A Novel Strategy in Electromagnetic Wave Absorbing and Shielding Materials Design: Multi-Responsive Field Effect

In recent years, tunable metamaterials have attracted intensive research interest due to their outstanding characteristics, which are dependent on the geometrical dimensions rather than the material composition of the nanostructure. Among tuning approaches, micro-electro-mechanical systems (MEMS) is a well-known technology that mechanically reconfigures the metamaterial unit cells. In this study, the development of MEMS-based metamaterial is reviewed and analyzed based on several types of actuators, including electrothermal, electrostatic, electromagnetic, and stretching actuation mechanisms. The moveable displacement and driving power are the key factors in evaluating the performance of actuators. Therefore, a comparison of actuating methods is offered as a basic guideline for selecting micro-actuators integrated with metamaterial. Additionally, by exploiting electro-mechanical inputs, MEMS-based metamaterials make possible the manipulation of incident electromagnetic waves, including amplitude, frequency, phase, and the polarization state, which enables many implementations of potential applications in optics. In particular, two typical applications of MEMS-based tunable metamaterials are reviewed, i.e., logic operation and sensing. These integrations of MEMS with metamaterial provide a novel route for the enhancement of conventional optical devices and exhibit great potentials in innovative applications, such as intelligent optical networks, invisibility cloaks, photonic signal processing, and so on.

/pdf/actively-mems-based-tunable-metamaterials-for-advanced-and-1hkkipn5.pdf

Actively MEMS-Based Tunable Metamaterials for Advanced and Emerging Applications

In this paper, a hybrid mechanism metasurface (HMM) that incorporates absorption, polarization conversion and phase cancellation mechanisms is proposed for wideband and wide-angle radar cross section (RCS) reduction. The polarization conversion absorber (PCA) is proposed by embedding the lumped resistors into the polarization conversion structure, which integrates the absorption and polarization conversion mechanisms. Then, the phase cancellation mechanism is employed to redirect the scattering energy to the non-incident directions through the chessboard configuration, which exploits the opposite phase between the PCA and its mirror structure. Unlike previous HMMs that depended on nested or cascaded structures, the proposed strategy integrates the absorption and polarization conversion mechanisms in the same structure, and the two mechanisms are complementary to each other. Through the integration of multiple mechanisms, the HMM can achieve more than a 10 dB monostatic and bistatic RCS reduction in 8.7-32.5 GHz and 8.6-31.2 GHz, respectively. Furthermore, the specular and bistatic RCS reduction performances under oblique incident waves are also studied, and the stable scattering suppression performances are determined. The proposed hybrid mechanism strategy exhibits significant scattering suppression capability through the incorporation of multiple mechanisms, which have potential applications in the multifunctional metasurface.

Wideband and wide-angle radar cross section reduction using a hybrid mechanism metasurface.

Reconfigurable intelligent surfaces (RISs) that dynamically manipulate scattered waves have attracted much attention regarding accommodating coverage holes in wireless communication systems using radio wave frequencies higher than millimeter waves. RISs generally actualized through metasurface technologies must be visually unaffected so that they can be installed in various locations such as existing walls and glass windows in environments where propagation should be controlled. We propose a novel method that dynamically controls scattering characteristics of metasurfaces while achieving a large area and high optical transparency. For transparency in the visible light range, we use transparent glass as a substrate and meshed metal patterns. Furthermore, by stacking a metasurface substrate onto another transparent substrate and controlling the interlayer distance, we achieve dynamic control of the scattered waves over a large area in the 28-GHz band. Fabricated prototypes successfully operate when switching transmission and reflection modes, exhibiting extremely low loss of less than -1 dB. In metasurface lenses that can be attached to glass windows in outdoor-to-indoor scenarios, the lens gain of 25.4 dB is achieved for a static lens, and dynamic switching operation between single focus and dual focus is also successfully verified for a dynamic lens.

Transparent dynamic metasurface for a visually unaffected reconfigurable intelligent surface: controlling transmission/reflection and making a window into an RF lens.

• A flexible metamaterial absorber is designed and prepared via the 3D printing. • A low and high frequency cooperative electromagnetic absorption in 4–40 GHz. • Temperature insensitivity and broad absorption at wide incidence angles is realized. • Excellent conformal absorption is achieved by the designed flexible metamaterial absorber. Water-based electromagnetic wave absorbers have attracted significant attention due to their potential applications for conformal absorbing structures. In this paper, a flexible broadband electromagnetic wave metamaterial absorber (MMA) based on sandwiched cylindrical water resonators is designed and prepared via the 3D printing, which realizes a low and high frequency cooperative electromagnetic absorption in 4–40 GHz. Additionally, the proposed absorber shows a comprehensive performance with temperature insensitivity and broad absorption characteristics at wide incidence angles. The broadband perfection electromagnetic absorption is discussed based on the improved impedance matching induced by the sandwiched water resonators, and the enhanced electromagnetic wave loss introduced by connected water resonators would further improve the absorption efficiency. Particularly, the radar cross section (RCS) of the designed flexible MMA with different curvature also shows excellent conformal absorption in the evaluated frequency range. Therefore, the proposed flexible ultra-broadband MMA based optimized 3D patterned cylindrical water resonators shows excellent comprehensive performances, which could be widely utilized in electromagnetic protection applications for conformal devices. 

Ultra Broadband Electromagnetic Wave Absorbing and Scattering properties of Flexible Sandwich Cylindrical Water-based Metamaterials

An optically transparent broadband metamaterial absorber for radar-infrared bi-stealth

Optically transparent metamaterials with the performance of infrared radar compatible stealth have been designed and manufactured on the basis of the continuous in-depth research on single-band stealth technology. In this paper, metamaterials are designed through theoretical calculations and modeling simulations. The designed structure can achieve higher than 90% broadband (8.7-32 GHz) absorption at wide-angle (45 degrees), emissivity of 0.3 in infrared atmospheric window, and optical transparency. In addition, the material can be bent, which greatly expands its application scenarios. The experimental results are consistent with the theoretical calculation and simulation results.

Ultra-wideband flexible transparent metamaterial with wide-angle microwave absorption and low infrared emissivity.

Multifunctional ultra-thin metasurface with low infrared emissivity, microwave absorption and high optical transmission

In this paper, a metamaterial structure with radar and infrared (IR) compatible stealth characteristics is designed based on the principle of plasmonic absorbing structure (PAS). Due to the lack of reports on PAS-based IR radar compatible stealth, this article combines PAS and IR frequency selective surfaces to achieve the desired purpose. Through mathematical modeling and dispersion engineering of the unit cell proposed, a PAS with ultra-wideband wave absorption is realized. The low emissivity of the IR atmospheric window band is realized by means of the simulation and analysis of the IR frequency selective surface with different indium tin oxide (ITO) occupation ratios. The absorptivity of designed structure is higher than 90% from 4GHz to 28.6GHz, and the emissivity of the IR atmospheric window is only 0.3. The experience of the fabricated sample is consistent with the theoretical analysis and the simulation. Our method enriches the implementation strategies of radar-IR compatibility and has reference significance for multi-spectrum compatible stealth.

Zhiqiang Gao

Papers

An optically transparent broadband metamaterial absorber for radar-infrared bi-stealth

Ultra-wideband flexible transparent metamaterial with wide-angle microwave absorption and low infrared emissivity.

Multifunctional ultra-thin metasurface with low infrared emissivity, microwave absorption and high optical transmission

Compatible stealth design of infrared and radar based on plasmonic absorption structure.

Multifunctional anisotropic coding metasurface with low emissivity and high optical transmittance