Uniaxial Metamaterials Research Articles

Uniaxial epsilon-near-zero metamaterial for angular filtering and polarization control

We describe a unique class of metamaterials that exhibit strong uniaxial anisotropy with epsilon-zero response along the optical axis and which optical properties depend strongly on polarization. In an example of array of silver nanowires grown in anodic alumina membrane, the proposed singular uniaxial metamaterial is shown to function as a polarizer and narrowband angular transmittance filter.

Chiral metamaterials with negative refractive index based on four “U” split ring resonators

A uniaxial chiral metamaterial is constructed by double-layered four “U” split ring resonators mutually twisted by 90°. It shows a giant optical activity and circular dichroism. The retrieval results reveal that a negative refractive index is realized for circularly polarized waves due to the large chirality. The experimental results are in good agreement with the numerical results.

Composite left/right-handed stacked hole arrays at submillimeter wavelengths

High-transmissivity composite left/right-handed uniaxial bulk metamaterials were fabricated in a multilayered dielectric/hole metal array technology and experimentally assessed at submillimeter wavelengths (0.4–0.9 THz) by time-domain spectroscopy. From the frequency dependence of the complex scattering parameters, we show the possibility to close the gap between the left- and right-handed dispersion branches by increasing the number of layers from 3 to 5. Such a demonstration paves the way of balance composite propagation characteristics with a gapless transition between the negative and positive values of refractive index at a frequency of 0.5 THz.

Ultradirective antenna via transformation optics

Spatial coordinate transformation is used as a reliable tool to control electromagnetic fields. In this paper, we derive the permeability and permittivity tensors of a metamaterial able to transform an isotropically radiating source into a compact ultradirective antenna in the microwave domain. We show that the directivity of this antenna is competitive with regard to conventional directive antennas (horn and reflector antennas), besides its dimensions are smaller. Numerical simulations using finite element method are performed to illustrate these properties. A reduction in the electromagnetic material parameters is also proposed for an easy fabrication of this antenna from existing materials. Following that, the design of the proposed antenna using a layered metamaterial is presented. The different layers are all composed of homogeneous and uniaxial anisotropic metamaterials, which can be obtained from simple metal-dielectric structures. When the radiating source is embedded in the layered metamaterial, a highly directive beam is radiated from the antenna.

Fundamental modal properties of SRR metamaterials and metamaterial based waveguiding structures

A rigorous full wave analysis of bianisotropic split ring resonator (SRR) metamaterials is presented for different electromagnetic field polarization and propagation directions. An alternative physical explanation is gained by revealing the fact that imaginary wave number leads to the SRR resonance. Metamaterial based parallel plate waveguide and rectangular waveguide are then examined to explore the resonance response to transverse magnetic and transverse electric waves. It is shown that different dispersion properties, such as non-cutoff frequency mode propagation and enhanced bandwidth of single mode operation, become into existence under certain circumstances. In addition, salient dispersion properties are imparted to non-radiative dielectric waveguides and H waveguides by uniaxial bianisotropic SRR metamaterials. Both longitudinal-section magnetic and longitudinal-section electric modes are capable of propagating very slowly due to metamaterial bianisotropic effects. Particularly, the abnormal falling behavior of some higher-order modes, eventually leading to the leakage, may appear when metamaterials are double negative. Fortunately, for other modes, leakage can be reduced due to the magnetoelectric coupling. When the metamaterials are of single negative parameters, leakage elimination can be achieved.

S-Shaped Ring Resonator as Anisotropic Uniaxial Metamaterial Used in Waveguide Tunneling

In a novel application a slab of S-shaped ring resonators is used in the form of an anisotropic uniaxial metamaterial with transversal negative effective permeability to fill a rectangular waveguide. Theory and experimental results show that the operational bandwidth of the dominant mode can be extended below the cutoff frequency with low insertion loss. On the other hand, this structure can be used as a band-rejection filter with adjustable bandwidth. The stopband bandwidth can be varied from few MHz to GHz. The width of the stopband can be decreased by increasing the distance of the slab from the central plane of waveguide.

Wave scattering and splitting by magnetic metamaterials

We study experimentally propagation of electromagnetic waves through a slab of uniaxial magnetic metamaterial. We observe a range of novel phenomena including partial focusing and splitting into multiple transmitted beams.We demonstrate that while some of these experimentally observed effects can be described within the approximation of an effective medium, a deeper understanding of the experimental results requires a rigorous study of internal eigenmodes of the lattice of resonators.

Uniaxial metallo-dielectric metamaterials with scalar positive permeability

The dispersion relation for plane waves in uniaxial metamaterials with indefinite dielectric tensors and scalar positive permeability is theoretically investigated. It is found, that the isofrequency surfaces of the plane extraordinary waves have a hyperbolic shape which allows the propagation of waves with infinitely long wave vectors. As an example a metallodielectric multilayer was considered and the dispersion relations were determined using an effective medium approximation and an analytically exact Bloch wave calculation. The extraordinary waves in this structure are identified as multilayer plasmons and the validity of the effective medium approximation is examined.