Multilayered Cylindrical Structures Research Articles

Anisotropic circular topological structures

We design cylindrical multilayer structures characterized by anisotropy and topological features. This provides a new approach to tailor electromagnetic fields into desired patterns with orbital angular momentum in cylindrical geometries as ring resonators and fibers. We use transformation optics to deal with anisotropic circular structures, and rigorously define the edge states. The resulting topologically protected high-localized modes, at the core/cladding interface, with angular momentum may trigger the developments of new disorder-robust devices and high Q-microcavities for applications in light transmission, quantum technology, nonlinear optics, TeraHertz devices, and biophysical sensors.

RESEARCH OF THE TEMPERATURE FIELD IN THE SYSTEM OF MULTILAYER CYLINDRICAL SOLID BODIES UNDER FIRE CONDITIONS

Introduction. The current urgent task is to find the temperature field distribution in cylindrical structures such as "solid cylinder inside a multilayer cylindrical shell". A characteristic feature of such structures is different mechanical and thermophysical characteristics of the layers combination, which makes them more perfect. However, this approach causes significant difficulties in developing analytical methods for their study. Therefore, new research methods development for multilayer, in particular, cylindrical structures is an urgent task today.Purpose. Direct method is used to study the heat transfer processes in the system "one-piece cylinder inside a multilayer cylindrical shell".Methods. To solve the initial parallel, the auxiliary problem of determining the distribution of a nonstationary temperature field in a multilayer hollow cylindrical structure with a "removed" cylinder of a sufficiently small radius is set. The solution of the auxiliary problem is realized by applying the method of reduction using the concept of quasi-derivatives. The Fourier schemeis used by using a modified method of eigenfunctions.Results. To find the solution to the problem, we used the idea of a boundary transition by directing the radius of the removedcylinder to zero. It is established that in this approach, all eigenfunctions of the corresponding problem have no singularities atzero, which means that the solutions of the original problem are limited in the whole structure. To illustrate the proposed method,a model example of finding the temperature field distribution in a four-layer column of circular cross-section (tubular concretecolumn) under the influence of the standard temperature of the fire. The results of the calculations are presented in the form of athree-dimensional graph of temperature changes depending on time and spatial coordinates.Conclusions. A direct method was used to solve the initial problem, using the idea of a boundary transition for the first time.In the general formulation (the function of changing the temperature of the environment is considered arbitrary, no restrictionsare imposed on the thickness of the shell and the number of layers) such a problem is solved for the first time.The structure of the obtained explicit exact formulas allows creating an algorithm for calculating the temperature field inthe form of automated programs, where it is enough to enter the initial data. Note that such algorithms include: a) calculating theroots of the characteristic equation; b) multiplication of a finite number of known matrices; c) calculation of definite integrals; d)summation of the required number of members of the series to obtain a given accuracy of the calculation.

Phase Stability and Miscibility in Ethanol/AOT/n-Heptane Systems: Evidence of Multilayered Cylindrical and Spherical Microemulsion Morphologies.

We describe the effects of ethanol on the phase behavior of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in n-heptane. Using dynamic light scattering (DLS), molecular dynamics (MD) simulations, and nuclear magnetic resonance (1H NMR) spectroscopy, we investigate the aggregation behavior of AOT across a wide range of ethanol/AOT/n-heptane compositions. We conclude that reverse micelles do not form at any of the investigated concentrations. Instead, we observe the formation of other surfactant aggregate morphologies unique to this system, namely, multilayered cylindrical structures and spherical AOT-in-ethanol structures, which vary significantly with changes in ethanol concentration. We also identify mixed-solvent polarity as a driving factor for the surfactant behavior in the system. When the concentration of ethanol is 20 wt % or below, the system is inhomogeneous with varying sizes of AOT, ethanol, and AOT + ethanol aggregates, with the ethanol primarily exhibiting a cosurfactant behavior, almost exclusively binding at the surface of AOT aggregates. With increased ethanol concentration, the ethanol in the system also exhibits solvent-like behaviors in addition to the cosurfactant behaviors. Most significantly, when the ethanol concentration is raised above 35 wt %, the transition to solvent-like behavior allows AOT Na+ counterions to dissociate from the headgroups and they are dissolved in the ethanol. We use these results to construct a preliminary phase diagram for the ethanol/AOT/n-heptane system.

