Fotoninis kristalas sudarytas iš medžiagų su skirtingais lūžio rodikliais. Dėl stop juostos valdymas fotoniniame kristale yra diskutuotinas klausimas.Vienas iš metodų valdyti stop juostą, užpildyti jį skystuoju kristalu. užpildant opalą skystuoju kristalu, buvo sukurtas LC defektas. Keičiant elektrinį laiuką, intervale nuo 1V iki 6V, defektą galima valdyti. defekto poslinkis gautas per 4m.defektas opale juda šviesos greičiu 300 000 km/s, o stop juostoje greitis lygus 0m/s. / Photonic crystals (PCs) are periodic dielectric materials that can control the propagation of photons. Control of stop band position in photonic crystals was discussed.A method was developed to adjust the opal stop band position by controlling the refractive index.When filling in the opal LC the result was a LC defect. Changing the electric field wichin the interval from 1 V to 6 V it is possible handle the defect. The movement of the defect was 4nm. The defect in the opal in moving with light speed that is 300 000 km/s and the speed on the bang is 0 m/s.

Elastic Wave propagation in structures with irregular boundaries is studied by transforming the plates with irregular surfaces to sinusoidal wave-guides. Guided elastic wave in a two-dimensional periodically corrugated plate is studied analytically. The plate material is considered as homogeneous, isotropic and linearly elastic. In a periodically corrugated wave-guide, all possible spectral orders of wave numbers are considered. The dispersion equation is obtained by applying the traction free boundary conditions at the two surfaces. The analysis is carried out in the wave-number domain for both symmetric and anti-symmetric modes. Non-propagating 'stop bands' and propagating 'pass bands' are investigated. Experimental analyses with two different pairs of transducers are also performed and compared with the results from the mathematical analysis. Newly developed semi-analytical DPSM technique has been also adopted in this dissertation to model the ultrasonic field in sinusoidally corrugated plate. Distributed Point Source Method (DPSM) is gradually gaining popularity in the field of Non-Destructive Evaluation (NDE). DPSM can be used to calculate the ultrasonic field (pressure, velocity and displacement in a fluid or stress and displacement in a solid) generated by ultrasonic transducers. So far the technique has been used to model ultrasonic field in homogeneous or multilayered fluid structures. In this dissertation the method is extended to model the ultrasonic field generated in both fluid and solid media. The Prime objective of using DPSM technique in this dissertation is to model the ultrasonic field generated in the corrugated wave guide. This method has never been used to model ultrasonic field in solids. Development of stress and displacement Green's functions in solids are presented. In addition to the wave propagation problem in the sinusoidal wave guide, a few unsolved problems such as ultrasonic field generated by bounded acoustic beams in multilayered fluid structures, near a fluid-solid interface and in flat solid isotropic plates are also presented in this dissertation.

Yes / A Novel design of a curved single-layered frequency selective surface with an 11 × 11 array of a 13 × 13 mm-sized unit cell has been merged with a miniaturized, CPW-fed ultra-wideband monopole of dimensions (20 × 25 mm2) for gain enhancement. The suggested prototype, crafted on an FR-4 dielectric substrate and demonstrates a very broad bandwidth starting from 2.66 to 17.98 GHz (148%), which covers the entire UWB frequency band. The combined antenna-curved FSS reflector shows a very important gain improvement from 0.2–5.4 dB to 8.8–14.9 dB, having a peak gain increase of 10 dB at 10.6 GHz. Basic design features were studied and discussed through simulations, yielding promising results The proposed structure can be used in UWB and GPR applications. / The full-text of this article will be released for public view at the end of the publisher embargo on 31 Oct 2024.

A miniaturization technique that allows the size of microstrip square open loop resonators to be reduced by more than 80% is presented and studied. The technique is based on the loading of the resonator with a series surface mount capacitor. It is shown that this technique allows the design of microwave bandpass filters with a wider stopband when compared with conventional designs. It is also proved that the insertion loss of the miniaturized filter is not degraded, but in fact can be maintained or even enhanced by the miniaturization process; this is true whenever the quality factor of the lumped capacitor is higher than the quality factor of the microstrip resonator. Finally, the feasibility of using the effect of the capacitor loss in the miniaturized resonator quality factor as a method to measure the effective series resistance of surface mount capacitors is studied, and recommendations towards its implementation are presented.

