Design and optimization of broadband metamaterial absorber based on manganese for visible applications

A novel portable anechoic chamber using ultra-thin 2D microwave absorber for industrial 5.0

In this paper, the authors, for the first time, have shown the use of 2D conformal microwave absorbing material (MAM) in the design and fabrication of a portable Anechoic chamber (AC). The MAM is fabricated on the transparent and conductive metal oxide layer named indium-tin-oxide (ITO) with Polyethylene terephthalate as the substrate and the ground plane for zero transmission having overall thickness of 0.012 λ where λ is calculated at 0.7 GHz. The MAM is characterized for 0.7 to 18 GHz for both TE- and TM-polarisation and oblique incidence. High sheet resistance, dipole-like resonance structure patterned on the ITO, and the air-spacing between the layers is optimized to achieve broadband absorption. The MAM is used to line the six sides of the rectangular anechoic chamber having inner dimensions of: (L × W × H: 850 × 650 × 720 mm3). The return loss (RL), gain, and radiation pattern of three antenna working at 1.56, 2.43, and 4.93 GHz are analyzed inside the AC. The measurement results for all frequencies very well match with the simulation studies, thus validating and opening the door for the future use of ultra-thin and planar MAM in the AC.

Multi-band perfect absorber based on an elliptical cavity coupled with an elliptical metal nanorod

We proposed a triple-band narrowband device based on a metal-insulator-metal (MIM) structure in visible and near-infrared regions. The finite difference time domain (FDTD) simulated results illustrated that the absorber possessed three perfect absorption peaks under TM polarization, and the absorption efficiencies were about 99.76%, 99.99%, and 99.92% at 785 nm, 975 nm, and 1132 nm, respectively. Simulation results matched well with the results of coupled-mode theory (CMT). Analyses of the distributions of the electric field indicated the "perfect" absorption was due to localized surface plasmon polaritons resonance (LSPPR) and Fabry-Perot resonance. We developed a multi-band absorber with more ellipsoid pillars. The four band-absorbing device presented perfect absorption at 767 nm, 1046 nm, 1122 nm, and 1303 nm, and the absorption rates were 99.45%, 99.41%, 99.99%, and 99.94%, respectively. By changing the refractive index of the surrounding medium, the resonant wavelengths could be tuned linearly. The maximum sensitivity and Figure of Merit were 230 nm RIU-1 and 10.84 RIU-1, respectively. The elliptical structural design provides more tuning degrees of freedom. The absorber possessed several satisfactory performances: excellent absorption behavior, multiple bands, tunability, incident insensitivity, and simple structure. Therefore, the designed absorbing device has enormous potential in optoelectronic detection, optical switching, and imaging.

Metamaterial absorber optimization method based on an artificial neural network surrogate

Finding the optimal design parameters for the target EM response of a metamaterial absorber is still a challenging task even if the layout of the absorber has been determined. To effectively address this issue, we introduce the idea of surrogate-based optimization into the area of metamaterial absorber design. This paper proposes a surrogate based optimization method combining artificial neural network (ANN) and trust region algorithm for metamaterial absorbers. Each optimization iteration utilizes the optimal solution from the previous iteration and the sample points surrounding it as the training dataset to build an effective ANN surrogate model. To improve the convergence of the optimization method for metamaterial absorbers based on ANN surrogate model, we incorporate a trust region algorithm. The proposed method employs a simple forward neural network architecture and requires less training data, leading to a quick convergence towards the target solution after only a few iterations. Compared to the three commonly used alternative methods, the proposed method can optimize geometric and material parameters more efficiently in the same time. The validity of the proposed method is demonstrated by two examples of electromagnetic optimizations of metamaterial absorbers.