It is a tough task to greatly improve the working bandwidth for the traditional flat microwave absorbers because of the restriction of available material parameters. In this work, a simple patterning method is proposed to drastically broaden the absorption bandwidth of a conventional magnetic absorber. As a demonstration, an ultra-broadband microwave absorber with more than 90% absorption in the frequency range of 4–40 GHz is designed and experimentally realized, which has a thin thickness of 3.7 mm and a light weight equivalent to a 2-mm-thick flat absorber. In such a patterned absorber, the broadband strong absorption is mainly originated from the simultaneous incorporation of multiple λ/4 resonances and edge diffraction effects. This work provides a facile route to greatly extend the microwave absorption bandwidth for the currently available absorbing materials.

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...

Articles you may be interested inA novel ultrathin and broadband microwave metamaterial absorber J. Appl. Phys. 116, 094504 (2014); 10.1063/1.4894824 Ultra-broadband terahertz metamaterial absorber Appl. Phys. Lett. 105, 021102 (2014); 10.1063/1.4890521Bandwidth-enhanced polarization-insensitive microwave metamaterial absorber and its equivalent circuit model

Responsive chromic materials are highly desirable in the fields of displays, anti-counterfeitings, and camouflages but their advanced applications usually limit by the unrealized delicate and independent tunability in the three...