Novel analytical model of anisotropic multi-layer cylindrical waveguides incorporating graphene layers

We propose a novel analytical model for anisotropic multi-layer cylindrical structures containing graphene layers. The general structure is formed by the aperiodic repetition of a three-layer sub-structure, where a graphene layer with isotropic surface conductivity of σ is sandwiched between two adjacent magnetic materials. Each anisotropic material has permittivity and permeability tensors of ε̿ and μ̿, respectively. An external magnetic bias is applied in the axial direction. The general matrix representation is obtained for our proposed analytical model to determine the dispersion relation. The relation is used to find the effective index of the structure and its other propagation parameters. Two special exemplary structures are introduced and employed to illustrate the richness of the proposed general structure in terms of the related specific plasmonic wave phenomena and effects. Several simulations were conducted to demonstrate the notable wave-guiding properties of the structure in the 10–40 THz band. Very good agreement was obtained between the analytical and simulation results. The proposed structure can be utilized to design novel plasmonic devices, such as absorbers, modulators, plasmonic sensors, and tunable antennas in the THz frequencies.

3D Printing of Cytocompatible Gelatin‐Cellulose‐Alginate Blend Hydrogels

3D bioprinting of hydrogels has gained great attention due to its potential to manufacture intricate and customized scaffolds that provide favored conditions for cell proliferation. Nevertheless, plain natural hydrogels can be easily disintegrated, and their mechanical strengths are usually insufficient for printing process. Hence, composite hydrogels are developed for 3D printing. This study aims to develop a hydrogel ink for extrusion-based 3D printing which is entirely composed of natural polymers, gelatin, alginate, and cellulose. Physicochemical interactionsbetween the components of the intertwined gelatin-cellulose-alginate network are studied via altering copolymer ratios. The structure of the materials and porosity are assessed using infrared spectroscopy, swelling, and degradation experiments. The utility of this approach is examined with two different crosslinking strategies using glutaraldehyde or CaCl2 . Multilayer cylindrical structures are successfully 3D printed, and their porous structure is confirmed by scanning electron microscopy and Brunauer-Emmett-Teller surface area analyses. Moreover, cytocompatibility of the hydrogel scaffolds is confirmed on fibroblast cells. The developed material is completely natural, biocompatible, economical, and the method is facile. Thus, this study is important for the development of advanced functional 3D hydrogels that have considerable potential for biomedical devices and artificial tissues.

CONCEPTION QUASIDERIVATIVES IN THE PROBLEMS OF MATHEMATICAL MODELING OF HEAT TRANSFER

In this paper, in closed form, the problems of determining stationary temperature fields in multilayer (flat, cylindrical and spherical) structures in the presence of discrete-continuous internal and point heat sources are solved. The one-dimensional differential equation of thermal conductivity in different coordinate systems is given through one parametric family of quasi-differential equations. It is assumed that the coefficients of the differential equation of thermal conductivity are piecewise constant functions. A system of two linearly independent boundary conditions is added to the equation, which in the general case are nonlocal. The solutions of such problems are constructive and are expressed exclusively through their initial data. The basic provisions of the concept of quasi-derivatives, the provisions of the theory of heat transfer, the theory of generalized systems of linear differential equations, elements of the theory of generalized functions are used. For the mathematical model of stationary thermal conductivity, the practical use of the concept of quasi-derivatives is illustrated, for the efficient construction, in a closed form, of solutions of boundary value problems with the most general boundary conditions. As an example, the problem of finding the critical radii of thermal insulation of multilayer hollow cylinders and spheres, taking into account the internal heat sources in the layers. Boundary conditions of the first and third kind. It is established that the value of the critical radius does not depend on the number of layers and the intensity of internal heat sources, but only on the thermal conductivity of the outer layer of the structure and the heat transfer coefficient between the structure and the environment. The formula for determining the critical radius of thermal insulation for a multilayer cylindrical and spherical structure is derived. The methods developed in this work have the prospect of further development and can be used in engineering calculations.

