Cellular system information capacity change at higher frequencies due to propagation loss and system parameters

In this paper, mathematical analysis supported by computer simulation is used to study cellular system information capacity change due to propagation loss and system parameters (such as path loss exponent, shadowing and antenna height) at microwave carrier frequencies greater than 2 GHz and smaller cell size radius. An improved co-channel interference model, which includes the second tier co-channel interfering cells is used for the analysis. The system performance is measured in terms of the uplink information capacity of a time-division multiple access (TDMA) based cellular wireless system. The analysis and simulation results show that the second tier co-channel interfering cells become active at higher microwave carrier frequencies and smaller cell size radius. The results show that for both distance-dependent: path loss, shadowing and effective road height the uplink information capacity of the cellular wireless system decreases as carrier frequency increases and cell size radius R decreases. For example at a carrier frequency fc = 15.75 GHz, basic path loss exponent α = 2 and cell size radius R = 100, 500 and 1000m the decrease in information capacity was 20, 5.29 and 2.68%

Modeling and characterization of urban radio channels for mobile communications

Results of this thesis contribute in modeling and characterization of radio channels for future mobile communications. The results are presented mainly in three parts: a) modeling of propagation mechanisms, b) methodology of developing a propagation model, c) characterization of urban radio channel. One of the main propagation physical phenomena that have an important role in diverting signals to non line of sight scenarios is the diffraction process. This thesis proposes diffraction coefficients that have better agreement with finite difference time domain solution and rigorous diffraction theory than the coefficient commonly used in propagation predictions for mobile communications. The importance of diffuse scattering has also been investigated and showed that this physical process may have a key role in urban propagation, with a particular impact on the delay spread and angular spread of the signal at the receiver. This thesis proposes wideband propagation models for main and perpendicular streets of urban street grids. The propagation models are ray-based and are given in explicit mathematical expressions. Each ray is characterized in terms of its amplitude, delay, and angle of arrival, angle of departure for vertical and horizontal polarizations. Each of these characteristics is given in a closed mathematical form. Having wideband propagation model in explicit expression makes its implementation easy and computation fast. Secondary source modeling approach for perpendicular streets has also been introduced in this thesis. The last part of the thesis deals with characterization of urban radio channels for extracting parameters that help in successful design of mobile communication systems. Knowledge of channel characteristics enables reaching optimum trade off between system performance and complexity. This thesis analyzes measurement results at 2 GHz to extract channel parameters in terms of Rake finger characteristics in order to get information that helps to optimize Rake receiver design for enhanced-IMT2000 systems. Finger life distance has also been investigated for both micro- and small cell scenarios. This part of the thesis also presents orthogonality factor of radio channel for W-CDMA downlink at different bandwidths. Characterization of dispersion metrics in delay and angular domains for microcellular channels is also presented at different base station antenna heights. A measure of (dis-) similarity between multipath components in terms of separation distance in delay and angular domains is introduced by the concept of distance function, which is a step toward in development of algorithm extraction and analysis multipath clustering. In summary, the significant contributions of the thesis are in three parts. 1) Development of new diffraction coefficients and corrections of limitations of existing one for accurate propagation predictions for mobile communications. 2) Development of wideband propagation models for urban street grid. The novelty of the model is the development in explicit mathematical expressions. The developed models can be used to study propagation problem in microcellular urban street grids. 3) Presenting channel parameters that will help in the design of future mobile communication systems (enhanced-IMT2000), like number of active fingers, finger life distance, and orthogonality factors for different bandwidths. In addition, a technique based on multipath separation distance is proposed as a step toward in development of algorithms for extraction and analysis of multipath clusters.reviewe

Characterization of microcellular plastics for weight reduction in automotive interior parts

