Dielectric loss

Résumé

In electrical engineering, dielectric loss quantifies a dielectric material's inherent dissipation of electromagnetic energy (e.g. heat). It can be parameterized in terms of either the loss angle δ or the corresponding loss tangent tan(δ). Both refer to the phasor in the complex plane whose real and imaginary parts are the resistive (lossy) component of an electromagnetic field and its reactive (lossless) counterpart. Electromagnetic field perspective For time-varying electromagnetic fields, the electromagnetic energy is typically viewed as waves propagating either through free space, in a transmission line, in a microstrip line, or through a waveguide. Dielectrics are often used in all of these environments to mechanically support electrical conductors and keep them at a fixed separation, or to provide a barrier between different gas pressures yet still transmit electromagnetic power. Maxwell’s equations are solved for the electric and magnetic field comp

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https://en.wikipedia.org/wiki/Dielectric_loss

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For the universities of the emergent countries, and those of Cameroon in particular, the fight to reach a durable development requires to know the needed scientific and technical information for their development, how to get it and to spread it out among partners in the country. Obviously, the complete answer to these preoccupations lies well beyond the framework of this project, but a projection, partial but highly significant, can nevertheless be obtained if one concentrates one's efforts on a specific technological field : in the present study, we shall treat of antennas for telecommunications systems. This subject is highly suitable as example and potential incubator for future achievements. The ultimate goal is to design and carry out the fabrication of a system of satellite communications adapted to the financial resources and to the development needs of the universities of the South. First of all, we will review the state of the art in satellite communication systems, both for already operating ones and also for new systems, still under development. Then we will determine which system of satellite telecommunications has a receiver and communication fees with affordable costs : our choice will be made on Worldspace satellite system, which was actually designed for developing countries. We will also review the status of planar antenna and low noise amplifier technology, and then explicit the basic challenge involved in our thesis project. One of the aims of this project is to use local wood as dielectric in SSFIP type antennas. Before using a material as dielectric in an antenna design, it must be characterized. Before carrying the characterization of local wood species, we will begin by reviewing some commonly used dielectric measurement techniques. Then we will carry out a series of measurements to characterize the species of wood growing in the Cameroonian forest. At the end of the series of measurements and according to the dielectric losses observed, we will select the species of wood best suited to make a good substrate for a microstrip antenna. Next, we will design, manufacture and test low cost antennas. These antennas must satisfy not only technical criteria compatible with those of the telecommunications system chosen but, even most importantly, it must meet socioeconomic criteria : the antennas must be manufactured with low cost and locally available materials, making use of simple technological processes. Once we have found the wood species that exhibits the lowest dielectric losses, we will simulate, and then manufacture the SSFIP type antenna with wood as substrate and aluminium as conducting element. Then we will measure its characteristics and check whether they are compatible with those of a Worldspace receiver. The signal received from the satellite by the antenna is very weak. It will be important to strengthen the received signal with a low noise amplifier (LNA) before connecting the antenna to the receiver. Thus the antenna and the LNA constitute an active antenna and form what we call here the radiofrequency (RF) front-end. We will design, manufacture and measure the LNA characteristics. A simple manufacturing process must be used to realize these antennas, because later on they must be manufactured locally in Cameroon : this is a determining challenge to ensure the economic independence, which is essential in our thesis project. Afterwards we will join the LNA to the planar antenna and connect the active antenna obtained in this manner to a commercial Worldspace receiver. Finally, we will perform receiving tests of the Worldspace radio station with the system designed. In parallel, our project includes a second goal, which presents an equivalent significance. We will use existing Matlab codes to develop an online course to teach antenna theory. In addition, at the end of the project and when the Cameroonian local manufacture would have started, we will put all algorithms used for the antenna design on the web site in a multi-media applet, together with a complete documentation of all the manufacturing technologies used. The courses that already exist in Lausanne and Yaounde, relating to the description of other types of antennas will be added, thus leading to a complete teachware that would ensure the durability and the dissemination of the results obtained, and would provide an invaluable tool for teaching and training.

EPFL2007

Chargement

Synthesis and Functionalization of Silver Nanoparticles for the Preparation of High Permittivity Nanocomposites