Mode excitation and radiation characteristics of antennas in cylindrically stratified media

Guided modes excited by a current source in a multilayer cylindrical structure is thoroughly investigated. The guidance condition in the multilayer structure is formulated. Based on this, three antenna configurations in cylindrical stratified media that are of strong practical interest are rigorously investigated: viz. a monopole antenna, a conformal axially-directed slot antenna and an azimuthal slot antenna in a cylindrical layered medium. While previous treatments of such configurations did not investigate the mode-excitation problem of antennas in stratified cylindrical media and were limited in their applicability for a dipole antenna in a cylindrical medium or assumed the slot-current distribution for a slot antenna over a conducting cylinder only, the current investigation provides an in-depth and rigorous insight to the modes excited and power coupled to the excited modes for the antenna configurations and removes such restrictions. In addition to the efficient and rigorous investigation of the coupling problem for the three antenna structures, the radiation characteristics of the antenna configurations are also evaluated using the method of stationary phase, enabling a comprehensive treatment of the antenna structures from both the coupling and radiation aspects.

PROPAGATION OF LINEAR WAVES IN MULTILAYERED STRUCTURAL - INHOMOGENEOUS CYLINDRICAL SHELLS

In this paper, axisymmetric viscoelastic waves in an extended cylindrical shell of circular cross section are considered. The study of axisymmetric viscoelastic waves in multilayer cylindrical systems with the maximum possible use of analytical methods is relevant for the development of a new generation of sounding techniques for wells. The aim of the work is to study the propagation of axisymmetric viscoelastic waves in extended multilayer cylindrical structures, to determine the volumetric structure variant from the responses of one-way sounding using a priori information about the possible structure of the system. The paper uses classical methods of mathematical physics, applied to solving boundary value problems in a cylindrical coordinate system, the spatial Fourier transform, the method of complex amplitudes for the variable components of the displacement vector and the stress tensor. The low-frequency resonances of a cylindrical shell are investigated. The physical laws of the formation of the pitch of its fundamental tone are determined sounding. The impossibility of propagation along the casing of wells is proved low-frequency surface waves, as well as SH-polarization waves at axisymmetric excitation. The thin-walled cylindrical shell in the low-frequency region has two fundamental resonance associated with the resonance of the shell as a whole and resonance of each individual section as a ring. Beats of these frequencies the basic tone of the sound of an extended shell of this type is determined. At frequencies below the cutoff of higher modes, all the features of the dispersion natural waves in the wall of a circular cylinder shell are described approximate algebraic equation of the third degree. One the real root of this equation corresponds to the zero mode antisymmetric Lamb wave, and one of the other two complex conjugate, describes the zero mode of the symmetric wave.

Exact frequency domain method for the analysis of scattering from multilayer bi-anisotropic cylindrical structures.

Bi-anisotropic materials have enormous and interesting applications in electromagnetic (EM) engineering. In this study, based on the state space concept, an exact and rigorous analysis of EM propagation and scattering from multilayer bi-anisotropic cylindrical structures of the general case is proposed. In comparison to the other commonly used methods in the literature, the presented method reveals a faster and more accurate analytical framework. The similar works mostly presented approximated and numerical methods for the analysis of cylindrical structures containing bi-isotropic and/or anisotropic materials as special bi-anisotropic cases. Throughout the study, the geometrical specifications and the EM excitations are chosen based on practical considerations. Since the multilayer composite is practical especially for the realization of the inhomogeneous material, the proposed approach is applied to analyze inhomogeneous bi-anisotropic cylindrical structures with more degrees of freedom in manipulation of EM waves. Our results depict an excellent conformity to the other possible solutions to compute scattering from bi-anisotropic cylindrical configurations. The mentioned comprehensiveness is one of the main advantages of our work. The suggested approach can be used as a basic step for future research related to the analysis of forward and inverse scattering problems of practical types of cylindrical structures made by complex media.

Dynamics behavior and imperfection sensitivity of a fluid-filled multilayered FGM cylindrical structure

The paper aims to investigate the transient response of an air-filled multilayer hollow functionally graded (FGM) cylinder with interlaminar bonding imperfection in the presence of load which is extensively put to use in aerospace structure. The material properties of each layer are assumed to vary continuously within the cylinder along the thickness direction with arbitrary grading pattern. A linear spring model is used to define imperfectly bonded interfaces of the multilayer cylinder. The solution of problem is obtained by means of the laminate approximation theory along with the Durbin's numerical Laplace transform inversion with regard to the time coordinate. Detailed numerical study of transient response of multilayer FGM cylinder with imperfect bonding under a pulse excitation are presented. In the following, the effect of imperfection on radial and circumferential stresses is presented and in view of the lack of any data, only the obtained results with the perfect bond are compared to those of other researchers have published in the literature. Also, by displaying contours of the internal pressure field, dynamic features in the fluid-structure interaction are investigated. Finally the effect of load duration and various loads, including step load and exponential load on radial and circumferential stresses are examined in detailed and the results obtained show the effect of step load is more critical than exponential load.

