Theory Of Surface Waves Research Articles

Magnetopause MHD surface wave theory: progress & challenges

Sharp boundaries are a key feature of space plasma environments universally, with their wave-like motion (driven by pressure variations or flow shears) playing a key role in mass, momentum, and energy transfer. This review summarises magnetohydrodynamic surface wave theory with particular reference to Earth’s magnetopause, due to its mediation of the solar-terrestrial interaction. Basic analytic theory of propagating and standing surface waves within simple models are presented, highlighting many of the typically-used assumptions. We raise several conceptual challenges to understanding the nature of surface waves within a complex environment such as a magnetosphere, including the effects of magnetic topology and curvilinear geometry, plasma inhomogeneity, finite boundary width, the presence of multiple boundaries, turbulent driving, and wave nonlinearity. Approaches to gain physical insight into these challenges are suggested. We also discuss how global simulations have proven a fruitful tool in studying surface waves in more representative environments than analytic theory allows. Finally, we highlight strong interdisciplinary links with solar physics which might help the magnetospheric community. Ultimately several upcoming missions provide motivation for advancing magnetopause surface wave theory towards understanding their global role in filtering, accumulating, and guiding turbulent solar wind driving.

A study on soil propagation mechanism of traffic-induced vibration based on numerical analysis and theoretical approach

In order to clarify soil propagation mechanism of traffic-induced vibration, soil surface responses excited by vertical and horizontal force focused on the frequency characteristics are examined based on numerical analyses, theory of surface wave, and field observations. Relationships between natural frequency of surface soil and frequency at which wave with large amplitude propagates at distant points are examined. In the case of two-layer soil, vertical displacement amplitude excited by vertical point force becomes the largest at twice the natural frequency at distant points. Horizontal displacement amplitude excited by horizontal point force becomes the largest at the natural frequency at distant points.

Disentangling electric field effect on spin waves in ferromagnetic insulators

In this paper we extend the micromagnetic theory of magnetostatic surface waves in insulating ferromagnetic thin films to include the applied electric field effects. We start by identifying the two main effects on the dispersion relation: the first one is of relativistic nature and emerges as a consequence of the Aharonov–Casher effect, while the second one is a consequence of the electric field induced symmetry breaking operating at the level of magnetic exchange interactions. We support our theory by comparing its predictions with experimental data on ittrium iron garnet thin films taken from the literature. The main result is to evidence the limitations of using the same value of the applied electric field to address both effects and to emphasize that crystal symmetry breaking due to the applied electric field brings about the contributions of the crystal field and determines different amplitudes for the two effects.

Improving the procedure for modeling low-frequency oscillations of the free surface liquid in a tractor tank

This paper considers the influence of hydrodynamic processes in the movement of the free surface of liquid in partially filled tractor tanks. Splashing liquid in partially filled containers is a significant problem in the study of functional stability of movement in the marine, aerospace, rail, and automotive industries. After all, it affects productivity and traffic safety. The same effect was observed when performing transportation work while delivering liquid cargoes in the agricultural sector. That was due to increasing the transportation speeds of wheeled tractors. In the procedure, using the Rayleigh theory of surface waves, a linearized problem of motion of the free surface of a liquid is obtained. Based on Helmholtz's theorem, the components of scalar and Laplace field vector potentials of fluid velocity vector are separated. The potential problem for translational motion of fluid, in which vortex component of the field is absent, is considered. Instead of the fluid velocity potential, a scalar fluid displacement potential in Rayleigh surface waves was introduced. Comparing the results of calculating fluid splashing with the work of other scientists, a high convergence of natural frequencies of partial oscillators in 3D space was found. This is noticeable in the last quarter of the filling of the tank, in which significant displacements of the deep liquid occur. A feature of the results is the introduction, instead of the real shape of the container, an equivalent form of a parallelepiped, the final shape of which depends on the level of fullness. The frequency properties of movement of the free surface of liquid based on the standard size of tanks used in agriculture are separated. The proposed improved methodology could be used to increase stability, controllability, and smoothness when operating tanks with a wheeled tractor.

Investigation on the Electromagnetic Surface Waves for Single-Wire Power Transmission

Single-wire power transmission (SWPT) is a power transmission method that uses only one wire to realize long-distance transmission of power. For deep insight, the theory of electromagnetic surface waves in this article is applied to reveal the principle of a long-distance large-scale SWPT system. Maxwell's equations under two different media in this system are established, based on them and the boundary conditions on the interface of the media, the propagation law of electromagnetic field energy in the SWPT system is analyzed. A simulation model is built by high frequency simulator structure (HFSS). The distribution law of the Poynting vector in different situations is studied to verify the correctness of the theoretical analysis. Moreover, long-distance transmission experiments are carried in the campus. It is shown that the transmission power can reach 300 W or 135 W when the transmission distance is 100 m or 200 m, respectively.

