Corrugation Period Research Articles

Infrared Propagating Electromagnetic Surface Waves Excited by Induction

AbstractPropagating inhomogeneous electromagnetic waves called surface plasmon polaritons (SPPs) can be excited by free-space beams on corrugated conducting surfaces at resonance angles determined by corrugation period, permittivity, and optical frequency. SPPs are coupled to and co-propagate with surface charge displacements. Complete electrical isolation of individual conducting corrugations prevents the charge displacement necessary to sustain an SPP, such that excitation resonances of traveling SPPs are absent. However, SPPs can be excited via electric induction if a smooth conducting surface exists below and nearby the isolated conducting corrugations. The dependence of SPP excitation resonances on that separation is experimentally investigated here at long-wave infrared wavelengths. We find that excitation resonances for traveling SPPs broaden and disappear as the dielectric’s physical thickness is increased beyond ~1% of the free-space wavelength. The resonance line width increases with refractive index and optical thickness of the dielectric.

Terahertz Thermal Sensing by Using a Defect-Containing Periodically Corrugated Gold Waveguide

A terahertz (THz) thermal sensor has been developed by using a periodically corrugated gold waveguide. A defect was positioned in the middle of this waveguide. The periodicities of waveguides can result in Bragg and non-Bragg gaps with identical and different transverse mode resonances, respectively. Due to the local resonance of the energy concentration in the inserted tube, a non-Bragg defect state (NBDS) was observed to arise in the non-Bragg gap. It exhibited an extremely narrow transmission peak. The numerical results showed that by using the here proposed waveguide structure, a NBDS would appear at a resonance frequency of 0.695 THz. In addition, a redshift of this frequency was observed to occur with an increase in the ambient temperature. It was also found that the maximum sensitivity can reach 11.5 MHz/K for an optimized defect radius of 0.9 times the mean value of the waveguide inner tube radius, and for a defect length of 0.2 (or 0.8) times the corrugation period. In the present simulations, a temperature modification of the Drude model was also used. By using this model, the thermal sensing could be realized with an impressive sensitivity. This THz thermal sensor is thereby very promising for applications based on high-precision temperature measurements and control.

Generalized analytical dispersion equations for guided Rayleigh-Lamb (RL) waves and shear horizontal (SH) waves in corrugated waveguides

Corrugated waveguides are periodic structures that exhibit important acoustic features. Features like acoustic bandgaps exhibit the ability to filter acoustic and ultrasonic frequencies. By varying the mean thickness, corrugation height, and periodicity, one can tune the propagating wave modes in the guide and thus can modify the bandgaps. This study aims to obtain a generalized Rayleigh–Lamb equation for corrugated waveguides such that a single equation is sufficient for both flat waveguides such as plates as well as corrugated and tapered plates. Further, the objective was to understand the effects of the corrugation height, periodicity, and mean thickness such that a physics-based predictive design of wave filters can be achieved. Instead of applying the Bloch–Floquet theorem to the displacement function directly, which is conventional, the theorem is applied to the scalar and vector wave potentials obtained from Helmholtz decomposition. The governing equations from these relationships after applying boundary conditions were then solved using a logical root-finding algorithm. To verify the generalized expressions guided wave band structure for a plate was obtained using Rayleigh–Lamb equation and compared with the generalized form setting the corrugation height to zero. The analytical solutions are then validated through a comparison with the results obtained from a rigorous finite element simulation. Finally, the effects on the propagating and evanescent wave modes due to the corrugation height and periodicity are studied for future reference.

Dispersion of electromagnetic waves in coaxial cylindrical rippled-wall waveguide including plasma layer

Electronic technologies, especially in the microwave and terahertz frequency ranges, including plasma show better interaction efficiency and higher output power as compared to apparatus with the vacuum. Also, in these frequency ranges, the plasma-filled high-power waveguides can support TE and TM modes. Therefore, in this study, the dispersion relation of electromagnetic (EM) waves in a new rippled-wall waveguide structure contain the plasma layer and coaxial dielectric geometry is numerically studied. The Maxwell equations and boundary conditions are employed to investigate and analyze the dispersion relation in TM mode for coaxial geometry dielectric rippled-wall waveguide contain the plasma layer. High-frequency radiations are observed from the proposed configuration. It is found that the frequency of the wave increases with a decrease in the corrugation amplitude and period. Moreover, a decrease in frequency is observed with an increase in dielectric radius and a decrease in plasma radius.