Magistro baigiamajame darbe tiriamos nevienalyčių plačiajuosčių periodinių sistemų užtvarinės savybės. Aptariamos periodinės sistemos ir jų charakteristikų skaičiavimo metodai. Nevienalyčių periodinių savybių tyrimui panaudoti du modeliai. Pradžioje nagrinėjamos periodinės ilgosios linijos savybės, vėliau taikomas spiralinės sistemos modelis. Modelių analizė atliekama klasikiniu, matriciniu ir daugialaidžių linijų metodais. Taikomas kompiuterinis modeliavimas. Sudarytos įėjimo varžos, perdavimo ir lėtinimo koeficientų, vėlinimo laikų bei pereinamosios charakteristikos skaičiavimo programos. Parodyta, kad linijos su periodiniais netolygumais įgyja užtvarinio filtro savybes, kurios ryškėja, didėjant sistemos nevienalytiškumui. / In order to reveal general properties of the structures, containing periodical inhomogeneities, the inhomogeneous electromagnetic line and the inhomogeneous helical retard structure are considered. The overview of periodical systems and methods of their analysis are presented. The structures, containing periodical inhomogeneities, are analyzed using classical, matrix and multiconductor line methods. The programs for calculation of line input impedance, transfer coefficient, delay coefficient and width of the stop-band are developed. The results show that the stop–band appears due to periodical inhomogeneities and the width of the stop-band and the attenuation in it depend on intensities of periodical inhomogeneities.

Deux exemples de tunnels optiques sont étudiés par des méthodes de l'optique femtoseconde pour leurs propriétés propagatives. Le premier est une opale artificielle : un matériau de la famille des cristaux photoniques aux propriétés analogues dans le domaine optique à celles des semiconducteurs. Ils possèdent une bande interdite photonique (BIP) empêchant pour toutes les directions la propagation de photons dont l'énergie se trouve dans cette bande. Le second système est un bi-prisme en réflexion totale.<br> La première partie est consacrée aux opales : empilements réguliers de sphères de silice submicrométriques. Chaque phase de l'élaboration est en revue. Une description théorique des propriétés des cristaux photoniques est faite pour plusieurs structures. On en déduit que les opales n'ont pas de BIP mais une "stop-band" inhibant la transmission des photons dont la bande d'énergies dépend de la direction. Les caractéristiques structurelles, mises en relation avec les propriétés spectrales, sont abordées par des méthodes microscopiques et optiques. Un dispositif de temps de vol a été réalisé pour déterminer les propriétés propagatives d'opales sondées par un continuum en utilisant un fenêtrage temporel par absorption à deux photons dans du ZnS. Après des corrections en fréquence et en temps, on dispose du profil spectral de vitesse de groupe. Celui-ci est expliqué par un modèle basé sur la relation de Kramers-Krönig. Cela permet de décrire la "stop-band" comme un système à "deux niveaux photoniques".<br> La dernière partie est dédiée à l'étude de la transposition en optique d'un nouvel effet prédit dans les conditions de l'effet tunnel : "l'évaporation quantique". Il se manifeste par l'augmentation drastique de la transmission d'un paquet d'onde. Il se produit en transférant à l'instant de la réflexion une petite quantité de mouvement au paquet d'onde. Un bi-prisme en réflexion totale séparé par une lame d'air est employé pour reproduire les conditions de cet effet. On utilise une technique pompe-sonde qui simule le transfert de moment par effet Kerr. Après analyse des effets en compétition avec l'évaporation quantique, nous observons des signaux qui, une fois traités selon des critères précis, ont les caractéristiques de l'effet recherché. Ceci constitue une présomption de la première observation en optique de ce nouvel effet.