Wide-angle transmissions of electromagnetic fields through the sandwiched transparent epsilon-near-zero metamaterial screen.

We propose a sandwiched transparent epsilon-near-zero (ENZ) metamaterial screen to release the obliquely incident electromagnetic fields. More specifically, the transmission properties through ENZ metamaterials are investigated when incorporated with an interlayer of a meta-surface having periodic complementary spiral-resonator-matrixes. We show that both TE- and TM-polarized electromagnetic waves are capable of penetrating the ENZ metamaterials under a wide-angle range of illuminations, and the greatly enhanced transmissions are turning out to be frequency dispersionless for different polarized electromagnetic fields with different incident angles. Our design, breaking the notion of the angular filter of ENZ metamaterials, should readily be applied to other extreme-parameter materials and pave the way to explore more unexpected transmission properties of these metamaterials.

Negative Reflecting Meta-Mirrors.

Using the gradient phase discontinuities that meta-mirrors provide, we show that the incident wave can be reflected anomalously with a broad angle range of negative reflections. Such reversed behaviors promote the immediate applications for the planar meta-mirrors to steer the signals more arbitrarily and the convex meta-mirrors to focus and collimate electromagnetic fields. We practically implement these negative reflecting meta-mirrors through an arrangement of subwavelength ring patches and generate the desired phase distribution by also considering the incident angle. Finally, the experiments are carried out to verify the functionality of the convex meta-mirror firstly, and the performances of the planar meta-mirror are also tested by further building up a dual reflector system with the demonstration of obtaining the plane wave from the convex meta-mirror and then having the well collimated beam negative reflected by the planar meta-mirror. The proposed design should be readily applicable to a wide range of electromagnetic problems, especially for devising smart planar illusion devices, and highly directive antennas mounting on convex surfaces of various platforms.

Enhanced Transmissions Through Three-dimensional Cascade Sharp Waveguide Bends Using C-slit Diaphragms.

Transmission properties through sharp rectangular waveguide bends are investigated to determine the cut-off bending angles of the wave propagation. We show that a simple metallic diaphragm at the bending corner with properly devised sub-wavelength defect apertures of C-slits would be readily to turn on the transmissions with scarce reflections of the propagating modes, while preserving the integrity of the transmitting fields soon after the bends. In particularly, our design also demonstrates the capability of eliminating all the unwanted cavity resonant transmissions that exist in the three-dimensional cascade sharp waveguide bends, and solely let the desired signals travel along the whole passage of the waveguide. The present approach, using C-slit diaphragms to support the sharp bending behaviors of the guided waves with greatly enhanced transmissions, would be especially effective in constructing novel waveguides and pave the way for the development of more compact and miniaturized electromagnetic systems that exploit these waveguide bends.

Transformation-optical Fan-beam Synthesis.

Gradient-index dielectric lenses are generated based on the coordinate transformation by compressing the homogeneous air spaces quasi-conformally towards and outwards the primary source. The three-dimensional modeling is then performed through revolving the prescribed transformational media 180 degrees around the focal point to reach the architecture of barrel-vaults. It is found that all these two- and three-dimensional transformation-optical designs are capable of producing fan-beams efficiently over a broad frequency range with their main lobes possessing the narrow beamwidth in one dimension and the wide beamwidth in the other, while having the great ability of the wide angular scanning. Finally, we propose to construct such four types of fan-beam lenses through multiple-layered dielectrics with non-uniformed perforations and experimentally demonstrate their excellent performances in the fan-beam synthesis.

Broadband converging plano-concave lens.

A plano-concave lens with source-tailored geometric profile and transformational gradient index is proposed for broadband illumination. Such a design, capable of focusing and collimating the electromagnetic fields, fulfils the functionality of a converging lens and can also achieve a steerable beam and multiple beams efficiently. Nonresonant synthesis with a perforated dielectric plate and dielectric rod arrays is demonstrated for the lensing realization, promising a wide operating frequency band in the practical implementation.