Kuang Zhang

A circular-polarized vortex beams generation with orbital angular momentum (OAM) based on a leaky-wave antenna with substrate integrated waveguide (SIW) is proposed in this letter. The loop leaky-wave antenna is designed to transmit vortex beams with various OAM modes controlled by the operating frequency. With the frequency change from 11GHz to 12GHz, the OAM modes change accordingly. The OAM antenna realizes a low profile by use of the leaky-wave structure. Meanwhile, two transverse slots and one longitudinal slot are utilized to realize circular polarization to improve the mode purity of OAM. Notably, the measured results demonstrate that the gain reaches 7.18 dBi with vortex beams generated by four OAM modes (+2, +1, 0, -1). And the axial ratio (AR) is good from 11GHz to 12GHz, indicating that circular polarization is achieved.

In this literature, a force generator based on plasmonic metamaterial in terhaertz band is presented. An SPP-like (Surface Plasmon Polariton) field trapping can be obtained and this field trapping leads to a enhanced field density and a large force. To excite SPP in terahertz band, the semiconductor(InSb) is utilized to obatain a lower plasmonic frequency so that SPP phenomenon can take place at the terahertz band. A multi-layered structure which consists of a dielectric layer, an air gap and a semiconductor layer is presented. Simulated results show a repulsive force which is 2 orders of magnitude higher than that by a force generator in visible band.

In this paper, a novel structure for a four-face polarization twister based on three-dimensional magnetic toroidal dipoles is proposed. This structure could rotate left-circularly polarized wave into right-circularly polarized wave, which is different from the traditional case. This polarization twister can be excited from four incident directions for efficiency as high as 86.26% or more. After the optimization, polarization twister constructed by toroidal dipoles is confirmed to be reasonable and successful based on simulation results.

Metamaterials with tunable negative permeability are proposed and investigated theoretically in this paper. First, the model of the dielectric bilayer sphere embedded in the dielectric substrate is put forward. Second, expressions of the electromagnetic fields in the model are derived based on the Mie scattering theory, and the general formula for the effective permeability of the model is deduced via the Maxwell-Garnett theory, which is further verified through the simulation results. Finally, the tunable bandwidth of the negative permeability of the metamaterials changing with the geometrical parameters is investigated based on the full-wave simulations, and the relative mechanisms are also discussed. It is believed that the results would be helpful for the practical applications of the metamaterials, and the metamaterials with tunable negative permeability proposed in the paper would facilitate the constructions of the left-handed materials in some degree.

A type of electromagnetic concentrator with radial and tangential constitutive parameters as constants is proposed. Only the z component of the constitutive tensor is spatially variant, and all the constitutive parameters are nonsingular and positive, which makes it possible to construct it with two-dimensional (2D) metamaterials. The effects of loss and perturbations of parameters on the performance of the concentrator are also investigated. Finally, a simplified concentrator suitable for the case that is not sensitive to the omnidirectional scattering field is proposed. This study provides a feasible method for the fabrication of a 2D electromagnetic concentrator.

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.

Arbitrarily three-dimensional (3D) pyramidal cloaks are proposed and designed theoretically based on the coordinate transformation. First, the general expressions of constitutive tensors of the cloaks are derived, and then there are some full-wave simulations which show that the cloak would bend incoming electromagnetic waves and guide them to propagate around inner region. Furthermore, the lossy cases are also considered and simulated. The results validate the constitutive tensors of the 3D pyramidal cloaks, and it is believed that the results are helpful for the practical design and analyze of the 3D cloaks.

The reflection of a normally incident plane wave due to the interface between vacuum and a Faraday chiral medium (FCM) supported by a perfect electric conductor was rigorously derived. Numerical results strongly indicated that arbitrary polarization conversions are realizable from the incident plane wave to the reflected plane wave by properly choosing the constitutive parameters of the FCM.