David Rainwater

Experimental verification of three-dimensional plasmonic cloaking in free-space

We report the experimental verification of metamaterial cloaking for a 3D object in free space. We apply the plasmonic cloaking technique, based on scattering cancellation, to suppress microwave scattering from a finite-length dielectric cylinder. We verify that scattering suppression is obtained all around the object in the near- and far-field and for different incidence angles, validating our measurements with analytical results and full-wave simulations. Our near- field and far-field measurements confirm that realistic and robust plasmonic metamaterial cloaks may be realized for elongated 3D objects with moderate transverse cross-section at microwave frequencies.

Demonstration of an ultralow profile cloak for scattering suppression of a finite-length rod in free space

We present the first experimental realization and verification of a three-dimensional stand-alone mantle cloak designed to suppress the total scattering of a finite-length dielectric rod of moderate cross-section. Mantle cloaking has been proposed to realize ultralow-profile conformal covers that may achieve substantial camouflage, transparency and high-performance non-invasive near-field sensing. Here, we realize and verify a mantle cloak for radio-waves. We report an extensive campaign of far- and near-field free-space measurements demonstrating that conformal cloaks can indeed produce strong scattering suppression in all directions and over a relatively broad bandwidth of operation.

Plasmonic cloaking of cylinders: finite length, oblique illumination and cross-polarization coupling

Metamaterial cloaking has been proposed and studied in recent years by following several interesting approaches. One of them, the scattering-cancelation technique or plasmonic cloaking, exploits the plasmonic effects of suitably designed thin homogeneous metamaterial covers to drastically suppress the scattering of moderately sized objects within specific frequency ranges of interest. In addition to its inherent simplicity, this technique also holds the promise of an isotropic response and weak polarization dependence. Its theory has been applied extensively to symmetrical geometries and canonical three-dimensional (3D) shapes, but the application of it to elongated objects has not been explored with the same level of detail. We derive here closed-form theoretical formulae for infinitely long cylinders under arbitrary wave incidence, and validate their performance with full-wave numerical simulations, also considering the effects of finite lengths and truncation effects in cylindrical objects. In particular, we find that a single isotropic (idealized) cloaking layer may successfully suppress the dominant scattering coefficients of moderately thin elongated objects, even for finite lengths comparable with the incident wavelength, providing weak dependence on the incidence angle. These results may pave the way for application of plasmonic cloaking in a variety of practical scenarios of interest.

Scattering suppression and wideband tunability of a flexible mantle cloak for finite-length conducting rods

A simple, thin, flexible mantle cloak for conducting rods based on scattering cancellation is analyzed, designed and experimentally realized. We show strong scattering suppression at all angles of incidence, for both far-field plane-wave and near-field Gaussian excitations. The required effective shunt surface impedance is realized by a subwavelength patch array, targeting the suppression of the dominant omnidirectional scattering contribution of a conductive rod. Full-wave simulations predict a total radar cross-section reduction better than 14 dB in the lossless case and nearly 8 dB when considering a lossy substrate in the cover. Measurements of the realized cloak are consistent and validate these numerical predictions. The proposed geometry is also shown to be an ideal platform for monolithic integration of varactor diodes, allowing real-time tuning of the effective surface capacitance of the cloak. We show with numerical simulations the possibility of tunable scattering suppression over 1 GHz of bandwidth by seamlessly integrating varactor diodes in our mantle cloak design.

Experimental demonstration of a conformal mantle cloak for radio-waves

We present the first experimental realization and verification of a stand-alone 3D mantle cloak designed to suppress the total scattering of a finite-length dielectric rod. Mantle cloaking has been theoretically proposed as a convenient way to realize ultralow-profile, conformal covers to achieve complete camouflaging, transparency and non-invasive near-field sensing. After theoretically analyzing, designing and realizing a mantle cloak working for all polarizations and incidence angles, we have conducted an extensive campaign of near-field and far-field free-space measurements verifying strong suppression of scattering in all directions and over a relative broad bandwidth. The measured results agree well with analytical theory and full-wave simulations.