A 3D boundary element method for analysing the hydrodynamic performance of a land-fixed oscillating water column device

In this work, the theoretical hydrodynamic performance of an onshore Oscillating Water Column (OWC) device, subjected to normal wave incidence, is investigated. Based on linear surface-wave theory, the full solution of the boundary value problem (BVP) is obtained by using a three-dimensional (3D) boundary element method (BEM) with nine-noded quadrilateral elements. The method of subdomains is used to solve the BVP by applying the BEM separately to each of its regions, and the continuity of velocity potential and flux are used to match the problem. The capture width, hydrodynamical coefficients and free surface elevations are analysed for different OWC geometric parameters of the chamber. Numerical results for the hydrodynamic performance were found to be in good agreement with cases reported elsewhere. The findings show that the chamber configuration and the linearized air compressibility have a significant impact on the capture width bandwidth, the resonant frequency and the free surface elevation within the chamber.

The conjunct effects of ISO and CLVD sources in underground explosions on the spectral null in Rg waves

The compensated liner vector dipole（CLVD）source is usually induced by underground explosions and could lead to a null in the Rg spectra. There is a theoretical scale between the null frequency and the depth of the CLVD source. Therefore we can estimate the depth of underground explosions with the null frequency. However, this relationship is based on simply considering the CLVD source while the conjunct effects of ISO and CLVD source is neglected. This study researches the conjunct effects of ISO and CLVD sources in underground explosions on the spectral null in Rg waves by numerical calculating the Rg spectra with seismology theory of surface waves. The results indicate that the null in mixed signals is quite different from the results of single CLVD source. Thus the null frequency of Rg waves is not simply corresponding to the theoretical value in practical underground explosions and it is improper to estimate the depth of explosions by directly applying the theoretical formula.

Mathematical Theory of Surface Waves in a Lossy Inhomogeneous Dielectric Waveguide of Arbitrary Cross Section

Mathematical Theory of Surface Waves in a Lossy Inhomogeneous Dielectric Waveguide of Arbitrary Cross Section

Antenna Parameters for On-Body Communications With Wearable and Implantable Antennas

In this article, redefined antenna parameters regarding the additional effects occurring with on-body propagation are derived to enable a standardized characterization of on-body antennas. A model for the on-body propagation of arbitrary wearable and implantable antennas using Green's functions based on the Norton surface wave theory and the surface equivalence principle is presented, which subsequently is used as an on-body near-field-to-far-field transformation. The defined on-body far-field enables the redefinition of the antenna parameters (gain, effective area, and efficiency) for the on-body case. Based thereon, the antennas can be deembedded from the on-body channel and the on-body link between two antennas can be calculated by an adapted Friis transmission equation similar to free-space propagation. It is demonstrated by two examples, one of a hearing aid antenna and another of an antenna of an implantable pacemaker, that the on-body antenna parameters allow for an educated design of the antennas without the necessity of electromagnetic modeling of the entire system.

Studies on preparation and formation mechanism of poly(lactide-co-glycolide) microrods via one-step electrospray and an application for drug delivery system

Rod-like microparticles are important drug delivery systems for their large specific surface area and high cell uptake rate. However, complex preparation methods, such as mechanical stretching and cutting after electrospinning restrict applications of rod-like microparticles. In this study, uniformly sized microrods were fabricated via one-step electrospray by using poly(lactide-co-glycolide) (PLGA) solutions with low viscosity, mainly low concentration, and low molecular weights. In contrast to previous results that polymer beads are usually obtained with low-concentration precursor solutions, we prepared 0.5–2.0 μm diameter and 4–20 μm long microrods when the concentration of the solution and molecular weight of the polymer were further decreased. Moreover, the aspect ratio of the microrods decreased significantly after upregulating the loading voltage, adding salt, and using high permittivity solvents. It is suggested that the formation of microrods with an aspect ratio of 4.51·N (N = 1, 2, 3…) was based on the surface wave theory, which was tallied with the experimental data. Furthermore, the doxorubicin(DOX)@PLGA microrods showed higher entrapment efficiency and drug-loading capacity as a drug delivery system compared with those of DOX@PLGA microspheres. Microrods have the potential for a broader range of applications in biomedicine due to the easy preparation process of one-step electrospray.

