With the rapid development of detection technology and artificial intelligence, the widespread use of multispectral detectors has increased challenges to stealth capabilities. In this paper, an optically transparent ITO/dielectric/ITO sandwich structure with high microwave absorption and a spatially tunable infrared radiation is designed. The absorption in the 8.1-9.8 GHz band more than 90% in the microwave band is realized. By changing the ITO ratio on the surface of the absorbing layer, a customizable infrared emissivity can be realized. The tunable IR emissivity ranges from 0.2 to 0.7 with good thermal insulation. The structure has good wideband radar absorption, spatially adjustable infrared emissivity and optical transparency characteristics, and has broad application prospects in the field of multispectrum stealth.
An optically transparent metamaterial structure with broadband microwave absorptivity is proposed. A specifically designed optically transparent metasurfaces was designed to control the microwave absorption though properly modifying the impedance and resonance peaks of the meta-atom. Within a wide incident angle of ±60o, the proposed structure displays high absorptivity greater than 90% in the region of 33.7-44.7GHz for TE polarization. For TM polarization, the absorptivity in the region of 11.8-37.2GHz is greater than 90%. The perfect consistency between experimental results and simulation results demonstrates that the proposal has practical application of multispectral stealth technology.
Antireflection (AR), that is, to enhance the transmittance of electromagnetic (EM) waves through dielectric plate, and reduce loss, plays a critical role in improving the performance of devices such as communication, sensing and detection, and has long been pursued for a wide range of applications. However, existing methods tend to concentrate on the properties of materials itself, which encounters thorny difficulties to make breakthroughs in material system, angle of incidence, and bandwidth, particularly restricting their implementation in the long wavelength microwave regime. Herein, we propose a general and robust approach of overcoming impedance mismatching in broadband and extreme-angle AR device in microwave regime. By incorporating double-layered “U”-shaped structure and double-layered metal wires circular patch structure with symmetrical distribution into dielectric plate, Drude-Lorentzian resonances model is induced to decrease effective permittivity for transverse electric (TE)-polarization and increase that for transverse magnetic (TM)-polarization, so as to improve impedance on one side of the half-wave wall (left or right), link two adjacent half-wave walls and suppress reflection. As a proof-of-principle, an AR device was designed and analyzed in simulation. Encouragingly, a distinct transmission peak appears beside one side of the medium half-wave wall, and average dual-polarized transmission coefficients are increased by 30% compared with dielectric plate of equal size in 13- 21GHz under incident angle [70º, 80º], especially for TM-polarization, which has apparent AR effect in 8-20GHz. This work provides an effective approach of enhancing polarization-insensitive broadband transmission of EM waves at extreme angles and may be readily extended to terahertz and optical frequencies.
In recent years, the research on radar and infrared compatible stealth has attracted much attention. In this paper, metamaterials are designed by means of theoretical calculation and modeling simulation. The entire structure consists of an infrared shielding layer (IRSL), a radar absorbing layer (RAL) and a backplane. The simulation results show that when the angle between the incident microwave and the normal of the metamaterial is in the range of 0-40°, the average absorption rate of the structure in the 7-27 GHz band is relatively stable and reaches more than 90%. In the infrared band, the emissivity of the structure is lower than 0.28 and 0.32 at 3-5 μm and 8-14 μm, respectively. In addition, through the rational design of structure and materials, the metamaterial not only achieves dual stealth functions of low infrared emission and broad microwave absorption, but also has high transparency and flexibility, providing a new method for the study of multi-band stealth materials.
Infrared (IR) camouflage, which is used to conceal objects in infrared vision for confrontation with infrared detection in civilian and military applications, is gathered interest increasingly. Here, the tunable selective emitter depended on temperature is proposed. When the temperature is below 341K, the emitter has low emissivity in 3-5μm and 8-14μm, and high emissivity in 5-8μm. The bandwidth with the emissivity above 50% is 3μm; With the temperature above 341K, the average emissivity in 3-14μm is 0.23, which can achieve excellent infrared camouflage. The maximum modulation depth of emissivity is 51.56%. It is believed that the emitter can explore further applications in thermal management, adaptive thermal camouflage and energy harvesting.
In this paper, we proposed an infrared absorber based on multilayer film. Through the thickness resonance of ZnS dielectric layers and the loss properties of ultra-thin titanium film, a good absorption is achieved in the infrared band. The outermost ZnS is employed to reduce impedance mismatch and protects ultra-thin Ti film. This sample does not need inplane microstructure design, which reduces the processing difficulty and can be prepared on large scales.
In this paper, an active frequency selective surface (AFSS) with tunable frequency passbands is proposed. The AFSS structure is composed of three metallic layers that separated by two thin dielectric substrates. The tunable passband characteristics can be achieved by embedding PIN diodes on the top and bottom metallic layer. By switching the on-off state of PIN diodes on the top and bottom layer, the resonant frequency will change, thus realizing the passband tunability. Meanwhile, the AFSS structure has good angular stability in the large oblique incidence.
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