In this paper, we present a three dimension (3D) metamaterial absorber (MMA) based on the cross resistive film array. The MMA consists of the cross resistive film backed by a cross substrate and a metallic ground plane. Because of MMA has symmetrical structure, so the proposed MMA has polarization independent property in wideband absorption. Moreover, the designed MMA possesses wide angle domain property. By simulating, we obtain the absorption above 90% in the frequency range from 8 GHz to 50 GHz. Moreover, the proposed absorber possesses extremely broadband, especially in high frequency absorptivity is equal to one. Based on its broadband and polarization independent properties, it is expected that the proposed design may find potential applications, such as electromagnetic interference and stealth technologies.
Impedance mismatch generally exists upon interfaces between different media. This is especially true for TE-polarized waves with large incident angles since there is no Brewster effect. As a result, high-efficiency transmission can only be guaranteed within limited incident angle range. It is desirable that transparent windows possess robust angle-stability. In this work, we propose a strategy of realizing transparent windows with extreme angle-stability using anisotropic metasurfaces. Different from traditional isotropic materials, anisotropic metasurfaces require specific three-dimensional permittivity and permeability parameters. Theoretical formulas are derived to realize a highly efficient transmission response without angular dispersion. To validate our design concept, a two-layer cascaded electromagnetic anti-reflector is designed, and it exhibits a characteristic impedance matching for nearly all incidence angles under TE-polarization illumination. As a proof-of-concept, a prototype of extremely angle-stable transparent window is fabricated and measured. Compared with the pure dielectric plate, the reflection coefficients are on average reduced by 40% at 13.5 GHz for TE-polarized waves from 0° to 80°. Therefore, we think, anisotropic cascaded electromagnetic transparent windows are capable of tailoring the electromagnetic parameter tensors as desired, and provide more adjustable degrees of freedom for manipulating electromagnetic wavefronts, which might open up a promising way for electromagnetic antireflection and find applications in radomes, IR windows and others.
Tantalum hafnium carbide (Ta 4 HfC 5 ) powders were synthesized by solvothermal treatment and carbothermal reduction reactions from an inorganic hybrid. Tantalum pentachloride, hafnium chloride, and phenolic resin were used as the sources of tantalum, hafnium, and carbon, respectively. Pyrolysis of the complexes at 1000°C/1 h initiated the carbothermal reduction to result in multiplex phases including tantalum carbide and hafnium oxide which after heat treatment at 1400°C–1600°C transformed to single‐phase solid solution Ta 4 HfC 5 by solid solution reaction. The mean crystallite size of Ta 4 HfC 5 particles was less than 80 nm, and the composition of Ta, Hf, and C elements was near stoichiometric and homogeneously distributed in the powder samples. XRD pattern for Ta 4 HfC 5 powders was analyzed.
〈110〉 60° and 〈100〉 edge misfit dislocations in In0.06Ga0.94As heterostructures grown on patterned GaAs (001) substrates with relatively low misfit f(f=0.0043) have been investigated. The reduction of 〈110〉 misfit dislocation density on mesas is observed by cathodoluminescence, while the 〈100〉 misfit dislocation density on mesas observed by synchrotron radiation double crystal topography remains unchanged. The critical thickness is calculated by modifying the Matthews mechanical equilibrium theory introduced by Chidambarrao et al. The calculated results can be applied to both the nonpatterned area and the sidewalls of the mesa. The critical thickness of one side of the mesa is larger than that of nonpatterned areas. The critical thickness of both sides of mesas is dependent on the angle between the sidewall and (001) GaAs. This is likely due to different values of cos φ/sin ψ, which determines the values of the friction force FF with different sidewall angles. It is suggested that the 〈100〉 misfit dislocations are generated by climb and they can cross mesas by climbing along 〈100〉 directions.
The transmission of electromagnetic (EM) waves through a dielectric plate will be decreased significantly when the incident angle becomes extremely large, regardless of transverse electric (TE)- or transverse magnetic (TM)- polarization. In this regard, we propose a facile way of tailoring the permittivity of the dielectric material using metasurface to enhance the transmissions of both TE- and TM-polarized waves under extremely large incidence angles. Due to parallel or antiparallel electric fields induced by the metasurface, the net electric susceptibility is altered, and hence the effective permittivity can be tailored to improve the impedance matching on the two air-dielectric interfaces, which enhances the wave transmissions significantly under extreme incident angles. As an example, we apply this method to a typical ceramic-matrix composite (CMC) plate. By incorporating orthogonal meta-gratings into the CMC plate, its effective permittivity is reduced for the TE-polarized waves but increased for the TM-polarized waves under the extreme incidence angle, which can reduce the impedance for the TE-polarization and increase the Brewster angle for the TM-polarization. Therefore, the impedance matchings for both TE- and TM-polarizations are improved simultaneously and dual-polarized transmission enhancements are achieved under the extreme angles. Here, the transmission responses have been numerically and investigated using the finite-difference-time-domain (FDTD) method. A proof-of-principle prototype is designed, fabricated, and measured to verify this method. Both numerical simulations and measurement results show that the prototype can operate under extremely large incidence angles θi ∈[75°,85°] with significant transmission enhancement for both TE- and TM-polarizations compared to the pure dielectric plate. This work provides a facile way to enhance the transmissions under extreme angles and can be readily extended to terahertz and optical frequencies.
Metamaterials provide amazing opportunities for developing frequency selective radiation because of their unique electromagnetic resonance properties. However most frequency-selective thermal radiation metamaterials currently do not have an optical transparency property, which prevents them from being used in some special occasions. Here, an optically transparent frequency-selective thermal radiator is designed and fabricated using the metallic-like properties of ITO. The emissivity of the metamaterial in the atmospheric transparent windows (3.0-5.0μm and 8.0-14.0μm) is less than 0.1, while the emissivity outside the windows (5.5-7.6μm) is very high, thus achieving strong thermal radiation efficiency. Finally, the thermal radiation power of frequency-selective thermal radiator, low-emissivity coatings, and black body was analyzed using the thermal radiation model. Compared to traditional low-emissivity coatings, the advantage of frequency-selective thermal radiators is that it provides an efficient thermal radiation window for the target, further enhancing its infrared stealth capability through radiative cooling.
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