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.
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.
The Fatamogana Mirage is a complex and changeable mirage that forms in a special environment.Starting from the formation environment of Fatamoogana, we construct the medium system of refractive index gradient change, conduct simulation experiments, and reproduce the process and scene of Fatamoogana formation, and the characteristics of the mirage and the propagation of the light in refractive index gradient are analyzed.Subsequently, based on the propagation process and mechanism of light in a variable refractive index gradient medium, starting with the monotonic changing media environment of the refractive index, this paper establishes a variety of medium change gradient models, solving the path equation of light according to the infinitesimal element method , then, using symmetric principles and classification discuss ideas,the paper establishes the propagation path model of light in a complex index gradient medium, and the light path propagation equation is calculated through the model.On this basis, the paper analyzes the propagation characteristics of light in complex refractive index gradient media, and the mathematical relationship between the observer, mirage source and mirage is calculated, which explains the reasons for the complex and changeable nature of Fatamogana mirage.Finally, the paper analyzes the significance of research results in the design of laser aiming system and radio communication communication.
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