Studies of metamaterial structures

Imperial Users onl

Metamaterials for optical and THz ranges: design and characterization

The thesis is devoted to the field of metamaterials (MtMs) - effectively continuous artificial composites with advantageous electromagnetic properties not normally met in nature. The main goal of the work is the engineering of MtMs with new and extreme electromagnetic properties and their electromagnetic characterization.  The first part of the thesis is focused on the artificial magnetism and isotropic negative permittivity and permeability in the near-infrared and visible ranges. Several design solutions based on resonant complex-shaped inclusions are proposed and studied analytically and numerically. In the first design utilization of clusters of plasmonic dimers leads to the negative permeability in the near-infrared range. Next suggested MtM consisting of the clusters of plasmonic triangular nanoprisms possesses isotropic negative permeability on the boundary between the near-infrared and visible ranges. The third design based on core-shell metal-dielectric particles allows for the isotropic negative refractive index in the near-infrared range.  The second part of the thesis is devoted to the problem of characterization of planar and bulk MtMs. At first, the applicability of the so-called Holloway-Kuester method is studied for the planar arrays of complex inclusions. It is shown, that despite the fact that the approach initially was developed for the arrays of solid particles in the quasi-static approximation, it is also applicable for the arrays of rather optically substantial resonant clusters of plasmonic nanoparticles. Then, the method of homogenization of bulk MtMs is suggested, based on the account of electromagnetic interaction between crystal planes forming an orthorhombic lattice. The method reveals the electromagnetic properties not covered by the standard quasi-static homogenization procedures.  The last research problem studied in the thesis is the engineering of planar multifunctional MtMs for the THz range. The suggested MtM consists of resonant metal stripes put on both sides of an elastic polymer film and allows for the combination of polarization transformation properties with sensitivity to the applied strain. The design is studied theoretically, numerically, and experimentally. For the last purpose an original fabrication method is developed, allowing for the rather simple creation of optically large samples. The fabricated sample experimentally demonstrates a high sensitivity to stretching in the transmission coefficient for the co-polarized field

Electromagnetic modeling of split-ring resonators

In this paper, we report our efforts to model splitring resonators (SRRs) and their large arrays accurately and efficiently in a sophisticated simulation environment based on recent advances in the computational electromagnetics. The resulting linear system obtained from the simultaneous discretization of the geometry and Maxwell's equations is solved iteratively with the multilevel fast multipole algorithm. As an example, we present an array of 125 SRRs showing a negative effective permeability about 92 GHz. © 2006 EuMA

Metamaterials, Surface Waves, and Their Applications

Thesis advisor: Willie J. PadillaThe field of metamaterials (MMs) has garnered a great deal of attention ever since the experimental demonstration of negative refractive indexes. Such an exotic response stemmed from the engineering capability of MMs, as they can obtain almost any optical responses at any given frequency by carefully structuring the geometries. There are countless examples where MMs have posed promising results in tailoring free space radiation. However, their usage beyond this common platform is far less explored. For examples, surface electromagnetic waves, which offer great potentials for future device applications, could be an intriguing place for the further development of metamateirals. In this dissertation, we study various MM configurations where the interplay between surface waves and metamaterials has a significant impact on the device performance. Firstly, Chapter 1 introduces some fundamental concepts of metamaterials and surface electromagnetic waves, and outline the fabrication, experiments, and characterization details. In Chapter 2, we investigate whether the effective optical parameters of MMs have the exact physical meaning as those of natural substances. Two types of MM resonators are studied, and we found the thickness of the host matrix plays a crucial role in such a homogenization process. Next, we present a computational and experimental study of MMs in conjunction with a novel gigahertz/terahertz transmission line, in Chapter 3. By optimizing the coupling between the MMs and the signal, information can be encoded. Chapter 4 presents a study of designing an extremely subwavelength magnetic MM. By maximizing the effective inductance and capacitance of the structure, the final geometry obtains a strong magnetic resonance with the size of merely λₒ/2000, where λₒ is the resonant wavelength. A novel time-domain spectroscopic method is also proposed to determine the frequency-dependent permeability of the samples. In Chapter 5, we characterize two hidden channels of MM perfect absorbers : scattering and generation of surface electromagnetic waves. In particular, we unveil lossy surface waves are generated during the process resulting in an enhancement of angular absorbance. The study provides a new insight to the working principle of MMAs. In Chapter 6, we investigate complementary MM structures that exhibit strong extraordinary optical transmission with higher transmission efficiency. We discover the origin of the fundamental mode is irrelevant to the Bloch modes. Lastly, we summarize all achievements and give an outlook in Chapter 7.Thesis (PhD) — Boston College, 2014.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Physics