Patrick T. Bowen

Large-Area Metasurface Perfect Absorbers from Visible to Near-Infrared.

An absorptive metasurface based on film-coupled colloidal silver nanocubes is demonstrated. The metasurfaces are fabricated using simple dip-coating methods and can be deposited over large areas and on arbitrarily shaped objects. The surfaces show nearly complete absorption, good off-angle performance, and the resonance can be tuned from the visible to the near-infrared.

Discrete Dipole Approximation Applied to Highly Directive Slotted Waveguide Antennas

We present an analysis of a slotted waveguide antenna (SWA) whose directivity has been enhanced by using metamaterial parasitic elements. We apply an adapted form of the discrete dipole approximation (DDA) as a modeling tool and verify the accuracy and versatility of this method for different configurations, including matched and shorted SWAs, and with and without parasitic elements. The results presented in this letter demonstrate the capabilities of the DDA for the fast and accurate simulation of aperture antennas composed of small radiators, and its further application for the design of complex metamaterial structures.

Transformation-optics simulation method for stimulated Brillouin scattering

We develop an approach to enable the full-wave simulation of stimulated Brillouin scattering and related phenomena in a frequency-domain, finite-element environment. The method uses transformation-optics techniques to implement a time-harmonic coordinate transform that reconciles the different frames of reference used by electromagnetic and mechanical finite-element solvers. We show how this strategy can be successfully applied to bulk and guided systems, comparing the results with the predictions of established theory.

Wake control with permeable multilayer structures: The spherical symmetry case.

We explore the possibility of controlling the wake and drag of a spherical object independently of each other, using radial distributions of permeability in the Brinkman-Stokes formalism. By discretizing a graded-permeability shell into discrete, macroscopically homogeneous layers, we are able to sample the entire functional space of spherically-symmetric permeabilities and observe quick convergence to a certain manifold in the wake-drag coordinates. Monte Carlo samplings with 10^{4}-10^{5} points have become possible thanks to our new algorithm, which is based on exact analytical solutions for the Stokes flow through an arbitrary multilayer porous sphere. The algorithm is not restricted to the Brinkman-Stokes equation and can be modified to account for other types of scattering problems for spherically-symmetric systems with arbitrary radial complexity. Our main practical finding for Stokes flow is that it is possible to reduce a certain measure of wake of a spherical object without any energy penalty and without active (power-consuming) force generation.

Polarizability extraction of complementary metamaterial elements in waveguides for aperture modeling

We consider the design and modeling of metasurfaces that couple energy from guided waves to propagating wavefronts. This is a first step towards a comprehensive, multiscale modeling platform for metasurface antennas—large arrays of metamaterial elements embedded in a waveguide structure that radiates intro free-space—in which the detailed electromagnetic responses of metamaterial elements are replaced by polarizable dipoles. We present two methods to extract the effective polarizability of a metamaterial element embedded in a oneor two-dimensional waveguide. The first method invokes surface equivalence principles, averaging over the effective surface currents and charges within an element to obtain the effective dipole moments; the second method is based on computing the coefficients of the scattered waves within the waveguide, from which the effective polarizability can be inferred. We demonstrate these methods on several variants of waveguidefed metasurface elements, finding excellent agreement between the two, as well as with analytical expressions derived for irises with simpler geometries. Extending the polarizability extraction technique to higher order multipoles, we confirm the validity of the dipole approximation for common metamaterial elements. With the effective polarizabilities of the metamaterial elements accurately determined, the radiated fields generated by a metasurface antenna (inside and outside the antenna) can be found self-consistently by including the interactions between polarizable dipoles. The dipole description provides an alternative language and computational framework for engineering metasurface antennas, holograms, lenses, beam-forming arrays, and other electrically large, waveguide-fed metasurface structures.

Analytic modeling of metmaterial absorbers

We present a fully analytical model that describes ideal absorbing metasurfaces composed of film-coupled optical nanoantennas. The model predicts the spectrum and the angular dependence of the absorption and is compared to full-wave numerical simulations.