Surface radiation of a charged particle bunch passing through a corrugated surface with a relatively small period

We investigate radiation of a charged particle bunch moving through a corrugated planar conductive surface. It is assumed that the corrugation period and depth are much less than the wavelengths under consideration. In this case, the corrugated structure can be replaced with some smooth surface on which the so-called equivalent boundary conditions (EBC) are fulfilled. Using the EBC method we obtain expressions for the electromagnetic field of the bunch which are presented in form of spectral integrals. It is demonstrated that the bunch generates surface waves propagating along the corrugations with the light velocity. Also we present results of numerical calculations for electromagnetic field components of surface waves depending on coordinates and show that these dependences can be used for determination of the bunch size.

Formation of a Corrugated Surface on a Carbon Fiber under High-Fluence Irradiation with Nitrogen Ions

The behavior of the surface of carbon fibers based on polyacrylonitrile, which reinforce the KUP-VM composite, upon corrugation under high-fluence irradiation with $${\text{N}}_{2}^{ + }$$ ions with an energy of 15 and 30 keV and a temperature of the irradiated composite in the range from 100°C to 600°C is described and discussed. In contrast to irradiation with ions of noble gases, it is found that the main parameters of the corrugated structure, such as the tilt angles of corrugations and their fractions on the surface of a fiber, are practically independent of the composite temperature. The corrugation periodicity is hundreds of nanometers, as in the case of irradiation with neon and argon ions. In the case of using ion energies of 15 and 30 keV, the tilt angles are 30° and 40°, respectively. The difference between the temperature dependences of the tilt angle of the corrugations and their fraction on the fiber surface and similar dependences in the case of irradiation with noble gas ions is determined by the peculiarities of the dynamic annealing of radiation-induced damage in the fiber shell due to the chemical activity of nitrogen associated with the creation of C–N bonds and a larger proportion of the amorphous component.

Terahertz cherenkov radiation excited by an electron beam in a cylindrical metallic rippled-wall waveguide

The Cherenkov excitation of terahertz (THz) radiation by the interaction of an electron beam with the transverse magnetic modes of electromagnetic waves in a new configuration of cylindrical metallic rippled-wall waveguide (CMRWW) including an unmagnetized degenerate plasma layer and a dielectric rod is studied. In addition, the electric field profiles and the growth rates of these waves are investigated by deriving the wave equation and the dispersion relation for the proposed configuration. The effects of physical parameters such as dielectric and plasma radii, corrugation amplitude, and corrugation period on the dispersion relation, electric field profiles and growth rates of the terahertz radiation are discussed. It is shown that by choosing appropriate parameters of the electron beam and the waveguide, one can generate high power radiation in the terahertz range.

The Identification and Assessment of Rail Corrugation Based on Computer Vision

The identification and assessment of rail corrugation are two of the essential tasks of daily railway inspection to guarantee the safety of train operation and promote the development of an efficient maintenance strategy. In view of the requirements for automatic identification and smart decision-making, computer vision-based rail corrugation identification and assessment methods are presented in this paper. Firstly, an improved Spatial Pyramid Matching (SPM) model, integrating multi-features and locality-constrained linear coding (IMFLLC), is proposed for rail corrugation identification. After that, an innovative period estimation method for rail corrugation is proposed based on the frequency domain analysis of each column in the corrugation region. Finally, the severity of the rail corrugation is assessed with the help of the wear saliency calculation and fuzzy theory. The experiment results demonstrate that the proposed corrugation identification method achieves a higher precision rate and recall rate than those of traditional methods, reaching 99.67% and 98.34%, respectively. Besides, the validity and feasibility of the proposed methods for the rail corrugation period estimation and severity assessment are also investigated.

A numerical evaluation of next generation additive layer manufactured inter-layer channel heat exchanger

