Existence Of Surface Waves Research Articles

Characteristics of surface signature generated by an underwater sphere with regular free surface waves

The characteristics of the wake generated by an underwater sphere in the presence of regular free surface waves are investigated. Based on the spectral wave explicit Navier–Stokes equations decomposition strategy, the incident waves are prescribed based on spectral wave models, and the wake characteristics generated by the underwater sphere are determined using a computational fluid dynamics solver. The effects of the wavelength of the surface waves and the Froude number on the wake characteristics are investigated. The results show that the existence of free surface waves can distort the wake patterns, causing them to shift from the classical V-shaped Kelvin wake to an Ω-shape. Analysis of the spectrum indicates that the distortion of wake patterns is mainly determined by the wave–wave interactions.

Full waveform inversion of surface wave based on instantaneous frequency

Abstract Surface wave has many advantages, such as low attenuation, high signal-to-noise ratio, strong anti-interference ability and dispersion characteristics in layered media. It is widely used in engineering measurement and nondestructive testing. However, the applicability and reliability of surface wave processing methods are severely restricted by velocity inversion or strong heterogeneity of the medium. To overcome these shortcomings, in recent years, scholars have studied full-wave inversion methods including data preprocessing, wave field forward, gradient calculation, and inversion optimization to avoid any assumptions about underground complexity. However, the classical waveform difference mismatch function is apt to fall into a local minimum, which leads to the non-convergence of inversion. At the same time, the existence of surface waves greatly increases the non-linearity of full waveform inversion. Even small perturbations, especially in the S wave velocity structure, can cause dispersion for uniform backgrounds. To overcome this difficulty, a mismatch function based on instantaneous frequency is proposed and the adjoint wave equation is derived. Taking a layered model as an example, the effectiveness of the method is verified.

Discovery of Electromagnetic Surface Waves at the Interface between Perfect Electric Conductor and Perfect Magnetic Conductor Parallel-Plate Waveguides.

We propose new electromagnetic surface waves at the interface formed by connecting perfect electric conductor (PEC) and perfect magnetic conductor (PMC) parallel plate waveguides containing materials with positive permittivities and permeabilities. This challenges the conventional understanding that surface waves require materials with negative permittivity or permeability. Theoretical mode analysis and numerical simulations have confirmed the existence of surface waves at the PEC-PMC interface. Additionally, a simulated prism coupling experiment validated the excitation of the surface watpdel 1ve at the PEC-PMC interface. The resonant response of the localized surface waves on the enclosed PEC-PMC surface of a cylinder also closely resembles that of a Drude cylinder. Our finding broadens the understanding of the conditions for generating electromagnetic surface waves and deepens our comprehension of electromagnetic phenomena.

Electromagnetic surface waves guided by the interface of a metal and a tightly interlaced matched ambidextrous bilayer

The existence and characteristics of electromagnetic surface waves (ESWs) whose propagation is guided by the planar interface of metal and a tightly interlaced matched ambidextrous bilayer (TIMAB) were theoretically investigated, a TIMAB being a periodic unidirectionally nonhomogeneous material whose unit cell consists of one period each of two structurally chiral materials that are identical except in structural handedness. Thus, the structural handedness flips in the center of the unit cell. A canonical boundary-value problem was formulated and a dispersion equation was solved, the ESWs being classified as surface-plasmon-polariton (SPP) waves. Flipping the structural handedness once in the unit cell can greatly enhance the number of possible SPP waves, one or more of which may be superluminal.

Dyakonov surface waves in a thin interfacial waveguide formed by negatively anisotropic dielectrics.

Dyakonov surface waves (DSWs) are electromagnetic surface waves that exist at the interface of two dissimilar materials, with at least one material being anisotropic. Although there are various types of these waves, they all exist in anisotropic materials with positive anisotropy. The requirement for positive anisotropy limits the choice of materials that can support these waves. In this study, we present a type of Dyakonov surface wave that occurs at the interface of negatively anisotropic materials. Specifically, we demonstrate their existence in a system consisting of two negatively anisotropic slabs confined between two perfect electric conductor (PEC) walls. By assuming a small distance between the walls, we derive analytical expressions for the propagation constant, penetration depth, and field distribution of these surface waves. We numerically demonstrate that these surface waves can also exist in structures beyond the approximations used to develop the theoretical framework. The existence of Dyakonov surface waves in negative crystals broadens the range of materials suitable for their practical implementation.

Dyakonov surface waves in dielectric crystals with negative anisotropy.

