Design of Thin and Wideband Microwave Absorbers Using General Closed-Form Solutions

Abstract

A new design method for RLC reactive absorbers is presented. This method is based on closed-form solutions to help realize the widest absorption bandwidth for an arbitrarily specified thickness. The solutions for the RLC values of the reactive screen are derived using an equivalent circuit in which the thickness of the substrate used, the permittivity and tangential loss of the substrate, and the frequency are all considered. A perfect match and maximum bandwidth at a design frequency can be achieved with the proposed method. Various aspects of the absorber characteristics, depending on the thickness and loss of the substrate, are analyzed using the presented solutions and electromagnetic (EM) simulations. To validate the proposed design method, an X-band microwave absorber with a crossed-dipole structure patterned on a silver nanowire resistive film is designed, fabricated, and measured. The substrate electrical thickness of the absorber is 70° at 10 GHz, with a permittivity of 2.2. The 90% absorption bandwidth is 8 GHz in the frequency range of 8.2–16.2 GHz. The measured absorption agrees well with the results obtained using circuit and EM simulations.

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 ].…”

“…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.…”

“…Even though the metasurface absorbers described above have been successfully verified, each of them suffers from some inherent limitations. First, the metasurface absorber with a lossy metapattern must be printed on or combined with the top surface of the substrate [ 15 , 16 , 17 , 18 , 19 ]. In such cases, it may be difficult to integrate the metasurface absorber with other electronic components, such as microwave circuits or antennas.…”

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

“…이를 위해 기판의 유전율은 낮추고, 그 높이는 증가시키거나 [5], [12] , 패턴의 층수 증가 [6] , 또는 저항을 추가 [4], [7] 하여 흡수 대역폭을 넓히는 방법이 보고되었다. 하지 만 기존 연구는 개방형 공진기(split resonator) [1]∼ [5] , 막대 [6], [7] , 또는 십자가 구조 [8] 등 정형화된 패턴을 이용하므로 패턴 설계 자유도가 낮아 흡수 대역폭을 물리적인 한계 치까지 극대화하는 데 한계가 있다.…”