Wave Diffraction Research Articles

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 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.

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.

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.

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.

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.

A Study on the interaction of shock tube-generated blast waves with a circular object at different pressure ratios

The interaction of high peak overpressure blast waves with a circular object placed at two different axial locations from the shock tube exit is studied through numerical simulation using an in-house developed multi-component Navier–Stokes solver. The driver and driven sections of the shock tube were 0.8 m and 6 m, respectively. Helium is used in the driver section, while atmospheric air is used in the driven section and outside the shock tube. The evolution of blast waves inside an open-ended shock tube and its interaction with a rectangular object is reported in Murugan et al.. (2022). Here, the blast wave interacting with a circular object is examined for diaphragm pressure ratios of 13 and 57 by placing the objects at 250 mm and 500 mm from the shock tube exit. The flow field is evaluated through numerical Schlieren, vorticity, density, pressure plots, and the enstrophy plot, which shows the vortical structures that originated in the flow field. The blast load acting on the circular object is calculated for two diaphragm pressure ratios and axial locations. This study helps understand the reflection and diffraction of blast waves and associated flow fields around circular objects used in blast wave attenuation.

Analytical Method for the Wave Diffraction of Asymmetrically Arranged Breakwaters

Analytical Method for the Wave Diffraction of Asymmetrically Arranged Breakwaters

Ultrasonic Rough Crack Characterization Using Time-of-Flight Diffraction With Self-Attention Neural Network.

Time-of-flight diffraction (ToFD) is a widely used ultrasonic nondestructive evaluation (NDE) method for locating and characterizing rough defects, with high accuracy in sizing smooth cracks. However, naturally grown defects often have irregular surfaces, complicating the received tip diffraction waves and affecting the accuracy of defect characterization. This article proposes a self-attention (SA) deep learning method to interpret the ToFD A-scan signals for sizing rough defects. A high-fidelity finite-element (FE) simulation software Pogo is used to generate the synthetic datasets for training and testing the deep learning model. Besides, the transfer learning (TL) method is used to fine-tune the deep learning model trained by the Gaussian rough defects to boost the performance of characterizing realistic thermal fatigue rough defects. An ultrasonic experiment using 2-D rough crack samples made by additive manufacturing is conducted to validate the performance of the developed deep learning model. To demonstrate the accuracy of the proposed method, the crack characterization results are compared with those obtained using the conventional Hilbert peak-to-peak sizing method. The results indicate that the deep learning method achieves significantly reduced uncertainty and error in rough defect characterization, in comparison with traditional sizing approaches used in ToFD measurements.

Simulation and Experimental Research of V-Crack Testing of Rail Surfaces Based on Laser Ultrasound

Rail surface cracks are widespread damage that can lead to uneven surfaces of railheads and affect traveling safety. Non-destructive testing is needed to inspect rails regularly to ensure the normal operation of railroads. This paper proposes a laser ultrasonic testing method combining variational mode decomposition and diffractive Rayleigh wave time-of-flight to detect tiny cracks on the rail surface quantitatively. The finite element method was combined with experiments to simulate and experimentally investigate cracks of different sizes numerically. In the numerical simulation, the location of the crack was determined by B-scan. Afterward, the interaction between various types of ultrasound and cracks was comparatively analyzed, and the crack size was quantitatively characterized using useful information from the ultrasound signals. The results show that the time-of-flight method can detect arbitrary cracks with low error. Therefore, the experimentally acquired ultrasound signals used the time difference between the diffracted Rayleigh wave and other ultrasound waves to detect the crack information quantitatively. The variational mode decomposition method was used to separate the ultrasonic signals and extract the best surface wave modes to improve the signal-to-noise ratio. The results show that the combination of variational mode decomposition and time-of-flight method can effectively detect the size of cracks.

A Compact All-Band Spacecraft Antenna with Stable Gain for Multi-Band GNSS Applications

This study presents a compact and stable gain spacecraft antenna that operates in all Global Navigation Satellite System (GNSS) bands from 1.164 GHz to 1.610 GHz. The proposed antenna structure based on the single-feed crossed bowtie antenna concept consists of four triangular patches excited with a 90° phase difference in between to generate right-hand circular polarization (RHCP), without needing complex feed networks. The radiator part of the antenna is covered by a radome and is also supported by a cylindrical dielectric cavity frame (DCF) to weaken the diffracted waves propagating along the ground plane while increasing vibration resistance. The fabricated antenna provides a return loss better than 10 dB with lower than 3 dB axial ratio and a stable gain around 7.2 ± 0.3 dBic over the entire GNSS bands, as well as a more compact and lightweight structural performance. It is also verified that the structural integrity and functional performance of the fabricated antenna remain consistent despite exposure to an equivalent vibration level in the launch process. The presented all-band spacecraft GNSS antenna is an innovative implementation with space industry insight for multi-band space applications that have application-specific limitations and provides consistent performance, as well as operational safety with the antenna design simplicity.