Detection of anti-seepage effect of building stress wall structure based on transient Rayleigh surface wave method

Aiming at the problem that the traditional core drilling detection method has certain damage to the impervious body, and the detection points are limited, which leads to the limitation of the evaluation results; this paper proposes a detection method of seepage control effect of building stress wall structure based on transient Rayleigh surface wave method. The wave velocity of Rayleigh wave under plane stress is obtained by combining wave equation with plane stress. Under the three boundary conditions, it is theoretically feasible to detect the cutoff wall with transient Rayleigh surface wave technique. Therefore, based on the transient Rayleigh surface wave theory, the 24 channel broadband signal input channel and the minisis24 integrated engineering detector with advanced computer are used as the carrier to detect the anti-seepage effect of the stress wall structure. The practical engineering test shows that the permeability coefficient of the wall measured by this method is in good agreement with the core drilling method, and it is a reliable non-destructive testing method for wall anti-seepage.

Cauchy Formalism in the Theory of Acoustic Surface Waves

To describe the propagation of acoustic surface waves in an anisotropic layer, a six-dimensional complex formalism is introduced, a Hamiltonian is constructed, an analogue of the Rayleigh dissipative function, and an exponential fundamental matrix. Dispersion equations are obtained for a multilayer plate with different conditions on the boundary surfaces. Examples of the application of the Cauchy formalism to the analysis of the dispersion of Lamb waves are given.

The effect of body waves on phase-velocity determined by the spatial autocorrelation (SPAC) method, evaluated using full-wave modelling

Body waves may affect phase velocity obtained from microtremor array surveys in some rare cases. Fitting theoretical phase velocities based on a surface-wave theory to observed phase velocities affected by body waves would therefore result in distorted images of subsurface S-wave velocity structure. In this study, we present a method for the theoretical calculation of phase velocities in which the full-wave field (i.e. a wavefield including not only surface waves but also body waves) is taken into account. In numerical experiments conducted in this study, in which we considered the full-wave field, we generated synthetic microtremors by randomly distributing point vibration sources on the surface of a horizontally stratified velocity model. We then determined the phase velocities by applying the spatial autocorrelation (SPAC) method to the synthetic vertical-component wave data. The phase-velocity dispersion curve thus obtained exhibited a shape with a clear peak, with a peak value (peak phase velocity) exceeding the S-wave velocity of a bedrock in the model, which was not explainable with a surface-wave (Rayleigh-wave) theory. We conducted systematic numerical experiments and clarified the following two features of the peak phase velocity: (1) the peak phase velocity becomes large as the contrast of the S-wave velocities between the surface layer and the bedrock, or the P-to-S-wave velocity ratio (related to the Poisson’s ratio) in the surface layer gets large, and (2) the frequency at which peak phase velocity occurs (peak frequency) lies in the vicinity of the S-wave resonance frequency of the ground. Both the peak phase velocity and the peak frequency were theoretically reproduced by the calculation method that we propose in this study, based on a SPAC method modified to consider the full-wave field. These results imply the possible improvement in the accuracy of microtremor array survey analysis for velocity-structure inference, by applying a full-wave theory to the peak phase velocity.

Boundary-polarized subsonic Rayleigh waves under conditions of semi-simple Stroh degeneracy

We undertake a study of subsonic free surface (Rayleigh) waves in linear elastic half-spaces of general anisotropy when the wave polarization vector lies in the half-space boundary , if and when the formalism due to A. N. Stroh exhibits semi-simple degeneracy at the Rayleigh speed v R . It is shown that the class of subsonic steady wave motions at any subsonic velocity exhibiting semi-simple degeneracy includes a free surface wave whenever the first transonic state is not exceptional, in accordance with general surface wave theory. Furthermore, such a free surface wave is always necessarily boundary-polarized ! In general, the restrictions on the half-space elastic constants permitting the existence of semi-simplicity in steady motion at a subsonic phase speed are not satisfied in any physically realized medium which is elastically stable, but we outline an algorithm which allows one to construct the elastic stiffnesses of media which exist mathematically and allow for the existence of subsonic free surface waves (which are necessarily boundary-polarized) under conditions of semi-simple degeneracy in the sense of Stroh's formalism.

