Surface Waves Research Articles

Unveiling Cryosphere Dynamics by Distributed Acoustic Sensing and Data‐Driven Hydro‐Thermo Coupled Simulation

AbstractAs global warming continues, the Earth's cryosphere is experiencing severe degradation. This study leverages a novel combination of distributed acoustic sensing (DAS) and artificial intelligence to monitor and decipher cryospheric dynamics. We have developed an advanced time‐lapse surface wave analysis workflow to capture shear wave velocity changes during a 2‐month controlled permafrost thaw experiment in Fairbanks, Alaska. To understand the underlying physical mechanisms of , multimodal rock‐physics simulations were conducted to associate the observed to hydrological and thermal processes like heating and rainfall events. Furthermore, we employ a physics‐guided deep learning algorithm alongside interpretable techniques to evaluate the impact of various physical factors and shed light on the cryospheric hydro‐thermo coupling mechanisms. This study highlights the potential of using DAS and data‐driven rock‐physics simulation for complex cryosphere monitoring and offers a comprehensive view of the permafrost's thawing dynamics.

Performance Assessment of a Coupled Circulation–Wave Modelling System for the Northwest Atlantic

We present a modified version of a coupled circulation–wave modelling system for the northwest Atlantic (CWMS-NWA) by including additional physics associated with wave–current interactions. The latest modifications include a parameterization of Langmuir turbulence and surface flux of turbulent kinetic energy from wave breaking in vertical mixing. The performance of the modified version of CWMS-NWA during Hurricane Arthur in 2014 is assessed using in situ measurements and satellite data. Several error statistics are used to evaluate the model performance, including correlation (R), root mean square error (RMSE), normalized model variance of model errors (γ2) and relative bias (RB). It is found that the simulated surface waves (R ≈ 94.0%, RMSE ≈ 27.5 cm, γ2≈ 0.16) and surface elevations (R ≈ 97.3%, RMSE ≈ 24.0 cm, γ2≈ 0.07) are in a good agreement with observations. The large-scale circulation, hydrography and associated storm-induced changes in the upper ocean during Arthur are reproduced satisfactorily by the modified version of CWMS-NWA. Relative to satellite observations of the daily averaged sea surface temperature (SST), the model reproduces large-scale features as demonstrated by the error metrics: R ≈ 97.8%, RMSE ≈ 1.6 ∘C and RB ≈ 8.6 ×10−3∘C.

Observed surface wave variations in the background current field of the Kuroshio Extension

Observed surface wave variations in the background current field of the Kuroshio Extension

Improvement of Seismic Noise Cross-correlation Function by Phase-velocity Probability Density Selection

TThe noise cross-correlation function (NCF) derived from continuous seismic records approximates the Green's Function (GF) of the far-field surface wave, which is crucial for S-wave velocity tomography. A critical step is stacking short-term NCFs over extended periods to improve the signal-to-noise ratio (S/N) and enhance the imaging quality of seismic data. However, incoherent noise significantly affects the accuracy of NCF calculations. Moreover, strong directional sources in the wavefield pose a challenge to conventional linear or phase-weighted stacking (PWS), often leading to overestimates of surface-wave phase velocity due to unresolved azimuthal effects. Selecting stationary phase zone (SPZ) data and correcting surface wave propagation paths based on source orientation requires a 2D array setup, which imposes stringent layout constraints. To address these challenges, we propose a novel data selection workflow for a 1D linear array based on the probability density distribution of surface-wave phase velocity. Firstly, we divide the noise data into different frequency bands and calculate the probability density curve of the phase velocity distribution for each frequency band. Then, based on the differences in phase velocities between SPZ data, directional source data, and incoherent noise, we select the probability density segments of SPZ data in each frequency band for stacking, effectively reducing the impact of incoherent noise and strong directional sources. The typical synthetic data and distributed acoustic sensing (DAS) field data examples demonstrate that the proposed workflow significantly improves the S/N in NCF and increases the useful bandwidth of the surface- waves dispersion curve, which furnishes reliable dispersion curve and waveform data, thereby facilitating subsequent S-wave velocity tomography.

