Showing papers on "Wave propagation published in 2020"

Antireflection temporal coatings

Abstract: It is known that complete transmission of waves through the interface between two different media can be achieved by proper impedance matching between them. One of the most common techniques for such reflectionless propagation is the quarter-wave impedance transformer, where an additional slab of material with proper material parameters and carefully engineered dimensions is added between the two media, minimizing reflections. Metamaterials, with properly designed spatial inhomogeneity, have exhibited unprecedented ability to tailor and manipulate waves, and recently temporal metamaterials have also gained much attention, enabling spatiotemporal control of wave propagation. Here a temporal analogue of the quarter-wave impedance transformer technique, which we name “antireflection temporal coating,” is proposed using time-dependent materials. The proposed technique is demonstrated, analytically and numerically, using metamaterials with a time-dependent permittivity. Comparison with the conventional (spatial) impedance-matching technique is shown, demonstrating that both impedance matching and frequency conversion are achieved with our proposed temporal version. As an illustrative example, the present technique is also applied to match two waveguides with different cross sections, demonstrating an example of scenarios where it may be applied.

Photo-thermo-elastic wave propagation in an orthotropic semiconductor with a spherical cavity and memory responses

Abstract: This article highlights on the study of coupled plasma, thermal and elastic waves within an orthotropic infinite semiconducting medium in context of photothermal transport process having a spherica...

Surface ionization wave propagation in the nanosecond pulsed surface dielectric barrier discharge: the influence of dielectric material and pulse repetition rate

Abstract: In this work, the propagation of the surface ionization wave (SIW) in the nanosecond pulsed surface dielectric barrier discharge with different dielectric materials and pulse repetition rates is investigated. The current waveforms at different locations along the route of the SIW propagation are obtained, based on a specially designed ground strip array geometry. The temporal evolution and spatial distribution of the electric field during the SIW propagation are measured by using the electric field induced second harmonic (EFISH) generation method. The distribution of the residual surface potential after the discharge is mapped with a Kelvin electrostatic probe, which verifies both the existence of the residual electric field and its opposite direction to that during the SIW propagation. It is found that with the dielectric material on which the surface charges decay faster, there are the well-pronounced primary and secondary SIWs with a higher velocity on the voltage rising edge and both the peak current and the peak electric field are also higher, with a less spatial attenuation along the SIW propagation route. It is demonstrated that the residual surface charges with the same polarity as the high-voltage pulse suppress the development of the surface ionization wave.

Experimental Observation of Nonreciprocal Waves in a Resonant Metamaterial Beam

Abstract: Structures hosting nonreciprocal (one-way) wave propagation are of key interest in signal processing, sensing, and civil infrastructure, yet experimental realization has so far relied on adaptive materials and external stimulation, which require significant power and are not scalable beyond lab prototypes. This work presents an elastic metamaterial that exploits stiffness variations in an array of geometrically phase-shifted resonators to achieve a nonreciprocal tilt of dispersion modes within dynamic modulation regimes. The ability to induce asymmetric vibrational modes in a scalable, energy-efficient manner has direct implications for numerous applications.

Wave propagation and vibration responses in porous smart nanocomposite sandwich beam resting on Kerr foundation considering structural damping

Abstract: This paper deals with wave propagation and vibration of a porous beam embedded via nanocomposite piezoelectric layers Various patterns of reinforcement of the face sheets by non-uniform graphene nanoplatelets (GPLs) are considered through modified Halpin-Tsai micromechanics model to approximate the Young modulus and Poisson's ratio of graphene/piezoelectric polymer layers The sandwich's face sheets, due to their characteristics, are regarded as sensor and actuator with which the wave velocity and frequency of structure can be controlled and for this reason, a proportional-differential (PD) controller is handled So as to model the structure much more realistic, the material characteristic of whole system are hypothesized as viscoelastic state according to Kelvin-Voigt model and Kerr viscoelastic foundation is developed which include two springs, two dampers and one shear elements as well For mathematical modelling of system, refined zigzag theory (RZT) is exercised and using energy method, the motion equations are obtained Analytical procedure is utilized for solving the governing equations as well as calculating the wave velocity and frequency of the sandwich structure A precise parametric study is carried out focusing GPLs volume percent and distribution pattern, geometrical parameter of every layer, piezoelectric properties of GPLs, porosity dispersion of the core, exerted voltage and structural damping and their effects on the wave propagation and vibration of system Results show that increase in the porous coefficient lead to decline in the wave velocity and frequency In addition, considering the piezoelectric properties of GPLs enhances the wave velocity and frequency of the sandwich structure

