theoretical relation of Glyde. Using the model, the energy for cation vacancy formation and activation energy for migration are estimated.

Electrical Contact Resistance in Thin (<= 0.5 mu m) Gold Plated Contacts: Effect of Gold Plating Thickness

This paper describes the electrical contact resistance (ECR) measurements made on thin gold plated (gold plating of <= 0.5 mu m with a Ni underlayer of similar to 2 mu m) oxygen free high conductivity (OFHC) Cu contacts in vacuum environment. ECR in gold plated OFHC Cu contacts is found to be slightly higher than that in bare OFHC Cu contacts. Even though gold is a softer material than copper, the relatively high ECR values observed in gold plated contacts are mainly due to the higher hardness and electrical resistivity of the underlying Ni layer. It is well known that ECR is directly related to plating factor, which increases with increasing coating thickness when the electrical resistivity of coating material is more than that of substrate. Surprisingly, in the present case it is found that the ECR decreases with increasing gold layer thickness on OFHC Cu substrate (gold has higher electrical resistivity than OFHC Cu). It is analytically demonstrated from the topography and microhardness measurements results that this peculiar behavior is associated with thin gold platings, where the changes in surface roughness and microhardness with increasing layer thickness overshadow the effect of plating factor on ECR.

Resistivity imaging of a reconfigurable phantom with circular inhomogeneities in 2D-electrical impedance tomography

Resistivity imaging of a reconfigurable phantom with circular inhomogeneities is studied with a simple instrumentation and data acquisition system for Electrical Impedance Tomography. The reconfigurable phantom is developed with stainless steel electrodes and a sinusoidal current of constant amplitude is injected to the phantom boundary using opposite current injection protocol. Nylon and polypropylene cylinders with different cross sectional areas are kept inside the phantom and the boundary potential data are collected. The instrumentation and the data acquisition system with a DIP switch-based multiplexer board are used to inject a constant current of desired amplitude and frequency. Voltage data for the first eight current patterns (128 voltage data) are found to be sufficient to reconstruct the inhomogeneities and hence the acquisition time is reduced. Resistivity images are reconstructed from the boundary data for different inhomogeneity positions using EIDORS-2D. The results show that the shape and resistivity of the inhomogeneity as well as the background resistivity are successfully reconstructed from the potential data for single or double inhomogeneity phantoms. The resistivity images obtained from the single and double inhomogeneity phantom clearly indicate the inhomogeneity as the high resistive material. Contrast to noise ratio (CNR) and contrast recovery (CR) of the reconstructed images are found high for the inhomogeneities near all the electrodes arbitrarily chosen for the entire study. (C) 2010 Elsevier Ltd. All rights reserved.

Numerical Electromagnetic Analysis of Current and Voltage Distribution along Down Conductors and Towers Hit by Direct Lightning

In order to answer the practically important question of whether the down conductors of lightning protection systems to tall towers and buildings can be electrically isolated from the structure itself, this work is conducted. As a first step in this regard, it is presumed that the down conductor placed on metallic tower will be a pessimistic representation of the actual problem. This opinion was based on the fact that the proximity of heavy metallic structure will have a large damping effect. The post-stroke current distributions along the down conductors and towers, which can be quite different from that in the lightning channel, govern the post-stroke near field and the resulting gradient in the soil. Also, for a reliable estimation of the actual stroke current from the measured down conductor currents, it is essential to know the current distribution characteristics along the down conductors. In view of these, the present work attempts to deduce the post-stroke current and voltage distribution along typical down conductors and towers. A solution of the governing field equations on an electromagnetic model of the system is sought for the investigation. Simulation results providing the spatio-temporal distribution of the post-stroke current and voltage has provided very interesting results. It is concluded that it is almost impossible to achieve electrical isolation between the structure and the down conductor. Furthermore, there will be significant induction into the steel matrix of the supporting structure.

