Array Of Metallic Rods Research Articles

Tunable topological valley transport in two-dimensional photonic crystals

Recently, exploring the valley degree of freedom in photonic crystals has attracted considerable attentions since it opens up the possibility of extending valleytronics to optics. However, the fixed structural parameters limit the practical applications of valley photonic crystals. How to design steerable valley photonic structures becomes an important research topic. In this work, we design a tunable valley photonic crystal using an array of regular triangular metal rods embedded in liquid crystals. Electrically controlled valley-selective excitation, valley-locked beam splitting behavior and valley-projected edge transportation have been numerically demonstrated. Using these novel effects, a switchable valley filter device has also been designed. Our proposed valley-based photonic devices are beneficial for the development of robust wave manipulation.

Geometry-dependent modal field properties of metal-rod-array-based terahertz waveguides

One terahertz (THz) waveguide based on the metal rod array (MRA) structure is numerically demonstrated in 0.1–1 THz, including the fundamental and high-order transverse magnetic (TM) modes. The high-order TM-mode THz waves are strictly confined inside the MRA structure and are thus sensitive to the metal rod interspace for their spectral positions, bandwidths, transmittances, and attenuation coefficients. Arranging metal rods with fine-tuning the interspaces across the optic axis is presented as the critical stratagem to optimize the transportation efficiency of THz waves through an MRA structure. The maximum propagation length of MRA-confined THz waves is over 30 mm with the lowest attenuation coefficients of approximately 0.05–0.1 cm−1. The MRA is, therefore, applicable as one deformable artificial structure in THz frequency region because simply one-axial adjustment of the metal-rod interspace enables the modulation purpose without uniform adjustment on the two-dimensional metal rod interspace.

Investigation of spectral properties and lateral confinement of THz waves on a metal-rod-array-based photonic crystal waveguide.

Terahertz (THz) waves laterally confined in a 1 mm-thick microstructured planar waveguide are demonstrated on a free-standing metal rod array (MRA), and one apparent rejection band of a transmission spectrum, resembling the bandgap of a photonic crystal, is found in 0.1-0.6 THz. The visibility of the photonic bandgap in the spectral width and power distinction can be manipulated by changing the MRA geometry parameters, including the rod diameter, the interspace between adjacent rods, and the propagation length based on the interactive MRA-layer number. THz transmission ratio enhanced by a large interactive length is verified in 30 MRA layers due to the longitudinally resonant guidance of transverse-magnetic-polarized waveguide modes along the MRA length, which is critical to the interspace width of adjacent rods and the metal coating of the rod surface. For an MRA with respective rod diameter and interspace dimensions of about 0.16 and 0.26 mm, the highest transmission of the guided resonant THz waves are performed at 0.505-0.512 THz frequency with strong confinement on the metal rod tips and a low scattering loss of 0.003 cm-1.

Light confined to a single atomic layer

Nanophotonics The development of nanophotonic technology is reliant on the ability to confine light to spatial dimensions much less than the wavelength of the light itself. Typically, however, in metal plasmonic approaches, there is a trade-off between confinement and losses. Alcaraz Iranzo et al. fabricated heterostructures comprising monolayers of graphene and hexagonal boron nitride (hBN) and an array of metallic rods. The light was confined vertically (as propagating plasmons) between the metal and the graphene, even when the insulating hBN spacer was just a single monolayer. Such heterostructures should provide a powerful and versatile platform for nanophotonics. Science , this issue p. [291][1] [1]: /lookup/doi/10.1126/science.aar8438

Axion detection with negatively coupled cavity arrays

Using eigenmode analysis and full 3D FEM modelling, we demonstrate that a closed cavity built of an array of elementary harmonic oscillators with negative mutual couplings exhibits a dispersion curve with lower order modes corresponding to higher frequencies. Such cavity arrays may help to achieve large mode volumes for boosting sensitivity of the axion searches, where the mode volume for the composed array scales proportional to the number of elements, but the frequency remains constant. The negatively coupled cavity array is demonstrated with magnetically coupling coils, where the sign of next-neighbour coupling (controlled with their chirality) sets the dispersion curve properties of the resonator array medium. Furthermore, we show that similar effects can be achieved using only positively coupled cavities of different frequencies assembled in periodic cells. This principle is demonstrated for the multi-post re-entrant system, which can be realised with an array of straight metallic rods organised in chiral structures.

