Rod Modes Research Articles

Selectively Infiltrated PCF for Directional Bend Sensing With Large Bending Range

A directional bend sensor based on selectively infiltrated photonic crystal fiber is demonstrated. The device is fabricated by use of femtosecond laser micromachining technique and fusion splicing of photonic crystal fiber with single-mode fiber. By infiltrating refractive index liquid into one of the air holes of the photonic crystal fiber, the core mode can be coupled into the higher order liquid rod mode, thus producing a resonant dip in the transmission spectrum of the device. Such a dip wavelength is sensitive to both the bending curvature and the direction, and has a linear response to curvature within a large range from 0 to 10.7 m $^{-1}$ .

Torsion Test of Fiber Carbon Composite Core Rod Used in Overhead Stranded Wires

This paper analyzes the performance of fiber carbon composite core rod under torsion load through finite element simulation and full-scale test, providing technical basis for the failure mode and key parameter design of fiber carbon composite core rod.

Phase transition modeling of polytetrafluoroethylene during Taylor impact

The complex pressure and temperature dependent phase behavior of the semicrystalline polymer polytetrafluoroethylene (PTFE) has been investigated experimentally. One manifestation of this behavior has been observed as an anomalous abrupt ductile-to-brittle transition in the failure mode of PTFE rods in Taylor cylinder impact tests when impact velocity exceeds a narrow critical threshold. Earlier, hydrocode calculations and Hugoniot estimates have indicated that this critical velocity corresponds to the pressure in PTFE associated with the transition from a crystalline phase of helical structure to the high pressure crystalline phase (phase III) of a planar form. The present work represents PTFE as a material in a simplified phase structure with the transition between the modeled phases regulated by a kinetic description. The constitutive modeling describes the evolution of mechanical characteristics corresponding to the change of mechanical properties due to either an increase of crystallinity or the phase transition of a crystalline low-pressure component into phase III. The modeling results demonstrate that a change in the kinetics of the transition mechanism in PTFE when traversing the critical impact velocity can be used to explain the failure of the polymer in the Taylor cylinder impact tests.

Tunable Fano Resonance in Rod-Ring Plasmonic Nanocavities

Tunable Fano resonances in the gold rod-ring plasmonic nanocavities with strong coherent coupling are demonstrated by finite-difference time-domain (FDTD) method. For one rod-one ring nanocavity, symmetry breaking activates the high-order plasmon modes in the ring and causes a Fano resonance with a dip in the extinction spectrum of the cavity by the coherent coupling between the bright rod mode and dark ring mode. The addition of a non-resonant rod introduces a second dark mode, which could be successively excited by the first dark ring mode, and produces double Fano resonances. By adjusting the rod number and configuration of the nanocavity, the extinction line shape can be controlled and the near-field distribution can be dramatically modified. An intriguing phenomenon of superposition beats in the plasmon damping process is revealed, which induces an energy swap between the rod and ring. The antenna effect of the resonant rod as well as the energy transfer and distribution in the nanocavities are also discussed.

Strong dipole-quadrupole coupling and Fano resonance in H-like metallic nanostructures.

Under certain conditions of the incident light polarization direction a Fano resonance arises in small gold nanorods arranged in a H-like configuration. This stems from the coupling between a bright dipole plasmon mode excited in the horizontal rod and dark quadrupole plasmon modes in both vertical rods. We investigate these surface plasmon modes, and analyze the dependence of the Fano resonance on the geometry parameters such as rod size and interparticle separation, and refractive index of embedding medium. To describe the degree of this energy transfer, we introduce a new parameter: the Fano resonance efficiency. We calculate absorption cross-sections for visible and NIR spectrum in each element of the structure, and near-field distributions at different wavelengths. We show that Fano resonance in small H-like structures exhibits high sensitivity with respect to the refractive index of the host medium, outperforming the values for larger plasmonic structures based on nanorods already investigated.

