Wave Angle Research Articles

Enhancing the Terahertz Absorption Spectrum Based on the Low Refractive Index All-Dielectric Metasurface

We presented an angle-multiplexing low refractive index dielectric metasurface for terahertz absorption spectrum enhancement of lactose with high Q resonance properties. The unit cell structure of the acrylonitrile butadiene styrene (ABS) square structure is designed and optimized. The resonant peak shifts of the dielectric metasurface are analyzed by changing the incident angle of the terahertz wave. Then the α-lactose films with different thicknesses are added to investigate the enhancement effect. The resonant peak amplitude of the angle-multiplexing low refractive index dielectric metasurface absorption spectrum changes greatly with the absorption spectrum of the samples. The results illustrate that the enhanced absorption spectrum formed by the linked envelope can be up to 45 times stronger than that without the unit cell structures and also exhibits a high-quality factor. The proposed dielectric metasurface provides great potential in enhancing the terahertz absorption spectrum.

Wave transmission and its universal fluctuations in one-dimensional systems with Lévy-like disorder: Schrödinger, Klein-Gordon, and Dirac equations.

We investigate the propagation of waves in one-dimensional systems with Lévy-type disorder. We perform a complete analysis of nonrelativistic and relativistic wave transmission submitted to potential barriers whose width, separation, or both follow Lévy distributions characterized by an exponent 0<α<1. For the first two cases, where one of the parameters is fixed, nonrelativistic and relativistic waves present anomalous localization, 〈T〉∝L^{-α}. However, for the latter case, in which both parameters follow a Lévy distribution, nonrelativistic and relativistic waves present a transition between anomalous and standard localization as the incidence energy increases relative to the barrier height. Moreover, we obtain the localization diagram delimiting anomalous and standard localization regimes, in terms of incidence angle and energy. Finally, we verify that transmission fluctuations, characterized by its standard deviation, are universal, independent of barrier architecture, wave equationtype, incidence energy, and angle, further extending earlier studies on electronic localization.

Analysis of the peaks of ship motions in linear and nonlinear focused waves

Three focused waves, which have almost identical temporal profiles, are successfully generated in a numerical wave tank with both linear and nonlinear methods, and they are utilized to act upon an LNG carrier to study the induced differences of the ship peak responses for the first time. The influences of focal location and incident wave direction are taken into account and the fundamental reason for the response difference is revealed from the perspective of energy variation. It can be concluded that when the LNG carrier encounters the same temporal focused waves, the peak motion responses can be different due to the different hydrodynamic characteristics under the focused crests, which can be further attributed to the distinct physical mechanisms involved in the energy concentration of these focused waves. The focal location and incident wave angle can further enlarge the corresponding discrepancy under some circumstances. From a spectral point of view, the motion discrepancy is mainly caused by the actions of the distinct fundamental wave components. Specifically speaking, the relatively high-frequency components of the nonlinear focused waves tend to induce a smaller heave response and the quasi-monochromatic wave component cannot trigger a larger pitch motion than the linear focused waves.

Extending the Incidence Angle of Shear Vertical Wave Electromagnetic Acoustic Transducer with Horizontal Magnetization.

Angled shear vertical (SV) waves have been successfully employed in the non-destructive testing of welds, pipes, and railways. Non-contact meander-line coil electromagnetic acoustic transducers (EMAT) have many benefits in generating angled SV waves. The most important benefit is that the incidence angle of an SV wave can be controlled by the excitation frequency. However, the incidence angle of a traditional SV-wave EMAT is reported to be under 45 degrees in many cases. In this work, such cases are tested, and the problems of the received signal at large incidence angles are found to be due to wave interference and small signal amplitudes. An equivalent finite element (FE) model is established to analyze the problem, and the main reason is found to be the head wave. An alternative configuration of angled SV-wave EMAT with horizontal magnetization is proposed to reduce the influence of the head wave. Finally, the results from simulations and experiments show that the proposed EMAT has a larger signal amplitude and significantly reduced interference in large-incidence angle scenarios. Moreover, an incidence angle of an SV wave of up to 60 degrees can be achieved, which will help improve the performance and capability of nondestructive testing.