Rayleigh waves in a layered thermoelastic structure

This paper aims to establish a general exact secular equation for Rayleigh surface waves propagating in an isotropic thermoelastic half-space coated by an isotropic thermoelastic layer of arbitrary thickness. The contact between the layer and the half-space is assumed to be welded on the interface. The outer surface of the layer is free of traction, and no heat transfer is allowed with the surrounding environment. When passing through the contact surface, the displacements and temperature fields, as well as the stresses and heat flux fields, are supposed to vary continuously, no jump being allowed. The explicit expressions of free Rayleigh waves in both the layer and the half-space are first presented, and then they are used to establish the general exact secular equation. Numerical illustrations are presented for a layered structure consisting of an aluminum layer welded on a half-space made of various thermoelastic materials outlining the main characteristics of Rayleigh wave propagation: the dimensionless propagation speed and the dimensionless damping in time of the wave’s amplitude. The exact effective boundary conditions for the Rayleigh waves are established in the thermoelastic half-spaces covered with thin films. Some limiting cases are also discussed: (1) when the thermoelastic layer is absent and (2) when the thermal effects are neglected.

Study on time-frequency domain characteristics and cross-media communication of laser acoustic signals based on optical breakdown mechanism

Abstract Cross-media communication is a hot research issue at present. The use of sound waves generated by laser induced sound mechanism for cross-media communication is a new topic proposed in recent years. It is of great significance to study the characteristics of laser acoustic signal and the feasibility study for cross-media detection. The time-frequency characteristics and directivity of the laser induced sound signal are studied on the self-built experimental platform. The results show that the pulse duration of the laser acoustic signal is about 0.2ms, and the peak frequency is about 14.89kHz. The directivity is anisotropy, the signal strength in horizontal direction is the strongest, and the signal strength perpendicular to the water surface is the weakest, so it has a good horizontal distance transmission ability. This paper verifies the detection system of trans-air-sea interface communication and trans-air-sea interface communication based on laser sound and conducts the communication experiment of laser acoustic signal. By modulating laser energy, the underwater acoustic signal is modulated in time domain, and the signal communication with 0-bit error rate of 8bps within the meter is realized. The detection threshold of acoustic signal is calculated to be 44.93dB after horizontal transmission of 1km. The analysis and simulation of water surface micro-motion based on laser induced sound are carried out. The results show that the wave crest of water surface generated by laser acoustic signal through underwater reflection reaches the order of micron and can be detected by radar. The surface wave intensity is little affected by the depth of detection, so it could work in deep water. This study provides a certain experimental and theoretical basis for laser communication across the air and sea interface.

Synchronized acoustic emission and high-speed imaging of cavitation-induced atomization: The role of shock waves.

This study experimentally investigates the role of cavitation-induced shock waves in initiating and destabilizing capillary (surface) waves on a droplet surface, preceding atomization. Acoustic emissions and interfacial wave dynamics were simultaneously monitored in droplets of different liquids (water, isopropyl alcohol and glycerol), using a calibrated fiber-optic hydrophone and high-speed imaging. Spectral analysis of the hydrophone data revealed distinct subharmonic frequency peaks in the acoustic spectrum correlated with the wavelength of capillary waves, which were optically captured during the onset of atomization from the repetitive imploding bubbles. This finding provides the first direct evidence that the wavelength of the growing surface waves, which governs capillary instability resulting in droplet breakup, is linked to the periodicity of shock waves responsible for the onset of the subharmonic frequencies detected in the acoustic spectra. This work contributes to a deeper understanding of ultrasonic atomization, signifying the role of cavitation and shock waves in the atomization process.

Microwave Surface and Lamb Waves in a Thin Diamond Plate: Experimental and Theoretical Investigation.