Исследование методик определения констант поляризованной пьезокерамики

Amplitude-frequency characteristics of the piezoceramic elements in the forms of a thin plate and a rod are studied through ANSYS program. Resonance and antiresonance frequencies of the first two disk radial modes, the thickness mode of the thin plate, and the axial mode of the rectangular cross-section long rod are measured. The numerical results are compared to the known determination techniques of the elastic S ij , piezoelectric d ij, and dielectric ε ij constants of the piezoelectric materials. The improved procedure for determining elasticity constant S E 13 on one specimen of only radial disk oscillations is suggested and substantiated. The method is based upon the relationships between the elastic constants of piezoceramics and the dispersion of longitudinal waves. The new method usage domain is studied. As compared to the known techniques, the proposed method facilitates the measure procedure and allows determining the elastic constant with the extended precision. A fundamentally new technique of measuring resonant and antiresonant frequencies of piezoelements with losses is developed for defining a full range of material constants of ideal elements without losses according to the Russian branch standards and the Institute of Radio Engineers (USA) standards for piezoelectric crystals.

Crystal Structure Anisotropy Explains Anomalous Elastic Properties of Nanorods

It is demonstrated that the frequency of the extensional vibrational mode of a nanorod made of an elastically anisotropic crystalline material deviates widely from the predictions of the theories based on the analysis of the long-wavelength limit. The dispersion relation for the fundamental extensional mode of a gold rod grown in the [100] direction is calculated and found to be in excellent agreement with experimental data obtained from the transient optical absorption measurements on gold nanorods. This explains an anomaly in the elastic properties of nanorods which was previously attributed to a 26% decrease in Young's modulus for nanorods compared to its bulk value. The developed approach allows one to investigate the role of the crystal structure anisotropy for acoustic phonons in nanorods and nanowires made of any metal or semiconductor material having cubic crystal structure.

Theoretical analysis of the local orientation effect and the lift‐hyperlayer mode of rodlike particles in field‐flow fractionation

We investigated theoretically the effects of the cross-stream migration and the local average orientation of rodlike particles on the shape-based separation using field-flow fractionation. The separation behavior was analyzed by comparing the retention ratios of spheres and rods. The retention ratio of a rod was evaluated through the derivation of its cross-sectional concentration profile by considering the rod migration and the local average orientation. Our study in various flow conditions showed that the rod migration, caused by the hydrodynamic interaction with a wall, can affect the separation behavior as a lift-hyperlayer mode. We also demonstrated that the local average orientation, which is a function of a local shear rate and a rotational diffusivity, results in the transverse diffusivity that is different from its perpendicular diffusivity. These results suggest that the experimental separation behaviors of rods in field-flow fractionation may not be fully explained by the current theory based on the normal mode and the steric mode. We also characterized each condition where one of the normal mode, the steric mode of spheres, and the lift-hyperlayer mode of rods is dominant.

Structural studies show energy transfer within stabilized phycobilisomes independent of the mode of rod–core assembly

The major light harvesting complex in cyanobacteria and red algae is the phycobilisome (PBS), comprised of hundreds of seemingly similar chromophores, which are protein bound and assembled in a fashion that enables highly efficient uni-directional energy transfer to reaction centers. The PBS is comprised of a core containing 2–5 cylinders surrounded by 6–8 rods, and a number of models have been proposed describing the PBS structure. One of the most critical steps in the functionality of the PBS is energy transfer from the rod substructures to the core substructure. In this study we compare the structural and functional characteristics of high-phosphate stabilized PBS (the standard fashion of stabilization of isolated complexes) with cross-linked PBS in low ionic strength buffer from two cyanobacterial species, Thermosynechococcus vulcanus and Acaryochloris marina. We show that chemical cross-linking preserves efficient energy transfer from the phycocyanin containing rods to the allophycocyanin containing cores with fluorescent emission from the terminal emitters. However, this energy transfer is shown to exist in PBS complexes of different structures as characterized by determination of a 2.4Å structure by X-ray crystallography, single crystal confocal microscopy, mass spectrometry and transmission electron microscopy of negatively stained and cryogenically preserved complexes. We conclude that the PBS has intrinsic structural properties that enable efficient energy transfer from rod substructures to the core substructures without requiring a single unique structure. We discuss the significance of our observations on the functionality of the PBS in vivo.

Twin-resonance-coupling and high sensitivity sensing characteristics of a selectively fluid-filled microstructured optical fiber

A twin-resonance-coupling phenomenon and the sensing characteristics of a selectively fluid-filled microstructured optical fiber (SFMOF) are proposed and demonstrated. The SFMOF is realized by selectively infiltrating refractive index fluid into a single air hole located at the second ring near the core of the MOF. Twin-resonance dips are observed in the transmission spectrum. Theoretical and experimental investigations reveal that the twin-resonance dips both result from the coupling between LP(01)(C) silica core mode and LP(01)(L) liquid rod mode. Their sensitivities strongly depend on the dispersion curves of the silica and fluid material. Sensitivities of 290 nm/°C (739,796 nm/RIU) and 591.84 nm/N (701.2 pm/µɛ) are achieved, which are the highest for a SFMOF-based device to date, to our best knowledge. Furthermore, the twin-resonance dips appear to shift in the opposite directions with changes in temperature or axial strain, providing a method to achieve two- or multi-parameter measurement in such a compact structure.