The present PhD thesis is framed within the Industrial Doctorate Plan promoted by the Generalitat de Catalunya and has been developed in cooperation between the Universitat Politècnica de Catalunya-BarcelonaTech, the Centre Català del Plàstic, SEAT SA and Volkswagen AG. The research project has as main objective the characterization of microcellular plastics obtained by injection molding, motivated by a concern to reduce weight, cost and carbon footprint in automotive plastic parts. First, cylindrical bars and square plates made of Acrylonitrile-Butadiene-Styrene (ABS) and 20% Glass Fiber reinforced-Polypropylene (PP 20GF) were injection molded and foamed through the MuCell® technology. Shot volume was found as the most influencing parameter on cell structure and tensile and flexural properties. The effect of mold temperature and injection speed was secondary and not statistically significant for the mechanical performance. Tensile and flexural properties decreased almost linearly with the apparent density, whereas impact resistance was strongly reduced during foaming. Glass fibers contributed to partially overcome the loss of properties due to the reduction in density. Cells act as crack arrestors by blunting the crack tip. However, once the crack is propagating, cells acting as stress concentrators lead to a decrease in fracture toughness. Because of the low amount of blowing agent injected during the foaming process, no significant changes in the thermal properties were determined as compared to that of the solid counterpart. Simulation of the microcellular injection molding process with Moldex 3D® software and prediction models of the mechanical properties based on the apparent density and morphological characteristics provided a good approach to the experimental results. On the other hand, the Core Back tool technology was also employed in this study. By pulling the core and increasing the final thickness of the part, the apparent density decreased but the bending stiffness was greatly enhanced. Finally, a new alternative foaming technology, called IQ Foam® and developed by Volkswagen AG, was used to produce rectangular plates and compare their properties to that of the obtained by MuCell® process. By using a minimum amount of blowing agent, foamed plastic parts through IQ Foam® obtained through this process exhibited thicker solid skins and lower cell densities, but consequently higher mechanical properties. Additional benefits such as cost-effectiveness, easy-to-use and machine-independence are also offered by this new emerging technology.La presente tesis doctoral se enmarca dentro del Plan de Doctorats Industrials convocado por la Generalitat de Catalunya y se ha desarrollado como colaboración entre la Universitat Politècnica de Catalunya-BarcelonaTech, el Centre Català del Plàstic, SEAT SA y Volkswagen AG. El proyecto de investigación tiene como principal objetivo la caracterización de plásticos microcelulares, motivado por el interés en reducir peso, coste e impacto ambiental en piezas de plástico de automoción. En primer lugar, se obtuvieron mediante moldeo por inyección barras cilíndricas y placas cuadradas fabricadas con Acrilonitrilo-Butadieno-Estireno (ABS) y Polipropileno reforzado con un 20% de fibra de vidrio (PP 20GF), espumadas con la tecnología MuCell®. El volumen de dosificación es el parámetro más influyente sobre la estructura celular y las propiedades a tracción y a flexión. El efecto de la temperatura de molde y velocidad de inyección, en cambio, es secundario y no introduce variaciones estadísticamente significativas sobre el rendimiento mecánico. Las propiedades a tracción y flexión se reducen de manera prácticamente lineal con la disminución de densidad, mientras que la resistencia a impacto decrece drásticamente debido a la espumación. El efecto reforzante de las fibras de vidrio contribuye a compensar parcialmente la caída de propiedades debido a la reducción de densidad. Las celdas tienden a enromar el frente de grieta, retrasando así el inicio de propagación. Sin embargo, una vez la grieta comienza a propagar, las celdas actúan como concentradores de tensión provocando una disminución en la tenacidad a fractura. El reducido contenido de agente espumante inyectado durante el proceso de espumación no es suficiente para producir cambios en las propiedades térmicas en comparación con las del material macizo. La simulación del proceso de inyección microcelular con el software Moldex 3D® y los modelos de predicción de propiedades mecánicas basados en la densidad y características morfológicas proporcionaron valores cercanos a los obtenidos experimentalmente. Por otro lado, en este trabajo también se estudió el efecto de la tecnología de molde Core Back en combinación con el proceso de espumado mediante moldeo por inyección. A través del movimiento de la cavidad y el aumento del espesor final de la pieza inyectada, la densidad aparente se reduce al mismo tiempo que la rigidez a flexión se incrementa considerablemente. Finalmente, una nueva tecnología de espumación desarrollada por Volkswagen AG, llamada IQ Foam®, se utilizó para la inyección de placas rectangulares y la comparación de sus propiedades con las de placas análogas obtenidas mediante el proceso MuCell®. Mediante la utilización de un contenido mínimo de agente espumante, las placas espumadas con IQ Foam® exhibieron mayores espesores de piel y menores densidades celulares, y por tanto, propiedades mecánicas ligeramente superiores. Esta nueva tecnología ofrece también otras ventajas, como una menor inversión inicial, facilidad de operación y posibilidad de utilización en cualquier máquina de inyección convencional

A tree-scattering model for improved propagation prediction in urban microcells

This paper presents a model for the scattering of radiowaves from the canopy of a single tree. The canopy is modeled as a cylindrical volume containing randomly distributed and oriented cylinders, representing the branches, and thin disks, representing the leaves. A simple expression for the incoherent scattered field outside the canopy is obtained using Twersky's multiple scattering theory. This expression is shown to agree well with results of scattering measurements on a live tree typical of those found in urban environments. The scattering model can be readily incorporated in ray-based propagation prediction tools that assist the planning of microcellular radio networks. This involves the use of so-called tree-scattered rays, which interact at the tree centers. Path loss predictions generated with the aid of the new model are shown and compared with measured data to illustrate the considerable improvement in prediction accuracy that can be achieved in realistic urban microcellular scenarios by taking into account the scatter from trees