Nonlinear seismic response and index correlation of high arch dams under cross-stream oblique incidence of near-fault SV waves based on wavelet decomposition

This paper aims to propose an analysis framework for the response index correlation of high arch dams under cross-stream oblique incidence of near-fault pulse-like and non-pulse seismic waves. The influence of the dynamic pulse effect of near-fault seismic waves on the index correlation at different incidence angles is evaluated. Further, the seismic response through an arbitrary incident angle is quantitatively estimated. Several typical near-fault records of extracted strong velocity pulses are selected, and their decomposed non-pulse ground motions (GMs) are used to ensure the similarity and uniformity of the response spectra. Furthermore, a seismic input model of the oblique incidence of the SV wave is established based on the three-dimensional viscous-spring artificial boundary method, and its accuracy was confirmed through the numerical application. The engineering demand parameters (EDPs) of pulse-like SV waves and non-pulse SV waves, including dam damage, dynamic displacement, and joint opening, with cross-stream incident angles are discussed emphatically. Finally, the correlation between the response indices of near-fault SV waves at different incident angles is quantitatively analyzed. The numerical results indicate that pulse-like seismic waves with different input angles are more destructive than non-pulse seismic waves, and different response indices of the dam may have different most unfavorable incident angles. A prediction model of the dam response considering different input angles of seismic waves is proposed to roughly estimate the response index values of each input angle. The influence of the dynamic pulse characteristics on the correlation degree of response indices under different input angles is mainly divided into three types: no impact, increasing correlation degree, and decreasing correlation degree. In the seismic design and performance evaluation of arch dams, it should be suggested to comprehensively consider the influence of the oblique incident angle of GMs and near-fault pulse characteristics.

Scattering of SH wave by a crack in a functionally graded one dimensional hexagonal piezoelectric quasicrystals

AbstractIn this paper, the dynamic interaction between SH wave and a crack in functionally graded one‐dimensional hexagonal piezoelectric quasicrystals (PQCs) is studied by using integral transform technique. To make the analysis executable, the material properties are assumed to vary partially in the direction perpendicular to the crack face following an exponential function. The problem was transformed through Fourier transform into three pairs of dual integral equations, which are solved numerically by the Copson method. The explicit expressions of phonon field, phason field and electric field on crack surface are determined. The dynamic field intensity factors of crack tip are given and some special cases are discussed. Numerical examples are then conducted to reveal the influences of amplitude, incident angle and wave number of SH wave and crack length, gradient parameter on the normalized dynamic stress intensity factors (DSIFs). The results of this paper lay a theoretical foundation for the design and nondestructive testing of QCs structures.

Preparation and transmission characteristics of high-pass woven fabrics

To study the frequency response characteristics of high-pass woven fabric, samples with varying conductive grid structure, structure parameters, material conductivity, and electromagnetic (EM) wave parameters were prepared and measured by the shielding room method. Experimental results showed that conductive grid structure was effective in obtaining bidirectional shielding ability and conductive stripe structure had directional shielding property to the EM wave.. Depending on changing the ratios of dielectric and conductive yarns, structure parameters exerted influences on frequency response characteristics by affecting vertical inductances and horizontal capacities in the equivalent circuit. High-pass woven fabric with high-conductivity yarns could possess stronger shielding ability. Due to the different compactness in weft and warp directions after weaving, bidirectional grid structure fabrics showed distinct polarization selective characteristic as well as unidirectional structure fabric. When the incident angle of the EM wave increased, the incident component decreased and the transmittance became unstable. The experimental results were discussed in-depthbased on mechanism analysis, which could provide reference to the relevant research.

Optimum design for wavy fin tube in an air cooler with genetic algorithm

A strategy by multi-objective genetic algorithm (MOGA) combined with Kriging response surface is proposed for optimum design of wavy fin tube in an air cooler, while minimum pressure loss factor, maximum heat transfer factor and overall performance factor as three objective functions. The results show that the effects of fin height and fin density on the overall performance are positive and the wave number and wave angle are negative; The overall performance of parallel fin is higher than staggered fin; The overall performance of small pipe diameter of wave fin is higher than big pipe diameter; The overall performance reaches the optimum as fin height is 20.7 mm, fin density is 9.9, wave number is 11, wave angle is 4°; The multi-objective genetic algorithm combined with Kriging response surface eliminates the dependence on empirical relation. The results can be used to guide the optimum design of wavy fin tube.

