Design and fabrication of a 2D-isotropic flexible ultra-thin metasurface for ambient electromagnetic energy harvesting

In this paper, the design of a new flexible ultra-thin curvature metasurface energy harvester is presented. The use of cylindrical metasurface electromagnetic (EM) harvester would be desirable for the ambient EM energy harvesting since it can absorb the EM energy with maximum efficiency. The harvester is made by an 11×11 unit-cell metasurface with a flexible substrate to demonstrate the 2D-isotropic harvesting; as a small slice of the cylinder. We have proposed a sub-wavelength (∼0.13λ0) complementary quad split ring resonator (CQSRR) unit-cell which is loaded with a lump resistor mounted on the metal-backed substrate. The full-wave simulation shows that the efficiency of the flat metasurface energy harvester with thickness of 0.004λ0 at 5.33 GHz (WiFi) is up to 0.86 for normal radiation. It is 0.72 and 0.62 for 70° oblique angle of incidence from H- and E-plane. In addition to this, the experimental results show an agreement with the results of full-wave simulations. Due to the non-uniform mutual coupling between the cells in the finite array of the fabricated energy harvester and efficiency definition for the central cell as a metric of evaluating the device performance, an effective area for the central cell has been obtained experimentally which is 4.3 times greater than the physical area of a single unit-cell in an infinite array.