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Influence of Water Absorption on Volume Resistivity and the Dielectric Properties of Neat Epoxy MaterialSulaimani, Anwar Ali 15 July 2014 (has links)
Epoxy resins are widely used materials in the industry as electrical insulators, adhesives and in aircrafts structural components because of their high mechanical stiffness, strength and high temperature and chemical resistance properties. But still, the influence of water uptake due to moisture adsorption is not fully understood as it detrimentally modifies the electrical and chemical properties of the material. Here ,we investigate the influence of water moisture uptake on the neat epoxy material by monitoring the change in the volume resistivity and dielectric properties of epoxy material at three different thickness configurations: 0.250 mm, 0.50 mm and 1 mm thicknesses.
Gravimetric analysis was done to monitor the mass uptake behaviour, Volume Resistivity was measured to monitor the change in conductivity of the material, and the dielectric properties were mapped to characterise the type of water mechanism available within the material during two ageing processes of sorption and desorption.
Two-stage behaviours of diffusion and reaction have been identified by the mass uptake analysis. Moreover, the plot of volume resistivity versus mass uptake has indicated a non-uniform relationship between the two quantities. However, the analysis of the dielectric spectrum at medium range of frequency and time has showed a change in the dipolar activities and also showed the extent to which the water molecules can be segregated between bounding to the resin or existing as free water
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Design and Synthesis of MXene Derived Materials for Advanced Electronics and Energy Harvesting ApplicationsTu, Shao Bo 09 June 2020 (has links)
In this thesis, we capitalize on the two-dimensional (2D) nature of MXenes by using them as precursors for the synthesis of 2D functional material. MXenes are easily intercalated with monovalent cations K, Na, Li due to their expanded d-spacing after etching. Based on these ideas, we have developed new synthesis processes of texture functional materials using MXenes as precursors. We have successfully synthesized two-dimensional Nb2C MXene based high aspect ratio ferroelectric potassium niobate (KNbO3) and well-oriented photoluminescent rare earth doped lithium niobate (LiNbO3:Pr3+) crystals, which have great potential in opto-electronics applications. In addition, this thesis demonstrates that poly(vinylidene fluoride) (PVDF)-based percolative composites using two-dimensional (2D) MXene nanosheets as fillers exhibit significantly enhanced dielectric permittivity. Furthermore, we fabricated MXene/in-plane aligned PVDF photo-thermo-mechanical solar tracking actuator for energy harvesting applications.
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Elektrické vlastnosti alternativních kapalin pro elektrotechniku / Electrical properties of alternative liquids for electrical engineeringNaider, Jan January 2015 (has links)
Electrical insulating liquids, organic esters, conductivity, dielectric, permittivity
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Characterization, Microstructure, and Dielectric properties of cubic pyrochlore structural ceramicsLi, Yangyang 05 1900 (has links)
The (BMN) bulk materials were sintered at 1050°C, 1100°C,
1150°C, 1200°C by the conventional ceramic process, and their microstructure and
dielectric properties were investigated by Scanning electron microscopy (SEM), X-ray
diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM)
(including the X-ray energy dispersive spectrometry EDS and high resolution
transmission electron microscopy HRTEM) and dielectric impedance analyzer.
We systematically investigated the structure, dielectric properties and voltage
tunable property of the ceramics prepared at different sintering temperatures. The XRD
patterns demonstrated that the synthesized BMN solid solutions had cubic phase
pyrochlore-type structure when sintered at 1050°C or higher, and the lattice parameter
(a) of the unit cell in BMN solid solution was calculated to be about 10.56Å. The
vibrational peaks observed in the Raman spectra of BMN solid solutions also confirmed
the cubic phase pyrochlore-type structure of the synthesized BMN. According to the
Scanning Electron Microscope (SEM) images, the grain size increased with increasing
sintering temperature. Additionally, it was shown that the densities of the BMN ceramic
tablets vary with sintering temperature. The calculated theoretical density for the BMN
ceramic tablets sintered at different temperatures is about 6.7521 . The density
of the respective measured tablets is usually amounting more than 91% and
5
approaching a maximum value of 96.5% for sintering temperature of 1150°C. The
microstructure was investigated by using Scanning Transmission Electron Microscope
(STEM), X-ray diffraction (XRD). Combined with the results obtained from the STEM and
XRD, the impact of sintering temperature on the macroscopic and microscopic structure
was discussed.
The relative dielectric constant ( ) and dielectric loss ( ) of the BMN solid
solutions were measured to be 161-200 and (at room temperature and
100Hz-1MHz), respectively. The BMN solid solutions have relative high dielectric
constant and low dielectric loss. With increasing sintering temperature, the dielectric
constant showed the maximum at 1150°C. The leakage current of BMN ceramic material
is extraordinary small. When the voltage and thickness of the BMN capacitor are 4000V
and 300um, the leakage current amounts only about 0.13-0.65 . The excellent
physical and electrical properties make BMN thin films promising for potential tunable
capacitor applications.
