Metasurface Antennas: New Models, Applications and Realizations

This paper presents new designs, implementation and experiments of metasurface (MTS) antennas constituted by subwavelength elements printed on a grounded dielectric slab. These antennas exploit the interaction between a cylindrical surface wave (SW) wavefront and an anisotropic impedance boundary condition (BC) to produce an almost arbitrary aperture field. They are extremely thin and excited by a simple in-plane monopole. By tailoring the BC through the shaping of the printed elements, these antennas can be largely customized in terms of beam shape, bandwidth and polarization. In this paper, we describe new designs and their implementation and measurements. It is experimentally shown for the first time that these antennas can have aperture efficiency up to 70%, a bandwidth up to 30%, they can produce two different direction beams of high-gain and similar beams at two different frequencies, showing performances never reached before

Controlling the Electromagnetic Field Confinement with Metamaterials

The definition of a precise illumination region is essential in many applications where the electromagnetic field should be confined in some specific volume. By using conventional structures, it is difficult to achieve an adequate confinement distance (or volume) with negligible levels of radiation leakage beyond it. Although metamaterial structures and metasurfaces are well-known to provide high controllability of their electromagnetic properties, this feature has not yet been applied to solve this problem. We present a method of electromagnetic field confinement based on the generation of evanescent waves by means of metamaterial structures. With this method, the confinement volume can be controlled, namely, it is possible to define a large area with an intense field without radiation leakage. A prototype working in the microwave region has been implemented, and very good agreement between the measurements and the theoretical prediction of field distribution has been obtained

Binding of molecules to DNA and other semiflexible polymers

A theory is presented for the binding of small molecules such as surfactants to semiflexible polymers. The persistence length is assumed to be large compared to the monomer size but much smaller than the total chain length. Such polymers (e.g. DNA) represent an intermediate case between flexible polymers and stiff, rod-like ones, whose association with small molecules was previously studied. The chains are not flexible enough to actively participate in the self-assembly, yet their fluctuations induce long-range attractive interactions between bound molecules. In cases where the binding significantly affects the local chain stiffness, those interactions lead to a very sharp, cooperative association. This scenario is of relevance to the association of DNA with surfactants and compact proteins such as RecA. External tension exerted on the chain is found to significantly modify the binding by suppressing the fluctuation-induced interaction.Comment: 15 pages, 7 figures, RevTex, the published versio

Flat leaky-wave lenses

Dielectric leaky wave antennas based on modulation of surface reactance are presented. Changing the reactance surface pattern changes the radiated field properties. The operational principle is simple and promise to be suitable for reconfigurable surfaces. In this optic two devices based on a grounded dielectric slab with variable thickness are shown together with relevant numerical result

A stochastic extension of the Uniform Theory of Diffraction accounting for geometrical uncertainty or surface and edge roughness

We present a stochastic extension of the Uniform Theory of Diffraction (UTD) which is capable to account for some uncertainty in the objects position or geometry, including roughness of surfaces or edges. Namely, we derive a solution for the electromagnetic field scattered by a perfectly conducting wedge whose faces are described as a statistical perturbation of a standard flat wedge. We give a uniform closed form expressions for the evaluation of the main statistical moments of the total electric field. The proposed statistical UTD formulation is suitable for engineering applications which involve UTD ray based codes. Some numerical examples highlight the accuracy and the effectiveness of the proposed ray description

Leaky wave circularly polarized antennas based on surface impedance modulation

The concept of modulation of surface impedance is used to design very simple leaky wave lens antennas. The antennas are circularly polarized and realized on planar surfaces. Such antennas are designed by using a holographic principle and interpreting the holographic interference pattern in terms of modulation of surface impedance. The surface impedance is reconstructing by using two different approaches. In the first one, the modulation of the reactance is provided by varying the height of a grounded dielectric slab, realizing a full dielectric lens antenna. In the second one the surface impedance is synthesized by printing a dense texture of sub-wavelength metal patches on a flat grounded dielectric slab. The latter solution results in a completely flat planar antenna. Design guidelines for both lens antennas are presented and some numerical results discussed. © Copyright 2011 IEEE - All Rights Reserved