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Due to its high thermal stability, low cost and high theoretical charge capacity, LiFePO4 has emerged as one of the most promising cathode materials for large-scale lithium ion batteries. In this work, we systematically investigated the effect on structure and electrochemical properties brought by W doping on Fe site of LiFePO4. LiFe1−yWyPO4 (y = 0. 0.01, 0.02, 0.03) samples with carbon coating were...
In the present paper we use the recently-proposed early-time GPR (Ground Penetrating Radar) amplitude technique with the aim of detecting the variations of electric conductivity in a porous material having a uniform permittivity. A specific laboratory setup has been realised to evaluate the sensitivity of the early-time amplitudes to the variations of the subsurface salt concentration (i.e., conductivity)...
The electrical conductivity in semiconductors vs. temperature (Mott's equation) can be described by some nonlinear functional equations of the transcendental type. In this paper, the problem of finding the exact analytical closed-form solution for Mott's equation is studied, in some detail, by the Special Trans Functions Theory — STFT. The numerical results and graphical presentations confirm validity...
This work addresses the need for a closed form expression to calculate the two dimensional (2D) conductivity of graphene that allows researchers to include graphene either as a 2D or a 3D material in their theoretical and numerical electromagnetic analysis. The closed form expression is developed based on the Kubo formula and experimental results found in the literature. Numerical studies reveal that...
This paper explores the effective permittivity and permeability of the structure which has periodic lossy dielectric objects embedded in a matrix. The asymptotic expressions for both high conductivity and quasi-static are derived and discussed. Numerical results both from the MG formula and an integral equation approach are provided to verify all the asymptotic expressions and related conclusions.
Graphene is a promising material for many applications, and electromagnetic modeling for graphene is needed to aid the design of graphene based devices. We present an approach for the finite-difference time-domain (FDTD) simulation of graphene improving on accuracy and computational efficiency. This is accomplished using a surface impedance boundary conditions (SIBC) to model graphene as a surface,...
Charge packet under high electric dc fields has been observed in polyethylene and its formation has been closely associated with ageing and breakdown of the insulating material. To understand the mechanisms several models have been proposed. In this paper, two models originated from completely different approaches have been reviewed. The first model proposed is based on bipolar charge injection together...
Valve side outlet device, which consists of bushing terminal and surrounding barrier system, is the insulation structure located in the connection part between valve winding lead and bushing. The insulation structure of outlet device is made up of oil and paperboard. It is the most complicated and the most important insulation part in converter transformer, and it not only withstands AC voltage, but...
The influence of water inside an insulating material (epoxy resin with Alumina filler) on volume resistivity, is investigated. This parameter is measured versus temperature. The water content within samples is adjusted using a climatic chamber, and monitored by weighing. Measurements show a large enhancement of volume conductivity versus water concentration and temperature. The impact of a temperature...
Effect of electron beam irradiation on dielectric properties in various insulating materials for spacecraft is investigated using PEA (Pulsed Electro-Acoustic) method. In space environment, spacecraft is exposed to plasma or radioactive-rays. In such condition, multilayer insulating materials covering the spacecraft are charged up. Sometimes the charge accumulation causes to the serious damage to...
One of the major issues to be considered for the development of polymeric-type DC cable systems is the accumulation of space charges and the consequent distortion of the electric field. These phenomena occur both in the cable and in the accessories, especially at interfaces between different materials. In this respect, accessories, like joints and terminations are key points for the reliability of...
Graphene and graphene oxide are increasingly attracting worldwide attention from academia and industry. The physical properties of graphene have been documented recently, and we have known that the sea of electrons in the two-dimensional, single layer of sp2 hybridized carbon atoms causes graphene to act both as electrical and thermal conductors. In contrast, graphene oxide, an oxidized graphene sheet...
Finite Element Analysis (FEA) has evolved over the years from a purely academic pursuit into everyday product development due to the evolution of the computation power and software developments. Engineering simulation technology allows now the detailed analyses of complex sub-systems in different configurations, combined with physical conditions that equipment faces in the real word. It is shown how...
Surface resistance measurements on insulating solids are usually performed by measuring the current induced when an electric field tangential to the surface is applied. The measured current results from the addition of currents flowing along the surface, and also partly in the volume. In this paper, surface current measurements on an alumina-filled epoxy resin are performed under varying conditions...
This paper reports on the results of a numerical modeling that considers the field grading phenomena of SiC powder with a variable resistivity dependent on particle size. The particle shape and size of commercially available SiC powders were altered by ball milling. In an earlier work, we have determined the electrical properties of various SiC powders by using a controlled-pressure Ohmmeter. Different...
For nanoscaled integrated circuit interconnects as a performance metric play a crucial role. In this paper high frequency effect especially the skin effect for these nano interconnects has been analyzed. Here as a carbon nano interconnect graphene nano-ribbon (GNR), carbon nanotube (CNT) has been analyzed in GHz frequency range. Initially the skin depth of these interconnects has been analyzed and...
Insulation system is the backbone in any HV machine and as well as power system. However, degradation that always happens in the insulation system will reduce the lifespan of the machine. Thus, condition monitoring of the insulation system is highly recommended in order to maintain the reliability and efficiency of the machine during operation. Polarization and Depolarization Current (PDC) measurement...
The effects of different shapes of silver; particles, flakes and dendrites on the electrical property of polydimethyl siloxane (PDMS)-based electrically conductive adhesives (ECA) under mechanical deformation are investigated. It is found that the high aspect ratio of silver dendrites helps to construct more conduction pathways in the ECAs compared with silver particles and flakes, therefore reducing...
This paper describes first attempt to coarse-grained molecular dynamics study of heat transfer in thermal interface materials. All calculations and most of preparation steps are conducted using customized PERL scripts for Materials Studio 6.0. The first part introduces the developed approach to molecular modeling, which allows the study of the properties of thermal interface materials which provide...
A crucial issue in the field of high power lasers is the management of thermal effects, leading to mechanical distortions, thermal lenses and optical losses of the laser crystal. A suitable candidate for such application should combine a weak quantum defect and good thermo-mechanical properties in order to limit the heat production in the laser material. In this context, Yb3+:CaGdAlO4 is a promising...
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