Wave Propagation Research Articles

Acoustic Metagrating Holograms.

Metasurface holograms represent a common category of metasurface devices that utilize in-plane phase gradients to shape wavefronts, forming holographic images through the application of the generalized Snell's law (GSL). While conventional metasurfaces focus solely on phase gradients, metagratings, which incorporate higher-order wave diffraction, further expand the GSL's generality. Recent advances in certain acoustic metagratings have demonstrated an updated GSL extension capable of reversing anomalous transmission and reflection, whose reversal is characterized by the parity of the number of wave propagation trips through the metagrating. However, the current extension of GSL has remained limited to one-dimensional metagratings, unable to access two-dimensional (2D) holographic images in three-dimensional (3D) spaces. Here, we investigate the GSL extension to 2D metagratings for manipulating waves within 3D spaces. Through our analysis, we experimentally demonstrate a series of acoustic metagrating holograms. These holographic images exhibit the unique ability to switch between transmission and reflection types independently. Our study introduces an additional dimension to modern holography design and metasurface wavefront manipulation. This article is protected by copyright. All rights reserved.

Research on Acoustic Methods for Buried PE Pipeline Detection Based on LSTM Neural Networks

Abstract As an essential component of urban infrastructure construction, Polyethylene (PE) pipelines face the challenging task of underground detection due to the complex and dynamic nature of the subsurface environment, diverse installation paths, and the inherent insulating properties of PE materials. In order to address the non-excavation detection of buried PE pipelines, this paper proposes an acoustic method based on the Long Short-Term Memory (LSTM) neural network. The study begins by analyzing the propagation and reflection mechanisms of elastic waves in the pipe-soil coupling system, and a impact excitation source is designed to generate the excitation signal. After establishing the experimental environment and collecting experimental data, a comprehensive analysis is conducted, and the LSTM neural network is employed for data classification to determine the presence of buried PE pipelines. Through neural network training, accurate identification of the PE pipeline's existence and prediction of its burial depth are achieved, providing an efficient and reliable solution for buried PE pipeline detection. The practical results demonstrate the significant application prospects of the combined acoustic method and LSTM neural network in buried PE pipeline detection. This research contributes a novel solution to the field of non-destructive PE pipeline detection, with both theoretical and practical implications.

Analytical solution for forced vibration response of rectangular thin plates attached by straight and curved acoustic black hole beams based on symplectic and impedance method

In recent years, due to the excellent vibration reduction performance of the acoustic black hole (ABH), its application in engineering has become increasingly widespread. This paper proposes an analytical method which combines the symplectic method with the impedance method, for solving the forced response of the rectangular thin plates attached by the straight and curved ABH beams. The ABH beams and plate are connected by a short bar. Firstly, the impedance method is used to obtain the dynamic stiffness of the coupling end of the ABH beam. Secondly, the symplectic method is used to obtain analytical waves of the plates. By utilizing the relationship between force and displacement at plate-beam junction, the dynamic stiffness of the plate at the coupling point can be obtained. Finally, based on wave propagation analysis, the forced vibration response of the hybrid system are obtained. The numerical examples compared the calculation results of this method with the finite element method. The results show that the proposed method can effectively predict the forced response of the hybrid system considered in this paper. Then, the influence of the relative position between the coupling point and the excitation point on the vibration reduction effect was analyzed. This method is analytical, with accurate results and high computational efficiency.

Effects of void geometry on two-dimensional monolithic porous phononic crystals

Phononic crystals are renowned for their distinctive wave propagation characteristics, notably bandgaps that offer precise control over vibration phenomena, positioning them as a critical material in advanced vibro-elastic engineering and design. We investigate how pore shapes influence the bandgap in continuum two-dimensional phononic crystals made from a single material. Using the square lattice and unit cells with fourfold symmetry, our numerical analyses reveal that the normalized gap size is highly dependent on the minimum ligament width in the structure. Additionally, we find that fine geometric features represented by higher-order Fourier coefficients decrease the gap size. This study offers insight into the design of phononic crystals and vibro-elastic metamaterials for precise wave control through void patterning.

Mitigation of reentry blackout via gas injection in arc-heating facility

Communication blackouts during atmospheric reentry pose significant challenges to the safety and adaptability of spacecraft missions. This phenomenon, caused by the attenuation of electromagnetic waves by the plasma surrounding the spacecraft, disrupts communication with ground stations or orbiting satellites. Therefore, it is crucial to decrease the plasma density in the vicinity of the spacecraft to ensure an unobstructed electromagnetic wave communication path. This study proposes a methodology that involves the injection of gas from the vehicle’s wall to create an insulating layer near the surface. This thin layer maintains lower temperatures and reduced plasma density, enabling electromagnetic wave propagation without attenuation. Practical experiments were conducted in an arc-heating facility to simulate atmospheric reentry conditions. The results of the experiments provided empirical evidence of the effectiveness of the technique in mitigating communication blackout phenomena. Numerical fluid analysis within the wind tunnel chamber validated the formation of an air film layer near the experimental model owing to the injected gas. Schlieren imaging revealed distinctive jet shapes, which corroborated the findings of the numerical analysis. The wind tunnel tests that simulated atmospheric reentry environments confirmed the formation of an air film layer through gas injection, which substantiates the reduction in communication blackout. These results have the potential to improve communication reliability in space transport.

