Ultra-Wideband Wireless Channels - Estimation, Modeling and Material Characterization

This licentiate thesis is focused on the characterization of ultra-wideband wireless channels. The thesis presents results on ultra-wideband communications as well as on the ultra-wideband characterization of materials. The communications related work consisted in the measurement and modeling of outdoor scenarios envisioned for infostation systems. By infostation, we mean a communication system covering a small area, i.e., ranging up to 20 m, where mobile users can pass by or stop while receiving large amounts of data in a short period of time. Considering the expected (but perhaps overly optimistic) 480 Mbps for UWB systems, it should be possible to download a complete DVD in roughly two minutes, which is something not realizable with any of the current wireless technologies. Channel models, commonly based on measurements, can be used to evaluate the performance of such systems. We therefore, we started by performing measurements at one of the scenarios where infostation systems can exist in the future, namely, petrol stations. The idealized model, was one that could correctly describe the continuous evolution of the channel impulse response for a moving user within the system’s range, and therefore it was deemed necessary to track the multipath components defining the impulse responses along a path of several meters. To solve this problem we designed a novel high-resolution scatterer detection method, which is described in Paper I, capable of tracking individual multipath components for a moving user by identifying the originating point scatterers in a two dimensional geometrical space. The same paper also gives insight on some properties of clusters of scatterers, such as their direction-selective radiated power. The scatterer detection method described in Paper I provided us with the required tools to create the channel model described in Paper II. The proposed channel model has a geometrical basis, i.e., each realization of the channel is based on a virtual map containing point scatterers that contribute to the impulse response by multipath components. Some of the particular characteristics of the model include non-stationary effects, such as shadowing and cluster’s visibility regions. At the end of Paper II, in a simple validation step, the output of the channel model showed a good match with the measured impulse responses. The second part of our work, documented in Paper III, consisted on the dielectric characterization of soil samples using microwave measurements. This project was made in cooperation with the Department of Physical Geography and Ecosystem Analysis at Lund University, which had been developing research work on methane emissions from the wetlands in Zackenberg, Greenland. In recent years, a lot of attention has been put into the understanding of the methane emissions from soils, since methane is a greenhouse gas 20 times stronger than carbon dioxide. However, whereas the methane emissions from natural soils are well documented, the reason behind this effect is an open issue. The usage of microwave measurements to monitor soil samples, aims to address this problem by capturing the sub-surface changes in the soil during gas emissions. An experiment consisting on the monitoring of a soil sample was performed, and a good correlation was found between the variations of the microwave signals and the methane emissions. In addition, the soil dielectric constant was calculated, and from that, the volumetric fractions of the soil constituents which provided useful data for the elaboration of models to describe the gas emission triggering mechanisms. Based on this laboratory experiment, a complete soil monitoring system was created and is at the time of writing running at Zackenberg, Greenland

Code generation for RESTful APIs in HEADREST

Tese de mestrado, Engenharia Informática (Engenharia de Software) Universidade de Lisboa, Faculdade de Ciências, 2018Os serviços web com APIs que aderem ao estilo arquitetural REST, conhecidos por serviços web RESTful, são atualmente muito populares. Estes serviços seguem um estilo cliente-servidor, com interações sem estado baseadas nos verbos disponibilizados pela norma HTTP. Como meio de especificar formalmente a interação entre os clientes e fornecedores de serviços REST, várias linguagens de definição de interfaces (IDL) têm sido propostas. No entanto, na sua maioria, limitam-se ao nível sintático das interfaces que especificam e à descrição das estruturas de dados e dos pontos de interação. A linguagem HEADREST foi desenvolvida como uma IDL que permite ultrapassar estas limitações, suportando a descrição das APIs RESTful também ao nível semântico. Através de tipos e asserções é possível em HEADREST não só definir a estrutura dos dados trocados mas também correlacionar o output com input e o estado do servidor. Uma das principais vantagens de ter descrições formais de APIs RESTful é a capacidade de gerar código boilerplate tanto para clientes como fornecedores. Este trabalho endereça o problema de geração de código para as APIs RESTful descritas com HEADREST e investiga de que forma as técnicas de geração de código existentes para os aspectos sintáticos das APIs RESTful podem ser estendidas para levar em conta também as propriedades comportamentais que podem ser descritas em HEADREST. Tendo em conta que a linguagem HEADREST adota muitos conceitos da Open API Specification (OAS), o trabalho desenvolvido capitaliza nas técnicas de geração de código desenvolvidas para a OAS e envolveu o desenvolvimento de protótipos de geração de código cliente e servidor a partir de especificações HEADREST.Web services with APIs that adhere to the REST architectural style, known as RESTful web services, have become popular. These services follow a client-server style, with stateless interactions based on standard HTTP verbs. In an effort to formally specify the interaction between clients and providers of RESTful services, various interface definition languages (IDL) have been proposed. However, for the most part, they limit themselves to the syntactic level of the interfaces and the description of the data structures and the interaction points. The HEADREST language was developed as an IDL that addresses these limitations, supporting the description of the RESTful APIs also at the semantical level. Through the use of types and assertions we not only define the structure of the data transmitted but also relate output with input and the state of the server. One of the main advantages of having formal descriptions of RESTful APIs is the ability to generate a lot of boilerplate code for both clients and servers. This work addresses the problem of code generation for RESTful APIs described in HEADREST and aims to investigate how the existing code generation techniques for the syntactical aspects of RESTful APIs can be extended to take into account also the behavioural properties that can be described in HEADREST. Given that HEADREST adopts many concepts from the Open API Specification (OAS), this work capitalised on the code generation tools available for OAS and encompassed the development of a prototypical implementation of a code generator for clients and servers from HEADREST specifications