Optimization of polypropylene cellular films for piezoelectric applications

Cette thèse comporte deux objectifs principaux: la production en continu de films de polypropylène (PP) moussés ayant une structure cellulaire de forme oculaire, suivie par la préparation de films PP ferroélectrets par décharge corona pour des applications piézoélectriques. Dans la première partie de ce travail, une production en continu par extrusion-calandrage a été développée pour produire des films de PP moussés pour des applications piézoélectriques. Le système est basé sur un moussage physique en utilisant de l'azote supercritique (SC-N2) et le carbonate de calcium (CaCO3) comme agent de nucléation. Les paramètres de mise en œuvre (conception de vis, profil de température, agent gonflant et de nucléation ainsi que leur contenu, et la vitesse d'étirement) ont été optimisés pour obtenir une forme spécifique (oculaire) comme structure cellulaire avec une distribution uniforme de la taille des cellules. Les résultats ont montré qu'une structure cellulaire avec un plus grand rapport d'aspect (AR) des cellules possède un plus faible module de Young, ce qui est approprié pour les films cellulaires piézoélectriques. Dans la deuxième partie, des films PP ferroélectrets ont été produits. Suite à l'optimisation du procédé de décharge corona (tension de charge, distance de l'aiguille, temps de charge), les propriétés piézoélectriques des films obtenus ont été caractérisées et le coefficient piézoélectrique quasi-statique d33 a produit une valeur de 550 pC/N. Afin de mieux caractériser le comportement du film, l’analyse mécanique dynamique (DMA) a été proposée comme une méthode simple pour relier les propriétés piézoélectriques des films PP cellulaires à leur morphologie (taille, géométrie et densité des cellules). Finalement, grâce à un post-traitement basé sur la saturation du film PP moussé avec le SC-N2, une procédure en température et pression a été développée afin d’améliorer la structure cellulaire (cellules plus allongées). Ce traitement a permis d’augmenter de 45% le coefficient d33 (800 pC/N).This thesis is composed of two main objectives: the continuous production of thin foamed polypropylene (PP) films having an eye-like cellular structure, followed by the preparation of ferroelectret PP films through corona discharge for piezoelectric applications. In the first part of this work, a continuous extrusion-calendaring setup was developed to produce PP foamed films for piezoelectric applications. The setup is based on physical foaming using supercritical nitrogen (SC-N2) and calcium carbonate (CaCO3) as nucleating agent. The processing parameters (screw design, temperature profile, blowing agent and nucleating agent content, and stretching speed) were optimized to achieve a specific stretched eye-like cellular structure with a uniform cell size distribution. The results showed that a cellular structure with higher cell aspect ratio (AR) has lower Young’s modulus, which is appropriate for piezoelectric cellular films. In the second part, ferroelectret PP films were produced. After optimization of the corona discharge process (charging voltage, needle distance, charging time), the piezoelectric properties of the resulting films were characterized and the optimum quasi-static piezoelectric d33 coefficient value was 550 pC/N. To better characterize the film behavior, dynamic mechanical analysis (DMA) was proposed as a simple method to relate the piezoelectric properties of the cellular PP films to their morphology (cell size, geometry and density). Finally, through a post-processing treatment based on the saturation of the foamed PP film with SC-N2, a temperature-pressure procedure was developed to improve the cellular structure (more stretched eye-like cells). This treatment was shown to increase by 45% the d33 coefficient (800 pC/N)

Recent Progress in Processing Functionally Graded Polymer Foams.

Polymer foams are an important class of engineering material that are finding diverse applications, including as structural parts in automotive industry, insulation in construction, core materials for sandwich composites, and cushioning in mattresses. The vast majority of these manufactured foams are homogeneous with respect to porosity and structural properties. In contrast, while cellular materials are also ubiquitous in nature, nature mostly fabricates heterogeneous foams, e.g., cellulosic plant stems like bamboo, or a human femur bone. Foams with such engineered porosity distribution (graded density structure) have useful property gradients and are referred to as functionally graded foams. Functionally graded polymer foams are one of the key emerging innovations in polymer foam technology. They allow enhancement in properties such as energy absorption, more efficient use of material, and better design for specific applications, such as helmets and tissue restorative scaffolds. Here, following an overview of key processing parameters for polymer foams, we explore recent developments in processing functionally graded polymer foams and their emerging structures and properties. Processes can be as simple as utilizing different surface materials from which the foam forms, to as complex as using microfluidics. We also highlight principal challenges that need addressing in future research, the key one being development of viable generic processes that allow (complete) control and tailoring of porosity distribution on an application-by-application basis