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EFFECT OF BLEND COMPOSITION AND UNIAXIAL ORIENTATION ON THE EVOLUTION OF STRUCTURAL HIERARCHY AND RESULTING DIELECTRIC PROPERTIES OF PET/PEI, NYLON 12 AND PEI FILMSZeynep Mutlu (12697787) 16 June 2022 (has links)
<p> </p>
<p>To meet the needs of the high-end electronics and energy industry, it is important to operate these devices in elevated temperatures and under high voltage. The dielectric materials for advanced capacitors must have high temperature tolerance (Tg>80C) high dielectric constant, low loss and high breakdown strength to meet the demands of the future. In order to understand fundamental relationships between the processing, structural hierarchy and electrical properties, in this dissertation we focus on slow crystallizing PET/PEI polymer blends, crystallizable Nylon 12 and noncrystallizable Polyetherimide and its chemical variants. </p>
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Can Asymmetry Quench Self-Heating in MOS High Electron Mobility Transistors?ISLAM, MD SHAHRUL 01 September 2020 (has links)
High electron mobility transistors (HEMTs) have long been studied for high frequency and high-power application. Among widely known high electron mobility transistors, AlGaN/GaN HEMTs are having the upper hand due to high electron mobility of the GaN channel. Over the times, issues like current collapse, gate leakage, self-heating and gate lag have questioned the performance and reliability of these devices. In the recent years, engineers have come up with newer architectures to address some of these issues. Inserting a high-k dielectric oxide layer in the gate stack proved to be an effective solution to mitigate gate leakage, reduce interfacial traps and improve optimal working conditions. This work aims to study the reliability aspect of these so-called metal-oxide-semiconductor high electron mobility transistors (MOS-HEMT) specifically, HfO2 and HfZrO2 MOS-HEMTs. It was found through numerical simulations that though HfO2 and HfZrO2 dielectrics were able to mitigate gate leakage current, they tend to accumulate more heat in the channel region with respect to the conventional silicon nitride (SiN) passivated counterparts. Moreover, few asymmetric structures were proposed where silicon nitride was placed in the dielectric layer along with HfO2/HfZrO2. In this study it was found that these asymmetric structures showed superior thermal performance while showing near-zero gate leakage current.
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Computational Studies of Electrorheological EmulsionsBehjatian Esfahani, Ali 01 December 2016 (has links)
In this thesis we report the results of investigations on the rheological response of emulsions to the application of the electric field. A front-tracking finite difference scheme is used in conjunction with Taylor-Melcher leaky dielectric theory to study the problem. The numerical results in different regions of the deformation-circulation map show that the structure formation in regions I and III can be hindered by the hydrodynamic effect. This is opposite to what is observed in the perfect dielectric cases and region II of the map. For perfect dielectric systems, where the electrohydrodynamics effects are absent, droplets form chain-like structures spanning the distance between the electrodes after the application of the electric field. Subsequently, the chains interact with each other to form columns comprising two or more chains. Point-dipole approximation is used to analyze the structure formation and it is shown that it is also applicable to region II where the hydrodynamic effect is weak and the behavior of the system is mainly governed by the dielectrophoretic forces. It is shown that the chain formation is not possible in regions I and III due to the competition between the dipolar force and torque on one side and hydrodynamic effect on the other side. In region I, the hydrodynamic torque prevents the chain formation by competing with the dipolar torque, which tends to align the drops with the electric field. On the other hand, in region III, the repulsive nature of the hydrodynamic effect opposes the attractive dipolar force and does not allow the particles to form stable chains.
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Experimental Investigation of Snapover: The Sudden Increase of Plasma Current Drawn to a Positively Biased Conductor When Surrounded by a DielectricThomson, Clint D. 01 May 2001 (has links)
Snapover is particularly relevant to Earth-orbiting spacecraft powered by high-voltage solar arrays. During snapover, the current collected by a positively biased conductor that is immersed in a plasma suddenly increases when two conditions are met: i) there is an immediately adjacent insulator; ii) the conductor exceeds a positive threshold voltage with respect to the plasma. The enhanced current develops as a consequence of the insulator, either through secondary electron (SE) emission or by material ionization. Experiments were performed to examine snapover onset potential and current collection dependence on conductor and insulator materials, conductor size and shape, sample history, biasing rate, and contamination and smoothness of the dielectric surface. Numerous current jumps were observed between applied voltages of 100 V and 1000 V. Both surface roughening and surface coatings were found to inhibit snapover. In general, the results did not support previous simple interpretations of the SE model.
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AZADIPYRROMETHENE-BASED N-TYPE ORGANIC SEMICONDUCTORS AND HIGH DIELECTRIC CONSTANT POLYMERS FOR ELECTRONIC APPLICATIONSWang, Chunlai 28 January 2020 (has links)
No description available.
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DIELECTRIC AND ELECTRO-OPTICAL EFFECTS IN NEMATIC LIQUID CRYSTALSALMATANI, BDOOR 09 June 2023 (has links)
No description available.
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