A Concept Heat Exchanger (HE) design manufactured using the Additive Layer Manufacturing (ALM) technique Selective Laser Melting (SLM) is proposed and numerically evaluated. It is composed of a HE corrugation which introduces inter-layer flow conduits between the parallel HE layers of the same fluid. These pathways are provided by hollow elliptical tubes which serve several functions: to disturb the flow to promote heat transfer, to provide additional heat transfer area and to minimise flow maldistribution inside the HE core. The corrugation is incorporated into a counter-flow prototype HE unit model meaning to exploit the installation volume and design freedom made possible via ALM. Three Computational Fluid Dynamics (CFD) models are utilised to evaluate the performance of the proposed HE unit. Firstly, a traditional two step HE design methodology is utilised which works by initially evaluating a fully symmetric channel of the proposed HE corrugation (termed single channel). Then the results this model are incorporated into a simplified HE unit model. The second approach evaluates the HE unit performance based on a fully detailed CFD analysis that fully resolves flow and heat transfer inside the HE core. The third modelling approach involves splitting the inter-layer HE unit model into parts, which results in HE header models and allows simplification of the HE core into a single corrugation period width HE core model (termed superchannel). The results of these models are then compared to a conventional pin–fin HE unit model, formed by blocking the elliptical inter-layer conduits. It was found that in all the HE unit models the pressure drop is similar whilst the heat transfer was enhanced by between 7% and 13% in terms of the overall ΔT by the inter-layer channels (increasing with the Reynolds number). All simulations were completed using a CFD package OpenFOAM.

Scattering of Plane Waves From an Infinite Dielectric Periodic Surface

AbstractIn this paper, the scattering characteristics an infinite dielectric periodic surface are investigated in detail. The Fourier expression of scattering field of the periodic surface is obtained by using the Rayleigh hypothesis and the Floquet theorem. Using the extended boundary condition method and the T‐matrix method, the scattering amplitude factor is solved, and the correctness of the algorithm is verified by use of the law of energy conservation. The scattering cross section of the periodic surface in the infinitely long region is derived by improving the formula of the finite one as its length is increased. Furthermore, the effects of the incident wave parameters and geometric structure parameters on the scattering of the periodic surface are analyzed and discussed. The results show that the period and amplitude of the surface corrugations determine the number of scattering intensity peaks, and influence the scattering intensity distribution with permittivity significantly.

The regularities of surface corrugation of polyacrylonitrile based carbon fibers under high-fluence ion irradiation

The regularities of surface corrugation of polyacrylonitrile based carbon fibers reinforcing composite KUP-VM has been studied experimentally after high-fluence 30 keV Ne+, 20 and 30 keV Ar+, 30 keV N2+ ion irradiation at target temperatures ranging from 100 to 600 °C. It was found that periodic corrugated structure parameters, such as the angles of the inclination β of the corrugations and their fraction on the fiber surface have strong temperature dependences. The periodicity of corrugations for all used ions slightly decreases with increasing temperature and is of the order of hundreds of nanometers. For neon and argon ions the corrugation inclination angles and the fraction in contrary of nitrogen ions show minima at the temperatures near 400 °C which corresponds to the minimum of radiation-induced dimensional changes in carbon materials. The depth of the minima at 400 °C depends on the competition of the processes of ion-induced plastic deformation of carbon materials and ion bombardment sputtering. For nitrogen ions the inclination angles increase with temperature so that at temperature ∼270 °C they reach maximum values ∼40°, staying at this level at subsequent temperature elevation up to 600 °C. The qualitative difference in the temperature dependences of fiber corrugation for noble gas ions and nitrogen ones is connected to nitrogen chemical activity and the creation of CN bonds under nitrogen ion implantation.

Enhanced heat transfer in tubes based on vascular heat exchangers in fish: Experimental investigation

A double corrugated tube geometry for improved heat transfer performance inspired by vascular heat exchangers found in fish such as the tuna and the opah is presented. The geometry features a cross section that varies continuously in the flow direction while maintaining a constant hydraulic diameter, which gives enhanced heat transfer at a relatively low increase in pressure drop. Five ellipse-based tubes with varying corrugation severity and period that emulate blood vessels of fish were produced in an aluminium alloy using additive manufacturing technology. Thermal performance of the novel tube design was experimentally investigated in a counter flow tube-in-shell heat exchanger in a range of Reynolds numbers from 1000 to 2500. Correlations for the Nusselt number and friction factor for each tube are proposed and the experimental results show that the Nusselt number increases up to 500% in corrugated tubes compared to a straight tube. The global thermo-hydraulic performance, evaluated for the same pumping power, of the double corrugated tubes is up to 160% higher than that of a straight tube.

Stability of a thin film flow on a weakly wavy wall

We consider a thin viscous liquid film flow down an inclined plane with sinusoidal topography. We use the integral boundary layer approach to derive governing equations. By use of Floquet theory, we study linear stability of steady-state flow. For small values of the topography amplitude, perturbation analysis gives an analytical expression for corrections to the growth rate of a normal mode disturbance. This correction is proportional to the second power of the topography amplitude. The topography can both stabilize and destabilize the flow, depending on the corrugation period and the plane inclination angle. We study the topology of neutral curves and the critical Reynolds number dependence on topography parameters.

