Wave Diffraction Research Articles

Observation of Nonreciprocal Diffraction of Surface Acoustic Wave

Observation of Nonreciprocal Diffraction of Surface Acoustic Wave

Investigation of the Wave Field around a Monopile due to Long Crested Irregular Waves in Moderate Steepness

Monopile foundations are the most built foundations in the offshore wind industry. The diameter is also expected to increase in the near future to accomodate for larger wind turbines in deeper water depths. The large monopile diameter imposes additional challenge in planning the marine operations near the monopile, as the monopile can no longer be treated as a transparent monopile (i.e. the monopile gives negligible impact on the incident waves). Proper wave field estimation around the monopile that also accounts for the monopile existence is needed to assure the safety of the operations. Investigation of the wave field around a monopile due to long crested irregular incident waves is provided in the present study. Experimental study was performed with different irregular wave properties, varying the wave steepness and wave diffraction number. The present study explores further the available experimental studies that focus mostly on the runup of the monopile. Initially, Linear Transfer Function (LTF) of the wave field around a monopile from the experimental study is compared to the linear theory, which is found to match well in the high energy frequency range. The LTF differs with the linear theory in the low and high frequency ranges, indicating pronounced nonlinear effect in those frequency ranges. Further, time series analyis is also performed via exceedance probability analysis and significant value computation. It is found that the nonlinearity appears in the crest properties of the wave field around a monopile, while the wave height properties can still be predicted well with the linear theory. Moreover, Wave Type II, wave that travels in the clockwise/anti-clockwise direction around a monopile and not in radial direction, is seen to influence the crest properties.

Propagation of Non-stationary Skew-Symmetric Waves from a Spherical Cavity in a Porous-elastic Half-space

Problems of propagation and diffraction of non-stationary waves in porous-elastic mediums are of great theoretical and practical importance in such fields of science and technology as geophysics, seismic exploration of minerals, seismic resistance of structures, and many others. The work considers the problem of propagation of non-stationary skew-symmetric waves from a spherical cavity in a porous-elastic half-space saturated with liquid. To solve the problem, the integral Laplace transform in dimensionless time and the method of incomplete separation of variables were used. In the space of Laplace images in time, known and unknown functions are expanded into Gegenbauer polynomials. The problem is reduced to solving an infinite system of linear algebraic equations, the solution of which is sought in the form of an infinite exponential series. Recurrence relations for the coefficients of the series and initial conditions for them are obtained, which makes it possible to obtain a solution to the infinite system without using the reduction method. Recurrence relations make it possible to determine the coefficients of a series in the form of rational functions, which makes it possible to calculate their originals using the theory of residues. In image space, formulas are obtained for the coefficients of the series of components of the displacement vector and stress tensor. Numerical experiments were carried out, the results of which are presented in the form of graphs. The results obtained can be used in geophysics, seismology, and design organizations during the construction of structures, as well as in the design of underground reservoirs.

Polarization-Independent Focusing Vortex Beam Generation Based on Ultra-Thin Spiral Diffractive Lens on Fiber End-Facet

An ultra-thin spiral diffractive lens (SDL) was fabricated by using focused ion beam milling on a fiber end-facet coated with a 100 nm thick Au film. Focusing vortex beams (FVBs) were successfully excited by the SDLs due to the coherent superposition of diffracted waves and their azimuth dependence of the phase accumulated from the spiral aperture to the beam axis. The polarization and phase characteristics of the FVBs were experimentally investigated. Results show that the input beams with various polarization states were converted to FVBs, whose polarization states were the same as those of the input beams. Furthermore, the focal length of the SDL and the in-tensity and phase distribution at the focus spot of the FVBs were numerically simulated by the FDTD method in the ultra-wide near-infrared waveband from 1300 nm to 1800 nm. The focal length was tuned from 21.8 μm to 14.7 μm, the intensity profiles exhibited a doughnut-like shape, and the vortex phase was converted throughout the broadband range. The devices are expected to be candidates for widespread applications including optical communications, optical imaging, and optical tweezers.

