Manipulations Of Electromagnetic Waves By Metamaterial Lens And Metasurface And Their Applications

Metamaterials are artificial structures that are composed of subwavelength unit cells. Due to their unique electromagnetic properties of manipulating electromagnetic waves flexibly, they received long-held interests. More and more investigations on metamaterials have been reported. A series of devices based on metamateri-al were developed. Among them, metamaterial lenses and metasurfaces are two fundamental representations. Metamaterial lenses are a bulk structure, which are composed of a variety of artificial unit cells. The electro-magnetic waves will be controlled with high flexibility when propagating through the lenses. Metasurfaces are two-dimensional metamaterials, which have advantages of low profile, low loss, easy design and fabrica-tion. In this thesis, we will focus on manipulations of electromagnetic waves based on metamaterial lenses and metasurfaces. The main contents and contributions of the thesis are summarized as follows:· We propose and experimentally demonstrate a method to control the radiation patterns in broadband using metamaterials. By controlling the inhomogeneous refractive-index distribution of metamaterials, both am-plitudes and phases of electromagnetic waves on the antenna aperture are designed as required. We present an example to produce a new metamaterial lens antenna to possess high gain and low sidelobes simultane-ously. Experimental results show excellent performance of the antenna in a broad band from 12 GHz to 18 GHz.· A new approach is proposed to control the amplitude and phase distributions of electromagnetic fields over the aperture of a horn antenna. By loading a metamaterial lens inside the horn antenna, a tapered amplitude distribution of the aperture field is achieved, which can suppress the side-lobe radiations of the antenna. The metamaterial is further manipulated to achieve a flat phase distribution on the horn aperture to avoid the gain reduction that usually suffers in the conventional low-sidelobe antenna designs. A prototype of the metamaterial-loaded horn antenna is designed and fabricated. Both numerical simulations and measured results demonstrate the tapered aperture-field distribution and significant reduction of side-lobe and back-lobe radiations in the operating frequency band.· A new approach of generating broadband Bessel beams is presented. The broadband Bessel beams are produced by a gradient index metamaterial lens illuminated by broadband waveguide antenna. The meta-material lens serves as a convenor which transforms the spherical beams emitted from the feed into conical beams. The conical beams form quasi-Bessel beams in the near-field region. This kind of metamaterial lens can produce Bessel beams at arbitrary distance by designing the refractive-index distribution. To ver-ify the approach, we have designed, fabricated and tested a metamaterial lens. Full-wave simulation and experiment results have proved that the generated Bessel beams can be maintained in distance larger than 1 meter within a ranging from 12 GHz to 18 GHz.· We propose the concepts of codin g metamaterials, digital metamaterials and programmable metamaterials. We present "coding metamate-rials" that are composed of only two kinds of unit cells with 0 and π phase responses, which we name as "0" and "1" elements. By coding "0" and "1" elements with controlled sequences (i.e.,1-bit coding), we can manipulate electromagnetic (EM) waves and realize different functionalities. The concept of coding metamaterial can be extended from 1-bit coding to 2-bit or more. In 2-bit coding, four kinds of unit cells with phase responses 0, rc/2, n, and 3rc/2 are required to mimic "00", "01", "10" and "11" elements, which have larger freedom to control EM waves. We propose a unique metamaterial particle which has either "0" or "1" response controlled by a biased diode. Based on the particle, we present "digital metamaterials" with unit cells having either "0" or "1" state. Using the field-programmable gate array, we realize to control the digital metamaterial digitally. By programming different coding sequences, a single digital metama-terial has distinct abilities in manipulating EM waves, realizing the "programmable metamaterials". The above concepts and physical phenomena are confirmed by numerical simulations and experiments through metasurfaces.· We propose the concept of abnormal reflection of coding metasurface. The well-designed coding metasur-face reflects the incident plane waves in an abnormal way which is different from that of normal specular reflection. The phenomenon of abnormal reflection for coding metasurfaces include multi-beam reflection, broadened beam reflection, angular scanning based on dual-beam reflection. Based on abovementioned, more diversity of reflection can be achieved by combination of different codes along the two edges of cod-ing metasurface. The manipulation of the reflection beams can also be achieved by coding each element of the metasurface. We extend the design of coding metasurface to terahertz region by realizing diffusion of the terahertz waves using a two-dimensional coding metasurface.