The use of robots in the construction industry

This article first explains why it is currently not feasible to use robots on construction sites. The authors argue that robotics will be utilized in the upstream industries, either in component manufacture or in constructive processes capable of being undertaken in a traditional factory setting. Although the former would be a simple way of incorporating robotics into the construction industry, the second would have major implications for the constructive process that extends from the project design phase to the technologies employed on the building site

Bulldozer: o valor da aleatoriedade

Também do DETI e do DECAO Micro-Rato Bulldozer, foi construído, tanto no seu hardware, como sofware, de forma que seja simples e eficaz. Em particular é utilizada uma função aleatória para determinar o sentido da reacção perante obstáculos. Esta aleatoriedade aumenta a robustez do comportamento do robot, permitindo evitar situações de ciclos viciosos causados por determinadas configurações de obstáculos. Neste artigo serão brevemente explicados os seguintes aspectos: · O hardware construído que, apesar de muito simples, é suficiente para os requisitos do Concurso. · O software de controlo, desenvolvido sobre o kernel ReTMiK, com relevo para alguns detalhes considerados mais pertinentes

Dielectric Characterization of Soil Samples by Microwave Measurements

Northern high-latitude wetlands are well known to seasonally emit methane gas into the atmosphere, and therefore contribute to greenhouse effects. While these gas emissions are well documented, their causes are not well understood. The method described in this work can be used to analyze the changes happening in the soil during gas emissions, and therefore help the understanding of the sub-surface gas dynamics. We have monitored a sample of peat soil through an artificial freezing and thawing cycle, using both a gas detector to measure the methane flux at the soil surface and a vector network analyzer to measure the transmission of microwaves through the soil. It was observed that the results from the two measurement approaches had a very good match under specific microwave signal conditions. In addition, from the microwave measured data, the dielectric properties of the soil and the volumetric fractions of its constituents were also calculated based on a dielectric mixing model

BioTech agrifood innovation: a pre-acceleration program and contest to promote knowledge and technology transfer in agri-food and agri-environmental sectors

This study aims to develop and implement a contest and pre-acceleration program for business projects in the agri-food and agri-environment areas through academic entrepreneurship. This research involved a single exploratory case study, with primary data collected through instruments developed for the Lab2Business project and observations of different project actions.info:eu-repo/semantics/publishedVersio