Jose Enrico Quijano Quinsaat

Over the last decade, a growing interest in nanochemistry has emerged due to the interesting features of nanomaterials that vary with size, shape and surface structure. In particular, metal nanoparticles have received much attention due to their properties that enable their use in various scientific disciplines. Although metal nanoparticles exhibit a number of properties that differ from bulk, some properties, such as their infinite permittivity, remain unchanged. As a result, metal nanoparticles have also been used to prepare nanocomposites with polymers in order to provide dielectric materials featuring high permittivities which can be used for applications such as energy storage (capacitors) or as materials for the conversion of electrical energy into mechanical motion (actuators). Despite the large number of publications on the preparation of nanocomposites exhibiting high permittivities which have emerged over the years, there is still room for further improvement in the current materials properties. For instance, dielectric losses are still quite high in some materials, and the use of certain types of filler lead to a large deterioration in the mechanical properties of the nanocomposites, especially with increasing filler content. In addition, a large number of the fillers used for the preparation of the nanocomposites feature poor size and shape control as well as poorly defined surface properties thus adding to the complexity of understanding the resulting material properties. This work tries to address some of the current issues concerning the preparation of dielectric materials. Therefore, silver nanoparticles (AgNPs) were used as filler, while polydimethylsiloxane (PDMS) was employed as the polymeric matrix. The advantages of using AgNPs as filler consist of their relative facile preparation, as well as the possibility of controlling their surface properties due to their resistance towards oxidation and corrosion. The possibility of preparing AgNPs in large amounts with control over the average size of the particles was realized by conducting the polyol synthesis of AgNPs in a Segmented Flow Tubular Reactor (SFTR). A SiO2 layer was grown around the AgNPs to prevent the loss of the insulating nature of the composite due to the formation of conductive pathways, and the thickness dependency of the dielectric properties of the core-shell particles was also investigated in this work. Furthermore, the SiO2 shell also provided the possibility of further surface functionalization, which was conducted in order to compatibilize the core-shell particles with the PDMS matrix. PDMS was chosen as the polymeric matrix due to its good electromechanical properties, which include high elasticity, low viscosity as well as low conductivity and low tangent losses (tan ÎŽ). The resulting nanocomposites featured enhanced permittivities compared to PDMS, while further optimization in the reaction conditions as well as in the processing procedure yielded nanocomposites with high flexibility that can undergo strains as high as 800 % at a silver content of 20 vol%. Other properties such as electric conductivity and the tan ÎŽ were kept low which emphasizes the potential of the nanocomposites to being used as flexible dielectric materials.

EPFL2015

Chargement

Ferroelectric thin films are widely studied nowadays as potential replacements for semiconductors in modern tunable microwave devices such as tunable filters, phase-shifters, frequency mixers, power dividers, etc. Recent progress in the deposition of complex oxide films shows promise of significant improvements in the quality of ferroelectric thin films from the point of view of dielectric loss and electrical tunability. However, there still exist certain problems which limit a wide penetration of ferroelectric thin films into the market. The most crucial issue which needs further investigation is the difference in polarization response between ferroelectric thin films and bulk materials. In comparison to bulk materials, thin films show lower dielectric constants, and consequently a smaller electrical tunability, and much higher dielectric losses at microwave frequencies. Another important question which has rarely been investigated is the problem of the reliability of tunable devices based on ferroelectric films. Therefore, a systematic, experimental investigation to understand the physics behind these problems is a task of primary importance. The present work is devoted to the detailed theoretical and experimental investigation of the polarization response in SrTiO3 and KTaO3 thin films at radio and microwave frequencies over a wide range of temperatures and applied bias fields. Specifically, the following has been performed: The polarization response of SrTiO3 and KTaO3 ferroelectric thin films has been investigated at radio frequencies over a wide temperature range using a planar capacitor structure. The sensitivity of the dielectric properties to the deposition technique, conditions of films growth and type of the substrate used, and hence to the microstructure of the films, is clearly demonstrated. While SrTiO3 is paraelectric in bulk form, the appearance of a ferroelectric phase in SrTiO3 thin films on LaAlO3 substrate has been experimentally documented, with a transition temperature lying in the range of 90-120K. It is theoretically shown in terms of Landau theory, that the behavior of the SrTiO3 thin films can not be attributed to the effect of the film/substrate mechanical coupling. The ferroelectricity of SrTiO3 thin films on LaAlO3 substrates has been investigated in detail. The hysteresis loops have been monitored in a wide temperature range using thin film planar capacitors, the driving field being predominantly in the plane of the film. The microwave dielectric loss in perovskite ferroelectric materials has been theoretically investigated. A model of the quasi-Debye loss mechanism in SrTiO3 and Ba0.6Sr0.4TiO3 materials at microwave frequencies has been developed. Experimental investigations of the dielectric loss at microwave frequencies in SrTiO3 and KTaO3 thin films have been performed using a half-wave length microstrip resonator with a resonant frequency of around 8GHz. The field and temperature dependences of the loss tangent for the SrTiO3 and KTaO3 thin-film based planar capacitors have been measured. The impact of electrical stressing on the microwave performance of SrTiO3 films deposited onto different substrates (MgO and LaAlO3) has been investigated. The most important characteristics of tunable microwave components, including tunability and loss tangent, have been monitored. The influence of the addition of a low-loss linear dielectric material to a tunable ferroelectric material has been investigated in terms of electrostatic considerations. Calculations of the dielectric loss and dielectric non-linearity of ferroelectric-dielectric composites have been performed using three different models. On the basis of the results obtained, a figure of merit for the composite material has been evaluated.

EPFL2004

Chargement

EPFL2007

EPFL2004

Synthesis and Functionalization of Silver Nanoparticles for the Preparation of High Permittivity Nanocomposites

Jose Enrico Quijano Quinsaat

EPFL2015