Terahertz artificial material based on integrated metal-rod-array for phase sensitive fluid detection.

A terahertz artificial material composed of metal rod array is experimentally investigated on its transmission spectral property and successfully incorporated into microfluidics as a miniaturized terahertz waveguide with an extended optical-path-length for label-free fluidic sensing. Theoretical and experimental characterizations of terahertz transmission spectra show that the wave guidance along the metal rod array originates from the resonance of transverse-electric-polarized waves within the metal rod slits. The extended optical path length along three layers of metal-rod-array enables terahertz waves sufficiently overlapping the fluid molecules embedded among the rods, leading to strongly enhanced phase change by approximately one order of magnitude compared with the blank metal-parallel-plate waveguide. Based on the enhanced phase sensitivity, three kinds of colorless liquid analytes, namely, acetone, methanol, and ethanol, with different dipole moments are identified in situ using the metal-rod-array-based microfluidic sensor. The detection limit in molecular amounts of a liquid analyte is experimentally demonstrated to be less than 0.1 mmol, corresponding to 2.7 μmol/mm2. The phase sensitive terahertz metal-rod-array-based sensor potentially has good adaptability in lab-chip technology for various practical applications, such as industrial toxic fluid detection and medical breath inspection.

Corrected Drude model of thin circle metal rods’ periodic array

A corrected Drude model is presented for structural electromagnetic performance analysis of metamaterials with thin circle metal rods. The prediction model about periodic array of thin circle metal rods is theoretically derived; and the electric plasma frequency expression and the damping factor expression of Drude model are corrected. The numerical examples show that the modified theoretical prediction model has higher accuracy than other representing models. Then, the great robustness of the corrected Drude model is verified through number examples for different cases; and even the errors for the middle/thick circle rod and the middle square rod are still acceptable. Finally, as a result of the minimum and maximum ratio of the unit cell dimension to the radius, applicable conditions of the corrected Drude model are proposed.

Coupling between Fano and Bragg bands in the photonic band structure of two-dimensional metallic photonic structures

Frequency and transmission spectrum of two-dimensional array of metallic rods is investigated numerically. Based on the recent analysis of the band structure of two-dimensional photonic crystal with dielectric rods [P. Marko\v{s}, Phys. Rev. A 92 043814 (2015)] we identify two types of bands in the frequency spectrum: Bragg (P) bands resulting from a periodicity and Fano (F) bands which arise from Fano resonances associated with each of the cylinders within the periodic structure. It is shown that the existence of Fano band in a certain frequency range is manifested by a Fano resonance in the transmittance. In particular, we re-examine the symmetry properties of the H- polarized band structure in the frequency range where the spectrum consists of the localized modes associated with the single scatterer resonances and we explore process of formation of Fano bands by identifying individual terms in the expansion of the LCAO states. We demonstrate how the interplay between the two scattering mechanisms affects properties of the resulting band structure when the radius of cylinders is increased. We show that a different character of both kinds of bands is reflected in the spatial distribution of the magnetic field which displays patterns corresponding to the corresponding irreducible symmetry representations.

Substrate‐integrated waveguide phase shifter with rod‐loaded artificial dielectric slab

A substrate-integrated waveguide (SIW) broadband phase shifter is presented and studied. The phase shift mechanism is based on the synthesis of an artificial dielectric slab using an array of metallic rods in the middle of a SIW. This technique enables a large phase shift within a compact size and enhances the density of integration. As an example, 45° and 90° phase shifters are designed and showcased on a single-layer substrate at a centre frequency of 26 GHz. The amplitude imbalance between the two paths is also avoided while the phase error is less than 5° over a frequency band of 20–32 GHz or around 46% relative bandwidth. The measured return loss is found to be better than 12 dB over the whole frequency band.