Análise custo-benefício de obras longitudinais aderentes

Mestrado em Engenharia CivilDiversas ações antropogénicas têm enfraquecido o caudal sólido afluente ao litoral, reduzindo a alimentação de sedimentos nas praias e conduzindo a um recorrente e generalizado recuo da posição da linha de costa. Perante este cenário, diferentes alternativas de intervenção de defesa costeira têm sido efetuadas em zonas de maior sensibilidade, sendo uma das mais frequentes, a construção de obras longitudinais aderentes. No entanto, a falta de monitorização destas estruturas, conjugada com o agravamento do grau de exposição das frentes costeiras urbanizadas à erosão, têm conduzido a um aumento da frequência de ocorrência de danos em diversas localidades, não só nas próprias estruturas, mas também nas zonas marginais às obras aderentes (infraestruturas, estabelecimentos comerciais e habitações). No âmbito deste trabalho, o estudo dos diversos fenómenos de propagação de ondas possibilitou a obtenção das características de agitação marítima locais, o que, juntamente com a análise do espraiamento das ondas, permitiu a avaliação do limite máximo de espraio em estruturas de defesa costeira. Foi desenvolvida uma metodologia de cálculo para estimar a frequência de galgamentos de obras longitudinais aderentes, em função da profundidade de fundo à frente da obra e do desnível entre a cota de coroamento e o nível médio do mar. Tendo em conta que o clima de agitação marítima e o comportamento do perfil de praia estão intrinsecamente associados à evolução da frequência de galgamentos ao longo do tempo, identificaram-se os fatores que conduzem a uma tendência de abaixamento do perfil de praia. Analisaram-se diversas formulações para estimar a profundidade máxima de erosão, permitindo antecipar o aumento da frequência dos eventos de dano e dos custos associados ao longo do tempo. Face a este problema, estimaram-se as frequências de galgamento no caso de estudo (praia do Furadouro) e avaliou-se a eficiência de várias abordagens de intervenção para reduzir a frequência de galgamentos existente (aumento da cota de coroamento, alimentação artificial do perfil de praia e construção de um patamar intermédio no talude da obra). Para tal, procedeu-se a uma análise custo-benefício das diversas soluções de intervenção, tendo em conta os custos de reabilitação das obras, os encargos de limpeza da via pública e reparação de infraestruturas e os danos devido às inundações. Por outro lado, é fulcral avaliar os custos diretos e indiretos da construção e manutenção de obras aderentes comparativamente ao valor económico, social e histórico do património que protegem. Para isso, com o auxílio do modelo numérico LTC, foi simulada a evolução da posição da linha de costa para vários cenários de prolongamento da obra longitudinal aderente sul do Furadouro para fazer face ao problema da erosão. Novamente, procedeu-se a uma análise custo-benefício de forma a estudar a viabilidade económica da construção destas estruturas para fazer face ao recuo da linha de costa.Several anthropogenic actions have been weakening the sediment supplies to the coastal zones, reducing the amount of sediments available on the beaches and leading to a general and recurrent retreat of the shoreline position. Given this scenario, different coastal defence interventions, oftentimes longitudinal revetments, have been made in the past decades in certain areas with high erosion rates. However, the lack of monitoring of these coastal defence structures, combined with the degree of exposure of the urban areas to erosion, have led to an increased frequency of damage events in several locations, not only on the rubble mound revetments, but also in the marginal areas (damaging infrastructures, commercial establishments and housing). The study of wave propagation phenomena allows the prediction of the local wave characteristics, which, along with the analysis of the wave induced setup, enables the evaluation of the maximum run-up heights. A calculation methodology was developed in order to assess the overtopping frequency of longitudinal revetments, depending on the bottom depth at the toe of the structure and on the height difference between the mean water level and the crown level. Given that the wave climate and the beach profile are intrinsically associated with the evolution of the overtopping frequency over time, the causes for the lowering of the beach profile were identified and various formulations were analysed in order to estimate the maximum scour depth, to anticipate the frequency of damage events and the evolution of flood costs over time. Due to this problem, an estimative of overtopping and flooding events was applied to a case study (Furadouro beach) to evaluate the effectiveness of different intervention pathways to reduce wave overtopping (crown elevation, artificial beach nourishment and construction of an intermediate berm). A cost-benefit analysis was performed to assess the economic viability of each scenario based on the rehabilitation costs of the revetments and the flood damage costs over time (assessment of damaged property and buildings, cleaning up marginal areas and repairing infrastructures). Moreover, it is crucial to evaluate if the direct and indirect costs of construction and maintenance of longitudinal revetments compared with to the economic, social and historical value of the protected areas. Therefore, the numerical model LTC was used to simulate the shoreline evolution for different scenarios of increasing the extension of the longitudinal revetment located south of Furadouro. The economic viability of the construction of these coastal defence structures to prevent erosion was evaluated using a cost-benefit analysis taking into consideration the construction and maintenance costs of longitudinal revetments, the numerical modeling results for each scenario, the land cover values and the real estate values of urban areas

In situ monitoring of additive manufacturing using digital image correlation: A review

