Fan-Yi Meng

Polarization-Independent Metamaterial Analog of Electromagnetically Induced Transparency for a Refractive-Index-Based Sensor

A polarization-independent metamaterial analog of electromagnetically induced transparency (EIT) at microwave frequencies for normal incidence and linearly polarized waves is experimentally and numerically demonstrated. The metamaterial consists of coupled “bright” split-ring resonators (SRRs) and “dark” spiral resonators (SRs) with virtually equal resonance frequencies. Normally incident plane waves with linear polarization strongly couple to the SRR, but are weakly interacting with the SR, regardless of the polarization state. A sharp transmission peak (i.e., the transparency window) with narrow spectral width and slow wave property is observed for the metamaterial at the resonant frequency of both, the bright SRR and the dark SR. The influence of the coupling strength between the SRR and SR on the frequency, width, magnitude, and quality factor of the metamaterials transparency window is theoretically predicted by a two-particle model, and numerically validated using full-wave electromagnetic simulation. In addition, it is numerically demonstrated that the EIT-like metamaterial can be employed as a refractive-index-based sensor with a sensitivity of 77.25 mm/RIU, which means that the resonance wavelength of the sensor shifts 77.25 mm per unit change of refractive index of the surrounding medium.

Multi-band slow light metamaterial

In this paper, a multi-band slow light metamaterial is presented and investigated. The metamaterial unit cell is composed of three cut wires of different sizes and parallel to each other. Two transparency windows induced by two-two overlaps of absorption bands of three cut wires are observed. The multi-band transmission characteristics and the slow light properties of metamaterial are verified by numerical simulation, which is in a good agreement with theoretical predictions. The impacts of structure parameters on transparency windows are also investigated. Simulation results show the spectral properties can be tuned by adjusting structure parameters of metamaterial. The equivalent circuit model and the synthesis method of the multi-band slow light metamaterial are presented. It is seen from simulation results that the synthesis method accurately predicts the center frequency of the multi-band metamaterial, which opens a door to a quick and accurate construction for multi-band slow light metamaterial.

Material parameters characterization for arbitrary N-sided regular polygonal invisible cloak

Arbitrary N-sided regular polygonal cylindrical cloaks are proposed and designed based on the coordinate transformation theory. First, the general expressions of constitutive tensors of the N-sided regular polygonal cylindrical cloaks are derived, then there are some full-wave simulations of the cloaks that are composed of inhomogeneous and anisotropic metamaterials, which will bend incoming electromagnetic waves and guide them to propagate around the inner region; such electromagnetic waves will return to their original propagation directions without distorting the waves outside the polygonal cloak. The results of full-wave simulations validate the general expressions of constitutive tensors of the N-sided regular polygonal cylindrical cloaks we derived.

Arbitrary waveguide connector based on embedded optical transformation

Arbitrary connector for waveguides of different cross sections is proposed and designed theoretically based on the embedded optical transformation theory. First, the general expressions of constitutive tensors of the metamaterials filled in the connector are derived. Second, there are some full-wave simulations that validate the constitutive tensors derived. The results show that the connector with metamaterials inclusions with designed constitutive parameters can fulfill the reflectionless transmission of electromagnetic waves between waveguides of different cross sections. Finally, connectors of several forms are investigated parametrically, and two sets of constitutive tensors that can be physically achieved by existing metamaterials are gotten. It is believed that this study provides a feasible way to fulfill the efficient transmission of electromagnetic waves between waveguides of different cross sections.

Controllable Metamaterial-Loaded Waveguides Supporting Backward and Forward Waves

Rectangular waveguides loaded by anisotropic metamaterials are analyzed to assess the controllability of transmission characteristics of the involved electromagnetic waves. Dispersion relations of TEm0 modes in the metamaterial-loaded waveguide (MLW) are theoretically investigated. It is shown that all propagating modes (the forward wave, the backward wave and the evanescent wave) in the MLW can be realized below the cut-off frequency by changing transverse and longitudinal components of permeability tensors of the loading metamaterials. Numerical simulations are carried out to verify the proposed theory and the controllability. Transmission characteristics and effective constitutive parameters of three MLWs with different cells, which should theoretically support forward waves, backward waves and evanescent waves, respectively, are numerically calculated. Dispersion curves and magnetic field distribution for the backward wave MLW and the forward wave MLW are simulated. It is shown that the simulated results are in a good agreement with theoretical predictions. Implementation of the controllable MLW was achieved by using axially rotating control rods. Rotating the control rods can reconfigure the metamaterial and make propagating modes in the MLW switch from backward waves to forward waves or evanescent waves.