Since the initial discovery of Dyakonov surface waves at a flat infinite interface of two dielectrics, at least one of which is positively anisotropic, extensive research has been conducted towards their theoretical and experimental studies in materials with positive anisotropy. The potential applications of these waves were initially limited due to the stringent conditions for their existence and the requirement for position anisotropy. In our study, we present the theoretical prediction and experimental observation of a novel type of Dyakonov surface waves that propagate along the flat strip of the interface between two dielectrics with negative anisotropy. We demonstrate that the conditions for surface waves are satisfied for negatively anisotropic dielectrics owing to the specific boundaries of the strip waveguide confined between two metallic plates. We study such modes theoretically by using the perturbation theory in the approximation of weak anisotropy and demonstrate that the electromagnetic field distribution in these modes is chiral. Experimental verification of theoretical predictions is made in the microwave range using 3D-printed negatively anisotropic water-dielectric metamaterial slabs. The existence of Dyakonov surface waves in negative crystals prompts a reassessment of the list of materials suitable for practical realization of these waves in the visible and infrared ranges. Due to the ability of the considered modes to transmit chiral light, they have potential in the sensing of chiral organic molecules.

Experimental Observation of Surface Wave States at the Gold–Silver Interface

We demonstrate that a gradual interface between gold and silver supports the propagation of a novel kind of surface electromagnetic wave, which is different from the more well-known surface plasmon polaritons. The existence of such surface waves leads to a paradoxical situation in which a continuous metal barrier which does not have any pinholes may exhibit considerably increased light transmission if the barrier is made of two different metals. A spectroscopic study of this effect is reported.

Wave propagation analysis in transversely isotropic piezoelastic medium based on nonlocal strain gradient theory

The purpose of this research is to study the propagation of surface waves in transversely isotropic piezoelastic medium based on nonlocal strain gradient theory. A characteristics equation for the existence of surface waves is discussed. This equation could be easily reduced to the ones of the gradient strain theory, nonlocal theory, and classical theory. It has also been concluded that there exist cut-off frequency for the wave propagating in size-dependent materials based on the nonlocal strain gradient theory. The dispersion equation which surface wave speed satisfies is derived from the free traction condition on the surface of half-space with consideration of electrically open circuit conditions. The effect of the nonlocal parameter, the strain gradient parameter on the existence of surface waves as well as the Rayleigh wave propagation is illustrated through some numerical examples.

A nonlocal strain gradient theory for wave propagation analysis in transversely isotropic elastic medium

This paper has the objective of studying the propagation of surface waves in a transversely isotropic medium based on nonlocal strain gradient theory (NSGT). A characteristics equation for the existence of surface waves is discussed. This equation could be easily reduced to the ones of the gradient strain theory, nonlocal theory and classical theory. It has also been concluded that there exist escape frequency and cut-off frequency for the wave propagating in size-dependent materials based on the NSGT. Dispersion equation for the propagation of Rayleigh-type waves at the free surface has been derived. The effect of the nonlocal parameter, the strain gradient parameter on the Rayleigh wave propagation is considered through some numerical examples.

Statistical Properties of Long‐Period Plasmapause Surface Waves From Van Allen Probes Observations

AbstractRecent work revealed the existence of plasmapause surface waves (PSWs) with Van Allen Probes observations, which are characterized by the periodic modulations of both magnetic/electric fields and plasma densities, and suggested to be the driver of giant undulations (GUs). In this study, six years data from Van Allen Probes were used to investigate the spatial distributions and occurrence conditions of PSWs in the period of 5–30 min. PSWs are found to be mainly distributed at L = 3.5–7 and their occurrence rate is increasing with larger L shells. In the azimuth direction, the spatial distribution of PSWs exhibits an obvious dawn‐dusk asymmetry with highest occurrence rates at MLT = 15–21, which is consistent with the spatial distribution of GUs revealed in the previous study. This further demonstrates that PSWs and GUs are connected, and indicates that PSWs differ from Ps6 waves which have a similar wave period and irregular waveform but mainly concentrate in the dawnside and connect with Ω bands. PSWs preferentially occur under the condition of high solar wind velocities (VSW > 500 km/s) and high dynamic pressures (Pdyn > 5 nPa), and their occurrence rate has a negative correlation with IMF Bz, SYMH and AL. Statistical results also reveal that PSWs preferentially occur around the peak of both magnetic storms and substorms. These findings may shed new lights on the further understanding of PSWs' generation and propagation.

