Inverse Design of Three-Dimensional Nanoantennas for Metasurface Applications

Recent advances in manufacturing techniques have been made to match the demand for high performance optical devices. To this end, tremendous research activity has been focused on optical metasurfaces as they offer a unique potential to achieve disruptive designs when paired with innovative fabrication techniques and inverse design tools. However, most metasurface designs have revolved around canonical geometries. While these elements are relatively easy to fabricate, they represent only a small portion of the design space, and rarely offer peak performance in transmission, phase range or field of view. In this work, a Lazy Ant Colony Optimization (LACO) technique is applied in conjunction with a full-wave solver using the Periodic Finite Element Boundary Integral (PFEBI) method to reveal high performing three-dimensional nanoantenna designs with potential applications for a variety of optical devices

A Computationally Efficient Method for Simulating Metal-Nanowire Dipole Antennas at Infrared and Longer Visible Wavelengths

This paper presents a numerically efficient approach for simulating nanowires at infrared and long optical wavelengths. A computationally efficient circuit-equivalent modeling approach based on the electric-field integral-equation (EFIE) formulation is employed to simulate the highly dispersive behavior of nanowires at short wavelengths. The proposed approach can be used both for frequency-domain and for time-domain EFIE formulations. In comparison with widely used full-wave solutions achieved through the finite-difference time-domain method, the circuit-based EFIE formulation results in a sharp reduction of the computational resources while retaining high accuracy.This work was supported in part by the Spanish Ministry of Education under Project PR2009-0443, in part by the Penn State MRSEC under NSF Grant 0213623, in part by the EU FP7/2007-2013 under Grant GA 205294 (HIRF SE project), in part by the Spanish National Projects TEC2010-20841- C04-04, CSD200800068, and DEX-5300002008105, and in part by the Junta de Andalucia Project P09-TIC5327

Reconfigurable and Tunable Metamaterials: A Review of the Theory and Applications

Metamaterials are being applied to the development and construction of many new devices throughout the electromagnetic spectrum. Limitations posed by the metamaterial operational bandwidth and losses can be effectively mitigated through the incorporation of tunable elements into the metamaterial devices. There are a wide range of approaches that have been advanced in the literature for adding reconfiguration to metamaterial devices all the way from the RF through the optical regimes, but some techniques are useful only for certain wavelength bands. A range of tuning techniques span from active circuit elements introduced into the resonant conductive metamaterial geometries to constituent materials that change electromagnetic properties under specific environmental stimuli. This paper presents a survey of the development of reconfigurable and tunable metamaterial technology as well as of the applications where such capabilities are valuable

Design and Optimization of 3-D Frequency- Selective Surfaces Based on a Multiobjective Lazy Ant Colony Optimization Algorithm

Frequency-selective surfaces (FSSs) have many applications in spatial filtering of electromagnetic waves and are commonly used in antennas, polarizers, radomes, and intelligent architecture. Conventional FSS designs have ranged from canonical shapes and fractal patterns on planar surfaces to miniaturized and multilayer designs, with stable filtering responses up to 50°. Much less work has been done on 3-D FSS designs, which include multiresonant structures or cavities that offer improved angular stability, with fields of view up to 60°. Recent advances in additive manufacturing techniques have made fully 3-D FSS designs increasingly popular; however, powerful design tools to exploit such fabrication methods are currently unavailable. In this paper, multiobjective lazy ant colony optimization (MOLACO), an adaptive combinatorial optimization algorithm based on ant colony optimization, is introduced and applied to the problem of polarization and angle independent 3-D FSS design. It will be shown that the MOLACO algorithm generates several innovative and unintuitive unit cell geometries with a single-zero, single-pole response, less than 1% shift from center frequencies and −10 dB rejection and 3 dB transmission bandwidths between 6%–12% for angles of incidence up to 80° in TE and TM polarizations. Comparisons are made between designs generated by MOLACO and existing FSS designs

Fabrication and Characterization of Polarization Independent 3D Printed Frequency Selective Structures with Ultra-Wide Fields of View

Recently, a robust and versatile Multi-Objective Lazy Ant Colony Optimization (MOLACO) technique was introduced for inverse design of three-dimensional (3D) Frequency Selective Structures (FSSs) with remarkable polarization independent filtering performance for incidence angles up to 80°. However, fabricating and characterizing these elements presents many challenges that have yet to be addressed. For example, conventional free space measurement techniques require intractably large arrays to uniformly illuminate the sample and mitigate edge diffraction at extreme incidence angles. To mitigate these effects, a broadband focused beam measurement technique is proposed to characterize a finite 24x48 element 3D FSS array optimized for C-band operation. Elements are fabricated using PolyJet 3D Printing, metallized, and encapsulated in a Sylgard-527 substrate over a Polymethylmethacrylate (PMMA) lattice resulting in a low-loss, low-cost, low-profile and light-weight array that is suitable for conformal surfaces and can be easily repaired. A comparison of simulated and measured results is presented, and a discussion of the implications of the array and measurement system are offered. The fully fabricated 3D FSS array achieves a 6.25% -10 dB rejection band and 8.26% 3 dB pass band at 5.6 GHz and 7.75 GHz respectively, for both TE and TM polarizations and incidence angles up to 72°