In this paper a cascaded retrodirective metasurface is designed and demonstrated to operate simultaneously at a wide range of incident angles between -30 • to -10 • and 10 • to 30 • . It is based on the design of several retrodirective super-cells following the generalized Snell's law of reflection, where each super-cell is designed to redirect an incoming wave back in the same direction with high efficiency. This metasurface is a very good candidate as a retroreflector for radar cross-section enhancement of targets with poor backscattering. Retrodirective topologies have been a subject of interest and several engineered topologies exist such as the corner dihedral. Despite their good performances at a range of incident angles, their 3-dimensional bulky structure make them hard to implement for different applications and they do not address extreme incident angles. The metasurface proposed can be a complementary solution to existing topologies for addressing extreme oblique incident angles while being more compact due to its two dimensional (2D) subwavelength structure design. The monostatic RCS performance of the designed metasurface of dimensions 8.163 cm × 56.23 cm has been compared to that of a conventional corner dihedral of dimensions 8 cm × 15.5cm × 7.75 cm, a gain up to 50 dB of monostatic radar cross section (RCS) in the ranges -30 • to -20 • and 20 • to 30 • was obtained. Comparable performances are observed in the ranges -20 • to -10 • and 10 • to 20 • between the designed metasurface and the corner dihedral. Experimental results are shown to be in good agreement with simulation results.
Electromagnetic (EM) RF (radio frequency) energy harvesting in dynamic ambient environments is a challenge for conventional energy harvesting systems such as rectennas. The main challenges are the low efficiency of the collector and low ambient power levels, which makes it hard to consider in industrial applications. Several research works have focused on the design of high-efficiency antennas to achieve an efficient and maximum possible level of RF EM energy harvesting. Their main objective is to improve the EM energy harvesting system by overcoming the low efficiency of the collector, which is the main part of the rectenna system. In this work, we propose and investigate a methodology in terms of EM energy harvesting based on the concentration and focusing of EM energy in a small zone where it can be easily collected and transferred indirectly to the rectenna system. It consists of a focusing device and a methodology to associate the latter with existing RF energy harvesting systems. We demonstrate a focusing metasurface design implemented alongside an off-the-shelf rectenna device at 900 MHz, where an enhanced energy harvested power level up to a linear gain of 8 is achieved compared to the case when only the rectenna is used. Numerical results as well as measurements results in an anechoic chamber are shown. Experimental power received levels are given both in the focusing plane and in time for the validation of the concept.
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