Double Sided Wideband Concentric Ring Spatial Filters for Mid-Band 5G Devices

This paper presents the methodology, development, and implementation of the double concentric ring band-pass frequency selective surface (FSS) based spatial filters. The filters are designed to improve the active responses of the 5G antennas by incorporating them as superstrate or as substrates. A comparable circuit model is used to anticipate the resonant frequency bands required for predicting the FSS band-pass behavior. The designed spatial filter is composed of a combination of periodic circular loop structures engraved on both sides of a thin dielectric substrate. The proposed design of a double circular loop FSS exhibits band-pass characteristics for n77, n78, and n79 bands of the mid-band 5G spectrum (ranging from 3 GHz - 6 GHz) and provides insensitivity to polarization angles of the incident plane wave. The computed, simulated, and measured findings are all depicting a similar pattern that validates our structure.

Hydrodynamic performance of dual-chamber Oscillating Water Column array under oblique waves

A multiple Oscillating Water Column (OWC) device may provide better wave absorption over a wider frequency bandwidth than a single-chamber OWC due to multiple resonances. The scattering and radiation of three-dimensional oblique waves by an array of periodic dual-chamber OWCs are considered here along a coastal cliff. A semi-analytical model was developed based on potential flow theory and matching eigenfunction method to investigate the oblique wave interaction with a dual-chamber OWC array system. The velocity singularity at the tip of a chamber wall is resolved by introducing the Galerkin technique to accelerate the convergence. The semi-analytical solution is verified by the Haskind relation and energy conservation law. Hydrodynamics of the proposed system and the influence of wave and geometric parameters were investigated. Theoretical results indicate that a dual-chamber OWC array has a broader capture bandwidth than a single-chamber OWC array for both normal and oblique waves. The presence of the along-shore and cross-shore sloshing resonance is theoretically confirmed in each subchamber of OWC unit, which decreases the hydrodynamic efficiency and increases the wave reflection drastically. Although the wave loading on the chamber wall decreases with increasing incident wave angle θ, the wave loading on chamber/partition wall may increase sharply due to sloshing resonance at critical frequency kc. To our knowledge, this is the first attempt to investigate the hydrodynamics of dual-chamber OWC array under oblique waves. The present theoretical results indicate the potential risks of structural damage and total wave reflection due to sloshing resonance, which should be an important design consideration.

Improvement in sound insulation performance of pyramidal truss core cylindrical sandwich structure by adding a frame structure

Cylindrical structures are used in various fields owing to their good mechanical properties. At the same time, the requirements for their acoustic performances continue to increase in the application of cylindrical shell structures. Thus, the acoustic performance and application in sound insulation attract increasing attention. Sandwich cores have been inserted into cylindrical structures to improve the sound insulation performance of the structure. To improve both mechanical and acoustic properties of the cylindrical sandwich structure, a frame structure that strengthens the internal nodes of the pyramidal truss core was added. A theoretical model corresponding to the structure was established to study the sound insulation performance of the structure. The influences of the overall thickness of the structure, number of lattice unit cells, material density, and angle of incident sound waves on the sound insulation performance were analyzed.

Study on Reradiation Interference Characteristics of Steel Towers in Transmission Lines

With the development of ultrahigh-voltage transmission lines in China, the reradiation interference caused by the steel tower used in ultrahigh-voltage transmission becomes increasingly aggravating for nearby radio stations. In this paper, using the multilevel fast multipole algorithm, the reradiation interference of an ultrahigh-voltage transmission steel tower is investigated. Additionally, the reradiation interference characteristics of a transmission steel tower were investigated with various frequencies and azimuth angles of incidence wave. The results show that the frequency and the azimuth angle of incident wave are the impact factors for the reradiation interference of steel towers. It is better to use a detailed angle steel model for the truss structure of steel towers at high frequency, while a simplified structural model can be used at low frequency. Additionally, the diffraction at the edge of the angle steel has a great influence on the reradiation interference, particularly at high frequencies.

Fractal Analysis for Wave Propagation in Combustion–Explosion Fracturing Shale Reservoir

The in-situ combustion–explosion fracturing technology in shale reservoirs can promote continuous fracture expansion with a radial detonation wave first converging into a shock wave and then decaying into an elastic wave. The transformation scale of the shale reservoir is determined by the range of wave propagation during combustion–explosion. As wave propagation paths are usually tortuous and fractal, the previous integer wave models are not competent to describe the wave propagation and estimate the impact range of the combustion–explosion fracturing process. This study develops two fractional wave propagation models and seeks analytical solutions. Firstly, a novel fractional wave model of rotation angle is proposed to describe the process of detonation waves converting into shock waves in a bifurcated structure. The radial displacement gradient of the detonation wave is represented by the internal expansion and rotation deformation of the shale. Secondly, another fractional wave propagation model of radial displacement is proposed to show the process of a shock wave decaying into an elastic wave. Thirdly, the proposed models are analytically solved through the fractional variable separation method and variational iteration method, respectively. Analytical solutions for rotation angle and radial displacement with fractal time and space are obtained. Finally, the impacts of the branching parameter of the detonation wave converge bifurcation system, aggregation order of detonation compression wave, and different types of explosives on the rotation angle of the shock wave are investigated. The propagation mechanism of the primary wave (P-wave) with time and space is analyzed. The analytical solutions can well describe the wave propagation process in fractured shales. The proposed fractional wave propagation models can promote the research of wave propagation in the combustion–explosion fracturing process of shale reservoirs.