New Perspectives on the Physical Origin of Acoustic Wood Anomalies

Acoustic Wood anomaly is a pulsed ultrasound phenomenon in which sharp spectral anomalies such as tips or dips or both occur in the spectrum of a pulse reflected from or transmitted through a periodically corrugated interface for normal incidence. To date only surface acoustic waves generated on periodic interface through diffraction mechanism have been identified as the physical source of these spectral anomalies, and each anomaly has been proved being matched by specific order(s) of diffraction of related surface wave(s) with high accuracy. However, in this study, we report the observation of several anomalies that are not originated from surface waves, and an anomaly that cannot be matched by any individual order of diffraction. Using a proposed sectional analysis approach, comb filtering effect is proved to be a new source of spectral anomalies, and a multiple surface wave theory is developed not only to provide a satisfactory explanation for the unusual anomaly observed, but also to serve as a general guideline for understanding spectral anomaly formation.

Change of terahertz antenna spectrum when surrounding dielectric alters

The spectrum of terahertz antenna was studied when the dielectric’s covering dielectric as was changed in type, thickness or distance to electrodes. The surface wave theory was used to explain the physics of current pulse propagation in antenna electrodes, showing that the covering dielectric affected the propagation velocity of the current pulse on electrodes. Here, the emission spectrum of a dipole THz antenna on LTG GaAs was simulated via CST software. It was detected that the amount of thickness, permittivity and position of the covering dielectric influenced the spectrum of emitted THz as well electrode thickness. On the other way the capacitance equivalent of the antenna is calculated via COMSOL MultiPhysics software and it is detected the covering dielectric can affect capacitance and then resonance frequency antenna which is consistent with our CST results.

Development and numerical tests of a Bayesian approach to inferring shallow velocity structures using microtremor arrays

We propose an empirical Bayesian approach to inferring shallow (depth ranges from a few to several tens of metres) S-wave velocity structures using microtremor arrays and execute numerical tests to assess the feasibility of this approach. In our approach, the estimate of the S-wave structure (posterior) is derived from an empirical S-wave structure model (prior) and phase velocities of Rayleigh waves obtained with microtremor arrays. In other words, we aim to find a model that is close to the empirical model and is able to explain phase velocities with a 1D surface-wave theory. The inversion is stabilised by the constraints from the prior model so that model parameterisation with many thin layers can be adopted. The velocity structure is individually estimated for each of two cases (assumptions): the case where we assume fundamental-mode dominance and the case where we take into account the higher modes. Optimal values of the model parameters (e.g. a thickness parameter) are found, based on Akaike’s Bayesian Information Criterion (ABIC), and the choice of the better assumption of the surface-wave theory is also based on ABIC. Numerical tests, where synthetic data is generated from a horizontally stratified two-layer model, indicate that the relative weight between a prior model and the observed data is appropriately adjusted by ABIC. It is revealed that a value of the thickness parameter required to reproduce the given two-layer model is successfully found by ABIC. We also suggest that we can make a plausible choice of the assumption of the surface-wave theory with ABIC, unless observation error is extremely large.

Kinetic theory of electrostatic surface waves in a dusty plasma slab with electrons/ions featuring the Tsallis distribution

The linear excitation of surface dust-ion-acoustic waves in a semi-bounded dusty plasma and a dusty plasma slab comprising Tsallis distributed electrons and ions is studied. The propagation properties of surface modes (in semi-bounded dusty plasma) and both symmetric and anti-symmetric modes (in the dusty plasma slab) are investigated. It is found that the nonextensivity increases the phase velocities of surface modes in both dusty plasma structures, whereas the magnitude of the dust grain charge reduces the wave frequency. In the dusty plasma slab, the wave frequency of both symmetric and anti-symmetric modes decreases with the increasing number density of dust grains, also it leads to a decrease in the separation between two modes. The present investigation contributes to the physics of electrostatic surface wave structures in Saturn's E-ring or G-ring magnetosphere in which plasma components with Tsallis distribution exist.

Dyakonov waves in biaxial anisotropic crystals

We present the general analytical theory for Dyakonov surface waves at the interface of a biaxial anisotropic dielectric with an isotropic medium. We demonstrate that these surface waves can be divided into todo distinct classes, with qualitatively different spatial behavior. We obtain explicit expressions for the Dyakonov waves dispersion and the parameter range for their existence.

Theory of Electromagnetic Surface Waves in Plasma with Smooth Boundaries

A theory of nonpotential surface waves in plasma with smooth boundaries is developed. The complex frequencies of surface waves for plasma systems of different geometries and different profiles of the plasma density are calculated. Expressions for the rates of collisionless damping of surface waves due to their resonance interaction with local plasma waves of continuous spectrum are obtained. The influence of collisions in plasma is also considered.