Acoustic metamaterials are sub-wavelength structures designed to overcome limitations in the material properties of conventional materials. The present research focuses on the nonlinear acoustic and dynamic response of a specific type of engineered microstructure called a snapping acoustic metamaterial (SAMM). Snapping of these elements is defined as large, rapid deformations induced by infinitesimal perturbations in the time-varying external pressure. Snapping behavior in SAMM elements results from their non-monotonic stress-strain response, which displays regimes of positive and negative stiffness. This work presents a modeling study of the nonlinear behavior of both individual SAMM elements and a heterogeneous material containing a dilute concentration of SAMM elements embedded in a nearly incompressible viscoelastic solid. Two different scenarios are considered: (i) nonlinear wave propagation in the heterogeneous medium, and (ii) forced nonlinear dynamics of inclusions embedded in a viscoelastic medium. The nonlinearity of the SAMM elements is represented by a cubic pressure-volumetric strain relationship based on finite element model results from previous work. The effective nonlinear response of a heterogeneous mixture of SAMM elements embedded in a matrix, characterized by the parameters B/A and C/A, is then determined using both a nonlinear mixture law and a nonlinear Hashin-Shtrikman approach. The former estimate is limited to matrix materials with zero shear modulus, which cannot stabilize SAMM inclusions in regimes of negative stiffness. The augmented Hashin-Shtrikman method, however, includes nonlinear elasticity and the shear modulus of the matrix material. It therefore provides accurate estimates of the homogenized material when SAMM elements display negative stiffness and enhanced acoustical nonlinearity. The distortion of an acoustic wave propagating through the effective medium is studied through numerical solution of a nonlinear evolution equation that includes both quadratic and cubic nonlinearity. Finally, the forced nonlinear dynamic response of both a single SAMM element in a matrix and a domain of effective medium material embedded in matrix is considered. This behavior is of interest for generating enhanced absorption of acoustic wave energy because snapping leads to large hysteresis in the stress-strain response. A generalized Rayleigh-Plesset analysis is adapted to model the large-deformation dynamics associated with the system. / text

In the frequency domain all materials can be described electrically by their complex permittivity and permeability. These constitutive parameters determine the response of the material to electromagnetic (EM) radiation. The precise knowledge of complex permittivity and permeability is required not only for scientific but also for industrial applications. Due to the uncertainties in manufacturing processes, often the only way to find a material's parameters is to measure them. The concept of metamaterials, exhibiting negative permittivity and permeability, is attracting a lot of attention. Such materials are also termed left-handed materials (LHMs). This thesis examines several methods to determine the effective permittivity and permeability of both normal materials and metamaterials. CST Microwave Studio is used to model the materials in both free space and rectangular waveguide environments to calculate the S-parameters (S11 and S21) from which the constitutive parameters can be extracted.

Thesis advisor: Willie J. Padilla / The 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.

Sun, Lei = 利用梯度超穎材料實現對電磁場的操控 / 孫磊. / "October 2010." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 64-74). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Sun, Lei = Li yong ti du chao ying cai liao shi xian dui dian ci chang de cao kong / Sun Lei.

Lee, Hon Ping = 光學闊頻超材料設計 / 李翰屏. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 79-81). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Lee, Hon Ping = Guang xue kuo pin chao cai liao she ji / Li Hanpin.

No description available.

The focus of this thesis is the interaction of electromagnetic fields with chiral structures in the microwave regime. Through this study, which focuses on three regimes of electromagnetic interactions, I aim to develop a deeper understanding of the consequences and manifestations of chiral interactions The structures are on the order of, or smaller than, the wavelength of the probing radiation. As the structures are chiral, they have broken inversion symmetry, and exist in two states where one is the mirror image of the other. The results in this thesis can have impacts on future optical communications technologies and methods of sensing biological molecules. To begin with, the manipulation of the circular polarisation of a propagating beam by bilayer chiral metasurfaces is investigated. The metasurfaces consist of two layers of stacked crosses with a twist between top and bottom layers, forming chiral metamolecules. A broad frequency region of dispersionless polarisation rotation appears between two resonances, due to alignment between electric and magnetic dipoles. The dependence of this effect on the layer separation is studied for two similar metasurfaces. Evanescent chiral electromagnetic fields are the focus of the next chapter. An array of chiral antennas produces chiral near-fields at their resonant frequency. Aligned and subwavelength helices placed within this field interact differently depending on the handedness of the field with respect to the handedness of the helices. This difference in interaction strength is measured for the helices and an effective medium model where multipolar interactions are forbidden. Comparison of these two systems leads to the conclusion that the contribution to a chiral interaction from multipolar modes is minimal, in contrast to previous publications. The third study concentrates on the electromagnetic wave bound to an "infinitely long" metal helix. The helix has infinite-fold screw symmetry, and this leads to interesting features in the energy-dispersion of the waves it supports. The broad frequency range of high, tunable, dispersionless index is interpreted using a geometrical approach, and the factors that limit the bandwidth explained. A modified geometry is suggested for increased bandwidth. The final part of the thesis is dedicated to future work, based on the results presented thus far. Three suggestions for future study are presented, including chiroptical signals from higher-order chiral arrangements, the effect of reflecting surfaces next to chiral objects and the possible use of orbital angular momentum for chiroptical measurements.