Surface-wave-assisted nonreciprocity in spatio-temporally modulated metasurfaces

Abstract: Emerging photonic functionalities are mostly governed by the fundamental principle of Lorentz reciprocity. Lifting the constraints imposed by this principle could circumvent deleterious effects that limit the performance of photonic systems. Most efforts to date have been limited to waveguide platforms. Here, we propose and experimentally demonstrate a spatio-temporally modulated metasurface capable of complete violation of Lorentz reciprocity by reflecting an incident beam into far-field radiation in forward scattering, but into near-field surface waves in reverse scattering. These observations are shown both in nonreciprocal beam steering and nonreciprocal focusing. We also demonstrate nonreciprocal behavior of propagative-only waves in the frequency- and momentum-domains, and simultaneously in both. We develop a generalized Bloch-Floquet theory which offers physical insights into Lorentz nonreciprocity for arbitrary spatial phase gradients, and its predictions are in excellent agreement with experiments. Our work opens exciting opportunities in applications where free-space nonreciprocal wave propagation is desired.

Cellular Communications in Ocean Waves for Maritime Internet of Things

Abstract: The rapid advancement of Internet of Things (IoT) and fifth generation and beyond technologies is transforming the marine industry and research. Our understanding of the vast sea that covers 71% of the Earth’s surface is being enhanced by the various ocean sensor networks equipped with effective communication technologies. In this article, we begin with a review of the research and development status-quo of Maritime IoT (MIoT) enabled by multiple wireless communication technologies. Then, we study the impact of sea waves on radio propagation and the communications link quality. Due to the severe attenuation of sea water to radio-frequency electromagnetic wave propagation, large ocean waves can easily block the communication link between a buoy sensor and a cell tower near shore. This article for the first time uses the ocean wave modeling of coastal and oceanic waters to examine the condition of line-of-sight communications. Real wave measurement data parameters are applied in the numerical evaluation of the developed model. Finally, the critical antenna design taking into account the wave impact is numerically studied with implementation solutions proposed, and the system hardware and protocol aspects are discussed.

Effective Description of Anisotropic Wave Dispersion in Mechanical Band-Gap Metamaterials via the Relaxed Micromorphic Model

Abstract: In this paper the relaxed micromorphic material model for anisotropic elasticity is used to describe the dynamical behavior of a band-gap metamaterial with tetragonal symmetry. Unlike other continuum models (Cauchy, Cosserat, second gradient, classical Mindlin–Eringen micromorphic etc.), the relaxed micromorphic model is endowed to capture the main microscopic and macroscopic characteristics of the targeted metamaterial, namely, stiffness, anisotropy, dispersion and band-gaps. The simple structure of our material model, which simultaneously lives on a micro-, a meso- and a macroscopic scale, requires only the identification of a limited number of frequency-independent and thus truly constitutive parameters, valid for both static and wave-propagation analyses in the plane. The static macro- and micro-parameters are identified by numerical homogenization in static tests on the unit-cell level in Neff et al. (J. Elast., https://doi.org/10.1007/s10659-019-09752-w, 2019, in this volume). The remaining inertia parameters for dynamical analyses are calibrated on the dispersion curves of the same metamaterial as obtained by a classical Bloch–Floquet analysis for two wave directions. We demonstrate via polar plots that the obtained material parameters describe very well the response of the structural material for all wave directions in the plane, thus covering the complete panorama of anisotropy of the targeted metamaterial.

Nonreciprocal Dzyaloshinskii-Moriya Magnetoacoustic Waves.

Abstract: We study the interaction of surface acoustic waves with spin waves in ultrathin $\mathrm{CoFeB}/\mathrm{Pt}$ bilayers. Because of the interfacial Dzyaloshinskii--Moriya interaction (DMI), the spin wave dispersion is nondegenerate for oppositely propagating spin waves in $\mathrm{CoFeB}/\mathrm{Pt}$. In combination with the additional nonreciprocity of the magnetoacoustic coupling itself, which is independent of the DMI, highly nonreciprocal acoustic wave transmission through the magnetic film is observed. We systematically characterize the magnetoacoustic wave propagation in a thickness series of $\mathrm{CoFeB}(d)/\mathrm{Pt}$ samples as a function of magnetic field magnitude and direction, and at frequencies up to 7 GHz. We quantitatively model our results to extract the strength of the DMI and magnetoacoustic driving fields.