Enhancing spin-orbit interaction of light by plasmonic nanostructures

The spin orbit interactions (SOI) of light mediated by single scattering from plasmon resonant metal nanoparticles (nanorods and nanospheres) are investigated using Jones and Mueller matrix polarimetry formalism. The effect of neighboring resonances in plasmonic nanostructures (e.g., orthogonal electric dipolar modes in rods or electric dipolar and quadrupolar modes in spheres) on the individual SOI effects are analyzed and interpreted via the Mueller matrix-derived polarimetry characteristics, namely, diattenuation d and retardance δ. The results clearly reveal that each of these can be controllably tuned and enhanced by exploiting the interference of neighboring modes.

Hybrid Standing Wave and Whispering Gallery Modes in Needle-Shaped ZnO Rods: Simulation of Emission Microscopy Images Using Finite Difference Frequency Domain Methods with a Focused Gaussian Source

Two-photon emission microscopy is used to investigate the photoluminescence properties of individual ZnO rods. The rods are 10–20 μm in length with a tapered cross section that varies from 1 to 2 μm at the midpoint to several hundred nanometers at the ends. The tapered shape and hexagonal cross section result in complex optical resonator modes that lead to periodic patterns in the two-photon emission image. Finite-difference frequency domain methods using a series of excitation sources, including focused Gaussian, point dipole, and plane wave, suggest that resonator modes have both standing wave (Fabry-Perot) and whispering gallery mode character, whose relative contributions vary along the rod axis.

Embedded coupler based on selectively infiltrated photonic crystal fiber for strain measurement

A photonic crystal fiber (PCF) with embedded coupler is demonstrated for strain measurement. The embedded coupler is constructed by the selective filling of one of the air holes in the PCF. Light propagated in the fiber core can be efficiently coupled to the liquid-filled rod waveguide under phase-matching conditions, resulting in sharp decreasing of resonant wavelength intensity. The highest strain sensitivity is calculated to be ~23.8 pm/με due to the coupling between core mode and fundamental mode of the liquid rod, when the refractive index (RI) of the liquid is 1.46. With the increase of the RI, the resonance can also be observed between the core mode and the higher-order modes of the liquid rod, whereas the strain sensitivity drops to ~6.4 pm/με. The experimentally obtained static strain sensitivity values are ~22 and ~3.8 pm/με for the coupling between the core mode and the fundamental mode or linearly polarized LP(11) modes of the liquid rod, respectively, which are in good agreement with the simulations. The dynamic strain measurement resolution obtained is ~1.2 nε/(Hz)(1/2).

Surface Plasmon Mapping of Dumbbell-Shaped Gold Nanorods: The Effect of Silver Coating

We report on the identification of surface plasmons in individual gold dumbbell-shaped nanoparticles (AuDBs), as well as AuDBs coated with silver. We use spatially resolved electron energy-loss spectroscopy in a scanning electron microscope, which allows us to map plasmon-energy and intensity spatial distributions. Two dominant plasmon resonances are experimentally resolved in both AuDBs and silver-coated AuDBs. The intensity of these features is peaked either at the tips or at the sides of the nanoparticles. We present boundary element method simulations in good agreement with the experiment, allowing us to elucidate the nature of such modes. While the lower-energy, tip-focused plasmon is of longitudinal character for all dumbbells under consideration, the second side-bound plasmon has a more involved symmetry, starting as a longitudinal quadrupole in homogeneous AuDBs and picking up transversal components when silver coating is added. The longitudinal dipolar mode energy is found to blue-shift upon coating with silver. We find that the substrate produces sizable shifts in the plasmons of silver-coated AuDBs. Our analysis portraits a complex plasmonic scenario in metal nanoparticles coated with silver, including a transition from the original homogeneous gold dumbbell plasmons to the modes of homogeneous silver rods. We believe that these findings can have potential application to plasmon engineering.