Analysis of the Photonic Bandgaps for Gyrotron Devices

The global bandgaps of photonic crystal are theoretically analyzed in this paper. The electromagnetic-wave propagation characteristics of photonic bandgap (PBG) structures, which is used in the the millimeter-wave, submillimeter-wave, and terahertz regime vacuum electronic devices and accelerators, were numerically simulated using the finite-element method software high-frequency structural simulator. The dispersion curves of the lattices in different rod radius to-rod spacing ratios and the global bandgaps for the general 2-D PBG structures formed by triangular and square arrays of metal rods were simulated. A mode map that shows the relationship between the structures and the contained modes was plotted and a 220-GHz metallic PBG resonator operating in TE $_{\mathrm {\mathbf {04}}}$ mode was designed for a gyrotron device to verify the theoretical and numerical simulations, and a comparison of mode density and quality factor between the PBG resonator and the equivalent cylindrical resonator has been carried out.

Terahertz plasmonic waveguide based on metal rod arrays for nanofilm sensing.

A high-aspect-ratio metallic rod array is demonstrated to generate and propagate highly confined terahertz (THz) surface plasmonic waves under end-fire excitation. The transverse modal power distribution and spectral properties of the bound THz plasmonic wave are characterized in two metallic rod arrays with different periods and in two configurations with and without attaching a subwavelength superstrate. The integrated metallic rod array-based waveguide can be used to sense the various thin films deposited on the polypropylene superstrate based on the phase-sensitive mechanism. The sensor exhibits different phase detection sensitivities depending on the modal power immersed in the air gaps between the metallic rods. Deep-subwavelength SiO(2) and ZnO nanofilms with an optical path difference of 252 nm, which is equivalent to λ/3968 at 0.300 THz, are used as analytes to test the integrated plasmonic waveguide. Analysis of the refractive index and thickness of molecular membranes indicates that the metallic rod array-based THz waveguide can integrate various biochip platforms for minute molecular detection, which is extremely less than the coherent length of THz waves.

Simulation of a G-band sheet beam backward wave oscillator with double staggered metallic rod array

Backward wave oscillators (BWO) are promising high-power portable radiation sources in the terahertz frequency range. A G-band (140–220 GHz) sheet beam BWO based on a double staggered metallic rod array as the slow wave structure (SWS) has been designed and presented in this paper. The novel SWS allowed extension of the interaction area for the sheet beam with a uniform electric field if the height of the rod array is properly chosen. This could alleviate beam instability problems in the sheet beam transportation and potential parasitic oscillations. Moreover, a relatively broad bandwidth can be achieved due to its special dispersive properties. Particle-in-cell simulation had predicted that the G-band sheet beam BWO with the improved non-uniform double staggered metallic rod array can achieve output power of over 110 W in a continuous frequency tuning range of 186.3–227.2 GHz (relative bandwidth 20%) with a maximum electronic efficiency of 2.8% by using a 200 mA sheet beam and adjusting the beam voltage from 20 to 40 kV.

Fractional vaporization of tissue with an oscillatory array of high temperature rods – Part I: Ex vivo study

Background: Short pulse duration (∼0.1–5 milliseconds) CO2 lasers are perceived as excellent tools for vaporization of craters arrays in fractional skin resurfacing. Objectives: To present a thermo-mechanical ablation technology, which affects tissue identically to fractional CO2 lasers, however at a fraction of the size and cost of a laser. Material and methods: The new technology is based on heating an oscillating array of thin metallic rods to a temperature of 400°C and advancing the rods into tissue down to a precise pre-selected depth for a duration of 0.1–5 milliseconds. As a result, an array of crater is vaporized with identical properties of those produced by CO2 lasers. An ex vivo test was performed with a thermo- metallic rod array prototype. Results: Arrays of 10 × 10 vaporized micro-craters of 350 micron diameter, 200 micron depth have been produced with lateral thermal damage of 80 micron while thermal damage below craters was 80–250 micron. Conclusions: A resonating thermo-mechanical array of high temperature (350–400°C) rods is capable of producing an array of craters identical to those produced with pulsed CO2 lasers.

