<p>Efficient, but low-profile and small-footprint antennas for VHF-UHF range applications remains an ongoing work. VHF range spans approximately 54 - 88 MHz while UHF roughly ranges from 174 - 890 MHz. The inverse relationship between the physical length and resonant frequency of an antenna, which is a measure of its operating frequency range, is well known. A direct correlation between an antenna's physical length and radiation efficiency has also been established. Therefore, a combination of these constraints complicates the design of low-frequency antennas that have small physical size but with enough radiation resistance to be an efficient radiator when connected to a source having a comparable resistance. Given the frequency bands above, their corresponding wavelengths will be: 3.4-5.5 m (VHF) and 0.3-1.7 m (UHF). The length of an antenna operating at these wavelengths would need to be electrically-small i.e. a fraction of wavelength given size constraints for applications such as defense or commercial mobile communication equipment. As a consequence, the radiation resistance of the antenna, which is a function of its radiation efficiency, is greatly reduced. In other words, the input impedance or radiation impedance (assuming negligible ohmic losses in the antenna structure) features a small resistive component and a large capacitive component, causing reflections of most of the incident power to the antenna. Highly-reactive antennas are not desired for most transmitters and receivers. Therefore, the radiation resistance of an antenna must be increased by increasing its electrical length while simultaneously maintaining a low profile and footprint. This aim can be achieved by configuring the antenna to excite a resonance at, or very close to a desired operating frequency. An approach that I will explore in this dissertation is to exploit the broadband characteristics of meander-line and helical (or "spiral") antennas typically applied in the microwave frequency range to the UHF-VHF range. I will also propose novel antenna geometries that combine spiral and meander-line properties and analyze their performance. These antennas offer significant size reductions; for example, a bowtie meander dipole antenna studied yielded a height reduction of 55% at 64 MHz relative to a half-wave dipole antenna of the same resonant frequency. In addition, I will present a set of equations developed for predicting the fundamental resonant frequency and radiation resistance of meander-line antennas.</p> / Dissertation

This thesis deals with RFID tags design. It comprises an overview of the RDIF technology while focusing upon the passive tags in UHF band. The CST Microwave studio software has been used for draft simulations. The resulting tags have been subjected to parameter measuring – the reflection coefficient, the minimum capacity needed to switch on the tag, the maximum reading distance. The influence of the proximity of metal objects and other materials has also been examined.

Groundwater-surface water interactions between streams and shallow alluvial aquifers can significantly affect their thermal and chemical regimes and thus are critical for effective management of water resources and riparian ecosystems. Of particular significance is the hyporheic zone, an area delineated by subsurface flow paths that begin and end in surface water bodies. Although detailed work has examined hyporheic flow in the vertical dimension, some studies have suggested that the drop in a stream’s elevation as it flows downstream can laterally extend the hyporheic zone. This study examines intra-meander hyporheic flow using extensive field measurements in a full-scale experimental stream-aquifer system. Synoptic head measurements from 2008 and 2009 and a lithium tracer test were conducted to determine the extent and nature of hyporheic flow within the meander. Permeability was measured and sediment cores were analyzed from 2008 to 2009 to assess aquifer properties. Finally, transient head and temperature measurements were collected during flooding events to assess the sensitivity of intra-meander hyporheic flow and temperature to stream discharge. Results verify that hyporheic flow through meanders occurs, but show that it is sensitive to whether a stream is gaining or losing water to the subsurface overall. In addition, permeability and core grain size results indicate moderate heterogeneity in permeability can occur in aquifers composed of relatively uniform sediment. Results also demonstrate that permeability in alluvial aquifers can evolve through time. Such evolution may be driven by groundwater flow, which transports fine particles from areas where porosity and permeability are relatively high and deposits them where they are relatively low, thus creating a positive feedback loop. Finally, measurements during flooding indicate that steady-state hyporheic flow and the thermal regime within the aquifer are largely insensitive to stream discharge. Together, these results expand upon previous field studies of intra-meander hyporheic flow and verify previous modeling work, although they demonstrate a level of complexity within these systems that should be considered in future work. / text

This Master Thesis is about Meander publishing house and media reflection of three choosen titles from edition Blue Elephant. Theoretical part of this thesis introduces the development of publishing houses after the fall of communism in 1989, the development of the literature for children and youth, phenomenon of bilderbuch and the change of reading habits and reader's environment. The analytical part introduces the Meander publishing house and its edition Blue Elephant. Key artist for this edition is Petr Nikl, who is Meander's court artist as well. The analysis of media was performed on titles Záhádky by Petr Nikl, Jělěňovití by Petr Nikl and The Little's Man Great Journey by Lenka Uhlířová and Jiří Stach. The analysed media are literary and cultural magazines, newspapers and digital media.

