###### Abstract  
An ultra-wideband electromagnetic (EM) absorber is proposed. The proposed absorber consists of two thin metasurfaces, four dielectric layers, a glass fiber reinforced polymer (GFRP), and a carbon fiber reinforced polymer (CFRP) which works as a conductive reflector. The thin metasurfaces are accomplished with 1-bit pixelated patterns and optimized by a genetic algorithm. Composite materials of GFRP and CFRP are incorporated to improve the durability of the proposed absorber. From the full-wave simulation, more than 90% absorption rate bandwidth is computed from 2.2 to 18 GHz such that the fractional bandwidth is about 156% for the incidence angles from \(0^{\circ}\) to \(30^{\circ}\). Absorptivity is measured using the Naval Research Laboratory (NRL) arch method in an EM anechoic environment. It was shown that the measured results correlated with the simulated results. In addition, the proposed absorber underwent high temperature and humidity tests under military environment test conditions in order to investigate its durability. absorber; composite; genetic algorithm; metamaterials; metasurfaces; ultra-wideband Article Ultra-Wideband Electromagnetic Composite Absorber Based on Pixelated Metasurface with Optimization Algorithm  
202318 August  
periodic array of double square loops operating at 8-18 GHz. The loops are printed on a dielectric and four lumped resistors are added to four sides of the loop [6]. [PERSON] et al. described a dual-band EM absorber for C- and X-band applications which consists of two circular ring resonators with a thickness of \(\lambda 0/142.65\) at the lowest frequency. Its absorption is larger than 90% at 4.19 and 9.75 GHz with bandwidth of 665 MHz and 860 MHz, respectively [7]. These proposed absorbers utilize a conventional metallic pattern with an etching process and a surface mount device technology with lumped elements such as capacitor, resistor, diode, etc. Although this design can be realized with low cost, it has limited performance in terms of bandwidth extension. Focus on the design of realistic perspective and feasibility, a conventional microwave absorption based on printed circuit board (PCB) was performed in the C-, X-band region [8; 9; 10]. A single layered low-profile broadband co-polarization absorber was proposed and achieved more than 90% of absorption over the whole band from 5.6 to 9.1 GHz [8]. A meta-dome structure was presented for ultra-wideband (4.6-12 GHz) radar absorption using an FR-4 protective layer with lumped resistors [9]. To reduce the RCS level, a snowflake shaped unit-cell was proposed on the dielectric substrate. The absorptivity of 98% was achieved at 10.52 GHz with the normal incidence case [10]. Several research studies in designing an electromagnetic absorber using printing technologies with a resistive ink or paste have been introduced [11; 12; 13; 14; 15; 16; 17; 18]. Electromagnetic absorbers were presented using a transparent conductor with relatively high resistive losses [11; 12; 13; 14]. An absorber using indium tin oxide (ITO) films was reported [11; 12]. The proposed absorber achieved a 90% absorption bandwidth within 2.53-8.94 GHz and high angular stability (60\({}^{\circ}\)) [11]. [PERSON] et al. proposed a sandwich absorber that could realize more than 90% absorption over 8-18 GHz for both TE- and TM-polarization when the incident angle was less than 30\({}^{\circ}\) [12]. Absorbers based on graphene were developed for high transparency and good flexibility in practical applications in the microwave band [13; 14]. This was a broadband study involving controlling the sheet resistance of the graphene. To overcome the narrow bandwidth characteristic, a carbon paste for the printed conductive patterns of EM absorber was used [15; 16; 17; 18]. Inherently inhomogeneous structure based on 4-split ring resonators as the unit-cell was proposed and with the structure working in the 6.9-29 GHz range more than 80% absorption rate could be easily fabricated through conventional inkjet printing processes [15]. [PERSON] et al.