Naturally occurring water is a promising candidate for achieving broadband absorption. In this work, by virtue of the optically transparent character of the water, the water-based metamaterial absorbers (MAs) are proposed to achieve the broadband absorption at microwave frequencies and optical transparence simultaneously. For this purpose, the transparent indium tin oxide (ITO) and polymethyl methacrylate (PMMA) are chosen as the constitutive materials. The water is encapsulated between the ITO backed plate and PMMA, serving as the microwave loss as well as optically transparent material. Numerical simulations show that the broadband absorption with the efficiency over 90% in the frequency band of 6.4–30 GHz and highly optical transparency of about 85% in the visible region can be achieved and have been well demonstrated experimentally. Additionally, the proposed water-based MA displays a wide-angle absorption performance for both TE and TM waves and is also robust to the variations of the structure parameters, which is much desired in a practical application.

Absorption of electromagnetic waves in a medium is generally manipulated by controlling the frequency dispersion of constitutive parameters. However, it is still challenging to gain the desired constitutive parameters for customized absorption over a broad frequency range. Here, by virtue of spoof surface plasmonic polaritons (SPPs), we demonstrate capabilities of the spatialk-dispersion engineering for producing the customized broadband absorption. Incident waves can be efficiently converted to the spoof SPPs by plasmonic arrays and their propagation and/or absorption can be controlled by engineering the spatial dispersion ofk-vector. Based on this feature, we show how such concept is employed to achieve broadband as well as frequency-selective broadband absorptions as examples. It is expected that the proposed concept can be extended to other manipulations of propagating electromagnetic waves over a broad frequency range.

Controlling of electromagnetic wave radiation is of great importance in many fields. In this work, a hybrid metasurface (HMS) is designed to simultaneously reduce the microwave reflection and the infrared emission. The HMS is composed of the metal/dielectric/metal/dielectric/metal configuration. The reflection reduction at microwave frequencies mainly results from the phase cancellation technique, while the infrared emission reduction is due to the reflection of the metal with a high filling ration in the top layer. It has been analytically indicated that reflection reduction with an efficiency larger than 10 dB can be achieved in the frequency band of 8.2-18 GHz, and this has been well verified by the simulated and experimental results. Meanwhile, the designed HMS displays a low emission performance in the infrared band, with the emissivity less than 0.27 from 3 to 14 μm. It is believed that our proposal may find the application of multispectral stealth technology.

An optically transparent metamaterial structure with simultaneously broadband microwave absorptivity and low infrared (IR) emissivity is proposed. Two specifically designed optically transparent metasurfaces were combined to realize radar and IR bi-stealth. One was designed to control the microwave absorption though properly modifying the impedance and resonance peaks of the meta-atom. The other was designed to control the IR radiation. Within a wide incident angle of ±60°, the proposed structure displays high absorptivity greater than 90% in the region of 6.28–12.29 GHz for TE polarization. For TM polarization, the absorptivity in the region of 7.19–15.26 GHz is greater than 90%. The IR emissivity of the metamaterial structure is about 0.30 in the IR region from 3 µ m to 14 µ m. The perfect consistency between experimental results and simulation results demonstrates that the proposal has practical application of multispectral stealth technology.

In this paper, we propose the design of a hybrid surface with a low radar cross section (RCS) at lower frequencies and a transmission window at higher frequencies. The hybrid surface comprises two parts: a frequency selective surface (FSS) on the bottom and a checkerboard metasurface on the top. The FSS exhibits low-stop and high-pass properties, which reflects waves at lower frequencies and allows transmission of waves at higher frequencies. The checkerboard metasurface, with a reflective substrate, can reduce RCS at lower frequencies by means of scattering cancellation. Due to the low-stop property of the FSS, the hybrid surface can achieve broadband RCS reduction at low frequencies since the FSS acts as the reflective substrate. Simultaneously, the transmission window at higher frequencies of the FSS can be kept. Simulation results show that the RCS can be reduced by more than 10 dB in 4.1–7.7 GHz and the insertion loss in the transmission window is lower than 1.0 dB in 11.3–13.3 GHz. A prototype was fabricated and measured. The experimental results agree well with the simulation results. This work provides an effective alternative to the design of functional devices such as stealthy radomes, etc.

In this paper, a comprehensive scheme based on the dispersion engineering of spoof surface plasmon polariton (SSPP) is proposed which attempts to merge absorption bands of plasmonic structure into a continuous one. Theoretical investigation shows that multi-resonance can be tailored in a meandered wire structure, and thus, the closed interval of adjacent absorption is achieved. Then, the plasmonic absorbing structure (PAS) consisting of a meandered wire array with the gradient length are employed here to achieve spatial k-dispersion engineering of SSPP, and the original isolated absorption bands are demonstrated to be merged into a continuous one. On such a basis, a hybrid PAS consisting of a meandered wire array and a straight wire array is proposed. Simulation and experimental measurements show that the proposed hybrid PAS can achieve ultra-wideband absorption with an efficiency of more than 90% in the frequency range of 5.0–31.6 GHz, which is 107.7% broader with respect to the original PAS of the straight wire array at the same thickness. Our strategy overcomes the contradiction between broadening absorption bandwidth and keeping high absorption efficiency in PAS, enabling a wide range of applications, such as radar stealth technology, electromagnetic compatibility, and so on.