Optical wave packet compression using counterpropagating Scorer beams

Abstract We investigate the diffractive paraxial wave equation with an external potential, utilizing self-similarity and variable separation methods. The exact solution to this evolution equation, expressed through Scorer functions, gives rise to the new Scorer beams. We explore the dynamics of counterpropagating Scorer beams, as promising optical wave packets, focusing on their compression behavior. The Scorer beams are characterized by two key parameters: the attenuation factor and the initial pulse width. By appropriately adjusting these parameters, significant beam compression can be achieved. Specifically, increasing the attenuation factor enhances compression and raises pulse amplitude, while reducing the initial pulse width further amplifies these effects. Along the way, we observe interesting interference patterns of the counterpropagating Scorer beams, never seen before. This study introduces a novel approach to beam compression and opens up new possibilities for their practical applications.

Diffraction of Magnetoelastic Plane Waves through a Rigid Strip in an Orthotropic Medium: An Analytical Approach

Diffraction of Magnetoelastic Plane Waves through a Rigid Strip in an Orthotropic Medium: An Analytical Approach

Heuristic solution to the problem of diffraction of a TH-polarized electromagnetic field on a half-plane with generalized two-sided impedance boundary conditions

A technique for constructing heuristic formulas for solving the problem of electromagnetic wave diffraction on a half-plane with non-ideal boundary conditions is proposed based on the method of fundamental components. The problem of diffraction of a TH-polarized wave on a half-plane with generalized two-sided impedance boundary conditions was chosen as a verification solution. Two ways of influencing heuristic formulas are proposed, such as smoothing the transition areas and adjusting the slope of the tuning curve. Quantification of the results showed that the proposed methods of influence are effective. This approach represents a new way to obtain high-accuracy heuristic formulas and allows one to create solvers that simultaneously have both high accuracy and high performance. The main result is the development and description of adjustment methods for increasing the accuracy of heuristic formulas.

Enabling superresolution detection via dispersion-induced time diffraction of evanescent waves

Enabling superresolution detection via dispersion-induced time diffraction of evanescent waves

Methane sealed due to the formation of gas hydrate system in the South China Sea

Although the release of methane into oceans and potentially the atmosphere could accelerate climate change, detailed investigations on the gas source from deep-buried strata and its migration through the gas hydrate stability zone (GHSZ) to the seafloor are limited. These studies are often hindered by the presence of diffracted waves and inaccuracies in seismic velocity models, leading to poor seismic imaging that hampers the understanding of gas sources, migration pathways, and gas hydrate accumulation. In the study, we utilize the technique of common scatter point (CSP) gathers to build an accurate velocity model and obtain high-quality images for a complex gas-hydrate and natural-gas petroleum system. The CSP processing enables the accurate migration of reflected and diffracted waves, resulting in improvements in signal-to-noise ratio and lateral resolution. The improved seismic images offer clearer visualization of various petroleum elements. Specifically, we can identify the top of the hydrate zone and base of the free gas zone within a shallow-buried hydrate system, fault geometries within the free gas zone, a middle-buried natural gas reservoir, gas chimneys as migration pathways, and the deep-buried source rock strata beneath the intrusive volcanic rocks. As a result, we reveal a joint prospect of natural-gas reservoir and gas-hydrate system in the deep-water region of the South China Sea. Our results suggest that methane in the natural gas reservoir has migrated upwardly into the hydrate system, and it is unlikely to leak into the water column.

Multiple surface lattice resonances in symmetric nanocuboid dimer arrays

Abstract Surface lattice resonances based on nanoparticle arrays have significant characteristics such as localized field enhancement and high quality factor, and can be applied in fields such as optical sensors and lasers. In this work, we propose a symmetric Si/SiO2 nanocuboid dimer array that can generate and regulate two surface lattice resonances. One of the surface lattice resonances (named SLR1) is mainly due to the coupling between the electric dipole resonance of single Si/SiO2 nanocuboid dimers and the diffraction waves perpendicular to the applied electric field. Another surface lattice resonance (named SLR2) mainly originates from the coupling between the magnetic dipole resonance of single Si/SiO2 nanocuboid dimers and the diffraction waves parallel to the direction of the applied electric field. The research results indicate that the polarization direction of the incident field, the period of the array, the gap between the nanocuboids in the dimer, particle size, and the medium environment are all important for regulating the two surface lattice resonances. The sensing application of multiple surface lattice resonances is also investigated. The results show that under appropriate structural parameters, SLR1 can provide good stability for sensing applications, its sensitivity and figures of merit are 472 nm RIU−1 and 104, respectively. However, SLR2 is very weak or suppressed when the refractive index of the medium environment is greater than or equal to 1.2. This characteristic limits the application range of SLR2 in sensing. This work is of great significance for the design of micro-nano photonic devices based on multiple surface lattice resonances.