Resonance Energy Transfer Rate in the Presence of a Cylindrical Photonic Band-gap Structure

The resonance energy transfer rate between an excited atom and a ground-state one depends on various factors such as the matching between the donor and acceptor wavelengths, location of the atoms, and the environment that surrounds them. We investigate the interatomic resonance energy transfer rate in the presence of a cylindrical dielectric multi-layer structure using the Green’s tensor formalism. The permittivities of the layers are interchanged periodically between low and high values, so as to create a photonic band-gap system in the radial direction. We present results for atoms situated in a cross section normal to the cylinder axis. The contrast between low and high permittivities is varied to elucidate the effect of the band-gap structure. Furthermore, the results are compared with those for atoms located near a perfectly reflecting c-ylinder.

Three‐dimensional cylindrical design multiple‐input‐multiple‐output/diversity antenna with high isolation for wireless communication applications

In this article, a three-port nonplanar multiple-input-multiple-output/diversity antenna with very high isolation between the radiating elements is presented. To realize diversity from the proposed three-dimensional (3-D) antenna configuration, three monopole radiating elements are arranged at an angle of 120°. The isolation between the radiators is enhanced by using a multilayered cylindrical decoupling structure and defected ground structure (DGS). The DGS reduces the coupling due to surface waves while the cylindrical decoupling structure reduces the coupling due to space waves. The proposed antenna offers consistent pervasive connectivity in the wireless communication environment due to its 3-D geometry with multiple radiating elements and good diversity performance. The prototype is fabricated and measured result shows that more than 42 dB isolation is obtained at the center frequency 1.45 GHz. An increment of 1.2 dBi in the antenna gain is also achieved by using DGS and decoupling structure arrangement. The proposed antenna can be easily placed inside the cylindrical housing or it can be integrated with the existing electronics chip, thus nullifying the requirement for dedicated location in the system.

Polymer multimode waveguide bend based on a multilayered Eaton lens.

Reducing the bending radius of low-index-contrast waveguides is essential in reducing the size of the integrated optical components. A polymeric multimode waveguide bend is presented based on the Eaton lens. Ray-tracing calculations are utilized to truncate the Eaton lens in order to improve the performance of the bend. The truncation of the lens decreases the footprint of the bend as well. A designed waveguide bend with a radius of 18.4μm is implemented by a concentric cylindrical multilayer structure. Average bend losses of 0.69 and 0.87dB are achieved for the TM0 and TM1 modes, respectively, in the C-band of optical communication. The bend loss is lower than 1dB in a bandwidth of 1520-1675nm for both modes.

Tendencies of development of formation technology of multilayer cylindrical structures and residual technological stress evaluation methods

Tendencies of development of formation technology of multilayer cylindrical structures and residual technological stress evaluation methods

Nondestructive Evaluation of Microwave-Penetrable Pipes by Synthetic Aperture Imaging Enhanced by Full-Wave Field Propagation Model

A qualitative approach for microwave imaging multilayered cylindrical structures (e.g., dielectric pipes) is proposed in this paper. This approach relies on a modified circular synthetic aperture imaging technique that exploits closed-form Green’s function to account for the different propagation delays, internal reflections, and refractions. The image can then be computed by employing a matched filter expressed in terms of efficient Fourier Transforms. Consequently, a high-resolution and contactless approach for the inspection of this kind of structures is achieved. Moreover, the computational resources to render the images are negligible. Practical aspects of the technique such as sampling criteria, resolution, and limitations of the technique are discussed. The efficacy of the method is illustrated via several examples including imaging of objects and anomalies inside different types of dielectric pipes.