An electromagnetically induced transparency metamaterial with polarization insensitivity based on multi-quasi-dark modes

To investigate the polarization and angle insensitive mechanism of an electromagnetically induced transparency (EIT) metamaterial, we designed, fabricated and measured a planar symmetry metamaterial structure. The planar symmetry metamaterials cell consists of eight identical inner rings surrounded by a bigger outer ring, which serve as multi-quasi-dark elements and a bright element, respectively. A polarization and angle insensitive transparency window is clearly observed in the spectrum owing to the coupling between the multi-quasi-dark modes and the bright mode, which is verified by numerical simulations and experiments. A wider angle consistency is achieved because the multi-quasi-dark modes commonly participate in the destructive interference of scattering field. In addition, the excited principle and the resonance nature of EIT-like effects are investigated numerically. Simulation results show that the EIT-like effect is associated with the anti-symmetry current, which is induced by coupling fields introducing the phase delay. Finally, the slow wave property of the metamaterial is verified by numerical simulation.

A Method of Using Nonidentical Resonant Coils for Frequency Splitting Elimination in Wireless Power Transfer

In this paper, an efficient method is proposed to eliminate frequency splitting in nonradiative wireless power transfer via magnetic resonance coupling. In this method, two nonidentical resonant coils (NIRCs) are used as wireless power transmitter and receiver, respectively. According to the elliptic integral term in the analytical expression, the pole of the mutual inductance function with respect to transfer distance can be eliminated by using the two NIRCs, and hence overcoupling between transmitter and receiver with close transfer distance is avoided. Therefore, frequency splitting caused by overcoupling can be suppressed and stable output power can be achieved. The NIRCs are analytically calculated, numerically simulated and finally, fabricated and tested to verify the theory. All the calculated and experimental results show that frequency splitting is completely eliminated and uniform voltage across the load is achieved. Furthermore, lateral misalignment between the NIRCs barely introduces frequency splitting, and the suppression level of frequency splitting can also be controlled freely.

A Detached Zero Index Metamaterial Lens for Antenna Gain Enhancement

In this paper, a detached zero index metamaterial lens (ZIML) consisting of metal strips and modifled split ring resonators (MSRRs) is proposed for antenna gain enhancement. The efiective permittivity and permeability of the detached ZIML are designed to synchronously approach zero, which leads the ZIML to having an efiective wave impedance matching with air and near-zero index simultaneously. As a result, neither does the detached ZIML need to be embedded in horns aperture nor depends on auxiliary re∞ectors in enhancing antenna gain, which is quite difierent from conventional ZIMLs. Moreover, the distance between antenna and the detached ZIML slightly afiect the gain enhancement, which further conflrms that the ZIML can be detached from antennas. Simulated results show that the efiective refractive index of the detached ZIML is near zero in a broad frequency range where the efiective relative wave impedance is close to 1. The detached ZIML is fabricated and tested by placing it in front of an H-plane horn antenna. One flnds that evident gain enhancement is obtained from 8.9GHz to 10.8GHz and the greatest gain enhancement reaches up to 4.02dB. In addition, the detached ZIML can also work well at other frequencies by adjusting its geometric parameters to scale, which is demonstrated by designing and simulating two detached ZIMLs with center frequencies of 2.4GHz and 5.8GHz, respectively.

Electrically tunable terahertz wave modulator based on complementary metamaterial and graphene

In this paper, we design and numerically demonstrate an electrically controllable light-matter interaction in a hybrid material/metamaterial system consisting of an artificially constructed cross cut-wire complementary metamaterial and an atomically thin graphene layer to realize terahertz (THz) wave modulator. By applying a bias voltage between the metamaterial and the graphene layer, this modulator can dynamically control the amplitude and phase of the transmitted wave near 1.43 THz. Moreover, the distributions of current density show that this large modulation depth can be attributed to the resonant electric field parallel to the graphene sheet. Therefore, the modulator performance indicates the enormous potential of graphene for developing sophisticated THz communication systems.

Polarization manipulation based on electromagnetically induced transparency-like (EIT-like) effect

We proposed, designed and fabricated a high transparency of metasurface-based polarization controller at microwave frequencies, which consists of orthogonal two pairs of cut wires. The high transmission and the strong dispersion properties governed by electromagnetically induced transparency-like (EIT-like) effects for both incident polarizations make our device efficiently manipulating the polarization of EM waves. In particular, the proposed polarization device is ultrathin (~0.017λ), as opposed to bulky polarization devices. Microwave experiments are performed to successfully demonstrate our ideas, and measured results are in reasonable agreement with numerical simulations.