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No. of bitstreams: 1 Cristiano Henrique Schuster 2018.pdf: 4202405 bytes, checksum: 730f564dd132126eb49b0f1d88a6ed54 (MD5) Previous issue date: 2018-02-23 / A camada limite estável (CLE) começa a se desenvolver logo após o ocaso, quando a radiação de onda curta proveniente do Sol cessa e a superfície terrestre para de aquecer, nessas condições, devido a grande perda radiativa da superfície terrestre, a turbulência pode ter sua intensidade reduzida em várias ordens de grandeza, em um regime com estas características os níveis verticais estão energicamente desacoplados. Durante uma mesma noite, pode ocorrer alternância entre intervalos em que os níveis verticais estão energicamente desacoplados e momentos em que existe grande mistura turbulenta, a transição entre esses dois estados ocorre em um valor específico da velocidade média do vento, conhecida como velocidade de conexão. Em regimes de baixas turbulência, que é uma característica de um estado de desacoplamento enérgico vertical, o escoamento próximo à superfície passa a ser governado pro fenômenos de maiores escalas, como por exemplo escalas de submeso, dentre os quais pode-se citar o fenômeno de meandro das componentes horizontais do vento, que é caracterizado pela oscilação da direção horizontal do vento. O meandro do ventos exerce papel fundamental na difusão de escalares, além disso, a maioria dos modelos de dispersão falham em representar a influência do meandro, principalmente pelo fato de que o meandro dos ventos ainda não é totalmente entendido e caracterizado, destacando assim a relevância deste trabalho, cujo tema de relaciona a dependência dos parâmetros de identificação do meandro do vento com o acoplamento do escoamento na camada limite atmosférica noturna e tem objetivo relacionar o estado de acoplamento atmosférico com a ocorrência de meandro dos ventos, utilizando a velocidade necessária para o acoplamento (velocidade de conexão) como critério inicial para a identificação do meandro dos ventos. Para tal, dados do experimento Fluxes Over Snow-covered Surfaces II (FLOSSII) serão submetidos a dois métodos para a identificação de parâmetros característicos de meandro, sendo o primeiro o ajuste da autocorrelação dos dados à Função de Autocorrelação (ACF) através do parâmetro de loop (m) e o período do meandro (T*) e o segundo a Transformada de Hilbert-Huang (HHT) utilizando o espectro marginal para determinação do período do meandro (T*). Com os parâmetros característicos de meandro será realizada uma análise estatística utilizando-se o critério clássico de vento fraco (Ū > 1,5 ms-1 ) e a velocidade de conexão (Ūcoup) para encontrar intervalos de um hora em que existe a possibilidade de ocorrência de meandro. Comparando os dois critérios, as análises realizadas mostram que o critério de Ūcoup encontrou aproximadamente 4 vezes mais intervalos, mantendo a mesma porcentagem de casos em que o parâmetro de loop é maior que um, mostrando-se um critério mais adequado para encontrar casos de possível meandro, principalmente para os níveis de medições mais altos. Em sítios que possuem torres de medição com níveis altos i critério de Ū < 1,5 ms-1 pode restringir a maioria dos casos, enquanto que a velocidade de conexão faz a separação natural dos regimes de escoamento. Permitindo assim, que todos os possíveis casos sejam analisados. / The stable boundary layer (CLE) begins to develop after the sunset, when short-wave radiation from the Sun ceases and the Earth’s surface ceases to heat, in these conditions, due to the great radioactive loss of the earth’s surface, turbulence intensity is reduced by several orders of magnitude, in a regime with these characteristics the vertical levels are energetically decoupled. During one night, alternations can occur between intervals in which vertical levels are energetically decoupled and times when there is a large turbulent mixture, the transition between these two states occurs at a specific value of wind speed. In low turbulence regimes, which is a characteristic of a state of vertical energy decoupling, the flow near the surface is governed by phenomena of larger scales, such as submeso scales, among which we can mention the phenomenon of meander of the horizontal components of the wind, which is characterized by oscillation of the horizontal direction of the wind. The meander of the winds plays a fundamental role in the diffusion of scalars cite anfossi2005, in addition, most dispersion models fail to represent the influence of the meander, mainly because the meander of the winds is not yet fully understood and characterized, highlighting the relevance of this work, whose research theme is “Study of the dependence of the wind meander identification parameters with the coupling in the atmospheric nocturnal boundary layer” and has as objective to relate the state of atmospheric coupling with the occurrence of winds meander, using the velocity required for the coupling as the initial criterion for wind meander identification. For this, data from the experiment Fluxes Over Snow-covered Surfaces II (FLOSSII) will be submitted to two methods for the identification of meander characteristic parameters, the first being the adjustment of the autocorrelation of the data to the Autocorrelation Function (ACF) through of the loop parameter (m) and the meander period (T*) and the second the Hilbert-Huang Transform (HHT) using the marginal spectrum for meander period determination (T*). With the characteristic meander parameters, a statistical analysis will be performed using the classical criterion of weak wind (Ū > 1,5 ms-1 ) and the coupling speed (Ūcoup) to find one hour intervals in which there is the possibility of meander occurrence. Comparing the two criteria, the analyses performed show that the Ūcoup criterion found approximately 4 times more intervals, maintaining the same percentage of cases of possible meander, especially for the higher measurement levels. In sites that have high-level measurement towers, the criterion of Ū < 1,5 ms-1 may restrict most cases, while the coupling speed causes the natural separation of flow regimes. Thus allowing all possible cases to be analysed.