Failure modes and failure mechanisms of RC members strengthened by NSM CFRP composites – Analysis of pull-out failure mode

The aim of the experimental programme developed in this work was to study the failure modes and the pull-out failure mechanism of RC members strengthened by Near Surface Mounted reinforcement (NSM) technique. The global behaviour of reinforced concrete beams strengthened by NSM and subjected to flexure was investigated. The rods were 6- and 12-mm-diameter carbon–epoxy pultruded FRP. Two vibrated concrete compositions were tested: conventional (VC30) and high-strength (VC60), and one filling material: epoxy resin. The study was carried out up to the failure load, and focused on the failure modes of the beams. The experimental results were compared with the analytical model for the pull-out failure mode of FRP rods. Based on the concept of the anchorage length beyond the last crack, the calculation gives a good approximation of the ultimate bond stress in the cross-section located at the last crack.

Selectively Infiltrated Photonic Crystal Fiber With Ultrahigh Temperature Sensitivity

By selective filling of one of the air holes in the photonic crystal fiber, the fundamental core mode can be effectively coupled to the fundamental mode of the adjacent liquid rod waveguide at the resonant wavelength with extremely high temperature sensitivity. The spectral power of the rod mode can be filtered out by fusion splicing the selectively infiltrated photonic crystal fiber with conventional single-mode fiber, resulting in a sharp dip in the transmission spectrum. Such a device is demonstrated in our experiment by filling standard 1.46 refractive index liquid into one of the air holes of the commercially available photonic crystal fiber by use of femtosecond laser-assisted selective infiltration technique. The average temperature sensitivity achieved is ~54.3 nm/°C.

Complex resonance and localized vibrations at the edge of a semi-infinite elastic cylinder

The effect of the free edge of a semi-infinite elastic cylinder with circular cross section is considered. It is shown that there exists a complex resonance frequency associated with an axially symmetric localized vibration near the free edge for every value of the Poisson ratio v. For two particular values of v, v = 0 and v = 0.1267, the imaginary part of the complex resonance frequency is zero which corresponds to a trapped mode of the semi-infinite rod. This resonance is also shown to be associated with two eigenfrequencies of the finite length cylinder.

Fatigue Analysis of the Pipeline Robot's Swing Rod

Put forward and develop a pipeline cleaning robot. Relying on finite element analysis software ANSYS，establishing finite element model of pipeline robot swinging rod with the solid92 as the basic unit，it was found that the swing rod of the pipeline robot was the weak link by a large number of on-site experiments. After analysis the fatigue properties of pipeline robot's swing rod，compared with the results of its static analysis and evaluation of failure mode of pipe robot's swing rod，reasonable proposals are put forward for the follow-up study of the pipeline robot.

Experimental realization of all-dielectric composite cubes/rods left-handed metamaterial

We present a novel all-dielectric left-handed metamaterial (LHM) in the X-band microwave regime. The LHM is formed by cubes and square rods, which are made of microwave ceramic with high permittivity and low loss. Both Mie theory and dielectric resonator theory are found to play important roles in generating negative effective parameters. The effective permeability is negative in the designed frequency range due to the first Mie resonance associated with the cubes, while the effective permittivity is negative below the plasma frequency owing to the second resonance mode of the square rods. The parameter retrieval method, transmission spectra method and wedge-shaped negative refraction method are used to demonstrate that the composite has a double-negative regime. Experiments are carried out to verify the designed all-dielectric LHM. The proposed method presents new ways to realize all-dielectric LHMs.

Design of high-index broken-ring-based all-solid photonic bandgap fibers

The design of all-solid photonic bandgap fibers based on a high-index broken ring is investigated, where the background material is silica and the broken ring consists of several individual high-index rods. Density of states maps and Bloch mode field distributions obtained by plane wave expansion method show that a high-order bandgap in such fibers can be engineered and broadened. The principle is that both the azimuthal and the radial orders of the LP modes of the high-index rods in the cladding can be controlled by the broken ring. It is demonstrated that the highest azimuthal order of the group of less affected LP modes is determined by the rod number and the bandgap width is largely affected by the rod size. The high-order bandgap can be used to design all-solid photonic bandgap fiber with broad transmission ranges of 488 nm and 944 nm for a center wavelength of 800 nm and 1550 nm, respectively, and the transmission window features the typical normal-zero-anomalous dispersion profile.