Evaluation of hydrogen permeation rate through zirconium pipe

To launch a fusion reactor stably, it is necessary to prepare sufficient amount of tritium by an external tritium source. Tritium production using nuclear reactions by neutron and Li in a high temperature gas-cooled reactor (HTGR) is an attractive method. An important issue is tritium confinement in high temperature conditions of HTGR. Covering Li compound by Al2O3 is a promising method because hydrogen permeability in Al2O3 is quite low. Furthermore, it is expected that inserting Zr between Li compound and Al2O3 suppresses tritium permeation because Zr has a large hydrogen absorption capacity. For example, a cylindrical multilayer structure consisted of Zr – Li compound – Zr – Al2O3 is a candidate structure to confine generated tritium. To evaluate hydrogen permeation rate through cylindrical Zr material, in this work, hydrogen permeation experiments were carried out for two samples of one-side sealed Zr pipe. Hydrogen permeation rate in one sample was proportional to as the square root of hydrogen pressure but that in another sample, which had retained a certain amount of hydrogen before the experiment, did not indicate an obvious pressure dependence regardless of almost the same experimental procedure except hydrogen permeation direction. Since observed hydrogen permeation rate in Zr was faster than that in Al2O3, under the multi confinement structure by Zr – Li compound – Zr – Al2O3, the generated tritium in Li compound diffuses promptly in whole Zr inside Al2O3 layer and it is expected tritium is stored stably in the structure.

Highly Subwavelength, Superdirective Cylindrical Nanoantenna.

A superdirective cylindrical nanoantenna is demonstrated with a multilayered cylindrical metamaterial-inspired structure. Targeting specific scattering coefficients for the dipole and higher-order modes, the ideal limit of needle radiation is demonstrated. A five-layer system is optimized to demonstrate its approach to the theoretical directivity bound. While the resulting structure is scalable to any frequency regime, its highly subwavelength overall size (λ_{0}/10) takes advantage of combinations of positive and negative permittivity materials in the optical regime.

Estimation of photonic band gap in the hollow core cylindrical multilayer structure

The propagation characteristic of two hollow core cylindrical multilayer structures having high and low refractive index contrast of cladding regions have been studied and compared at two design wavelengths i.e. 1550 nm and 632.8 nm. With the help of transfer matrix method a relation between the incoming light wave and outgoing light wave has been developed using the boundary matching technique. In high refractive index contrast, small numbers of layers are sufficient to provide perfect band gap in both design wavelengths. The spectral position and width of band gap is highly depending on the optical path of incident light in all considered cases. For sensing application, the sensitivity of waveguide can be obtained either by monitoring the width of photonic band gap or by monitoring the spectral shift of photonic band gap. Change in the width of photonic band gap with the core refractive index is larger in high refractive index contrast of cladding materials. However, in the case of monitoring the spectral shift of band gap, the obtained sensitivity is large for low refractive index contrast of cladding materials and further it increases with increase of design wavelength.

A contribution of the reliability based approach for cylindrical composite of sensitivity analytical design

The present paper focuses on the sensitivity evaluation of analytical design tool of cylindrical composite structures to geometrical and mechanical uncertainties through a reliability approach based on the Monte Carlo method. The present tool design is developed to study the analytical mechanical response of multilayered cylindrical composite structures under pressure and to access strain and stress states. Using the hoop stress for each ply, the Monte Carlo method is used to predict the distribution function of the mechanical response, for random design variables of composite structure. Three random design variables with uncertainties are selected, namely: composite elastic constants, ply angles and finally the mechanical loading (pressure). To ensure accuracy of results, we performed 104 simulations. The results obtained show that the probability of failure increases significantly when all the random variables are considered simultaneously.

Evaluation of Efficient Closed-Form Green’s Function in a Cylindrically Stratified Medium

An efficient technique is proposed for the removal of the spatial singularity for a z-directed current source in a cylindrically layered structure by decomposing the spectral domain Green’s function into the particular and homogeneous parts. The particular part with the singularity is converted into the spatial domain using Sommerfeld’s identity, while the DCIM with general pencil of function technique is applied on the spectral domain homogeneous part. The use of the ratio form of the reflection/transmission matrices, the Debye approximation, and the subsequent envelope extraction for the treatment of the spatial domain singularity is thus avoided. In addition, a very significant reduction in the number of modes required for convergence is also achieved. The technique is applied for evaluating the input impedance of several antennas in the cylindrical multilayer structure together with a coupling configuration for the excitation of the multilayer structure.