Microwave surface and Lamb waves in a multilayered piezoelectric "Al-IDT/(Al0.72Sc0.28)N/(001)[110] diamond" structure designed as a SAW resonator were studied using both the experimental and modeling methods. In this structure, it is possible to generate Rayleigh, surface horizontal (SHn) and Lamb waves simultaneously. The successful excitation of Lamb waves at operating frequencies up to 20GHz has been obtained. We have developed a method for identifying mode types based on an analysis of the elastic displacement fields and the frequency dependences of the dispersive phase velocities of each wave, as the frequency increases. The experimental data on the frequency response is in close agreement with the calculated values. The influence of Pt film deposition on the shifts in the resonant frequency of Lamb wave modes has been studied in detail. Since the Pt film was deposited on the free surface of a diamond substrate, shifts in the resonant frequency of Rayleigh-type waves are absent, as expected. This serves as an additional indication to distinguish these types of waves from others. The effect of film deposition on the frequency response of Lamb waves could be taken into account when designing acoustoelectronic sensors that use this type of wave as an operational mode.

Theoretical Investigation of Terahertz Spoof Surface-Plasmon-Polariton Devices Based on Ring Resonators

Terahertz is one of the most promising technologies for high-speed communication and large-scale data transmission. As a classical optical component, ring resonators are extensively utilized in the design of band-pass and frequency-selective devices across various wavebands, owing to their unique characteristics, including optical comb generation, compactness, and low manufacturing cost. While substantial progress has been made in the study of ring resonators, their application in terahertz surface wave systems remains less than fully optimized. This paper presents several spoof surface plasmon polariton-based devices, which were realized using ring resonators at terahertz frequencies. The influence of both the radius of the ring resonator and the width of the waveguide coupling gap on the coupling coefficient are investigated. The band-stop filters based on the cascaded ring resonator exhibit a 0.005 THz broader frequency bandwidth compared to the single-ring resonator filter and achieve a minimum stopband attenuation of 28 dB. The add–drop multiplexers based on the asymmetric ring resonator enable selective surface wave outputs at different ports by rotating the ring resonator. The devices designed in this study offer valuable insights for the development of on-chip terahertz components.

A metal-only transmission metasurface with dual-layer configuration for generation of orbital angular momentum wave

In this paper, we present a metal-only transmission metasurface adopting dual-layer elements with I-shaped grooves etched on each layer, which is designed for orbital angular momentum (OAM) generation. The special arrangement of the grooves on the elements results in a wider phase compensation range, and by varying the length of the grooves, a full 360° phase coverage with a transmission amplitude of more than −2 dB can be achieved at 10 GHz. As a proof of concept, a metal-only transmission metasurface composed of 400 elements is designed, fabricated, and measured. The simulated and measured results suggest that the OAM transmitted waves with the mode l = −1 can be efficiently generated by a double-layer metal-only metasurface at around 10 GHz. Compared with conventional configurations of OAM transmitted beam generation, this configuration has great potential for high power microwave and space environment applications.

Rayleigh-type wave in thermo-poroelastic media with dual-phase-lag heat conduction

Purpose The purpose of this paper is to investigate the propagation of Rayleigh-type surface wave in a porothermoelastic half-space. This study addresses the impact of surface pores characteristics, specific heat, temperature, porosity, wave frequency, types of rock frame and types of pore fluids on the propagation characteristics of Rayleigh-type wave. Design/methodology/approach A secular equation is derived, based on the potential functions for both sealed and open surface pores boundary conditions at the stress-free insulated surface of the porothermoelastic medium. Findings Propagation characteristics (velocity, attenuation and particle motions) of Rayleigh wave are significantly influenced by boundary conditions (opened or sealed surface pores) and thermal characteristics of materials. Furthermore, the path of particles throughout the propagation of Rayleigh-type waves is identified as elliptical. Originality/value A numerical example is considered to examine the effect of thermal characteristics of materials on the existing Rayleigh wave’s propagation characteristics. Graphical analysis is used to evaluate the behavior of particle motion (such as elliptical) at both open and sealed surface of the porothermoelastic medium.