Homogenization of a metallic metamaterial and electrostatic resonances

The homogenization of arrays of metallic rods was studied. Using standard homogenization theory, the effective permittivity was obtained. The onset of resonances was evidenced and showned to be linked with the negative sign of the real part of the permittivity. Numerical computations were performed to test the homogeneous model.

Super-Resolution Imaging by using a Metallic Rod Array in the Near Infrared Region

An array of metallic rods can transport details below the diffraction limit of an object from the front face to the back face. This super-resolution imaging system has been studied in the microwave, mid-infrared and optical range. We investigate its performance in the near infrared (1550 nm) region. Numerical simulations show that the near-field components of dipole sources are transferred by the excitation and propagation of the surface plasmon mode of the rods. The appropriate length of rods is determined by the excited surface plasmon mode. The spatial resolution is greatly affected by the loss of metal.

Dielectric Slab Photonic Crystals Containing Metallic Components for E Polarization Mode

By using plane wave expansion method, we calculated the photonic band structure of metal cylinders in a dielectric medium. The photonic crystal is an identical, symmetrical structure with an infinite array of metallic rods. Arrangement of the metallic rods used is square lattice. The dielectric function of the metal from which the cylinders are formed has a simple, free electron form e(ω)=1-(ωp 2 /ω 2 ) where ωp is the plasma frequency of the conducting electron. We manage to show the band structure of the square lattice. We found the relation between the band gap size and the filling fraction for some widely used material. For an example, FR-4, silicon, resin, teflon etc. The relation between the band gap size and the dielectric constant of the medium was studied.

Artificial metal with effective plasma frequency in near-infrared region

We have proposed and demonstrated an artificial medium consisting of arrays of circular metal rods embedded in a dielectric host, which holds a real metal behavior but the extracted effective plasma frequency is in near-infrared region. The electromagnetic responses of such medium and the retrieved effective material parameters have been particularly shown. In addition, an analytic model about effective plasma frequency is constructed by uniquely considering the skin effect and introducing the parameter-skin depth, whose predicting results are in well accordance with the FDTD simulation. This artificial material may open possibilities for many metal-based applications in near-infrared regime.

Periscope-like endoscope for transmission of a near field in the infrared range

A possibility to transmit near field through a periscope-like endoscope formed by an array of bent metallic rods is investigated. This is a first step on the way to development of flexible near-field endoscopes. An effort to tunnel the near field of a crown-shaped object through the periscope with 45 degrees bending angle is made, and a shift in the operating frequency band with respect to that of the straight endoscope is observed. An analysis of transmission coefficient as a function of transverse wave vector has been provided for a better understanding of the device operation. A distinctive nature of surface waves appearing at both interfaces has also been reported.

Negative refraction can make non-diffracting beams

We report the results of simulations relating to the illumination of a structure consisting of a slab constructed from a 2-D hexagonal array of metal rods with a terahertz frequency source. As a consequence of negative refraction an essentially non-divergent beam pattern is observed. Although the results presented relate to the terahertz regime they should also be applicable at other frequencies.

Ultimate limit of resolution of subwavelength imaging devices formed by metallic rods

It is demonstrated that the ultimate physical limit of resolution of novel imaging devices based on arrays of metallic rods is determined by the skin depth of the metal. Our theoretical and numerical results show that wire medium lenses may provide a unique solution for subwavelength imaging at frequencies up to the terahertz range and may enable image formation at a significant distance from the source plane.