Maxwellian evolution equations along the uniform optical fiber in Minkowski space

Abstract: We firstly discuss the geometric phase rotation for an electromagnetic wave traveling along the optical fiber in Minkowski space We define two types of novel geometric phases associated with the evolution of the polarization vectors in the normal and binormal directions along the optical fiber by identifying the normal-Rytov parallel transportation law and binormal-Rytov parallel transportation law and derive their relationships with the new types of Fermi-Walker transportation law in Minkowski space Then we describe a novel approach of solving Maxwell's equations in terms of electromagnetic field vectors and geometric quantities associated with the curved path characterizing the path uniform optical fiber by using the traveling wave transformation method Finally, we investigate that electromagnetic wave propagation along the uniform optical fiber admits an interesting family of Maxwellian evolution equation having numerous physical and geometric applications for anholonomic coordinate system in Minkowski space

Experimental realization of a reconfigurable electroacoustic topological insulator

Abstract: A substantial challenge in guiding elastic waves is the presence of reflection and scattering at sharp edges, defects, and disorder. Recently, mechanical topological insulators have sought to overcome this challenge by supporting back-scattering resistant wave transmission. In this paper, we propose and experimentally demonstrate a reconfigurable electroacoustic topological insulator exhibiting an analog to the quantum valley Hall effect (QVHE). Using programmable switches, this phononic structure allows for rapid reconfiguration of domain walls and thus the ability to control back-scattering resistant wave propagation along dynamic interfaces for phonons lying in static and finite-frequency regimes. Accordingly, a graphene-like polyactic acid (PLA) layer serves as the host medium, equipped with periodically arranged and bonded piezoelectric (PZT) patches, resulting in two Dirac cones at the K points. The PZT patches are then connected to negative capacitance external circuits to break inversion symmetry and create nontrivial topologically protected bandgaps. As such, topologically protected interface waves are demonstrated numerically and validated experimentally for different predefined trajectories over a broad frequency range.

Wavenumber explicit convergence analysis for finite element discretizations of general wave propagation problems

Abstract: We analyze the convergence of finite element discretizations of time-harmonic wave propagation problems. We propose a general methodology to derive stability conditions and error estimates that are explicit with respect to the wavenumber. This methodology is formally based on an expansion of the solution in powers of k, which permits to split the solution into a regular, but oscillating part, and another component that is rough, but behaves nicely when the wavenumber increases. The method is developed in its full generality and is illustrated by two particular cases: the elastic and convected sound waves. Numerical experiments are provided which confirm that the stability conditions and error estimates are sharp.

Slow-Wave-Based Nanomagnonic Diode

Abstract: Nonreciprocal wave propagation is important for signal processing and wave-based computing, but has not been realized in spin-wave devices. The authors engineer such nonreciprocity for spin waves in a transversely magnetized ferromagnetic bilayer so that the waves completely stop in one direction while still propagating with significant velocity in the opposite one. Electrical and optical measurements are combined with analytical and numerical modeling to provide a picture of the chiral mode hybridization responsible for this phenomenon. This work is an experimental realization of a magnonic diode and paves the way for designing complex spin-wave devices required for magnon computing.

Pure S0 and SH0 detections of various damage types in aerospace composites

Abstract: This paper proposes a new single-mode guided wave-based method to detect various types of damage in aerospace composites. In this method, single-mode guided wave excitation was achieved using adjustable angle beam transducers (ABT). The ABT tuning angles of various pure-mode guided waves were calculated based on Snell's law applied to the composite dispersion curves. A finite element (FE) simulation of pure S0 mode excitation in a crossply composite plate was conducted and the simulation results were validated by the experiment. For the first time, angle beam transducers were applied to generate pure shear horizontal (SH0) wave in a thick quasi-isotropic composite plate. The pure SH0 wave excitation was successfully verified by a three-dimensional (3D) FE simulation. SH0-mode wave propagation and interaction with delaminations were further conducted and strong trapped waves within the delamination regions were observed. Experiments using S0 or SH0 pure-mode guided waves were conducted to detect various types of composite damage, such as wrinkle damage in the crossply composite plate, multilayer delaminations by Teflon inserts, and actual impact damage in the thick quasi-isotropic composite plate. A significant amplitude drop was observed due to the presence of different composite damage types. In addition, a linear scanning method using pure SH0 wave was also developed to estimate the sizes of delaminations and impact damage. Both numerical and experimental results demonstrated the validity and usefulness of the proposed method for the detection of various damage types in composites.

