Analysis of Bandwidth of Pixelated Metallic Metasurface Absorber for Its Unit Cell Size

Abstract

The absorption bandwidth of a metasurface absorber can be adjusted by varying the thickness of the substrate, shape of the conductive pattern attached on top of the substrate, or conductivity of the pattern. In this study, the bandwidth of a pixelated metallic metasurface absorber was analyzed with respect to its unit cell size. The genetic algorithm (GA) was used to determine the best combination of the metallic pixels among 16 × 16 square pixels for each unit cell size. The size of the unit cell was adjusted around the 1/2 wavelength, which guarantees the suppression of the grating lobe for the normal-incidence condition. Based on full-wave simulation results, the -10 dB reflectance bandwidth was expanded as the size of the unit cell was increased from 3/8 to 3/4 wavelength with an interval of 1/8 wavelength at the center frequency of 5.8 GHz. The results demonstrate that the absorption bandwidth of the metasurface absorber is expanded by increasing the size of the unit cell around the 1/2 wavelength.

Broadband Metasurface Absorber Based on an Optimal Combination of Copper Tiles and Chip Resistors

“…Electromagnetic (EM) metasurfaces are two-dimensional (2D) versions of metamaterials, i.e., engineered artificial materials that can realize unnatural constitutive parameters such as negative permittivity and/or permeability [ 1 , 2 , 3 ]. Based on their versatile functionalities, the metasurfaces have been adopted in many research topics such as transmissive [ 4 , 5 ] or reflective [ 6 , 7 ] antennas, cloaks [ 8 , 9 ], sensors [ 10 , 11 ], and absorbers [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Among them, EM metasurface absorbers have attracted great attention from the perspective of a wide range of possible applications such as sensing [ 14 ], energy harvesting [ 28 ], and stealth technologies [ 29 ].…”

“…An electromagnetic (EM) metasurface absorber is a kind of absorbing resonator of which the conductive pattern on the top side of a dielectric substrate is critically coupled with an incident EM wave [ 12 , 13 ]. Since its bottom side is blocked by a metallic sheet [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ], a reflected EM wave ends up interfering with the incident one. By satisfying the constructive interference condition between the incident and reflected waves at the top surface, the electric current induced on the metapattern can be maximized [ 15 , 31 ].…”

“…For a metapattern composed of lossy material, such as carbon paste [ 15 , 16 ], indium tin oxide (ITO) [ 17 , 18 ], or silver nanowire [ 19 ], the incident EM wave is absorbed by the ohmic loss inside the pattern. When both the top metapattern and the substrate consist of a metal, such as copper, as well as a lossy substrate, such as flame retardant 4 (FR4) [ 20 , 21 , 22 , 23 ], the EM wave is dominantly dissipated by the dielectric loss. Since the electric (E) field inside the substrate is coupled with the maximized electric current induced on the metapattern, the dielectric loss can be boosted as long as the constructive interference condition is maintained.…”

“…However, the metasurface absorber utilizing a metal metapattern suffers from a narrow absorption bandwidth [ 20 , 21 , 22 , 23 ]. To overcome this limitation, metasurface absorbers connected with chip resistors have been proposed [ 24 , 25 , 26 , 27 ].…”

“…In this paper, a broadband metasurface absorber consisting of an optimal combination of square copper tiles connected with four chip resistors is designed and experimentally verified. The most significant advantage of the proposed metasurface absorber is that it can be designed via an automatic procedure by utilizing the genetic algorithm (GA) [ 15 , 16 , 22 , 23 , 32 , 33 ], which mimics the meiosis of a chromosome using a pair of two-bit sequences. After pixelating the top surface of the absorber with square tiles and fixing the resistance and location of the chip resistors, the copper-or-air states of the square tiles are determined automatically by matching them with the one- or zero states of a bit sequence optimally identified using GA.…”