Ion-Induced Corrugation and Surface Erosion of PAN-Based Carbon Fiber

The regularities of ion-induced corrugation of a VMN-4 carbon-fiber shell of the KUP-VM unidirectional composite under high-fluence irradiation with Ar+ ions at energies of 20 and 30 keV have been experimentally studied in the range from room temperature to 600°C. A developed submicron corrugated structure of the carbon fiber surface at an ion path length of 20–40 nm in graphite is registered starting from temperatures around 200°C. The corrugation period is a few hundred nanometers, weakly depends on the temperature of the irradiated carbon fiber, and decreases with a decrease in the ion energy or an increase in the incidence angle of the ion beam on the cylindrical fiber surface. The temperature of an irradiated fiber has a strong effect on the geometry and the fraction of corrugations in the fiber surface part irradiated with ions at normal incidence. For an ion energy of 20 keV in the temperature range of 350–500°C, the apical part of the fiber is similar to the initial surface. A stronger effect of corrugation reduction for an argon-ion beam energy of 20 keV in comparison with an irradiation energy of 30 keV is explained by the competition between the processes of ion-induced corrugation under plastic deformation of the modified layer and the surface erosion at sputtering, which leads to the smoothing of the surface.

Dissipative Rayleigh–Taylor Instability and its Contribution to the Formation of an Interface between Biomaterials at Their Electric Welding

The dissipative Rayleigh–Taylor instability, which can arise at the interface between biomaterials under the action of high-frequency currents, has been considered. A mechanism describing the formation of a corrugated boundary of the mesomorphic phase is proposed. The corrugation period and depth are evaluated.

Design of optimum rear passivated submicron Al corrugation in very thin textured silicon back-contact back-junction solar cell for absorption enhancement up to near-infrared region

The optical reflection and absorption in a very thin textured back-contact back-junction silicon (Si) solar cell are investigated. The introduction of nanotexturing on front Si surface has significantly increased the absorption in the ultraviolet (UV)–visible region with a low reflection of below 0.05. The introduction of rear surface corrugation formed by a combination of SiO2-Al has successfully enhanced the absorption up to near-infrared (NI) region. The optimum crest width, periodicity, and trough depth of corrugation are derived, which lead to high absorption up to 0.97. The internal reflection and scattering that occur near the plasmonic Al corrugation are contributing to the local maximum electric field intensity in both transverse magnetic (TM) and transverse electric (TE) modes. Since there is no perpendicular electric component in TE mode, a coupling of electric field within a corrugation trough is not observed but is only observed in TM mode. On 10-μm-thick Si, the application of Si nanocones (NCs) and optimized rear Al corrugation results in 56% improvement in photogenerated current, Jsc, compared to the reference flat Si. Thinning down the Si to only 2 μm severely limits the Jsc. Our optimized Al corrugation manages to compensate net 9% and 7% Jsc loss in 2-μm Si in respect to 10-μm-thick Si for the model with and without front Si NCs. The results seem to reveal the optimum design of rear Al corrugation for the absorption enhancement from UV up to NI wavelength region.

