We present the design for a hexagonal cell made of quasi-periodic dendritic arranged collections of plasmonic metallic wires that may exhibit a resonant magnetic collective response. When such quasi-periodic dendritic cells are etched on a host medium, they may provide metamaterials with negative effective permeability. We also show that a clear point image is observed, as expected, with our left-handed metamaterials (LHMs) lens composed of metallic dendritic cells and wire strips. These prominent characteristics of quasi-periodic dendritic cells potentially enable us to prepare infrared or visible domain LHMs by using a general chemical method.

Negative permeability and subwavelength focusing of quasi-periodic dendritic cell metamaterials.

We demonstrate that a two-dimensional isotropic left-handed materials (LHMs) can be built based on unitary dendritic structure units. Utilizing parameter design, we theoretically deduce a resonant condition in unitary dendritic structure unit, which provided an overlapping negative permittivity and negative permeability response over a frequency band. Employing microwave transmission and prism refractive index experiments, the medium with dendritic structure exhibits a distinct left-handed effect. The proposed implementation of the dendritic structure opens the possibility of realizing integrative isotropic LHMs, especially for simple chemical prepared infrared or visible frequency LHMs.

Resonant condition of unitary dendritic structure with overlapping negative permittivity and permeability

We demonstrate that the multibands of negative refraction indexes in the left-handed metamaterials may be appeared based on multiple dendritic structures cells. Employing microwave transmission experiment, the medium exhibits simultaneous negative refraction at the frequencies of 9.50, 10.24, and 10.78 GHz for the electromagnetic wave parallel incidence, and at the frequencies of 9.24, 9.98, and 10.78 GHz for normal incidence. The multiple dendritic metamaterials here open a way to prepare the cloak suitable for multifrequencies, especially for the cloak of infrared or visible frequency.

Multibands of negative refractive indexes in the left-handed metamaterials with multiple dendritic structures

We report on a negative-zero-positive metamaterial based on an omega-type microstructure with special attention on the nonvanishing group velocity for a zero refractive index. We first investigate the dispersion characteristics by full wave analysis, by stressing the necessary conditions of equality between the electric and magnetic plasma frequencies which are characteristic of the dispersion of the effective permittivity and permeability. Also, tuning of the gapless transition frequency between the left and right-handed dispersion branches was analyzed when the permittivity of the host substrate is changed. Last, we demonstrate experimentally the balanced composite character of the dispersion by frequency and angle-resolved transmission measurements, carried out at centimeter wavelengths on slabs and wedge-type prototypes, respectively.

Negative-zero-positive metamaterial with omega-type metal inclusions

Defect effect of split ring resonators in left-handed metamaterials

We used a rectangular waveguide system to measure the X-band (8–12 GHz) transmission of hexagon split ring resonators (SRRs) alone and the left-handed metamaterials (LHMs) consisting of hexagon SRR array and wire array. The experimental results show that for an individual SRR, the resonance frequency increases with the azimuthal gap, but decreases with the radial gap. For two identical SRRs, the resonance peak has a shift because of the electromagnetic interaction, and the resonance frequency and the strength decrease with the separation distance. Finally, we demonstrate the left-handed effect of the LHMs.

Behaviour of Hexagon Split Ring Resonators and Left-Handed Metamaterials

We introduce a structure made of periodic arrays of H-shaped metallic pattern that offers a potentially simple approach in building left-handed metamaterials with simultaneous negative permittivity and permeability. We have investigated experimentally the transmittance in the rectangle waveguide and found unambiguously a passband that can be tuned easily at microwave frequencies by changing the parameter t . Using phase shift experiment, prism refraction experiment and S-parameter retrieval method, we have confirmed that the H-shaped metamaterials have negative refractive indices, negative permittivity and negative permeability at the passband frequencies. Compared with the conventional left-handed metamaterials consisting of arrays of wires and split ring resonators, H-shaped left-handed metamaterials show not only magnetic resonance but also electric resonance, so they will be a good candidate in the microwave applications due to their simple structure and easy preparation.

H-shaped structure of left-handed metamaterials with simultaneous negative permittivity and permeability

The defect effect in the two_dimensional (2D) negative permeability material, co nsisting of copper hexagon split ring resonators (SRRs), is investigated. The pr inted circuit boards with SRRs on one side are fabricated using a shadow mask/et ching technique. We use a rectangular waveguide system to measure the X_band tra nsmission in 2D negative permeability materials with different dot and line defe cts. The measured data shows that there is only one resonance frequency and high quality factor \%Q\% for a 2D negative permeability material without defects. T he main resonance frequency has a shift and the resonant peak value decreases wh en the defect SRRs are introduced into the samples. We consider that the defect SRRs break the periodic structure of the samples, which results in the shift of the main resonance frequency and the resonant intensity. The investigation of th e defect effects is important not only for the understanding of the characterisf ics of the negative permeability material, but also for the realization of the l eft_handed metamaterials in the infrared and visible region.

The defect effect in the one-dimensional negative permeability material

Stopband phenomena are reported in the passband of left-handed metamaterials. The samples with linear defect are designed by removing one layer of split ring resonators (SRRs). It is shown that the left-handed transmission peaks have a distinct transform with the relative deviation of the SRRs centre from the wire centre δ, from a single left-handed peak, double left-handed peaks with different magnitude to no transmission peak, i.e. left-handed properties of metamaterials disappear. Numerical simulation shows that the change of δ makes the effective permeability shift at a frequency range, where stopband occurs. It is thought that the stopband in left-handed passband is due to the symmetry breaking between SRRs and wires in the metamaterials.

Liu Ya-Hong

Papers

Behaviour of Hexagon Split Ring Resonators and Left-Handed Metamaterials

H-shaped structure of left-handed metamaterials with simultaneous negative permittivity and permeability

The defect effect in the one-dimensional negative permeability material

Stopband Phenomena in the Passband of Left-Handed Metamaterials

Multiband and broadband metamterial absorbers