The challenge of modeling grounded metasurfaces: a new approach to obtain their constitutive parameters

A new technique to retrieve the constitutive parameters of grounded metamaterials is proposed in this article. Previous methods presented in the literature used to retrieve the constitutive parameters of materials in general and metamaterials, in particular. are not applicable since they rely on both reflectivity and transmittivity data. In grounded metamaterials, there is no transmission and hence, a new method is needed to obtain the metamaterial constitutive parameters (both permittivity and permeability) by means of just reflectivity data. The proposed methodology is based on extracting the aforementioned constitutive parameters using the reflectivity response to two different angles of the incident plane wave. First, the solution to the problem is presented from a mathematical perspective. Then, the methodology is applied to a grounded metasurface and their constitutive parameters are extracted. From these parameters, interesting phenomena that occurs in the metasurface are explained. Finally, the range of validity of the method is also analysed.

Shape optimization for the strong routing of light in periodic diffraction gratings

In the quest for the development of faster and more reliable technologies, the ability to control the propagation, confinement, and emission of light has become crucial. The design of guide mode resonators and perfect absorbers has proven to be of fundamental importance. In this project, we consider the shape optimization of a periodic dielectric slab aiming at efficient directional routing of light to reproduce similar features of a guide mode resonator. For this, the design objective is to maximize the routing efficiency of an incoming wave. That is, the goal is to promote wave propagation along the periodic slab. A Helmholtz problem with a piecewise constant and periodic refractive index medium models the wave propagation, and an accurate Robin-to-Robin map models an exterior domain. We propose an optimal design strategy that consists of representing the dielectric interface by a finite Fourier formula and using its coefficients as the design variables. Moreover, we use a high order finite element (FE) discretization combined with a bilinear Transfinite Interpolation formula. This setting admits explicit differentiation with respect to the design variables, from where an exact discrete adjoint method computes the sensitivities. We show in detail how the sensitivities are obtained in the quasi-periodic discrete setting. The design strategy employs gradient-based numerical optimization, which consists of a BFGS quasi-Newton method with backtracking line search. As a test case example, we present results for the optimization of a so-called single port perfect absorber. We test our strategy for a variety of incoming wave angles and different polarizations. In all cases, we efficiently reach designs featuring high routing efficiencies that satisfy the required criteria.

Dynamic response characteristics of the 67-type railway pontoon bridge

In China at present, the 67-type railway pontoon bridge is part of the main reserve standard equipment that can be utilized for traffic emergency of cross-river bridges. Based on the potential flow theory and boundary element method (the three-dimensional source distribution method), this paper studies the dynamic response characteristics of the 67- type railway pontoon bridge under the action of waves and train loads (the live load of the Chinese Standard-18). First of all, the hydrodynamic characteristics based on application of other computation models applied in relation to floating bridges are compared with the results obtained by the present approach. Secondly, the effects of varying the related wave parameters (i.e. wave period and angle of incidence) on the dynamic response of the 67-type emergency railway pontoon bridge (as installed across the Ji Canal within the Beijing-Shanhaiguan line) are investigated. Finally, the load effects in the girder when this bridge is subjected to the action of various wave and train loads are analyzed. The calculation results indicate that the method proposed in this paper has good generality which enables it to perform a better analysis of the hydrodynamic characteristics of this kind of practical emergency pontoon.Article highlightsResearch on dynamic response for the major railway emergency pontoon in China are carried out;The three-dimensional source distribution method and FEM is adopted;Simulate traffic loads with the live load of the Chinese Standard-18.