Formation of periodic ripples on silicon surface ablated by femtosecond laser

The formation mechanism of low-spatial-frequency laser-induced periodic surface structure (LSFL) on single-crystalline silicon irradiated by single femtosecond-laser pulse (pulse duration =150 fs and central wavelength =800 nm) in air is investigated theoretically based on the interference theory of Sipe-Drude model and surface plasmon polariton (SPP). In order to account for transient intrapulse changes in the optical properties of the material due to the excitation of a dense electron-hole plasma, we model the maximum of the electron density as a function of laser fluence by solving the generally accepted two-temperature equation and Drude model. The results show that both theories are applicable to explaining the LSFL formation on the high-excited silicon. In the Sipe-Drude theory, the factor (k) is used to describe the efficacy with which the surface roughness at position k leads to inhomogeneous absorption of radiation. We find that the value of (k) first increases until reaching a maximum at an electron density of 61021 cm-3 and then decreases with the laser fluence increasing. When the incident laser fluence is 0.38 J/cm2, which is the threshold for excited plasma, the period reaches a minimum value in a small range of the top. Besides, the law of period is calculated according to the relationship between the (k) and period. In the SPP theory, the ripple period on the highly excited silicon increases with the laser fluence increasing. Comparing the scopes of application of two theories, the Sipe-Drude theory is found to be suitable for the analysis of more extensive periodic surface structures, while the SPP theory is applicable only for the case that laser fluence is close to the damage threshold. Moreover, our results are capable of explaining that the delay direction of periodic ripples are always perpendicular to the incident laser polarization direction by using the Sipe-Drude theory. When laser fluence approaches to the damage threshold, the LIPSS period is calculated sightly to be below the laser wavelength. It also reveals that the periodic surface structures are approximately the same in the different polarization directions with the increase of incident angle. Taking into account a single pulse, the corrugation period decreases with the increase of angle of incidence in the S polarization direction. And under different polarizations, with the increase of incident angle, the changes of the ripple period show an opposite trend. The obtained dependence provides a way to better control the properties of the periodic structures induced by femtosecond laser on the surface of a semiconductor material, which is of great significance for understanding the formation of periodic structure of silicon surface, caused by femtosecond laser, and its application in the field of silicon materials processing.

Design of chirped distributed Bragg reflector for octave-spanning frequency group velocity dispersion compensation in terahertz quantum cascade laser

The strategies and approaches of designing chirped Distributed Bragg Reflector for group velocity compensation in metal-metal waveguide terahertz quantum cascade laser are investigated through 1D and 3D models. The results show the depth of the corrugation periods plays an important role on achieving broad-band group velocity compensation in terahertz range. However, the deep corrugation also brings distortion to the group delay behavior. A two-section chirped DBR is proposed to provide smoother group delay compensation while still maintain the broad frequency range (octave) operation within 2 THz to 4 THz.

Formation of Periodically Arranged Nanobubbles in Mesopores: Capillary Bridge Formation and Cavitation during Sorption and Solidification in an Hierarchical Porous SBA-15 Matrix.

We report synchrotron-based small-angle X-ray scattering experiments on a template-grown porous silica matrix (Santa Barbara Amorphous-15) upon in situ sorption of fluorinated pentane C5F12 along with volumetric gas sorption isotherm measurements. Within the mean-field model of Saam and Cole for vapor condensation in cylindrical pores, a nitrogen and C5F12 sorption isotherm is well described by a bimodal pore radius distribution dominated by meso- and micropores with 3.4 and 1.6 nm mean radius, respectively. In the scattering experiments, two different periodicities become evident. One of them (d1 = 11.5 nm) reflects the next nearest neighbor distance in a 2D-hexagonal lattice of tubular mesopores. A second periodicity (d2 = 11.4 nm) found during in situ sorption and freezing experiments is traced back to a superstructure along the cylindrical mesopores. It is compatible with periodic pore corrugations found in electron tomograms of empty SBA-15 by Gommes et al. ( Chem. Mater. 2009, 21, 1311 - 1317). A Rayleigh-Plateau instability occurring at the cylindrical blockcopolymer micelles characteristic of the SBA-15 templating process quantitatively accounts for the superstructure and thus the spatial periodicity of the pore wall corrugation. The consequences of this peculiar morphological feature on the spatial arrangement of C5F12, in particular the formation of periodically arranged nanobubbles (or voids) upon adsorption, desorption, and freezing of liquids, are discussed in terms of capillary bridge formation and cavitation in tubular but periodically corrugated pores.

Influence of surface corrugation on the sputtering of carbon materials under high-fluence ion bombardment

The results of experimental and computer-based studies of the sputtering and erosion of carbonmaterial surfaces under high-fluence irradiation with 30-keV Ar+ ions at various angles of ion incidence are given. The irradiation of highly oriented pyrolytic graphite (HOPG) and polyacrylonitrile fibers of carbon–carbon composites, which are characterized by surface corrugation, is considered. A model is proposed for taking into account the influence of parameters of symmetric corrugation on the characteristics of sputtering of the irradiated materials. Calculation shows that taking experimental values of the corrugation slopes into account allows one to explain the angular dependence of the sputtering yield of HOPG. It is found that the pronounced (about two times) suppression of sputtering within the range of incidence angles of 60°–80° is connected with the rear (relative to the ion beam) faces of the corrugation being obscured. Unlike the case of the normal incidence of ions, the sputtering yield at large incidence angles decreases as the corrugation period increases due to blocking of the sputtering of the rear and neighboring faces of microrelief elements.