We present a metamaterial for simultaneous optical transparency and microwave absorption in broadband, which can be used as an optically transparent radar-wave absorber. The proposed metamaterial absorber is made of windmill-shaped elements with the reflection spectra featured by three absorption bands. By properly tailoring the resonances of the structure, we achieve the optimized metamaterial absorptivity that is greater than 90% from 8.3 to 17.4 GHz. In the meantime, excellent optical transmittance is achieved by use of the indium tin oxide (ITO) film with moderate surface resistance, implying that the optical properties of the metamaterial are hardly affected by the periodic meta-atoms. Both numerical simulations and experimental results demonstrate the good performance of the proposed metamaterial, thereby enabling a wide range of applications such as ultrathin detectors and photovoltaic solar cells in the future.
We present a thin metasurface with large microwave absorptivity and low infrared emissivity simultaneously. By properly tuning the resonance peaks and impedance of the meta-atom, broadband microwave absorptivity greater than 90% from 8.2 to 16.0 GHz is achieved. In the meantime, owing to large coverage of periodic metal patches on the top surface, low infrared emissivity is exhibited in the infrared region (IR) of 8 µm–14 µm. The excellent agreement between numerical simulation and experimental result demonstrates the good performance of the proposed metasurface. Due to the usage of polymethacrylimide (PMI) and polyethylene terephthalate (PET) as the substrate, the metasurface is especially advantageous for the light weight, making it a favorite in real engineering applications.
scattering so as to improve the performance or reduce the EM pollution. [1][2][3][4][5] With the extensive investigation in the past decades, various types of MAs have been developed and widely applied. Among them, magnetic MAs typically represented by composites containing ferrites or magnetic metal particles manifest much broader absorption bandwidth than nonmagnetic absorbers at the same thickness because of their high magnetic permeability. [6][7][8] However, they are reaching the ceiling of microwave absorption performance due to physical laws such as Snoek's limit, [9] as well as limited maneuverability of the material parameters. Moreover, they are all opaque due to the requirement of magnetic fillers with dark color. This makes them impossible to have the applications in window glass of stealth aircrafts and warships, [10] wireless local area network system, [11] radio frequency identification systems, [12] and electronic toll collection (ETC) system. [13] Recently, there have been increasing interests in metamaterials (MMs), which consist of sub-wavelength artificial unit cells. [14] With the proper design of the unit cells, the permittivity and permeability of MMs can be manipulated separately in a vast range beyond the conventional materials, bringing about some extraordinary properties, e.g., near-zero refractive index, [15] negative refraction, [16,17] and stimulating their applications in invisibility cloaks, [18,19] photon computer, [20] and super lens. [21] The design flexibility and abundant potential of the MMs also provide a chance to further improve the performance of MAs. [22][23][24][25] As a matter of fact, metamaterial absorbers (MMAs) have been demonstrated to show advantages such as near perfect absorption, [26] thin thickness, and light weight, [27] while the absorption bandwidth of MMAs has also been expanded significantly by developing a quantity of methods including the integration of multiple resonance units, [28,29] multilayered gradually varied structures, and more since their first demonstration. [30][31][32] Furthermore, for the absorption properties of MMAs depend highly on the structure and dimension of the unit cells rather than the optically obstructive microwave absorbing fillers as in conventional absorbers, the MMAs may also possess optical transparency. For example, the simple metamaterial consisting of indium tin oxide (ITO) square patches and a reflective backing spaced by a Optically transparent metamaterial microwave absorbers (MMAs) developed so far unexceptionally encounter an intrinsic contradiction between extending the absorption bandwidth and improving optical transparency, hindering their practical applications. This work, in its experiment and calculation, demonstrates an MMA with both broadband microwave absorption and excellent optical transparency by standing-up closed-ring resonators (CRRs) in an indium tin oxide backed Plexiglas board. The as-designed MMA shows a strong microwave absorption of 85% covering a wide frequency of 5.5-19.7 and 22.5-27.5 GHz u...
Metamaterial absorbers and diffusers provide powerful routes to decrease the backward reflection significantly with advantages of ultrathin profile and customized bandwidth. Simultaneous control of the absorption and scattering behaviors of the metamaterials which helps to improve the suppression capabilities of backward reflection, however, still remains a challenge. Aiming at this goal, we propose a metasurface constituted by two kinds of elements in a pseudorandom arrangement. By the use of indium tin oxide with moderate sheet resistance in the meta-atoms, enhanced absorption of energy can be achieved in a broad spectrum when interacted with illuminated waves. In the meanwhile, electromagnetic diffusion will be invoked from the destructive interference among the elements, giving rise to significant reduction of specular reflection as a result. Excellent agreements are observed between simulation and experiment with pronounced reflection suppression from 6.8 GHz to 19.4 GHz. In addition, the optical transparence of the patterns and substrates makes the proposed metasurface a promising candidate for future applications like photovoltaic solar cells and electromagnetic shielding glasses.
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