Modeling thermodynamic trends of rotating detonation engines

Abstract: The formation of a number of co- and counter-rotating coherent combustion wave fronts is the hallmark feature of the Rotating Detonation Engine (RDE). The engineering implications of wave topology are not well understood nor quantified, especially with respect to parametric changes in combustor geometry, propellant chemistry, and injection and mixing schemes. In this article, a modeling framework that relates the time and spatial scales of the RDE to engineering performance metrics is developed and presented. The model is built under assumptions of backpressure-insensitivity and nominally choked gaseous propellant injection. The Euler equations of inviscid, compressible fluid flow in one dimension are adapted to model the combustion wave dynamics along the circumference of an annular-type RDE. These adaptations provide the necessary mass and energy input and output channels to shape the traveling wave fronts and decaying tails. The associated unit processes of injection, mixing, combustion, and exhaust are all assigned representative time scales necessary for successful wave propagation. We find that the separation, or lack, of these time scales is responsible for the behavior of the system, including wave co- and counter-propagation and bifurcations between these regimes and wave counts. Furthermore, as there is no imposition of wave topology, the model output is used to estimate the net available mechanical work output and thermodynamic efficiency from the closed trajectories through pressure–volume and temperature–entropy spaces. These metrics are investigated with respect to variation in the characteristic scales for the RDE unit physical processes.

Active control for acoustic wave propagation in nonlinear diatomic acoustic metamaterials

Abstract: Wave propagation through nonlinear acoustic metamaterials has generated numerous scientific interests for their enormous potential in practical applications these years. This study focuses on the effects of nonlinearity on the band properties of diatomic mass-in-mass chain with active control. By applying the Lindestedt–Poincare (L–P) perturbation method, analytical dispersion relations of the linear and nonlinear diatomic mass-in-mass system have been established and investigated by numerical simulation. Different from the monatomic mass-in-mass chain, this two mass-in-mass units forming a unit cell of the periodic structure results in four branches of the dispersion relation. The effects of nonlinearity on the band gaps of the system have been exhaustively illustrated. By only tuning the nonlinear constitutive relation parameter of the spring, the fourth branch and the third gap are found to be more sensitive compared to the other branches and gaps. It is concluded that closing and re-opening of the band-folding-induced gap in this nonlinear system is still possible. Here, a piezoelectric spring model is applied to the diatomic mass-in-mass to make the system available for wider applications. With the negative proportional control, a new stop band is generated which can be also captured in the monatomic nonlinear system. The new results here will help better analyze the band gap properties in nonlinear mechanical metamaterials and emphasize the great potentials of the topological analysis of such a nonlinear local resonance system that induces band-folding-induced band gaps.

On the wave dispersion in microstructured solids

Abstract: In this paper, elastic wave propagation in a one-dimensional micromorphic medium characterized by two internal variables is investigated. The evolution equations are deduced following two different approaches, namely using: (i) the balance of linear momentum and the Clausius–Duhem inequality, and (ii) an assumed Lagrangian functional (including a gyroscopic coupling) together with a variational principle. The dispersion relation is obtained and the possibility of the emerging band gaps is shown in such microstructured materials. Some numerical simulations are also performed in order to highlight the dispersive nature of the material under study.

Broadband non-reciprocity with robust signal integrity in a triangle-shaped nonlinear 1D metamaterial

Abstract: In this paper, we propose and numerically study a nonlinear, asymmetric, passive metamaterial that achieves giant non-reciprocity with (i) broadband frequency operation and (ii) robust signal integrity. Previous studies have shown that nonlinearity and geometric asymmetry are necessary to break reciprocity passively. Herein, we employ strongly nonlinear coupling, triangle-shaped asymmetric cell topology, and spatial periodicity to break reciprocity with minimal frequency distortion. To investigate the nonlinear band structure of this system, we propose a new representation, namely a wavenumber–frequency–amplitude band structure, where amplitude-dependent dispersion is quantitatively computed and analyzed. Additionally, we observe and document the new nonlinear phenomenon of time-delayed wave transmission, whereby wave propagation in one direction is initially impeded and resumes only after a duration delay. Based on numerical evidence, we construct a nonlinear reduced-order model (ROM) to further study this phenomenon and show that it is caused by energy accumulation, instability, and a transition between distinct branches of certain nonlinear normal modes of the ROM. The implications and possible practical applications of our findings are discussed.

Nonlinear self-adjointness, conserved quantities, bifurcation analysis and travelling wave solutions of a family of long-wave unstable lubrication model

Abstract: The paper investigates a class of long-wave unstable lubrication model using Lie theory. A nonlinear self-adjoint classification of the considered equation is carried out. Without having to go into microscopic details of the physical aspects, non-trivial conservation laws are computed. Then, minimal set of Lie point symmetries of the discussed model is classified up to one-dimensional conjugacy classes which are further utilised one by one to construct the similarity variables to reduce the dimension of the considered model. After that, all possible phase trajectories are classified with respect to the parameters of the equation. Some travelling wave and kink-wave solutions are also showed and graphical representations are displayed to depict their propagation.