Plane wave diffraction by a semi‐infinite parallel‐plate waveguide with partial material loading: The case of H polarisation

AbstractThe analysis of diffraction by a semi‐infinite parallel‐plate waveguide with partial material loading is rigorously carried out using the Wiener–Hopf technique for the H‐polarised plane wave incidence. In solving the Wiener–Hopf equations, the authors apply the Modified Residue Calculus Technique (MRCT) to achieve highly accurate solutions. The scattered field in real space is explicitly derived by performing the inverse Fourier transform of the solution in the transform domain. Within the waveguide, the scattered field is represented in terms of the waveguide TM modes, while the external field is asymptotically evaluated by applying the saddle‐point method to yield a far field expression. The authors present representative numerical examples of the radar cross section for various physical parameters and discuss the far‐field scattering characteristics in detail. Comparisons with the E‐polarisation are also given.

Dielectric Metasurfaces for Broadband Phase-Contrast Relief-Like Imaging.

The visualization of transparent specimens in traditional light microscopy is impeded by insufficient intrinsic contrast, prompting the development of advanced contrast-enhancement methodologies to transmute minute phase discrepancies into detectable amplitude alterations. While existing methods excel in either phase-contrast imaging (contrast-enhanced image of whole objects) or relief-like imaging (deceptive three-dimensional images), it would be of great significance to seamlessly integrate both capabilities in the same device. Here, we propose a novel metasurface-assisted half-side phase-contrast technique capable of simultaneous phase-contrast and relief-like imaging across the visible spectrum, which is realized by introducing a ±π/2 phase shift to a half-side diffracted wave emitted by the objects. Our method showcases successful application to diverse specimens, including a transparent silica disk and a frog egg cell. Our work substantiates high-quality microscopic imaging of various transparent specimens, which has profound implications in cellular biology, materials science, and medical diagnostics.

Diffraction of plane harmonic waves on a rigid cylindrical inclusion of an arbitrary cross section

Diffraction of plane harmonic waves on a rigid cylindrical inclusion of an arbitrary cross section

Thermo-optic tuning of quasi bound state in continuum in lithium niobate thin film hetero-nanograting

Lithium niobate (LN) is difficult to etch precisely due to its stable physical and chemical properties. In recent years, more and more research has focused on etchless thin film lithium niobate (TFLN). Here, a one-dimensional SiO2 nanograting structure fabricated on lithium niobate on insulator (LNOI) platform is designed in this study. This nanograting can generate one-dimensional diffraction waves. Then quasi-bound state in the continuum (q-BIC) can be introduced by aligning with the waveguide mode supported by the TFLN, which can achieve a high-quality factor and strong field enhancement, thus improving the interaction between light and matter. Furthermore, we validate the polarization characteristics of the nanograting structure, and measure the thermo-optical tuning sensitivity of the device to be 26.67 pm/K. This finding opens up potential avenues for realizing multi-dimensional tunable and dynamic photonic devices.

Theoretical and experimental study of diffraction by a thin cone

A problem of diffraction of ultrasound acoustic waves by an acute-angled hard cone is studied. Within the framework of the parabolic equation method, an analytical solution of the problem for an arbitrarily located point source is built. Specifically, the problem is reduced to the Volterra boundary integral equation, which can be solved using the Fourier transform. An experimental measurement of the diffracted field is carried out. The experiment is based on the MLS method adapted for narrowband sound sources. A comparison of experimental and theoretical results is provided.

Three-dimensional Reverse Time Migration for Detecting Tree Trunk Defects Using Ground Penetrating Radar

Abstract Due to environmental degradation and external intrusions, trees may develop various defects that diminish their stability and survival rates, leading to significant losses. Ground penetrating radar (GPR), characterized by its rapid and non-destructive advantages, has been regarded as a potentially effective method for assessing tree health conditions. However, existing GPR-based tree imaging techniques are predominantly two-dimensional (2D), making it difficult to diagnose three-dimensional (3D) structural features of defects. Therefore, this paper introduces, for the first time, 3D reverse time migration (RTM) into trunk defect detection. Compared to 2D RTM, 3D RTM can simultaneously back-propagate in-line and cross-line signals, accurately locate reflection waves, and focus diffracted waves, reconstructing the true interfaces and defect positions within the tree trunk. Experimental results on irregular trunk models containing a cavity demonstrate the feasibility of 3D RTM in trunk defect detection, providing specific and comprehensive guidance for formulating tree protection and restoration measures.

