Image reconstruction of inhomogeneous biaxial dielectric cylinders buried in a slab medium

100學年度研究獎補助論文[[abstract]]The image reconstruction of inhomogeneous biaxial dielectric cylinders buried in a slab medium is investigated. A biaxial dielectric cylinder of unknown permittivities buried in a slab scatters a group of unrelated incident waves from outside. The scattered field is recorded outside the slab. By proper arrangement of the various unrelated incident fields, the difficulties of ill-posedness and nonlinearity are circumvented, and the permittivity distribution can be reconstructed through simple matrix operations. The algorithm is based on the moment method and the unrelated illumination method. Numerical results are given to demonstrate the capability of the inverse algorithm. Good reconstructed results are obtained even in the presence of additive Gaussian random noise in measured data. In addition, the effect of noise on the reconstruction result is also investigated.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙

Metamaterial

In-depth analysis of the theory, properties and description of the most potential technological applications of metamaterials for the realization of novel devices such as subwavelength lenses, invisibility cloaks, dipole and reflector antennas, high frequency telecommunications, new designs of bandpass filters, absorbers and concentrators of EM waves etc. In order to create a new devices it is necessary to know the main electrodynamical characteristics of metamaterial structures on the basis of which the device is supposed to be created. The electromagnetic wave scattering surfaces built with metamaterials are primarily based on the ability of metamaterials to control the surrounded electromagnetic fields by varying their permeability and permittivity characteristics. The book covers some solutions for microwave wavelength scales as well as exploitation of nanoscale EM wavelength such as visible specter using recent advances of nanotechnology, for instance in the field of nanowires, nanopolymers, carbon nanotubes and graphene. Metamaterial is suitable for scholars from extremely large scientific domain and therefore given to engineers, scientists, graduates and other interested professionals from photonics to nanoscience and from material science to antenna engineering as a comprehensive reference on this artificial materials of tomorrow

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Gratings: Theory and Numeric Applications

International audienceThe book containes 11 chapters written by an international team of specialist in electromagnetic theory, numerical methods for modelling of light diffraction by periodic structures having one-, two-, or three-dimensional periodicity, and aiming numerous applications in many classical domains like optical engineering, spectroscopy, and optical telecommunications, together with newly born fields such as photonics, plasmonics, photovoltaics, metamaterials studies, cloaking, negative refraction, and super-lensing. Each chapter presents in detail a specific theoretical method aiming to a direct numerical application by university and industrial researchers and engineers

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Application of polarized Raman spectroscopy for analysis of phase transitions and anisotropic behavior of soft condensed matter

The importance of soft matter research, as a major class of materials including liquid crystals, polymers, colloids, emulsions, and forms, is attributed to the behavior resemblances in each branch of soft matter responding to the external perturbations. Hence, one of the most required inquiries in soft matter physics is understanding how the structures with characteristic length scales evolve in response to external perturbations, and concomitant phase transitions. We have focused on adopting polarized Raman spectroscopy to probe phase transitions in soft materials consisting of anisometric components and the evolution of molecular orientational ordering as a complementary tool to other methodologies, but distinct in some respects. The primary task is quantifying the degree of molecular orientation, i.e., obtaining orientational order parameters, in liquid crystal (LCs) system. Thermal evolution of orientation degree in a hitherto elusive biaxial nematic (Nb) phase as well as a commonly known uniaxial nematic (Nu) phase were interrogated from the measurements of anisotropy in polarized Raman intensities. We demonstrated reliable and applicable method to quantify the orientation degree for systems possessing anisotropic ordering. We also addressed a strong potential of Raman spectroscopy that the changes of vibrational energy reflect the variations of intermolecular interactions and structural changes on the molecular level induced by phase transitions. As a subfield of soft matter, we characterized phase transitions and anisotropic ordering observed in an evaporating conjugated polymer solution and elucidated the mechanism of the entities undergoing phase transitions using mainly polarized Raman spectroscopy. In addition, we have shown that tracking Raman spectral changes can provide valuable information for understanding structure-property relations when the measurements of the evolution in physical properties are carried out simultaneously.PhDCommittee Chair: Srinivasarao, Mohan; Committee Member: El-Sayed, Mostafa; Committee Member: Fernandez, Alberto; Committee Member: Griffin, Anselm; Committee Member: Park, Jung Ok; Committee Member: Reichmanis, Elsa; Committee Member: Rey, Alejandro; Committee Member: Tolbert, Lare