On the probability estimates of broaching in irregular waves by direct counting on intensive repeated simulations

In the study, surf-riding and broaching in irregular waves are simulated using a previously developed 6-DOF numerical model. Cases in irregular waves with various speeds and wave directions are chosen for intensive repeated simulations. During the simulation, the instantaneous celerity calculated using the Hilbert transform is used to identify the “high run”. The direct counting scheme is applied on the simulation results to acquire the estimate of probability of high run, yaw exceedance within high run, yaw exceedance under “likely broaching”, and unconditional yaw exceedance. It is found that the ship capsizes after experiencing a relatively long duration of high run, which suggests correlation between capsizing and high run. High run in irregular wave is proved to be a good representation of surf-riding as they are highly related. The occurrence of broaching is strongly related with the wave angle. When the wave angle reaches 30°, the total time duration of yaw exceedance within high run can account for as much as 30%–50% of total time duration of high run under ±5°-yaw-exceeding and 5%–15% under ±10°-yaw-exceeding, especially for high Fn. The probability estimates of yaw exceedance under “likely broaching” can account for as much as 60% of those of yaw exceedance within high run using ±5°-yaw-exceeding and only 10% using ±5°-yaw-exceeding, which indicates ±5°-yaw-exceeding is not sufficient, as the yaw angle is too small and broaching is masked by a large amount of “normal” yaw motions. As Fn increasing, yaw exceedance after high run will become majority in unconditional yaw exceedances.

Origami tunable frequency selective fabric and its tuning mechanism

The tunable frequency selective surface can change its resonant frequency to better meet the complex and changeable electromagnetic (EM) environment. The traditional metal frequency selective surface (FSS) has high precision, but it is hard, making it not easy to bend and adapt to the surface. In this paper, an origami tunable frequency selective fabric (oTFSF) is proposed, which is thin, flexible, and bendable with precise resonant frequency adjustment function. The oTFSF is made by folding and ironing a single layer of FSF with a special three-dimensional spatial structure. By changing its state, the angle of the EM wave interacting with conductive units of the oTFSF can be altered to realize the precise adjustment of the resonant frequency. When the folding trace is parallel to the electric field, the three-dimensional structure of the oTFSF can be equivalent to the projected plane structure through simulation. Therefore, multiple oblique incidence situations can be converted into vertical incidence situations. The equivalent EM parameters of the oTFSF can be obtained by particle swarm optimization algorithm (PSO) to analyze the influence of unit size change on oTFSF. The results show that when the folding angle increases, the equivalent inductance (L) decreases, and the equivalent capacitance (C) increases. The oTFSF can be used to prepare intelligent EM functional materials with characteristics of broadband, lightweight, flexible, and adjustable frequency.

Terahertz Wave Conversion From Linear to Circular Polarization by Graphene Metasurface Featuring Ultrawideband Tunability

This paper reports a detailed study of a graphene-based metasurface to function as tunable broadband linear to circular polarization converter in the terahertz gap. This device provides a wide polarization conversion band of 2.25 THz (3.75 THz to 6 THz) with an enhanced fractional 3-dB axial ratio bandwidth (FARBW) of 46.15%. The proposed structure consists of a simple tri-layer configuration where the meta-atom comprises a patterned graphene layer on a gold-backed silicon dioxide substrate. The proposed reflective-type linear to circular polarization converter (RLCPC) exhibits both right-handed and left-handed circular orientations of the reflected wave in two halves of the operating spectrum, further validated in terms of polarization ellipses developed by an inhouse code. The lack of experimental setup at the above said frequencies available to the authors in their country has been paid off by verifying the response using a detailed circuit model. The RLCPC maintains a thickness of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_o</i> /7.69 with a lattice size of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_o</i> /8.33. The structure also promises a stable wideband circular polarization conversion up to 20° and a dual-band circular polarization conversion up to 40° incident angle of the electromagnetic wave. This device can be useful for THz beam scanning antennas, RCS reduction and THz antennas for space and military radar applications.

Detonation driving rules for cylindrical casings under asymmetrical multipoint initiations

The detonation wave–aiming warhead can effectively enhance the lethality efficiency. In the past, rules for casing rupture and velocity distribution under asymmetrical initiations were not adequately investigated. In this study, X-ray photography and numerical modelling are used to examine the casing expansions under centre point, asymmetrical one-point, and asymmetrical two-point (with central angles of 45° and 90°) initiations. The results indicate that early casing ruptures are caused by local high pressures, induced by the initiation, detonation wave interaction, and Mach wave onset. The fragment shapes are controlled by the impact angle of the detonation wave. The fragment velocity distributions differ under different initiation types, and the end rarefaction waves can affect the velocity distribution. This study can serve as a reference for the design and optimization of high-efficiency warheads.