High-Fidelity OC-Seislet Stacking Method for Low-SNR Seismic Data

Seismic stacking is a core technique in seismic data processing, aimed at enhancing the signal-to-noise ratio (SNR) of data by utilizing seismic data acquisition with multifold geometry. Traditional stacking methods always have certain limitations, such as the reliance on the accuracy of velocity analysis for dip moveout (DMO) in common midpoint (CMP) stacking. The seislet transform, a compression technique tailored to nonstationary seismic data, can compress and stack along the prediction direction of seismic data, which provides a new technical idea for high-fidelity seismic imaging based on the effectiveness of the compression. This paper introduces a high-order OC-seislet stacking method for low-SNR seismic data, capable of achieving the high-fidelity stacking of reflection and diffraction waves simultaneously. With the multi-scale analysis advantages of the seislet transform, this method addresses the dependency of DMO stacking on velocity analysis accuracy. In the frequency–wavenumber–scale domain, the correction compensation of the high-order CDF 9/7 basis function is used to obtain the compression coefficients of the high-order OC-seislet transform. This approach simultaneously stacks frequency–wavenumber information of reflection and diffraction waves with high fidelity while implementing DMO processing. After normalizing the weighting coefficients and applying soft thresholding for denoising, the final result is transformed back to the original time–space domain, yielding high-fidelity stacking sections. The results of applying this method to both synthetic and field data show that, compared with conventional DMO stacking methods, the high-order OC-seislet stacking technique reasonably represents dipping layers and fault amplitudes, and it can achieve a balance of a high SNR and high fidelity in stacked profiles.

3D experimental investigation of floating breakwater with symmetrical openings and wing structures

To enhance the efficiency of floating breakwaters (FB) in attenuating long-period waves, a novel design featuring wing structures and forward openings was proposed. Both experimental and numerical studies were conducted in a two-dimensional wave tank to validate the feasibility and efficiency of its innovative wave dissipation mechanism. Nevertheless, the three-dimensional (3D) performance of the new configuration has not been thoroughly explored. Additionally, a portion of the wave energy impacting the rear wall of the FB propagates to the sheltered area, negatively affecting wave dissipation. Therefore, this paper presents an improved design and experimentally investigates its 3D hydrodynamic performance. The enhanced FB incorporates wing structures and symmetrical opening tunnels to augment wave energy dissipation. A comprehensive FB system, including the main body, connection structures, and mooring system, was meticulously engineered. A series of experiments were conducted in a wave pool, and the results demonstrate superior wave attenuation performance and minimal motion response of the novel FB. Furthermore, the effect of diffraction waves on wave attenuation performance was also investigated. The mooring system experiences uniform and minimal loading, confirming its design effectiveness. Consequently, the proposed 3D FB system exhibits promising potential for practical engineering applications.

Scattering of Acoustic Waves by an Inhomogeneous Elastic Cylindrical Shell of Finite Length in a Half-Space

An analytical solution to the problem of diffraction of a plane acoustic wave on a radially inhomogeneous thick-walled elastic cylindrical shell of finite length is obtained. The cylindrical shell is located in an acoustic half-space filled with an ideal liquid. The boundary of the half-space is an acoustically rigid or acoustically soft surface. The results of calculations of the acoustic field in the far zone are presented.

Study on ground-penetrating radar wave field characteristics for earth dam disease considering the medium randomness

Ground-Penetrating Radar (GPR) has been widely used for non-destructive testing of earth dam disease. However, the forward simulation of GPR for earth dam disease often employs layered homogeneous models, neglecting the influence of medium randomness on its wave field characteristics. Therefore, considering the randomness of the medium, a geoelectrical model for earth dam disease is established, which is based on the mixed-type autocorrelation function and the finite element time-domain method. The influence of random medium model parameters on the single-channel wave of GPR is analyzed. The electromagnetic wave propagation characteristics under different medium models are explored. The forward simulation of GPR for earth dam disease such as panel voiding, concentrated seepage, and loosening are performed. The differences in propagation characteristics for earth dam disease between uniform medium model and random medium model are compared. Compared to the calculation results of the uniform medium model, the propagation speed and amplitude of electromagnetic waves in the random medium model changes, and a number of diffraction waves are present. When performing forward simulation of GPR for earth dam disease, considering medium randomness can deepen the understanding of the GPR section view and help improve the accuracy of image interpretation.