The advent of negative index materials has spawned extensive research into metamaterials over the past decade. Metamaterials are attractive not only for their exotic electromagnetic properties, but also their promise for applications. A particular branch–the metamaterial perfect absorber (MPA)–has garnered interest due to the fact that it can achieve unity absorptivity of electromagnetic waves. Since its first experimental demonstration in 2008, the MPA has progressed significantly with designs shown across the electromagnetic spectrum, from microwave to optical. In this Progress Report we give an overview of the field and discuss a selection of examples and related applications. The ability of the MPA to exhibit extreme performance flexibility will be discussed and the theory underlying their operation and limitations will be established. Insight is given into what we can expect from this rapidly expanding field and future challenges will be addressed.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201200674

Metamaterial Electromagnetic Wave Absorbers

Metasurfaces: From microwaves to visible

We present an ultrabroadband thin-film infrared absorber made of sawtoothed anisotropic metamaterial. Absorptivity of higher than 95% at normal incidence is supported in a wide range of frequencies, where the full absorption width at half-maximum is about 86%. Such property is retained well at a very wide range of incident angles too. Light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths. This phenomenon is explained by the slowlight modes in anisotropic metamaterial waveguide. Our study can be applied in the field of designing photovoltaic devices and thermal emitters.

/pdf/ultrabroadband-light-absorption-by-a-sawtooth-anisotropic-1dp1emuh97.pdf

Ultrabroadband light absorption by a sawtooth anisotropic metamaterial slab

We present an ultra broadband thin-film infrared absorber made of saw-toothed anisotropic metamaterial. Absorbtivity of higher than 95% at normal incidence is supported in a wide range of frequencies, where the full absorption width at half maximum is about 86%. Such property is retained well at a very wide range of incident angles too. Light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths. This phenomenon is explained by the slowlight modes in anisotropic metamaterial waveguide. Our study can be applied in the field of designing photovoltaic devices and thermal emitters.

Ultra-broadband Light Absorption by a Sawtooth Anisotropic Metamaterial Slab

Electromagnetic absorbers have drawn increasing attention in many areas. A series of plasmonic and metamaterial structures can work as efficient narrowband absorbers due to the excitation of plasmonic or photonic resonances, providing a great potential for applications in designing selective thermal emitters, biosensing, etc. In other applications such as solar-energy harvesting and photonic detection, the bandwidth of light absorbers is required to be quite broad. Under such a background, a variety of mechanisms of broadband/multiband absorption have been proposed, such as mixing multiple resonances together, exciting phase resonances, slowing down light by anisotropic metamaterials, employing high loss materials and so on.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.201400026

Plasmonic and metamaterial structures as electromagnetic absorbers

We propose ultrathin multiband metamaterial absorbers in the microwave frequencies in which the design, analysis, fabrication, and measurement of the absorbers working in multiple bands are presented. The metamaterial absorbers consist of a periodic arrangement of different scales of electric-field-coupled-LC (ELC) resonators and a metallic background plane, separated by only 1 mm dielectric spacer. By tuning the scale factor of the ELC unit cells, we achieve independently multiple absorptions at different customized frequencies. Experiments demonstrate excellent absorption rates in the designed frequency bands over wide angles of incident waves for both transverse electric and magnetic polarizations. The explanation to the physical mechanism of the multiband metamaterial absorber is presented and verified.

Ultrathin multiband gigahertz metamaterial absorbers

Vivaldi antennas have broad applications in real practice due to the ultra wideband properties. However, their gain and directivity are relatively low. In this paper, a new method is presented to improve the gain and directivity of Vivaldi antennas in a broad band using inhomogeneous and anisotropic (IA) zero-index metamaterials (ZIM). ZIM have the ability to enhance the antenna directivity; anisotropic ZIM with only one component of the permittivity or permeability tensor approaching to zero can make impedance match to improve the radiation e-ciency; and IA-ZIM can broaden the frequency bandwidth. Single- and multiple-layered planar IA-ZIM have been analyzed, designed, and fabricated, which can be embedded into the original Vivaldi antenna smoothly and compactly. The IA- ZIM-based Vivaldi antennas have good features of high gain, high directivity, low return loss, and broad bandwidth. Compared to the original Vivaldi antenna, the measurement results show that the gain has been increased by 3dB and the half-power beam width has been decreased by 20 degrees with the re∞ection coe-cient less than i10dB from 9.5GHz to 12.5GHz after using IA-ZIM.

