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In high contrast to traditional geometric meta-surfaces, which can only operate on the cross-polarized field, we propose a bi-functional meta-device with full energy utilization in both co- and cross-polarized fields. In this paper, co-polarized refraction and cross-polarized focusing are integrated in one single meta-surface by taking advantage of compound propagation and geometric phases. A multi-layer element structure with various geometric degrees of freedom is designed to realize simultaneous and independent phase modulation of both co- and cross-polarized transmitted waves. The derived criterion is verified in the microwave region, and the proof-of-concept experiments indicate that the proposed meta-surface can have distinct functionalities with orthogonal polarizations in the transmitted field with a specific circularly polarized illumination. This scheme for bi-functional meta-surface construction provides an effective method to manipulate both co- and cross-polarized output fields simultaneously, which can extremely enhance the modulation efficiency of output energy. Different output wavefronts can be conveniently switched by filtering only the polarization state of the output end, simplifying the operational complexity of the bi-functional meta-system. This criterion paves the way for flexible manipulation of electromagnetic waves with a higher degree of freedom and facilitates a larger diversity of applications across the whole frequency spectrum.

A reflective metasurface enabling linear-to-circular polarization (LP-to-CP) conversion is proposed. The metasurface polarizer is composed of active unit cells incorporating voltage-controlled varactor diodes, where the dispersion responses of the cells can be tailored. When illuminated by an incident wave, the metasurface converts the LP wave from the source to a CP one. Moreover, in a single voltage configuration, two circular polarized waves with different handedness can be obtained at distinct frequencies. Such operation can be tuned in frequency by changing the applied voltage along the metasurface. Simulations are performed to verify the concept, and measurements done on a fabricated prototype validate the polarization conversion performances at microwave frequencies.

We demonstrate numerically and experimentally an ultra-thin (≈ λ/240) metasurface-based invisibility cloak for low frequency antenna applications. We consider a monopole antenna mounted on a ground plane and a cylindrical metallic obstacle of diameter smaller than the wavelength located in its near-field. To restore the intrinsic radiation patterns of the antenna perturbed by this obstacle, a metasurface cloak consisting simply of a metallic patch printed on a dielectric substrate is wrapped around the obstacle. Using a finite element method based commercial electromagnetic solver, we show that the radiation patterns of the monopole antenna can be restored completely owing to electromagnetic modes of the resonant cavity formed between the patch and obstacle. The metasurface cloak is fabricated, and the concept is experimentally demonstrated at 125 MHz. Performed measurements are in good agreement with numerical simulations, verifying the efficiency of the proposed cloak.

International audience; A transformation optics based lens for beam control is experimentally realized and measured at microwave frequencies. Laplace's equation is adopted to constnict the mapping between the virtual and physical spaces. The metamaterial-based lens prototype is designed using electric LC resonators. A planar microstrip antenna source is used as transverse electric polarized wave launcher for the lens. Both the far field radiation patterns and the near-field distributions have been measured to experimentally demonstrate the beam steering properties. Measurements agree quantitatively and qualitatively with numerical simulations, and a non-narrow frequency bandwidth operation is observed. (C) 2015 AIP Publishing LLC.

International audience; The broadband directive in-phase emission from an array of sources conformed cylindrically is numerically and experimentally reported. Such manipulation is achieved through the use of a lens designed by transformation optics concept. The all-dielectric lens prototype is realized through three-dimensional (3D) polyjet printing and presents a graded refractive index. A microstrip antenna array fabricated using standard lithography techniques and conformed on a cylindrical surface is used as TE-polarized wave launcher for the lens. To experimentally demonstrate the broadband focusing properties and in-phase directive emissions, both the far-field radiation patterns and the near-field distributions have been measured. Experimental measurements agreeing qualitatively with numerical simulations validate the proposed lens and open the way to inexpensive all-dielectric microwave lenses for beam forming and collimation. (C) 2015 AIP Publishing LLC.

A printed planar Z-shaped meta-atom has recently been proposed as an alternative design to the conventional electric-LC resonator for achieving negative permittivity. Transforming the LC topology of the resonator helps to facilitate transposition of geometrical parameters for the optical regime and also to improve the metamaterial homogeneity. In this work, we discuss about the excitation of a dark or trapped mode in such Z-shaped meta-atom. The electromagnetic behavior of the meta-atom has been investigated through both simulations and experiments in the microwave regime. Our results show that the Z meta-atom exhibits a trapped mode resonance. Depending on the orientation of the polarized electromagnetic field with respect to the Z atom topology and the incident plane, the excitation of the dark mode can lead either to a narrowband resonance in reflection or to a very asymmetric Fano-like resonance in transmission, analog of electromagnetically induced transparency. Compared to other structures, the Z me...

The in-phase radiation from a conformal metamaterial surface is numerically and experimentally reported. The LC-resonant metasurface is composed of a simultaneously capacitive and an inductive grid constituted by copper strips printed on both sides of a dielectric board. The metasurface is designed to fit a curved surface by modifying its local phase. The latter phase-compensated metasurface is used as a reflector in a conformal Fabry-Pérot resonant cavity designed to operate at microwave frequencies. Far-field measurements performed on a fabricated prototype allow showing the good performances of such a phase-compensated metasurface in restoring in-phase emissions from the conformal surface and producing a directive emission in the desired direction.

The directive emission from a bilayered metamaterial surface is numerically and experimentally reported. The LC-resonant metasurface is composed of both a capacitive and an inductive grid constituted by copper strips printed on both sides of a dielectric board. By the incorporation of varactor diodes in the capacitive grid, resonance frequency and phase characteristics of the metamaterial can be tuned. The tunable phase metasurface is used as a partially reflecting surface in a Fabry–Perot resonance cavity. Far field radiation patterns obtained by direct measurements show the reconfigurability of emission frequency while maintaining an enhanced directivity.