Spectroscopic and electrical properties of SiO2 films prepared by simple and cost effective sol-gel process

Amorphous SiO2 thin films were prepared on glass and silicon substrates by cost effective sol-gel method. Tetra ethyl ortho silicate (TEOS) was used as the precursor material, ethanol as solvent and concentrated HCl as a catalyst. The films were characterized at different annealing temperatures. The optical transmittance was slightly increased with increase of annealing temperature. The refractive index was found to be 1.484 at 550 nm. The formation of SiO2 film was analyzed from FT-IR spectra. The MOS capacitors were designed using silicon (1 0 0) substrates. The current-voltage (I-V), capacitance-voltage (C-V) and dissipation-voltage (D-V) measurements were taken for all the annealed films deposited on Si (1 0 0). The variation of current density, resistivity and dielectric constant of SiO2 films with different annealing temperatures was investigated and discussed for its usage in applications like MOS capacitor. The results revealed the decrease of dielectric constant and increase of resistivity of SiO2 films with increasing annealing temperature. (C) 2010 Elsevier B.V. All rights reserved.

Temperature dependent electrical transport behavior of InN/GaN heterostructure based Schottky diodes

InN/GaN heterostructure based Schottky diodes were fabricated by plasma-assisted molecular beam epitaxy. The temperature dependent electrical transport properties were carried out for InN/GaN heterostructure. The barrier height and the ideality factor of the Schottky diodes were found to be temperature dependent. The temperature dependence of the barrier height indicates that the Schottky barrier height is inhomogeneous in nature at the heterostructure interface. The higher value of the ideality factor and its temperature dependence suggest that the current transport is primarily dominated by thermionic field emission (TFE) other than thermionic emission (TE). The room temperature barrier height obtained by using TE and TFE models were 1.08 and 1.43 eV, respectively. (C) 2011 American Institute of Physics. doi: 10.1063/1.3549685]

Electrical Relaxation and Transport in 0.5Cs(2)O-0.5Li(2)O-3B(2)O(3) Glasses

The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the transparent glasses in the composition 0.5Cs(2)O-0.5Li(2)O-3B(2)O(3) (CLBO) were investigated in the 100 Hz - 10 MHz frequency range. The dielectric constant for the as-quenched glass increased with increasing temperature, exhibiting anomalies in the vicinity of the glass transition and crystallization temperatures. The temperature coefficient of dielectric constant was estimated (35 +/- 2 ppm. K-1) using Havinga's formula. The dielectric loss at 313 K is 0.005 +/- 0.0005 at all the frequencies understudy. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.73 +/- 0.05 eV, close to that of the activation energy obtained for DC conductivity (1.6 +/- 0.06 eV). The frequency dependent electrical conductivity was analyzed using Jonscher's power law. The combination of these dielectric characteristics suggests that these are good candidates for electrical energy storage device applications.

Effect of sodium diffusion on the structural and electrical properties of Cu2ZnSnS4 thin films

Cu2ZnSnS4 (CZTS) is a kesterite semiconductor consisting of abundantly available elements. It has a band gap of 1.5 eV and a large absorption coefficient. Hence, thin films made of this material can be used as absorber layers of a solar cell. CZTS films were deposited on soda lime and Na free borosilicate glass substrates through Ultrasonic Spray Pyrolysis. The diffusion of sodium from soda lime glass was found to have a profound effect on characteristics like grain size, crystal texture and conductivity of CZTS thin films. Copper ion concentration also varied during the deposition and it was observed that the carrier concentration was enhanced when there was a deficiency of copper in the films. The effect of sodium diffusion and copper deficiency in enhancing the structural and electrical properties of CZTS films are presented in this paper. (C) 2010 Elsevier B.V. All rights reserved.

Preparation, Structural, and Electrical Studies of Polyaniline/ZnFe2O4 Nanocomposites

Polyaniline/ZnFe2O4 nanocomposites were synthesized by a simple and inexpensive one-step in situ polymerization method in the presence of ZnFe2O4 nanoparticles. The structural, morphological, and electrical properties of the samples were characterized by wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). WAXD and SEM revealed the formation of polyaniline/ZnFe2O4 nanocomposites. Infrared spectroscopy indicated that there was some interaction between the ZnFe2O4 nanoparticles and polyaniline. The dc electrical conductivity measurements were carried in the temperature range of 80 to 300 K. With increase in the doping concentration of ZnFe2O4, the conductivity of the nanocomposites found to be decreasing from 5.15 to 0.92 Scm(-1) and the temperature dependent resistivity follows ln rho(T) similar to T-1/2 behavior. The nanocomposites (80 wt % of ZnFe2O4) show a more negative magnetoresistance compared with that of pure polyaniline (PANI). These results suggest that the interaction between the polymer matrix PANI and zinc nanoparticles take place in these nanocomposites. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2856-2862, 2011