1,720,956 research outputs found
On the Control of Surface Waves in Integrated Antennas: Analysis and Design Exploiting Artificial Dielectric Layers
No full textPlanar printed antenna technologies, due to their light weight, low profile, cost effectiveness and ease of connection with the active devices (e.g., amplifiers etc.), are becoming an attractive solution for the commercial data-hungry applications, such as 60 GHz high-data rate communication. Another commercial application of planar antennas includes the exponentially growing lucrative industry of automotive radars. Such radar systems not only require highly reliability since human lives are involved, but also extreme integration to serve the purpose of compactness and cost. Therefore, it is desirable to have all the system functionalities on a single silicon chip, which can then easily be combined with either off- or on-chip antennas/antenna arrays. In such scenarios, planar printed antennas/arrays, because of their low profile and ability to be integrated, are emerging as an alternative to the bulky and expensive dielectric lenses. Although planar antennas show advantageous properties, there are two major challenges associated with their design, namely surface waves and front-to-back radiation ratio. In this thesis, a innovative planar methodology is presented to solve the aforementioned bottlenecks. The proposed technique can be used to obtain simultaneously high radiation efficiency (i.e., minimal surface wave excitation) and good front-to-back radiation ratio. This solution consist of engineering anisotropic equivalent materials, referred to as artificial dielectric layers (ADLs), and using them to enhance the performance of planar antennas. A practical planar realization of this concept can be achieved by embedding inside the host dielectric a periodic array of sub-wavelength square metal patches in a multilayer configuration. In this work, the main aspects pertaining to the theoretical development and the practical implementation of ADLs are investigated. The analysis of ADLs is extensively investigated in this thesis in order to understand the physical phenomena characterizing these structures. Moreover, this study also provides the guidelines to design such kind of engineered materials. The modeling of ADLs is first implemented for two-dimensional structures, and then generalized to three-dimensional geometries. A rigorous analytical formulation is presented to model ADLs of finite height by including the higher-order interaction between parallel sheets in closed form. From the equivalent impedance of the layers, a transmission line model that provides the spectral Green's function of ADLs is constructed. This allows to characterize the propagation through finite ADLs and to study their dispersion characteristics. The analysis shows that an ADL slab is equivalent to a dense material for the plane waves incident in directions close to the normal, whereas it exhibits lower effective permittivity for the waves that are incident close to the grazing angle. This peculiar anisotropic property can be exploited to design antenna superstrates which, one one hand, exhibit high surface-wave efficiency over a wide band and, on the other hand, provide high front-to-back ratio. The advantages of using ADL superstrates in the antenna designs is experimentally demonstrated by the development of two prototype demonstrators. The first design operates at X-band and is realized using commercial printed circuit board (PCB) technology. The second prototype consists of an on-chip antenna working at 0.3 THz, which is fabricated using an in-house integrated circuit process. This study highlights that the ADL superstrates can be designed and manufactured independently from the antenna and the circuit. This allows their use as add-on components, since no accurate alignment is required between the antenna and the superstrate layers. Moreover, ADL are broadband because of their non-resonant nature. The last part of this thesis deals with a novel concept of wideband wide-scanning phased array designs, based on connected arrays of slots loaded with ADL superstrates. The proposed structure has two main advantages with respect to the existing solutions. Firstly, it is completely planar and realized with a single multilayer PCB, with consequent reduction of the cost and the complexity of the array. Secondly, ADLs are used in place of real dielectric superstrates, to achieve much better efficiency in terms of surface-wave loss. For the design of the array loaded with ADL, including the adhesive layers, an analytical tool, based on spectral Green's function, is used. This tool allows to estimate the performance of the array with minimal computational resources. The design of a wideband feed structure is also proposed, which does not require balanced-to-unbalanced (balun) transitions that limit the matching bandwidth.Microelectronics-THz Sensing GroupElectrical Engineering, Mathematics and Computer Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Applications of Artificial Dielectric Layers for the Design of Planar Integrated Antennas
No full textIn this paper, we present an overview of our recent works on artificial dielectric layers (ADLs), used to enhance the radiation efficiency of planar printed antennas and arrays. The artificial material is realized by introducing planar sub-resonant metallic inclusions in a host material. This allows to enhance the permittivity of the host medium, which is characterized by high anisotropy. An analytical method has been developed to model the ADLs, valid for arbitrary number of layers and generic illumination. After a general description of this method, two design examples are presented. The first utilizes a single ADL slab as a superstrate of an on-chip double slot antenna operating at 300 GHz. Simulated and measured results show an improvement of the antenna gain and overall efficiency of about 2 dB. The second example exploits the use of the ADLs for the design of wideband, wide-scan planar phased arrays. A connected-slot array is loaded with an ADL superstate, to achieve wide-scan capability, up to 50 degrees in all azimuth planes, over an octave bandwidth.Accepted author manuscriptTera-Hertz Sensin
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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