Enhanced Light-Matter Interaction with Bloch Surface Wave Modulated Plasmonic Nanocavities.

Strong coupling between nanocavities and single excitons at room temperature is important for studying cavity quantum electrodynamics. However, the coupling strength is highly dependent on the spatial light-confinement ability of the cavity, the number of involved excitons, and the orientation of the electric field within the cavity. By constructing a hybrid cavity with a one-dimensional photonic crystal cavity and a plasmonic nanocavity, we effectively improve the quality factor, reduce the mode volume, and control the direction of the electric field using Bloch surface waves. After transferring a monolayer of WSe2 sandwiched in the hybrid nanocavities, a Rabi splitting of approximately 186 meV is obtained and the number of excitons involved in the coupling is reduced to 8. This is the smallest number reported to date for transition metal dichalcogenide (TMD) based systems, with an effective coupling strength per individual exciton reaching 17.6 meV, which is nearly double the highest reported value.

Dynamic Analysis of a Periodic Soil‐Structure Interaction System to Reduce Ground Vibration

ABSTRACTMetamaterials have been developed to control electromagnetic, acoustic, and elastic waves, and can also be employed to manage seismic waves. As building clusters can significantly affect ground vibrations, this study extends the concept of metamaterials to evaluate a periodic soil‐structure interaction (SSI) system capable of reducing the ground vibrations caused by seismic waves. Using the theory of SSI with Floquet–Bloch theorem, a governing equation for a unit cell in a periodic SSI system is derived with effective earthquake forces from exterior sources. The dispersion relations of the periodic SSI system are subsequently obtained, and its frequency band gaps (FBGs) for surface waves are identified. Furthermore, the dynamic stiffness of rigid foundation, on which periodic superstructures are installed, and corresponding input motion are calculated when Rayleigh surface waves are incident to the system. The results indicated that foundation input motion is significantly reduced resulting in a reduction of structural response, and the dynamic displacements of the soil surface are significantly reduced owing to the FBGs within the SSI system. Finally, a parametric study is conducted to examine the effects of clear spacing between buildings, building height, and shear wave velocity in the underlying half‐space on SSI system behavior. The results confirm that the dynamic characteristics of a periodic SSI system depend on these factors and it must be designed accordingly.

Time-dependent nonlinear gravity–capillary surface waves with viscous dissipation and wind forcing

We develop a time-dependent conformal method to study the effect of viscosity on steep surface waves. When the effect of surface tension is included, numerical solutions are found that contain highly oscillatory parasitic capillary ripples. These small-amplitude ripples are associated with the high curvature at the crest of the underlying viscous-gravity wave, and display asymmetry about the wave crest. Previous inviscid studies of steep surface waves have calculated intricate bifurcation structures that appear for small surface tension. We show numerically that viscosity suppresses these. While the discrete solution branches still appear, they collapse to form a single smooth branch in the limit of small surface tension. These solutions are shown to be temporally stable, both to small superharmonic perturbations in a linear stability analysis, and to some larger amplitude perturbations in different initial-value problems. Our work provides a convenient method for the numerical computation and analysis of water waves with viscosity, without evaluating the free-boundary problem for the full Navier–Stokes equations, which becomes increasingly challenging at larger Reynolds numbers.

Analysis on sensitivity and imperfect interfaces on the propagation of inter-facial anti-plane waves on the finely coated piezomagnetic reinforced composite structure

