|Title:||Research on structure-property relationships of micro-architectured metamaterials|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
|Pages:||115 pages : color illustrations|
|Abstract:||Metamaterials is a type of artificial materials with properties that cannot be found in nature while gaining their properties from structure rather than composition. During the last decade, studies on metamaterials have extended from electromagnetics all the way to the fields of optics, ultrasonics, mechanics, etc. Their potential applications have been found in various industries such as wave tuning/filtering in communication, medicine, remote sensing, detection, cloaking in military guise, radiation or sound shielding, etc. In particular, the application of metamaterial in structural material designs can result in superior properties such as ultralight weight with ultrahigh stiffness, negative Poisson's ratio, for engineering uses in extreme environment. This thesis focused on micro-architectured metamaterials with an emphasis on the investigation of structure-property relationships of a wide range of physical properties including elastic, dielectric, piezoelectric as well as optical properties. Based on an understanding of the symmetry and scaling behavior of the metamaterials, some designs of metamaterials with superior properties such as high piezoelectric response, high Terahertz or optical sensitivity have been achieved. The research was mainly conducted by numerical simulation. Tools for solving the mechanical as well as the optical problems include the finite element method (FEM) using a commercial software package COMSOL, and a high-throughput calculation software framework coded with Matlab. Some interesting results obtained in the research are detailed as follows. First, the symmetry types of the six designed models were analyzed by applying Euler rotations to the calculated elastic tensors, from which very different anisotropic properties for the models were identified. The elastic tensors of the metamaterial designs were found to exhibit a higher degree of symmetry than that of the geometry. Second, the scaling behavior of the elastic, dielectric and piezoelectric metamaterials compared with their relative density were systematically studied, from which different scaling behavior such as "stretching-dominated", "bending-dominated" and "immediate" type have been identified. There also exist some physical properties that do not conforms to the scaling law, such as Poisson's ratio v, and the piezoelectric constant d33, while a super-high d33 of 400 has been found for the helix-network model. Third, the terahertz properties of the piezoelectric substrate PMN-PT have been experimentally characterized, from which we have fabricated metamaterial patterns and tuned the dielectric properties of the meta-surface, which can alter the THz responses by 12%. Fourth, quadrupole resonances in gold nanorod metamaterials have been found to enhance the sensing figure of merit by 82 compared to the conventional dipole type resonances, which may find potential application in high sensitive micro-assays.|
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