/pdf/broadband-and-high-gain-planar-vivaldi-antennas-based-on-4hz4fljthu.pdf

Broadband and High-Gain Planar Vivaldi Antennas Based on Inhomogeneous Anisotropic Zero-Index Metamaterials

This study aims to investigate the preventive effect of oral nicorandil on contrast-induced nephropathy (CIN) in patients with renal insufficiency undergoing elective cardiac catheterization. A total of 240 patients with an estimated glomerular filtration rate (eGFR) of 60 mL/min or less, who were undergoing elective cardiac catheterization, were randomly assigned to nicorandil group (n = 120, 10 mg nicorandil, three times daily from 2 days before to 3 days after procedure) or control group (n = 120, matching placebo as the same method). The primary endpoint was the incidence of CIN defined as 25 % increase in serum creatinine (SCr) from baseline or 44 μmol/L (0.5 mg/dL) increase in absolute value within 72 h after exposure to contrast medium. The secondary endpoints were: (1) the changes of SCr, Cystatin-C (Cys-C) and eGFR within 72 h; (2) major adverse events (MACE) occurring within 30 days. Baseline characteristics of the patients in the two groups were similar. The incidence of CIN was significantly lower in nicorandil group compared with control group (6.67 vs. 17.5 %, P = 0.017). Compared with the control group, nicorandil group tended to have a lower SCr and Cys-C levels as well as a higher eGFR at 48 h after the procedure (all P < 0.05). There was no difference about the incidence of MACE within 30 days between nicorandil group and control group (4.16 vs. 5.83 %, P = 0.767). Multivariate logistic analysis showed that nicorandil was an independent protective factor against CIN (OR = 0.260, 95 % CI = 0.1-0.676, P = 0.006). Therefore, we concluded that oral nicorandil was associated with a decline in the incidence of CIN in patients with renal insufficiency undergoing elective cardiac catheterization.

Preventive effect of oral nicorandil on contrast-induced nephropathy in patients with renal insufficiency undergoing elective cardiac catheterization

Beam steering has found wide applications in many areas such as wireless communications, satellite communications, and intelligent transportation systems.Different approaches have been presented to achieve the beam steering, most of which, however, are complicated and expensive. In this paper, we propose a simple and efficient principle to realize this goal based on a partial Luneburg lens. In the experiment, a traditional Vivaldi antenna is used as the platform to test the principle, in which the partial Luneburg lens is constructed by drilled-holes dielectric composite material. The measurement results show that good beam-steering performance from −20 to 20° in a broad bandwidth (8–11 GHz) has been achieved using the proposed method, and the antenna’s gain and directivity have been significantly improved in the same bandwidth after using the special lens.

Beam-steering Vivaldi antenna based on partial Luneburg lens constructed with composite materials

In this paper, a new type of band-pass frequency-selective surface(FSS) element using complementary electric-field-coupled (ELC) structure is proposed and simulated. It has an isotropic response to electric field. When the FSS encounters lager variation of incident angles(0deg to 45deg), the response does not change significantly with these incident angles. It is previously demonstrated that our FSS is less sensitive to incident angles than many other differently-shaped elements, such as crossed dipoles, tripoles, etc.

Bin Zhou

Papers

Ultrathin multiband gigahertz metamaterial absorbers

Broadband and High-Gain Planar Vivaldi Antennas Based on Inhomogeneous Anisotropic Zero-Index Metamaterials

Preventive effect of oral nicorandil on contrast-induced nephropathy in patients with renal insufficiency undergoing elective cardiac catheterization

Beam-steering Vivaldi antenna based on partial Luneburg lens constructed with composite materials

A new type of band-pass FSS based on metamaterial structures