Recent advances in carbon-based polymer nanocomposites for electromagnetic interference shielding

Carbon-based nanoparticles have recently generated a great attention, as they could create polymer nanocomposites with enhanced transport properties, overcoming some limitations of electrically-conductive polymers for high demanding sectors. Particular importance has been given to the protection of electronic components from electromagnetic radiation emitted by other devices. This review considers the recent advances in carbon-based polymer nanocomposites for electromagnetic interference (EMI) shielding. After a revision of the types of carbon-based nanoparticles and respective polymer nanocomposites and preparation methods, the review considers the theoretical models for predicting the EMI shielding, divided in those based on electrical conductivity, models based on the EMI shielding efficiency, on the so-called parallel resistor-capacitor model and those based on multiscale hybrids. Recent advances in the EMI shielding of carbon-based polymer nanocomposites are presented and related to structure and processing, focusing on the effects of nanoparticle’s aspect ratio and possible functionalization, dispersion and alignment during processing, as well as the use of nanohybrids and 3D reinforcements. Examples of these effects are presented for nanocomposites with carbon nanotubes/nanofibres and graphene-based materials. A final section is dedicated to cellular nanocomposites, focusing on how the resulting morphology and cellular structures may generate lightweight multifunctional nanocomposites with enhanced absorption-based EMI shielding propertiesPostprint (author's final draft

CHANNEL MODELING FOR FIFTH GENERATION CELLULAR NETWORKS AND WIRELESS SENSOR NETWORKS

In view of exponential growth in data traffic demand, the wireless communications industry has aimed to increase the capacity of existing networks by 1000 times over the next 20 years. A combination of extreme cell densification, more bandwidth, and higher spectral efficiency is needed to support the data traffic requirements for fifth generation (5G) cellular communications. In this research, the potential improvements achieved by using three major 5G enabling technologies (i.e., small cells, millimeter-wave spectrum, and massive MIMO) in rural and urban environments are investigated. This work develops SPM and KA-based ray models to investigate the impact of geometrical parameters on terrain-based multiuser MIMO channel characteristic. Moreover, a new directional 3D channel model is developed for urban millimeter-wave (mmW) small cells. Path-loss, spatial correlation, coverage distance, and coherence length are studied in urban areas. Exploiting physical optics (PO) and geometric optics (GO) solutions, closed form expressions are derived for spatial correlation. Achievable spatial diversity is evaluated using horizontal and vertical linear arrays as well as planar 2D arrays. In another study, a versatile near-ground field prediction model is proposed to facilitate accurate wireless sensor network (WSN) simulations. Monte Carlo simulations are used to investigate the effects of antenna height, frequency of operation, polarization, and terrain dielectric and roughness properties on WSNs performance

Anisotropic Compressive Behavior of Rigid PVC and PES Foams at Elevated Strain Rates Up to 200 s-1

In this study, closed cell polyvinyl chloride (PVC) foam with five different densities ranging from 45 to 200 kg/m3, and polyethersulfone (PES) foam with three different densities ranging from 50 to 130 kg/m3, were subjected to compressive loading under quasi static and elevated strain rates for mechanical material assessment. Three orthogonal loading directions, (i.e., parallel and perpendicular to foam rise directions) were considered to investigate structural anisotropy. The elevated strain rate tests were performed using a customized drop tower device at three different strain rates of 50, 100, and 200 s-1. Engineering stress/strain behavior, energy dissipation, and maximum stress capacity were obtained for each density and compared against each other. Experimental results indicated that elastic modulus, compressive strength, plateau stress, and energy absorbing capacity of both PVC and PES foams were highly dependent on foam density. Except for the PVC foam with the lowest density of 45 kg/m3, strain rate effects were clearly observed through increased compressive strength and plateau stress when loading in the foam rise direction for both PVC and PES foams. The strain rate effect was more evident at higher densities. When loading perpendicular to the foam rise direction, no significant strain rate effect was observed for PVC foam. However, a slight strain rate effect was observed for PES foam at the highest density of 130 kg/m3 in one of the perpendicular to foam rise directions. Scanning electron microscopy (SEM) analysis showed that the cell wall thickness of both PVC and PES foams continuously increased with the increase of foam density. However, cell sizes were not simply dependent on foam density. For both quasi static and elevated strain rate tests, plastic hinges were the primary deformation mechanism for both PVC and PES foam cells