Leung, Lai Lai = 利用譜表示法設計隱形超材料 / 梁麗儷. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 63-64). / Abstracts in English and Chinese. / Leung, Lai Lai = Li yong pu biao shi fa she ji yin xing chao cai liao / Liang Lili. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Control Electromagnetic Field by Transformation Media Concept --- p.1 / Chapter 1.2 --- The invariance of Maxwell's equations under coordinate transformation --- p.2 / Chapter 1.3 --- Spatially dependent material parameters --- p.3 / Chapter 1.4 --- Objectives of the thesis --- p.4 / Chapter 2 --- Spectral Representation --- p.6 / Chapter 2.1 --- The Maxwell-Garnett approximation --- p.7 / Chapter 2.2 --- The Bruggeman theory --- p.10 / Chapter 2.3 --- The Bergman-Milton spectral representation theory --- p.11 / Chapter 2.4 --- Spectral representation of the effective dielectric constant of graded composites --- p.13 / Chapter 3 --- Design of perfect cloaking --- p.17 / Chapter 3.1 --- Pendry´ةs profile --- p.17 / Chapter 3.2 --- Slhalaev's profile --- p.21 / Chapter 4 --- Imperfect cloaking --- p.27 / Chapter 4.1 --- Sensitivity to loss effect --- p.27 / Chapter 4.2 --- Sensitivity to dispersion effect --- p.31 / Chapter 5 --- Ray Tracing --- p.38 / Chapter 5.1 --- Hamiltonian and ray equations --- p.39 / Chapter 5.2 --- Refraction --- p.41 / Chapter 5.3 --- Ray tracing of perfect spherical cloaking --- p.42 / Chapter 5.4 --- Ray tracing for imperfect spherical cloaking --- p.46 / Chapter 6 --- Other applications of the concept of transformation media --- p.52 / Chapter 6.1 --- Spherical concentrators --- p.52 / Chapter 6.2 --- Cylindrical concentrators --- p.55 / Chapter 6.3 --- Graded Drude model design --- p.58 / Chapter 7 --- Conclusion --- p.60 / A Scaling of ε and μ for a general coordinate transformation --- p.61 / Bibliography --- p.63

Fung, Tai Hang = 利用梯度超材料控制電場 / 馮泰恆. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 56-58). / Abstracts in English and Chinese. / Fung, Tai Hang = Li yong ti du chao cai liao kong zhi dian chang / Feng Taiheng. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- What are metamaterials? --- p.1 / Chapter 1.2 --- Negative refraction --- p.1 / Chapter 1.3 --- Transformation media --- p.2 / Chapter 1.4 --- Objectives of the thesis --- p.3 / Chapter 2 --- Mathematical formalism --- p.6 / Chapter 2.1 --- Boundary value problem of anisotropic media in spherical coordinates --- p.6 / Chapter 2.2 --- Boundary value problem of anisotropic media in cylindrical coordinates --- p.9 / Chapter 2.3 --- Anisotropic differential effective multipole moment theory --- p.11 / Chapter 2.4 --- Numerical solution of the radial equation for arbitrary profiles --- p.12 / Chapter 3 --- Perfect cloaking --- p.14 / Chapter 3.1 --- A review on Pendry´ةs cloaking model --- p.14 / Chapter 3.2 --- Perfect spherical cloak --- p.16 / Chapter 3.2.1 --- Perfect spherical cloak in uniform E-field --- p.16 / Chapter 3.2.2 --- Perfect spherical cloak and a point charge --- p.19 / Chapter 3.3 --- Perfect cylindrical cloak --- p.21 / Chapter 3.3.1 --- Perfect cylindrical cloak in uniform E-field --- p.22 / Chapter 3.3.2 --- Perfect cylindrical cloak and an infinite line charge --- p.24 / Chapter 3.4 --- ADEMMT analysis on perfect cloaking model --- p.27 / Chapter 3.4.1 --- Multipole factors of a perfect spherical cloak --- p.27 / Chapter 3.4.2 --- Equivalent dielectric constants of a perfect spherical cloak --- p.28 / Chapter 3.5 --- Remark --- p.29 / Chapter 4 --- Imperfect cloaking --- p.30 / Chapter 4.1 --- Designing cloaking materials via spectral representation theory --- p.31 / Chapter 4.2 --- Electric field distribution of an imperfect cloak --- p.32 / Chapter 4.3 --- ADEMMT analysis on imperfect cloaking model --- p.35 / Chapter 5 --- Confining electric fields spatially by graded metamaterials --- p.37 / Chapter 5.1 --- Graded solid cylinder --- p.38 / Chapter 5.1.1 --- Formalism --- p.38 / Chapter 5.1.2 --- Electric field distribution in graded cylinder --- p.40 / Chapter 5.1.3 --- Discussion --- p.43 / Chapter 5.2 --- Graded cylindrical shell --- p.44 / Chapter 5.3 --- Conclusion --- p.47 / Chapter 6 --- Future problems --- p.48 / Chapter A --- General coordinate transformation --- p.50 / Chapter A.1 --- The invariance of Maxwell´ةs equations --- p.50 / Chapter A.2 --- Scaling of ε and μ --- p.51 / Chapter B --- Designing cloaking model via spectral representation theory --- p.53 / Bibliography --- p.56

Two laptop antennas are presented using two different designs based on metamaterials. The first design consists of planar monopole loaded with an electric-LC resonator (ELC). This novel topology allows for the realization of a multi-band antenna by using the ELC to add multiple resonances. This structure is analyzed using full-wave simulations. A circuit model is also developed to gain further understanding. This technique is then used to design a Wi-Fi antenna. The second design uses a modified double-tuned matching network to create a single-band match for a planar monopole antenna. The matching network is implemented using a complementary-split-ring-resonator (CSRR). The design is once again analyzed using full-wave simulations and a circuit model is also developed. This technique is then applied to design a WiMax antenna. Both the Wi-Fi and WiMax antennas are fabricated and show good agreement between the simulated and measured results.