Diffraction Separation for the Ground Penetrating Radar Data by Masking Filters

Ground penetrating radar is a high-resolution, efficient, non-destructive geophysical detection method. It is widely used in various application scenarios such as tunnel geological prediction and road maintenance. Ground penetrating radar data contains a variety of valid signals as well as noise. The diffracted waves of ground penetrating radar contain high-resolution small target imaging information. A critical challenge in GPR applications is how to extract diffracted waves from the wave fields. We provide a strategy to achieve this goal by applying the masking filters. Considering the complexity of the ground penetrating radar wave field and the weak energy of the diffracted waves, the median filter is first employed to suppress the linear reflections and then the f-k filter and filter are implemented to further increase the proportion of diffractions in the wave fields. Three numerical experiments are employed to test the diffraction-separation method.

Diffraction by a right-angled no-contrast penetrable wedge: recovery of far-field asymptotics

Abstract We provide a description of the far-field encountered in the diffraction problem resulting from the interaction of a monochromatic plane-wave and a right-angled no-contrast penetrable wedge. To achieve this, we employ a two-complex-variable framework and use the analytical continuation formulae derived in Kunz & Assier (2023, Diffraction by a right-angled No-contrast penetrable wedge: analytical continuation of spectral functions. Q. J. Mech. Appl. Math., 76, 211−241) to recover the wave-field’s geometrical optics components, as well as the cylindrical and lateral diffracted waves. We prove that the corresponding cylindrical and lateral diffraction coefficients can be expressed in terms of certain two-complex-variable spectral functions, evaluated at some given points.

Diffraction of quasi-nondiffracting Bessel beam by an impedance disc in an anisotropic plasma

The diffraction of the so-called nondiffracting Bessel beam by an impedance disc immersed in an anisotropic medium is examined. The external uniform magnetic field, which makes the plasma anisotropic, is taken to be rotational as opposed to being parallel to the edge of the problem geometries in the literature. Thus, the appropriate dielectric matrix that models the anisotropic region under the rotational dc external magnetic field is derived for the first time, to the best of our knowledge. Upon considering the geometric optics waves, the total scattered waves are obtained with the diffracted waves by using the definition of high-frequency asymptotic expressions associated with the scattered waves at the transition regions. The results are expressed in terms of the Fresnel functions so that the wave behaviors in the transition regions are uniform. The solutions are compared numerically with existing studies in the literature, including limit values.

Resolution enhancement in terahertz imaging with multi-wavelength information

Thanks to the unique characteristics of terahertz waves, terahertz imaging has become one of the promising imaging technologies. However, due to the weak signal source and strong diffraction of terahertz waves, terahertz imaging has a significant amount of noise, which makes it is challenge to achieve satisfactory clarity in images. In this work, we propose an algorithm that uses multi-wavelength information to improve the resolution of terahertz imaging. The resolvability of the images has been improved by at least 1.4 times, and the noise has been effectively filtered out. This algorithm enhances the image resolution without requiring any hardware upgrades, benefiting the terahertz imaging system with multi-wavelength imaging capabilities.

Hydrodynamic analysis of an oscillating water column array in presence of variable bathymetry

In this study, hydrodynamic analysis of an oscillating water column (OWC) array in the presence of the variable bathymetry (seafloor depth) is performed by using a semi-analytical potential-flow solver. Within the framework of linear theory, the boundary-value problem associated with wave diffraction and radiation by an OWC array with variable bathymetry is formulated and the semi-analytical hydrodynamic model is developed using the matched eigenfunction expansion method. The fluid domain above variable bathymetry is mathematically discretized into multiple subdomains using the boundary approximation method. The Haskind relation and the energy flux conservation law are used to verify the semi-analytical model. The hydrodynamic performance of the OWC array in the presence of the ripple and coral reef bathymetries are investigated in further. Pronounced oscillations are observed for the curve of reflection coefficient Cr and hydrodynamic efficiency η for cases with ripple and coral reef bathymetries. Bragg resonance is identified as the triggering of the strong oscillations in Cr and η for case of ripple bathymetry. The primary frequency of Bragg resonance and the peaked value of Cr converge as the ripple number increases (i.e., Ns > 3). Particularly, for cases with coral reef bathymetry, the wave resonance modal in open-ended basins results in a significant wave amplification at the weather side of the OWC array.