UIDB/00667/2020 POCI-01-0145-FEDER-016414This paper is a critical review of in situ full-field measurements provided by digital image correlation (DIC) for inspecting and enhancing additive manufacturing (AM) processes. The principle of DIC is firstly recalled and its applicability during different AM processes systematically addressed. Relevant customisations of DIC in AM processes are highlighted regarding optical system, lighting and speckled pattern procedures. A perspective is given in view of the impact of in situ monitoring regarding AM processes based on target subjects concerning defect characterisation, evaluation of residual stresses, geometric distortions, strain measurements, numerical modelling validation and material characterisation. Finally, a case study on in situ measurements with DIC for wire and arc additive manufacturing (WAAM) is presented emphasizing opportunities, challenges and solutions.publishersversionpublishe

Aplicação do método de Elementos Finitos eXtendido (MEFX) para a previsão da resistência de juntas adesivas de sobreposição dupla

As ligações adesivas têm sido utilizadas em diversas áreas de aplicação. A utilização das juntas adesivas em aplicações industriais tem vindo a aumentar nos últimos anos, por causa das vantagens significativas que apresentam comparativamente com os métodos tradicionais de ligação tais como soldadura, ligações aparafusadas e rebitadas. A redução de peso, redução de concentrações de tensões e facilidade de fabrico são algumas das principais vantagens das ligações adesivas. Devido à crescente utilização das ligações adesivas, torna-se necessário a existência de ferramentas que permitam prever a resistência das juntas com elevada precisão. Assim, para a análise de juntas adesivas, está a ser cada vez mais utilizado o método de Elementos Finitos. Neste âmbito o Método de Elementos Finitos eXtendido (MEFX) perfila-se como um método capaz de prever o comportamento da junta, embora este ainda não esteja convenientemente estudado no que diz respeito à aplicação a juntas adesivas. Neste trabalho é apresentado um estudo experimental e numérico pelo MEFX de juntas de sobreposição dupla, nas quais são aplicados adesivos que variam desde frágeis e rígidos, como o caso do Araldite® AV138, até adesivos mais dúcteis, como o Araldite® 2015 e o Sikaforce® 7888. Foram considerados substratos de alumínio (AW6082-T651) em juntas com diferentes comprimentos de sobreposição, sendo sujeitos a esforços de tração de forma a avaliar o seu desempenho. Na análise numérica foi realizada uma análise da distribuição de tensões na camada adesiva, a previsão da resistência das juntas pelo MEFX segundo critérios de iniciação de dano baseados em tensões e deformações, e ainda um estudo sobre o critério energético de propagação de dano. A análise por MEFX revelou que este método é bastante preciso quando usados os critérios de iniciação de dano MAXS e QUADS, e parâmetro com valor de 1 no critério energético de propagação de dano. Apesar de ser um método pouco estudado na literatura comparativamente com outros, o MEFX apresentou resultados muito satisfatórios.Adhesive joints have been used in various application fields. The use of adhesive joints in industrial applications has been increasing in recent years because of the significant advantages offered compared to traditional joining methods such as welding, fastening and riveting. The weight reduction, reduced stress concentrations and ease of manufacture are some of the advantages of adhesive bonding. The existence of design tools is necessary to predict the strength of joints with high accuracy due to the increasing use of adhesive bonding. For the analysis of adhesively-bonded joints, the Finite Element Method is being increasingly used. In this context, the eXtended Finite Element Method (XFEM) is emerging as a method to predict the joints’ behaviour, although this has not yet been adequately studied for the application to adhesive joints. This work presents an experimental and numerical study by XFEM of double-lap joints, in which adhesives ranging from brittle and strong, as the case of the Araldite® AV138, to more ductile adhesives, as the Araldite® 2015 and the Sikaforce ® 7888, are applied. Aluminium substrates were considered (AW6082-T651) in joints with different overlap lengths, subjected to a tensile load, in order to evaluate their performance. In the numerical study, an analysis of the stress distributions in the adhesive layer, a strength prediction by XFEM considering damage initiation criteria based on stresses and strains, nd also a study on the energy criterion for damage propagation, were carried out. The XFEM analysis revealed that this method is very accurate when the MAXS and QUADS damage initiation criteria, and a parameter of 1 in the damage propagation criterion, are considered. Despite this method is not conveniently studied in the literature compared to others, it provided very satisfactory results