Ultra-broadband metamaterial absorbers from long to very long infrared regime

Broadband metamaterials absorbers with high absorption, ultrathin thickness and easy configurations are in great demand for many potential applications. In this paper, we first analyse the coupling resonances in a Ti/Ge/Ti three-layer absorber, which can realise broadband absorption from 8 to 12 μm. Then we experimentally demonstrate two types of absorbers based on the Ti/Ge/Si3N4/Ti configuration. By taking advantage of coupling surface plasmon resonances and intrinsic absorption of lossy material Si3N4, the average absorptions of two types of absorbers achieve almost 95% from 8 to 14 μm (experiment result: 78% from 6.5 to 13.5 μm). In order to expand the absorption bandwidth, we further propose two Ti/Si/SiO2/Ti absorbers which can absorb 92% and 87% of ultra-broadband light in the 14–30 μm and 8–30 μm spectral range, respectively. Our findings establish general and systematic strategies for guiding the design of metamaterial absorbers with excellent broadband absorption and pave the way for enhancing the optical performance in applications of infrared thermal emitters, imaging and photodetectors.

Design of Low-Cost Miniaturized Metamaterial-Based Circular Split-Ring Monopole Radiating System for LTE Applications

A compact low-cost metamaterial circular monopole antenna for LTE applications is presented here. This paper addresses an asymmetric circular split-ring radiator for 2.6[Formula: see text]GHz (LTE-7 band), 3.5[Formula: see text]GHz (LTE-22 band). The design here employs split rings with varying split gaps in the consecutive ring layers of the radiating element which helped in achieving better impedance matching for obtaining multiband operation. The work presented here demonstrates the feasibility of achieving double negative material property, without loading the SRR’s separately in the system. The antenna was modeled using a 1.6[Formula: see text]mm thick FR-4 lossy material. The simulated results were compared with measured results and found to be in good agreement with each other. Employing asymmetric split ring as radiator helped in achieving 29% of size reduction in the patch layer. The modified split-ring radiator achieved directional radiation pattern and minimum side-lobe levels with a peak gain of 1.29 and 0.204[Formula: see text]dB at the lower band and upper band, respectively. The compact dimension [Formula: see text] of the radiating system makes it suitable for LTE-WLAN/Wi-Max applications.

Wheeler Method for Evaluation of Antennas Submerged in Lossy Media

A Wheeler method for the evaluation of the radiation efficiency of submerged antennas within lossy media is presented and demonstrated for the first time in the literature. Extensive investigations have been devised by empirical and simulation methods. Normal-mode helical antenna (NMHA) was first designed and fabricated to exemplify a real-life application at the UHF band (0.3 to 3 GHz). The antenna under test (AUT) was evaluated within an artificial lossy material using a series of Wheeler caps featuring different radii to study the validity of this method. The error between the experimental and simulation radiation efficiency is below 3% near the theoretical radian length. The presented measurement method of radiation efficiency without any essential measurement facilities or accessories could be a promising candidate for fast and accurate evaluation for any wire-type antenna submerged within lossy media.

Robust Conformal Perfect Absorber Involving Lossy Ultrathin Film

Perfect absorbers have been extensively investigated due to their significant value in solar cell, photodetection, and stealth technologies. Various subwavelength structures have been proposed to improve the absorption performances, such as high absorptance, broad band, and wide absorption angle. However, excellent performances usually put forward higher requirements on structural designs, such as varying the geometry sizes or shapes to fit different center wavelengths, which inevitably increases the fabrication burden. Here, a planar sandwich structure involving a layer of highly lossy material is proposed to achieve a robust perfect absorption with 95% absorptance ranging from the visible to near infrared range. Such an excellent absorption performance is also polarization-independent and applicable to a wide incident angle. Furthermore, the proposed design can also be applied to conformal surfaces with a 90% fluctuation over a steep surface. We believe that the proposed perfect absorber with distinguished performances can find wide application.

Design of Tapered Periodic Meta-Surfaces for Suppressing Edge Electromagnetic Scattering

In this paper, a novel approach for designing tapered periodic meta-surfaces (TPMS) is proposed for suppressing electromagnetic scattering from a trailing edge of a square metallic plate with a given thickness. The TPMS is realized by periodic square metallic patches with tapered dimensions at the direction perpendicular to the considered edge but keeping its period unchanged. Based on the geometric phase interaction, the mechanism of suppressing electromagnetic scattering is analyzed. The lossy material is not required in this design, so it doesn’t generate thermal energy and benefits infrared stealth of military objects. The backscattering properties from the trailing edge with the proposed TPMS loading are analyzed and compared with that of original trailing edge. It is observed that wide angular trailing edge scattering suppressing can be obtained and the average value of mono-static radar cross section (RCS) reduction is 10 dB for L-band, S-band and C-band. Finally, the bi-static RCS properties and energy distribution of the proposed structure are also proposed to explain the mechanism of the electromagnetic scattering suppression of the trailing edge employed with the TPMS.

Attenuation Measurement of Lossy Coatings of Carbon for Ka-Band Helix TWT Applications

In a high efficiency traveling wave tube (TWT) amplifier, any reflections present in the device may cause oscillations and hence instability. A coating of lossy material on appropriate parts of the tubes (known as attenuators) is done to suppress these reflections. Carbon is a very commonly used material for this type of coating, and may be deposited by a number of techniques. In the present work, coatings of carbon were done on the dielectric substrate and evaluated for the attenuation performance at microwave frequencies. Three dielectric rods (APBN material) were coated with carbon by pyrolytic deposition method for different thickness. An experimental setup involving a rectangular wave-guide with a hole has been used for measuring the attenuation of the coated rods in the Ka-band frequency range. The same structure has been simulated using the Ansoft High Frequency Simulator (HFSS) and both the experimental and simulated results have been compared.