Analysis of wave characteristics near the pilot station

As one of the primary services ports provide, pilotage services aim to ensure the safe passage of vessels when entering and leaving the port. This study uses Taichung Port, located in the central part of the Taiwan Strait, as an example to analyze the impact of monsoon characteristics on wave conditions at pilot boarding points and to highlight their crucial role in safeguarding pilot boarding safety. By analyzing data from the ADCP (Acoustic Doppler Current Profiler) station north of the port’s northern breakwater and the Taichung buoy located southwest of the port, compare wave height distributions at the boarding point. The research addresses the impact of current and planned expansions, including constructing a new LNG receiving terminal with extended breakwaters, on wave dynamics and pilot operations. The study demonstrates that data from multiple sources—such as ADCP and buoy measurements—helps mitigate issues caused by missing data from specific stations. The analysis shows that numerical values differ slightly, while wave height trends at the boarding point are similar under current and expanded port conditions. The study concludes that the proposed expansion will likely affect wave diffraction patterns but will enhance the predictability and safety of boarding operations by reducing uncertainties associated with single measurement stations. Overall, the results of this study can enhance the understanding of marine meteorological information, improve the safety of pilot boarding operations, and thereby increase the efficiency and safety of port operations.

Qualitative validation on a numerical model for the direct stability assessment of surf-riding and broaching

A previously developed numerical model for surf-riding and broaching is qualitatively validated based on the criteria of direct stability assessment (DSA) proposed in SDC 7. Roll decay tests are conducted to obtain roll backbone curves, which are compared with calculated GZ curve to demonstrate their consistency. Then, roll response curves under different wave frequencies in regular beam wave are obtained. It is verified that roll response curve “fold around” the newly defined “peak backbone curve”. Cases with fixed yaw under different Fn are chosen to demonstrate the numerical model's capability of reproducing surf-riding equilibrium. Turning circle test is conduced to demonstrate correct modelling of maneuvering forces and the capability to reproduce heel due to ship turning. Wave surging forces are calculated under different wave numbers and amplitudes. The correct tendency of phase difference between wave surging force and the incident wave is observed, which reveals the correct modelling of wave forces in the model. Moreover, a preliminary quantitative validation is conducted under various cases. Through comparison with experimental results, it is recommended that the wave diffraction correction of the wave surging forces should be included in the simulation model in order to avoid overestimation of surf-riding and broaching.

Prediction of simultaneous enhancement of Goos-Hänchen shift and reflectance in VO2 grating structure

Vanadium dioxide (VO2) material stands out in the family of the phase change materials due to its temperature-dependent phase transition properties, which make it a promising candidate for the temperature-dependent optoelectronic devices. Enhancement of the Goos-Hänchen (GH) shift is essential in VO2-based nanostructures for their applications, but it has been limited to the multilayered structures with VO2 materials so far. Here, we theoretically investigate the GH shift and corresponding reflectance in the VO2-based grating structure. We evidence that this structure has two GH peaks (3107λ and 2266λ) and high reflectance values (both up to 1) when VO2 is in the insulating phase as well as the maximum GH valley (−1061λ) and low reflectance (0.19) when VO2 is in the metallic phase. The electromagnetic field distributions in this hybrid structure suggest that the guided mode resonances (GMRs) can be excited no matter whether VO2 is in its insulating or metallic phases due to the couplings between the incident waves and the adjacent evanescent diffracted order waves, which produces their enhanced GH shifts. Different from the former case with the high reflectances and the large GH shifts, the latter has the low maximum magnetic field intensity due to the lossy property of the metallic VO2, which leads to the low reflectance and small GH valley value. Additionally, we have also found that by the alterations of the temperature-dependent conductivity of VO2 and the geometric parameters of the structure allows for the control the magnitude and position of the GH peak or valley. The simultaneously enhanced GH shifts and reflectances in the VO2-based grating structure, associated with its controllable features, enable it an effective configuration for establishing the temperature sensors and optoelectronic switches.

Experimental study of wave diffraction loads on a vertical circular cylinder with heave plates at deep and shallow drafts

This study focuses on wave diffraction loads influenced by heave plates at deep and shallow submerged depths. An extensive experimental campaign is conducted on a fixed vertical and free-surface piercing circular cylinder with five different circular plates, including a perforated plate. The horizontal and vertical wave forces are studied in monochromatic and bichromatic waves. The results show that the heave plate significantly influences the forces varying in time and representative harmonics, including sum- and difference-frequency components. The study found that wave steepness and submerged depth of the plate contribute to the nonlinearity of the loads and that the porous plate reduces the loads compared to the solid plate. Corresponding results from a boundary element method (BEM) solver, HydroStar, provide a reasonable prediction of the harmonics. However, the first harmonic of the vertical force is underpredicted at low frequencies, specifically where the BEM results indicate the cancellation of the forces. Dedicated computational fluid dynamics (CFD) simulations are carried out to investigate the discrepancy, and it is observed that flow separation occurs around the edge of the plate. A simplified approach based on Morison’s equation is employed to model the flow separation effects using a quadratic drag force calculated with a constant drag coefficient. The approach shows that viscous drag is the dominant contributor to vertical wave forces on the heave plate in the low-frequency regime.