Design, Modeling and Fabrication of Metamaterials, 14-R8008

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Principal Investigators
A. Leigh Griffith
Jerome A. Helffrich
Diana Strickland
Jeremy Pruitt
Michael Miller

Inclusive Dates:  12/03/08 – Current

Background - Electromagnetic metamaterials are hybrid materials with unit periodicity designed to exhibit unique properties when they interact with an electromagnetic (EM) field, such as light, at a wavelength much larger than the unit structure. These materials consist of inclusions within a host background (e.g., polymer, ceramic, or air). Metamaterials have emerged recently as a subject of intense research by the physics, chemistry, and materials communities because they promise to become the building blocks for novel device applications, such as future-generation microprocessors based on the propagation of light (instead of current), small radio-frequency antennas, high-sensitivity chemical sensors, and optical cloaking, among many others. SwRI uses metamaterials in two different applications: electrically small antennas and plasmon-mediated chemical catalysis.

Small antennas are often necessary, yet they possess undesirable characteristics. It is difficult to match their impedance to the electronics. Small antennas with well-matched impedance and frequency tuning independent of the antenna's size are possible using metamaterials.

An important phenomenon in certain types of metamaterial structures is the proficiency in which surface plasmons (spatially intense oscillations of free electrons) are excited. SwRI's interests are directed toward the fundamental question of whether surface plasmons can be elicited from metamaterials at infrared (IR) frequencies to affect the binding interactions or chemical transformation of adsorbed molecules.

Approach - A novel, electrically small patch antenna incorporating metamaterials as the key component was selected from the literature for the feasibility study. The goal was to determine whether metamaterials improve electrically small antennas and whether they are practical to implement. SwRI designed, built and tested this metamaterial antenna at several frequencies and compared its antennas to conventional, electrically small antennas. Experimental validation of plasmon-mediated chemical binding and catalysis effects was accomplished by establishing a framework for modeling the EM scattering properties of three-dimensional periodic structures and exploring suitable techniques for fabricating the structures. Ab initio and classical computations were employed to determine what shapes and sizes of 3-D periodic structures could elicit surface plasmons at IR frequencies.

Accomplishments - SwRI researchers found that antenna resonance can be tuned independently of antenna dimensions. Excellent impedance match was achieved for antennas as small as a 30th of a wavelength (λ/30). The types of metamaterials used to load the antenna included spiral ring resonators printed on circuit board, an array of barium strontium titanate cubes, and Sievenpiper (or "mushroom") structures on printed circuit board. The SwRI team is one of the first to report results for this innovative antenna. In the plasmonics research, SwRI demonstrated via systematic computations that free-standing (3-D) wire grids of cubic symmetry can be tailored to evince surface plasmons with infrared frequencies. It was further shown that the oscillating EM field of these plasmons may directly couple with the ground-state fundamental vibrations of adsorbed molecules. Fabrication of these structures will involve proximity nano-patterning and optical phase-mask lithography.

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