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Application de la transformation d'espace à la conception d'antennes à diagramme de rayonnement contrôlé / Transformation electromagnetics : applications on beam controlled antenna designClemente Arenas, Mark 28 November 2014 (has links)
La transformation d'espace (TE) a été développée par J. B. Pendry et U. Leonhardt en 2006 et suscite un énorme intérêt depuis la démonstration expérimentale de la première cape d'invisibilité en micro-ondes. Cette technique permet de contrôler la propagation des ondes en modifiant les propriétés électromagnétiques de l'espace. Malgré quelques limitations liées à la bande passante ou aux pertes consécutives à l'utilisation de métamatériaux pour les dispositifs TE, cette technique a attiré l'attention de nombreux domaines (optique, microondes, acoustique, etc). L'objectif de cette thèse est de développer des applications de la TE dans le domaine antennaire à l'aide de matériaux conventionnels lorsque cela est possible et aussi d'ouvrir de nouvelles voies dans le contrôle du rayonnement des antennes. Trois applications ont été étudiées: le réflecteur « parabolique plat »; un superstrat tout diélectrique pour contrôler l'ouverture angulaire d'une antenne patch; et finalement un superstrat permettant de modifier drastiquement le rayonnement d'une antenne. Ce travail a été financé par les agences de défense du Royaume Uni et de la France (DSTL et DGA respectivement), dans le cadre du projet MIMiCRA (Metamaterial Inspired Microwave Conformai Radar Antennas). / Transformation Electromagnetics technique was introduced by J. B. Pendry and U. Leonahrdt in 2006 and it has become an emerging research field in physics and engineering in the last few years after the concept was validated experimentally with a invisibility cloak in microwave regime. This technique claims the possibility of an unprecedented technique to control electromagnetic waves interaction with engineered materials to achieve exotic electromagnetic behaviour. Despite some issues about narrow bandwidth or excessive dispersive losses related to the use of metamaterials for realization of TE devices, this technique caught the attention in many research fields (optics microwave, acoustics, etc). The final purpose of this these is to explore and propose applications of Transformation Electromagnetics in the antenna design field by using standard materials with the purpose of controlling the radiation pattern of an antenna. More precisely, three applications were explored : a fiat "parabolic reflector", an all-dielectric superstrate to control the half power beamwidth of a patch antenna and finally a superstrate that allows to control drastically the radiation pattern of a planar antenna This work was funded by France and UK defence agencies (DSTL and DGA respectively), within the framework of MIMiCRA project (Metamateriallnspired Microwave Conformai Radar Antennas).
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Analýza mikropáskových antén / Analysis of microstrip antennasKozák, Filip January 2010 (has links)
This work deals with the method for analysis of one-port microstrip circuits which is called as contour-integral method. The general procedure for evaluating of important parameters concerning the analysis of microstrip antennas is given. Next, the geometrical parameters necessary for the calculation of elements in U and H matrices are numerically solved. With the help of these matrices, the input impedance or the reflection coefficient can be easily found.
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[pt] APRIMORAMENTO DA GERAÇÃO UNIDIRECIONAL DE ONDAS ULTRASSÔNICAS DO TIPO SH COM TRANSDUTORES ACÚSTICOS ELETROMAGNÉTICOS DO TIPO ÍMÃS PERMANENTES PERIÓDICOS COM SEPARAÇÃO LATERAL E MÚLTIPLAS FILEIRAS DE ÍMÃS / [en] ENHANCEMENT OF UNIDIRECTIONAL GENERATION OF SH ULTRASONIC WAVES WITH SIDE-SHIFTED PERIODIC PERMANENT MAGNET ELECTROMAGNETIC ACOUSTIC TRANSDUCERS AND MULTIPLE ROWS OF MAGNETSLUCAS MONTEIRO MARTINHO 25 October 2022 (has links)
[pt] Ondas ultrassônicas do tipo SH (do inglês, shear horizontal), ou de cisalhamento
horizontal são úteis no campo de ensaios não-destrutivos. Essas podem
ser geradas, em meios metálicos, por transdutores acústicos eletromagnéticos
(EMAT) que utilizam um arranjo de ímãs permanentes periódicos (PPM),
chamados de EMATs PPM. Tais dispositivos em sua forma convencional, entretanto,
geram ondas ultrassônicas bidirecionalmente, ou seja, para frente
e para trás. Essa característica é geralmente indesejada. Recentemente, foi
proposto um EMAT tipo PPM duplo com separação lateral que gera ondas
nominalmente em uma única direção. Entretanto, seu diagrama de radiação
revela lóbulos traseiros laterais. Esta dissertação tem como objetivo aprimorar
o supracitado projeto através de seus parâmetros de construção, mais especificamente,
o número de fileiras de ímãs permanentes do arranjo PPM e a separação
lateral entre as mesmas. Foi desenvolvido um modelo analítico, baseado em
linhas de fontes lineares, que considera a projeção de cada espira como uma
fonte harmônica independente, para cálculo do campo ultrassônico gerado por
EMATs PPM, tanto os do tipo PPM duplo, quanto o convencional. Com isso, foi
possível obter o digrama de radiação teórico dos dispositivos, de forma a analisar
como os seus parâmetros de construção interferem em sua unidirecionalidade.