Abstract As is the case in many developed countries, tourism has come to be seen as an important driver for local economic development in South Africa as it provides opportunities for pro-poor and community-based initiatives. This study examines the theme of route tourism and local economic development. Two examples of route tourism, the Magalies Meander and Crocodile Ramble, in the Gauteng and the Northwest Provinces of South Africa, have been surveyed in order to assess what impact private sector route tourism initiatives have on local economic development in the Magaliesberg area. The results are compared with those of other similar route tourism initiatives in South Africa.

Small size of electronic product with high layout density is the future trend in today¡¦s high speed digital circuit design. A circuit designer is obliged to optimize the best solution of circuit layout in a limited area in order to both keep a good signal integrity¡]SI¡^, and save the layout space. Meander delay line is one of the challenging topic in high-speed circuit. In this dissertation, a effective method is provided to design a meander delay line, and FDTD and HFSS are matched up to predict the behavior and the character of the meander delay line; the differential meander delay line is compared with the single meander delay line, and the behavior and phenomena of the differential meander delay line are discussed. To reduce couple power, the differential meander line of design would be a new thinking. The most important point in this thesis, the complete flows of designing single meander lines and differential meander lines are provided, and designer could follow the steps of the proposed method to design a perfect and practical meander line with both keeping good SI and using least layout space. The effect of the design parameters of the meander line on the signal quality both in time-domain and frequency-domain is theoretically and experimentally investigated. FDTD method and the commercial tool HFSS are employed for the numerical study in this work.

No description available.

The objective of this paper is to present an efficient miniaturized antenna design and simulation of a highly isolated multi-port micro-strip antenna for multiple-input multiple-output communication (MIMO) systems. Three geometric configurations were proposed and compared to achieve an isolation of as low as –30 dB without affecting the antenna performance greatly. The antenna was designed to operate at a resonance frequency of 2.45 GHz (fc ). Ferrite material beneath each meander structure was used for miniaturization purposes as well as an FR4 substrate with a compact overall area of .75 lambda0 ×.5 lambda0 for a system board, where lambda0 is the free space wavelength. A ground plane with small etched slits was used for isolation purposes. A maximum gain of 4.6 dBi in the azimuthal plane was achieved. Index Terms: MIMO, meander antenna, four-port antenna, defected ground structure / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science

Σκοπός της εργασίας είναι η μελέτη των ηλεκτρικά μικρών επίπεδων μαιανδρικών κεραιών που λειτουργούν στη ζώνη συχνοτήτων 2.4 GHz, καθώς και συστήματα με μαιανδρικές κεραίες πολλαπλής ζώνης συχνοτήτων (επιπλέον ζώνες ενδιαφέροντος είναι η 1.8 και η 5.2 GHz). Πρόκειται για κεραίες με μεγάλο εύρος ζώνης γύρω από τη συχνότητα συντονισμού που χρησιμοποιούνται σε κινητά τερματικά, όπως κινητά τηλέφωνα και φορητοί υπολογιστές και παρουσιάζουν πολλά πλεονεκτήματα, με κυριότερα το χαμηλό κόστος, την ευκολία κατασκευής, το μικρό τους μέγεθος και τη δυνατότητα μαζικής παραγωγής. Συστήματα κεραιών πολλαπλής ζώνης συχνοτήτων είναι επίσης μια σύγχρονη τεχνολογική απαίτηση, καθώς υπάρχει ανάγκη για διασύνδεση διαφορετικών υπηρεσιών που λειτουργούν σε διαφορετικές περιοχές συχνοτήτων, ειδικά όσον αφορά στα ασύρματα τοπικά δίκτυα. / The purpose of this thesis is to study the behaviour of small electrical antennas formed in meander shape, which operate at the frequency of 2.4 GHz, and dual band system operating in the ISM band and the DECT band of 1.8 GHz. These types of antennas present a large bandwidth around the resonant frequency and have great benefits, such as small dimensions and great efficiency at resonance.