Abstract Surface acoustic waves are pivotal in modern technology due to their exceptional sensitivity and adaptability. The motivation for this study stems from the need to enhance the efficiency of surface wave sensors by advancing mass loading techniques and addressing the imperfections that can alter the magneto-mechanical properties, velocities, and propagation behavior of anti-plane waves in layered composite structures. The present work analyses the propagation behavior of Love-type and B-G-type waves in a piezomagnetic fiber-reinforced composite (PMFRC) structure underlying an Air medium (in Model-1) and under a coated thin filmed mass loading (in Model-2) in the presence of distinct inter-facial imperfections viz. Mechanically compliant magnetically weakly permeable (MCMWP), Mechanically compliant magnetically highly permeable (MCMHP), Low magnetic permeable (LMP), Magnetically grounded (MG), and welded. These inter-facial imperfections have been considered as five different submodels under both Model-1 and 2. At first, the micromechanical model of PMFRC has been developed, and closed-form expression for the material constants has been derived by harnessing the techniques of strength of materials and the rule of mixtures. Employing the suitable boundary conditions associated with distinct five inter-facial imperfections, velocity equations have been derived, validated, and graphically demonstrated for both magnetic cases (open (MO) and short (MS)) under various submodels of both models. Magneto-mechanical coupling, mass loading sensitivity, volume fraction, and imperfect interfaces affecting the phase velocity of Love-type and B-G type waves have been analyzed with a comparative approach under various models and submodels. The outcomes of the study can enhance detection capabilities in SAW devices, broadening their use in telecommunications, aerospace, and other industries.

Focussing of concentric free-surface waves

Gravito–capillary waves at free surfaces are ubiquitous in several natural and industrial processes involving quiescent liquid pools bounded by cylindrical walls. These waves emanate from the relaxation of initial interface distortions, which often take the form of a cavity (depression) centred on the symmetry axis of the container. The surface waves reflect from the container walls leading to a radially inward propagating wavetrain converging (focussing) onto the symmetry axis. Under the inviscid approximation and for sufficiently shallow cavities, the relaxation is well-described by the linearised potential-flow equations. Naturally, adding viscosity to such a system introduces viscous dissipation that enervates energy and dampens the oscillations at the symmetry axis. However, for viscous liquids and deeper cavities, these equations are qualitatively inaccurate. In this study, we decompose the initial localised interface distortion into several Bessel functions and study their time evolution governing the propagation of concentric gravito–capillary waves on a free surface. This is carried out for inviscid as well as viscous liquids. For a sufficiently deep cavity, the inward focussing of waves results in large interfacial oscillations at the axis, necessitating a second-order nonlinear theory. We demonstrate that this theory effectively models the interfacial behaviour and highlights the crucial role of nonlinearity near the symmetry axis. This is rationalised via demonstration of the contribution of bound wave components to the interface displacement at the symmetry axis Contrary to expectations, the addition of slight viscosity further intensifies the oscillations at the symmetry axis although the mechanism of wavetrain generation here is quite different compared with bubble bursting where such behaviour is well known (Duchemin et al., Phys. Fluids, vol. 14, issue 9, 2002, pp. 3000–3008). This finding underscores the limitations of the potential flow model and suggests avenues for more accurate modelling of such complex free-surface flows.

A frequency-domain beamforming procedure for extracting Rayleigh wave attenuation coefficients and small-strain damping ratio from 2D ambient noise array measurements

The small-strain damping ratio plays a crucial role in assessing the response of soil deposits to earthquake-induced ground motions and general dynamic loading. The damping ratio can theoretically be inverted for after extracting frequency-dependent Rayleigh wave attenuation coefficients from wavefields collected during surface wave testing. However, determining reliable estimates of in situ attenuation coefficients is much more challenging than achieving robust phase velocity dispersion data, which are commonly measured using both active-source and ambient-wavefield surface wave methods. This article introduces a new methodology for estimating frequency-dependent attenuation coefficients through the analysis of ambient noise wavefield data recorded by two-dimensional (2D) arrays of surface seismic sensors for the subsequent evaluation of the small-strain damping ratio. The approach relies on the application of an attenuation-specific wavefield conversion and frequency-domain beamforming. Numerical simulations are employed to verify the proposed approach and inform best practices for its application. Finally, the practical efficacy of the proposed approach is showcased through its application to field data collected at a deep, soft soil site in Logan, Utah, USA, where phase velocity and attenuation coefficients are extracted from surface wave data and then simultaneously inverted to develop deep shear wave velocity and damping ratio profiles.