Non-Hermitian elastodynamics in gyro-odd continuum media

Linear elasticity has long been considered a well-established research area using conservative field theory. However, the discovery of odd-elasticity challenges the essential energy conservation assumption, which together with gyroscopic ingredients compromise the fundamental theory of elasticity, but to the same effect, enable new directions in active elastodynamics. Here, we consider two-dimensional continuum mechanics in a more general framework containing active constituents from both gyroscopic and odd-elastic effects, which gives rise to non-reciprocal and non-Hermitian elastic waves in a highly unconventional guise. We discuss how these unusual media can extract energy from odd-elastic engine cycles comprising remarkable features of stability transitions, in which the energy exchange process reverses. Beyond bulk waves, akin to the unidirectional characteristics of a 2D quantum-Hall insulator, we demonstrate the existence of non-Hermitian Rayleigh surface waves which, in contrast to the classical ones in passive solids, display one-way and interference-free transport characteristics, which even remain resilient in finite sharp or curved geometries. The findings reported here may provide new possibilities to manipulate elastic waves in unusual ways.

Investigation of the existence domain for Dyakonov surface waves in the Sage computer algebra system

Surface electromagnetic waves (Dyakonov waves) propagating along a plane interface between an isotropic substance with a constant dielectric constant and an anisotropic crystal, whose dielectric tensor has a symmetry axis directed along the interface, are considered. It is well known that the question of the existence of such surface waves is reduced to the question of the existence of a solution to a certain system of algebraic equations and inequalities. In the present work, this system is investigated in the Sage computer algebra system. The built-in technique of exceptional ideals in Sage made it possible to describe the solution of a system of algebraic equations parametrically using a single parameter, with all the original quantities expressed in terms of this parameter using radicals. The remaining inequalities were only partially investigated analytically. For a complete study of the solvability of the system of equations and inequalities, a symbolic-numerical algorithm is proposed and implemented in Sage, and the results of computer experiments are presented. Based on these results, conclusions were drawn that require further theoretical substantiation.

Synchrotron mechanism of X-ray and gamma-ray emissions in lightning and spark discharges

X-ray and γ-ray emissions observed in lightning and long sparks are usually connected with the bremsstrahlung of high-energy runaway electrons. Here, an alternative physical mechanism for producing X-ray and gamma-ray emissions caused by the polarization current and associated electromagnetic field moving with relativistic velocity along a curved discharge channel has been proposed. The existence of fast electromagnetic surface waves propagating along the lightning discharge channel at a speed close to the speed of light in vacuum is shown. The possibility of the production of microwave, X-ray and gamma-ray emissions by a polarization current pulse moving along a curved path via synchrotron radiation mechanism is pointed out. The existence of long tails in the power spectrum is shown, which explains observations of photon energies in the range of 10–100 MeV in the terrestrial gamma-ray flashes, as well as measured power spectrum of laboratory spark discharge.

The Existence of Three-Dimensional Multi-Hump Gravity-Capillary Surface Waves on Water of Finite Depth

The paper considers three-dimensional (3D) traveling surface waves on water of finite depth under the forces of gravity and surface tension using the exact governing equations, also called Euler eq...

Generalised surface waves at the boundary of piezo-poroelastic medium with arbitrary anisotropy.

This study considers the propagation of surface waves along all directions on the plane boundary of piezo-poroelastic half-space with arbitrary anisotropy. This generalised propagation is characterized through an anisotropic phase velocity, which should ensure the decay of wave-field with depth into the medium. A linear homogeneous system of six equations with complex coefficients governs the existence and propagation of surface waves in the considered medium. The real phase velocity of surface waves lies implicit in a complex determinantal equation, which ensures a non-trivial solution to the system of equations. Through a specific transformation, the system of complex equations is modified to yield a real secular equation, with phase velocity being the only unknown. This equation can always be solved numerically for phase velocity of surface wave along any direction on the plane boundary of anisotropic piezo-poroelastic medium. The phase velocity has been used further to calculate the components of energy flux at the boundary. Horizontal components of energy flux define the group velocity and ray direction for the surface wave. A numerical example is solved to analyse the phase/group velocity curves at the boundary of the medium.

Steady-state antiplane crack considering the flexoelectrics effect: surface waves and flexoelectric metamaterials

