Optically Transparent Broadband Microwave Absorption Metamaterial By Standing‐Up Closed‐Ring Resonators

Abstract

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...

Graphene‐Based Materials toward Microwave and Terahertz Absorbing Stealth Technologies

“…Generally, the electromagnetic absorption performance can be characterized by the coaxial line, waveguide, NRL‐Arch, and free space methods. [7f,16c,24] Among them, the coaxial line and waveguide methods are usually used to obtain the electromagnetic parameters and the calculated RL results of lossy material ( Figure a). Based on the tested scattering parameters ( S parameters) from the vector network analyzer, the relative complex permittivity (ε r ) and permeability (μ r ) can be obtained.…”

“…The free space method can also be employed to evaluate the electromagnetic performance, as shown in Figure c,d. The experimentally measured reflection and transmission parameters can be used to calculate the electromagnetic parameters and the contribution of absorption.…”

Microwave Absorption of Crystalline Fe/MnO@C Nanocapsules Embedded in Amorphous Carbon

“…Overexposure to electromagnetic wave can not only affect the functioning of electronic equipment but also be potentially detrimental to human being and raise severe problems concerning the field of military applications [1][2][3]. Therefore, it has spurred internationally unprecedented interest in exploring microwave absorbing materials, which converts electromagnetic wave into energy in other forms [4,5]. For practical applications, desirable microwave absorbing materials are supposed to possess key features of high absorptive capacity, broad effective bandwidth, light weight, and low filler loading ratio [6][7][8].…”

Composite structure-based transparent ultra-broadband metamaterial absorber with multi-applications

“…In recent years, the OTMAs based on different material systems have drawn more attentions from researchers [11][12][13]. Compared with the traditional opaque MMA, OTMA can be applied to the occasions that require high transparency such as the window glass of stealth armament and photovoltaics [14][15][16][17].…”