Utilizou-se três tecnologias distintas de bobinas, a saber, bobinas fabricadas
manualmente, bobinas fabricadas a partir de placas de circuito impresso (PCB)
flexível de poliamida e PCB flexível de poliéster. Os arranjos PPM duplos
foram colocados sobre moldes impressos em impressora 3D. Realizou-se testes
experimentais em uma placa de alumínio 1.5 mm de espessura, com EMAT
PPM comercial utilizado como receptor, em diversos ângulos, com o objetivo
de calcular o diagrama de radiação experimental do EMAT PPM duplo. Ao
todo foram montadas 44 unidades quando combinadas todas as tecnologias de
fabricação de bobina, com separação lateral de 1 mm a 4 mm e 1 a 4 de fileiras
de ímãs. Resultados experimentais e teóricos mostraram boa concordância. Foi
observado que tanto aumentar o número de fileiras de ímãs, quanto diminuir
a sua separação lateral reduzem a intensidade dos lóbulos traseiros laterais.
Resultados experimentais mostraram que, com a configuração de 4 fileiras de ímãs, separados lateralmente por 1 mm e bobinas feitas a partir de PCB de
poliamida, a intensidade dos lóbulos traseiros laterais foi reduzida em 8.6 dB,
em relação à configuração original do PPM EMAT duplo . Sobre as tecnologias
de bobina, pode-se concluir que o uso de PCBs flexíveis tornou possível obter
menores separações laterais entre as fileiras de ímãs e simplificar o processo
de construção do EMAT PPM duplo, com destaque para a bobina feita com
PCB flexível de poliamida, que apresentou baixo erro médio entre medidas
experimentais e simuladas, apresentando também o mais fácil processo de
fabricação entre os três tipos de bobinas avaliados. / [en] Shear horizontal (SH) ultrasonic waves are useful in the non-destructive
evaluation field. They can be generated, in metallic media, by electromagnetic
acoustic transducers (EMAT) that use an array of periodic permanent magnets
(PPM). PPM EMATs, in their conventional form, generate forward and
backward traveling SH waves. This feature is generally undesired. Recently,
a side-shifted dual-PPM EMAT has been proposed. This device generates
waves predominantly in a single direction. However, its radiation pattern
reveals backward side lobes. This thesis aims to improve the aforementioned
design through its construction parameters, more specifically, the number of
rows of magnets in the PPM array and the lateral separation between them.
An analytical model, based on the line source method, which considers the
wires projections as independent wave sources, was developed to calculate the
ultrasonic field generated by PPM EMATs, either for the conventional one
or the dual-PPM EMAT. Exploiting the developed model, it was possible
to compute the theoretical radiation pattern of the device in order to better
analyse how its construction parameters affect its unidirectionality. Three
different coil technologies were used, namely hand-wound coils and coils made
with flexible printed circuit boards (PCBs), either of polyamide or polyester
material. The magnet arrays were mounted on 3D-printed molds to ensure
their positioning. Experimental tests were carried out where the fabricated
device was placed onto a 1.5 mm-thick aluminum plate, and a commercial PPM
EMAT was used as a receiver, at different reception angles, in order to calculate
the radiation pattern of the dual-PPM EMAT. Overall, 44 units, combining
all coil technologies, were manufactured with lateral separation from 1 mm
to 4 mm and 1 to 4 rows of magnets per PPM. Experiments and theoretical
results presented good agreement. It was observed that either increasing the
number of rows of magnets or decreasing their lateral separation reduced the
intensity of the backward side lobes. When using the configuration of 4 rows of
magnets and 1 mm side shift, fabricated with polyamide PCBs, results revealed
that the intensity of the backward side lobes was reduced by 8.6 dB, when
compared with the original configuration. Regarding the coil technologies, it can be concluded that the use of flexible PCBs allowed one to obtain shorter lateral
separations between rows of magnets and simplified the fabrication process
of the dual-EMAT. Mainly, the poliamide-based flexible PCB coil presented
low average error between experimental and simulated measurements and the
easiest fabrication process among all three coil technologies tested.
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