Electromagnetic Wave Propagation In Nonlinear Metamaterials

In the past ten years, people have come to know the propagation properties and the physical mechanism of the metamaterials, and the relevant theories and realizations of metamaterials have been utilized in many applications, such as electromagnetic invisibility cloaking, superlens that can overcome the diffraction limit, the left-handed microwave components and so on. So far, most research findings on metamaterials focused on the passive control and linear properties of these composite structures, i.e., the effective parameters of the structure do not depend on the intensity of the applied field or the propagating electromagnetic waves. However, recent preliminary explorations on nonlinear metamaterials have found the ability to dynamically control the material’s properties in real time through nonlinear response, which expand the space on the design and development of new electromagnetic components.The left-handed transmission line structure is one of the most important approaches to microwave metamaterials for its compact size, low loss and broad band. Most of all, such TL version of left-handed metamaterial provide a simple and easy-to-realize system to investigate the EM wave propagation in left-handed media. Therefore, this dissertation focuses on the unusual electromagnetic characteristics in left-handed nonlinear transmission line (LH NLTL) media. The main contributions of this dissertation are listed below: 1). We theoretically investigate the electromagnetic wave propagation in one-dimensional LH NLTL media. The nonlinear transmission line is periodically loaded with a nonlinear series capacitance composed of two back-to-back varactor diodes. By reducing the dispersion length and the nonlinear length, while increasing the dissipation of the transmission line, steady dark Schrodinger solitons are successfully realized in a short LH NLTL. The evolution of a Gaussian modulated pulse both in time and in frequency domain shows that increasing the dissipation in the metamaterials is helpful to attenuate the energy that prevents the steady soliton formation. The establishing of the Schrodinger solitons also results in harmonic generations in the transmission line, which may find potential applications in communication systems.2). we present the electromagnetic theory describing the generation and propagation of the fundamental wave and its high harmonics (the second harmonic and the third harmonic) in a two-dimensional nonlinear metamaterial. Then, we show the detailed design of the realizable two-dimensional LH NLTL metamaterial. We have found through microwave circuit simulations that due to its nonlinear performance, such NLTL metamaterial could switch between left-handed medium and right-handed medium by tuning the incident field intensity.3). we realize near-field focusing and near-perfect imaging at harmonic frequencies using the LH NLTL metamaterial. A detailed procedure is given to design LH NLTL and right-handed (RH) transmission line medium that matched at harmonic frequency. Then, with the aid of the microwave-circuit simulations we observe strong surface waves on the boundaries between RH and LH NLTL networks, which are consistent with the theoretical analysis of a LH linear superlens. We also show that the LH NLTL metamaterial can act as a flat nonlinear lens that can create, with a subwavelength resolution, an image of harmonic fields of the source being opaque for the fundamental frequency.4). By taking into account the loss and anisotropy of the metamaterials, we present the explicit expression of PBA in terms of complex permittivity and permeability through rigorous analysis. Based on the explicit expression and reasonalbe physical approximation, some interesting features and potential applications of the PBA are discussed.5). Films with high permeability, being thin and light, are very promising new microwave absorbers. We demonstrates analytically that the thickness of high-permeability thin films, which have the best absorption at certain frequencies, are less than a quarter dielectric wavelength. It also shows that the permeability of films has great impact on the bandwidth of absorption.