The antiplane dynamic flexoelectric problem is stated as a dielectric solid that incorporates gradients of electric polarization and flexoelectricity due to strain gradients. The work examines dielectric materials without piezoelectric coupling or nonlinear ferroelectric switching and considers the inverse flexoelectric effect. It is shown that the coupling of the mechanical with the electrical problem can be condensed in a single mechanical problem that falls in the area of dynamic couple stress elasticity. Moreover, static and steady state dynamic antiplane problems of flexoelectric and couple stress elastic materials can be modeled as anisotropic plates with a non-equal biaxial pre-stress. This analogy was materialized in a finite element code. In this work, we solved the steady-state problem of a semi-infinite antiplane crack located in the middle of an infinite flexoelectric material, with its crack-tip moving with constant velocity. The particular type of loading investigated serves to relate the present solutions with known results from classic elastodynamics. We investigated the influence of various parameters such as the shear wave velocity and two naturally emerging microstructural and micro-inertia lengths. In the context of flexoelectricity, the two lengths are due to the interplay of the elastic and the flexoelectric parameters. Furthermore, we investigated the subsonic and the supersonic steady state crack rupture and showed that the Mach cones depend on the microstructural as well as the micro-inertial lengths. An important finding of this work is the existence of surface waves of Bleustein–Gulyaev type that do not appear in classic elastodynamics, but have been found in piezoelectric materials. The case of dielectric metamaterials with negative electric susceptibility is examined for the first time. The results can be useful for other dispersive materials, provided we identify the pertinent microstructural and micro-inertial lengths in accord with the behavior of the material at high frequencies.

Surface electromagnetic waves in anisotropic superlattices

This paper studies the existence of electromagnetic surface waves localized on a boundary of half-infinite periodic superlattices formed by an arbitrary periodic sequence of layers of homogeneous or functionally graded materials with generally anisotropic dielectric permittivity and magnetic permeability tensors. The geometry in question implies either two superlattices attached together to form a photonic bicrystal or else a superlattice in contact with vacuum or any other homogeneous dielectric or metal. Using the formalism of transfer and impedance matrices, a series of statements is proved on the maximum number of surface waves which may exist within a forbidden band at a fixed tangential wave number. This number embraces possible occurrences of surface waves in a given bicrystal and in its counterpart obtained by swapping the upper and lower superlattices. A maximum total number of surface waves in both these structures with an arbitrary arrangement of their unit cells is 2 in the lowest forbidden band (extending from zero frequency) and 4 in any upper forbidden band. The same statements apply to the case where one of the half spaces is occupied by a homogeneous material. A factor 2 smaller number of surface waves occur in a bicrystal composed of superlattices with a symmetric arrangement of unit cells. The existence considerations are further specialized for the surface waves with TE and TM polarizations.

A Backward Zenneck Wave Propagating along a Plane Interface between Media

We consider a surface Zenneck wave that propagates along a plane interface between a vacuum and a medium that is described by an isotropic dielectric permittivity and a surface Zenneck wave that propagates along a plane interface between a vacuum and a medium that is described by isotropic dielectric permittivity and magnetic permeability. In the latter case, we also consider an H wave and the possibility that the real parts of the permittivity and permeability are negative. Forward and backward waves at the boundary of a material with inhomogeneous profiles of the dielectric permittivity and magnetic permeability are considered. The conditions of the existence of forward and backward surface and volume waves, as well as of fast and slow surface waves are investigated.

Waveguide Modes with Threshold Nonlinearity

A three-layer structure is considered consisting of a nonlinear optical medium with an abrupt change in the dielectric constant, inside which there is a dielectric layer of finite thickness. It is shown that surface waves of two types of symmetry with a special field structure can propagate along the layers. It has been established that in the border regions in a nonlinear medium, regions of finite width with differing optical properties are formed. The formation of such boundary regions, as well as the existence of surface waves, occurs at interlayer thickness not exceeding a certain critical value.

Surface elastic waves whispering gallery modes based subwavelength tunable waveguide and cavity modes of the phononic crystals

We studied the characteristics of a phononic crystal which consists of hollow pillars mounted on the surface of semi-infinite substrate. In this study, the existence of surface waves whispering gallery modes referred as localized cavity modes of the hollow pillars at the subwavelength frequency spectrum is reported. The interaction of the hollow pillars with the surface waves induce localized cavity modes and by tuning the inner radius of the hollow pillars these confined modes can be adjusted/tuned inside the bandgap region, thus introducing new applications for the surface waves based phononic crystals and acoustic metamaterial devices. These subwavelength confined cavity modes possess high-q narrow passband characteristics induced by the interaction of cavity modes with the surface waves propagating at the surface of semi-infinite substrate. We demonstrate the subwavelength waveguiding and other functionalities of these localized cavity modes by tuning the inner radius of the hollow pillars and allowing the specific wavelength frequencies to pass through the monochannel, multichannel, and linear cavity based compact waveguides. To make the study more general, we demonstrate the wave multiplexing phenomena for the identical frequencies (diameters of the hollow pillars are kept constant) for all types of waveguides. However, by varying the inner radii of the hollow pillars, the high-q localized frequencies can be tuned. All the physical phenomena presented shows excellent agreement and it indicates promising applications for the manipulation of surface waves in the surface acoustic waves devices, surface waves sensor and actuator technology, and other photonic/phononic and metamaterial applications.