Haiyu Zheng

Flexible and elastic metamaterial absorber for low frequency, based on small-size unit cell

Using a planar and flexible metamaterial (MM), we obtained the low-frequency perfect absorption even with very small unit-cell size in snake-shape structure. These shrunken, deep-sub-wavelength and thin MM absorbers were numerically and experimentally investigated by increasing the inductance. The periodicity/thickness (the figure of merit for perfect absorption) is achieved to be 10 and 2 for single-snake-bar and 5-snake-bar structures, respectively. The ratio between periodicity and resonance wavelength (in mm) is close to 1/12 and 1/30 at 2 GHz and 400 MHz, respectively. The absorbers are specially designed for absorption peaks around 2 GHz and 400 MHz, which can be used for depressing the electromagnetic noise from everyday electronic devices and mobile phones.

Highly-dispersive transparency at optical frequencies in planar metamaterials based on two-bright-mode coupling

Using a planar metamaterial, which consists of two silver strips, we theoretically demonstrate the plasmonic electromagnetically-induced transparency (EIT)-like spectral response at optical frequencies. The two silver strips serve as the bright modes, and are excited strongly by the incident wave. Based on the weak hybridization between the two bright modes, a highly-dispersive plasmonic EIT-like spectral response appears in our scheme. Moreover, the group index is higher than that of another scheme which utilizes the strong coupling between the bright and dark modes.

Plasmonic electromagnetically-induced transparency in symmetric structures

A broken symmetry is generally believed to be a prerequisite for plasmonic electromagnetically-induced transparency (EIT), since the asymmetry allows the excitation of the otherwise forbidden dark mode. Nevertheless, according to the picture of magnetic plasmon resonance (MPR)-mediated plasmonic EIT, we show that plasmonic EIT can be achieved even in symmetric structures based on the second-order MPR. This not only sharpens our understanding of the existing concept, but also provides a profound insight into the plasmonic coherent interference in the near-field zone.

Tunable dual-band perfect absorbers based on extraordinary optical transmission and Fabry-Perot cavity resonance.

Magnetic resonance is considered to be a necessary condition for metamaterial perfect absorbers, and dual-band absorbers can be composed of a pair of metallic layers with anti-parallel surface currents. We designed and fabricated a tunable dual-band perfect absorber based on extraordinary-optical-transmission (EOT) effect and Fabry-Perot cavity resonance. The idea and the mechanism are completely different from the absorber based on the near-field interaction. The important advantage of our structure is that we can switch a single-band absorber to a dual-band absorber by changing the distance between two metallic layers and/or incident angle. The peak originating from the EOT effect becomes significantly narrower, resulting in an increase of the Q-factor from 16.88 to 49. The dual-band absorber can be optimized to be insensitive to the polarization of the incident electromagnetic wave by slightly modifying the absorber structure.

Manipulation of electromagnetically-induced transparency in planar metamaterials based on phase coupling

We experimentally demonstrated a controllable electromagnetically induced transparency (EIT)-like spectral response at microwave frequencies in a planar metamaterial consisting of two identical split-ring resonators (SRRs) with side-by-side symmetry. In our scheme, phase coupling between the two SRRs (serving as the bright mode), which were excited strongly by the incident wave, was employed, and it was found that the EIT-like spectral response could be controlled by simply adjusting the incident angle. Thus, our scheme may be used for electromagnetic-wave switching. A high group index for slow-light application and a high quality factor could be obtained by simply controlling the incident angle.

Dual-absorption metamaterial controlled by electromagnetic polarization

Polarization is one of the fundamental properties of electromagnetic waves, conveying valuable information in signal transmission and sensitive measurements. We investigated the controllability of dual-band absorption metamaterials whose unit cells were designed and fabricated based on the conventional absorber model with proper manipulation of the structural pattern. Dual-band perfect absorption is achieved and gradually switched off according to the polarization angle. Moreover, another mode emerges concomitantly at higher frequencies. The electromagnetic properties were investigated to clarify the mechanisms of dual-band perfect absorption and polarization-sensitive switchable effects. Our work was demonstrated experimentally in the gigahertz range and applied to the terahertz region.

Improved rigorous coupled-wave analysis for polar magnetic gratings

The rigorous coupled-wave analysis method with Airy-like Internal-Reflection Series for the polar gyrotropic grating is improved with the Fourier factorization rule. In the process of derivation, Maxwells equation is reformulated in order to avoid type 3 product and, either Laurents rule or the inverse rule is used for the product of two Fourier series with discontinuities. The number of Fourier coefficients or the size of the coefficient matrix required for the proper convergence is reduced by more than 50% compared to our previous works for the calculation of the diffracted Kerr rotation from the polar magnetic gratings.

CLASSICAL ELECTROMAGNETICALLY-INDUCED TRANSPARENCY-LIKE SWITCHING CONTROLLED BY POLARIZATION IN METAMATERIALS

The classical electromagnetically-induced transparency (EIT)-like switching in metamaterials was experimentally demonstrated in the microwave-frequency region. The metameterial unit cell consists of two identical split-ring resonators, which are arranged on both sides of a dielectric substrate with 90°-rotation asymmetry. In our scheme, the classical EIT-like switching can be achieved by changing the polarization of the incident electromagnetic wave.