Nondestructive testing of railway embankments by measuring multi-modal dispersion of surface waves induced by high-speed trains with linear geophone arrays

To effectively address engineering challenges and risks, it is crucial to characterize mechanical properties of near-surface environments. The Multichannel Analysis of Surface Waves (MASW) has proven to be a valuable active seismic imaging technique by providing near-surface shear (S)-wave velocities estimations. However, its application to urban areas requires further development. This study leverages well-constrained experimental sites to assess the viability of a passive-MASW technique, utilizing seismic waves induced by high-speed train traffic instead of conventional active sources. We suggest employing short 96-geophone uniform linear arrays to capture surface waves in a broad frequency band (10-200 Hz). Train passages are automatically detected and categorized regarding to the train travel direction. Seismic interferometry and phase-weighted stack techniques are applied to generate virtual shot-gathers that are transformed into high-resolution multi-modal dispersion images. Our results demonstrate a strong coherence between the picked dispersion curves from the passive-MASW approach and those obtained through traditional active MASW with a hammer source. We discuss the validity of higher modes and explore array density limits to ensure reliable results. Our findings highlight that seismic interferometry, coupled with a high phase-weighted stack power, effectively recovers energy at high frequencies, enhancing the characterization of multi-modal surface-wave dispersion associated with thin near-surface layers.

Attenuation of progressive surface gravity waves by floating spheres

Laboratory experiments were performed to investigate the attenuation of progressive deep-water waves by a mono-layer of loose- and close-packed floating spheres. We measured the decay distance of waves having different incident wave frequency and steepness. The attenuation of waves was strong if the surface concentration of particles was close-packed, with the decay distance being shorter for incident waves with higher frequency and steepness. The amplitude of the highest-frequency (2.0 Hz) and largest amplitude incident waves (with steepness 0.25) decayed by half over a distance of approximately 3 wavelengths. Theoretical models used previously in the study of surface wave damping by sea ice do not capture correctly the physics of wave attenuation by floating spheres. We developed a new theory that estimates the influence upon wave attenuation of turbulent dissipation resulting from oscillatory flow under a close-packing of spheres. This theory predicts that the wave amplitude decays as a power law, and gives a correct order-of-magnitude estimate of the observed decay distance. We explore the potential implications of these findings for the attenuation of progressive waves by (pancake) sea ice and for the indirect detection of marine plastic pollution from space.

Sensor importance-based optimal seismic acquisition design for surface waves

Surface wave methods aim to monitor the shallow subsurface non-invasively. Traditional multichannel surface wave acquisitions adopt evenly spaced receivers for convenience and simplicity. However, seismic acquisitions are often performed with coarse sampling due to financial constraints and practical issues with physical access. Compressive sensing (CS) has been extensively studied for industrial-scale seismic explorations, predominantly utilizing random undersampling of tens of thousands of receivers. These undersampling methods do not answer the critical question of optimality when small-scale, shallow seismic surface wave acquisition only allows tens of receivers and a few source locations. We propose an optimal seismic acquisition design (OSAD) framework, where the importance of each receiver is evaluated in a constrained sparse inversion framework for more accurate data reconstruction. Instead of randomized sampling, OSAD exploits the physical information available in previously acquired or simulated synthetic data. The sparsity of the acquisition geometry and of the seismic data in a transform domain is explored by nested convex optimizations for alternating directions by solving each sub-problem to find a solution to an overarching minimization objective function. We apply the OSAD framework to synthetic and field datasets. We focus on deriving optimal receiver geometry for seismic acquisition with a single source. The derived geometry automatically honors wave physics where high- and low-frequency data are prevalent for near- and far-offsets, respectively. We explicitly demonstrate the optimality of the acquisition by comparing the data reconstruction error resulting from OSAD with two existing random undersampling methods adapted to surface wave acquisition.