Parallel FDTD Simulations on Optical and Acoustic Metamaterials
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1223-EE06-09
Parallel FDTD Simulations on Optical and Acoustic Metamaterials Kenji Tsuruta*, Shinji Nagai, Ryosuke Umeda, Tomoyuki Kurose, Noriaki Maetani Department of Electrical and Electronic Engineering, Okayama University, Okayama 700-8530, Japan. ABSTRACT We perform large-scale finite-difference time-domain (FDTD) simulations with the aid of efficient parallel-computing algorithms for designing optical and acoustic metamaterials, where either electromagnetic or elastic constants in the materials are artificially modulated via nano/micro-structuring. For optical metamaterials, effects of nanostructure on dielectric properties are taken into account by introducing the Drude-Lorentz model and a hybrid quantum-mechanical/classical FDTD method for optical dispersion of simple metal particles. Using these computational methods, we assess the materials dependence of light-confinement efficiency in the recently proposed novel structure that combines dielectrics and metamaterials periodically. In the acoustic case, we perform the parallel FDTD simulations of elastic-wave propagations in 2D phononic crystals. The negative refraction of acoustic wave is shown to occur via a negative effective mass appeared in their phonon band-structures. We demonstrate that the focal intensity by the lens effect and its energy-transfer efficiency can be optimized by adapting the filling fraction of the crystal. INTRODUCTION Possible features of the photonic metamaterial, which has negative permittivity and permeability simultaneously, has been predicted in 1968 [1]. A negative refractive index is one of these features. Conventional optical lenses have positive refractive index, so it needs curved surfaces to get an image focused, whereas a negative refraction allows flat slab to focus electromagnetic waves [2]. This phenomenon has been demonstrated experimentally for microwave frequencies [3]. Various types of structures and materials combinations have been proposed and tested for optical frequencies [4]. Nevertheless, metamaterials operating with low energy loss for visible light have not been fabricated so far. Given that such deficiency has been improved, optical metamaterials are anticipated as novel materials used for superlens, tunneling devices, compact resonators, and highly directional optical sources. Recently, analogous phenomena for acoustic and elastic wave propagation in phononic crystals have been predicted [5]. In Ref. [5], a negative refraction and an imaging effect of acoustic waves were achieved in the phononic crystal consisting of square arrays of rigid or liquid cylinders embedded in air background. Also, an acoustic negative refraction was observed experimentally in steel cylinders placed in air background [6]. This effect is expected to lead to novel mechanisms for acoustic devices, acoustic sensors, and acoustic energy carriers to piezoelectric generator, for example. In this paper, we analyze the electromagnetic response of nanostructured metamaterials at optical frequency via the FDTD simulations [7]. Effects
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