Bifurcation analysis and soliton solutions to the doubly dispersive equation in elastic inhomogeneous Murnaghan's rod.

The doubly dispersive (DD) equation finds extensive utility across scientific and engineering domains. It stands as a significant nonlinear physical model elucidating nonlinear wave propagation within the elastic inhomogeneous Murnaghan's rod (EIMR). With this in mind, we have focused on the integration of the DD model and the modified Khater (MK) method. Through the wave transformation, this model is effectively converted into an ordinary differential equation. In this paper, the goal of our work is to explore new wave solutions to the DD model by using the MK scheme. These solutions provide extremely helpful insights into the operation of the system. The three-dimensional (3D) plot and two-dimensional (2D) combined plot via the impacts of the parameters are provided for various parameters in this manuscript. We also discussed the dynamical properties of the model, which are accomplished through the bifurcation analysis, and also found the Hamiltonian function. This research makes a substantial contribution to the area by increasing our understanding of wave solutions in the DD, introducing novel investigation tools, and carrying out an in-depth investigation of the bifurcation and stability aspects of the system. As a direct result of this research, novel openings have been uncovered for further investigation and application in the various disciplines of science and engineering.

Systematic in-silico evaluation of fibrosis effects on re-entrant wave dynamics in atrial tissue.

Despite the key role of fibrosis in atrial fibrillation (AF), the effects of different spatial distributions and textures of fibrosis on wave propagation mechanisms in AF are not fully understood. To clarify these aspects, we performed a systematic computational study to assess fibrosis effects on the characteristics and stability of re-entrant waves in electrically-remodelled atrial tissues. A stochastic algorithm, which generated fibrotic distributions with controlled overall amount, average size, and orientation of fibrosis elements, was implemented on a monolayer spheric atrial model. 245 simulations were run at changing fibrosis parameters. The emerging propagation patterns were quantified in terms of rate, regularity, and coupling by frequency-domain analysis of correspondent synthetic bipolar electrograms. At the increase of fibrosis amount, the rate of reentrant waves significantly decreased and higher levels of regularity and coupling were observed (p < 0.0001). Higher spatial variability and pattern stochasticity over repetitions was observed for larger amount of fibrosis, especially in the presence of patchy and compact fibrosis. Overall, propagation slowing and organization led to higher stability of re-entrant waves. These results strengthen the evidence that the amount and spatial distribution of fibrosis concur in dictating re-entry dynamics in remodeled tissue and represent key factors in AF maintenance.

Ultrasound Elastography: Methods, Clinical Applications, and Limitations: A Review Article

Ultrasound is a highly adaptable medical imaging modality that offers several applications and a wide range of uses, both for diagnostic and therapeutic purposes. The principles of sound wave propagation and reflection enable ultrasound imaging to function as a highly secure modality. This technique facilitates the production of real-time visual representations, thereby assisting in the evaluation of various medical conditions such as cardiac, gynecologic, and abdominal diseases, among others. The ultrasound modality encompasses a diverse range of modes and mechanisms that serve to enhance the methodology of pathology and physiology assessment. Doppler imaging and US elastography, in particular, are two such techniques that contribute to this expansion. Elastography-based imaging methods have attracted significant interest in recent years for the non-invasive evaluation of tissue mechanical characteristics. These techniques utilize the changes in soft tissue elasticity in various diseases to generate both qualitative and quantitative data for diagnostic purposes. Specialized imaging techniques collect data by identifying tissue stiffness under mechanical forces such as compression or shear waves. However, in this review paper, we provide a comprehensive examination of the fundamental concepts, underlying physics, and limitations associated with ultrasound elastography. Additionally, we present a concise overview of its present-day clinical utilization and ongoing advancements across many clinical domains.

Research on the mechanism and application of wedge cutting blasting with hole-inner delay

To increase the efficiency of deep-hole blasting driving in mine rock tunnels, an innovative pattern of wedge cutting blasting with hole-inner delay was proposed. First, the blasting mechanisms of conventional and innovative wedge cutting patterns were theoretically investigated. The results showed that the resistance from large upper rock blocks and the clamping action from the surrounding rock were the major challenges of conventional cutting methods. For the innovative cutting pattern, under the conversion of the spatial distribution and release sequence of blasting energy, the first blasting of the upper charge can strengthen the breaking of the upper rock mass and create a new free surface, which provides favorable conditions for the delayed blasting of the bottom charge. Second, finite element models of two cutting patterns were established and solved, and the simulation results visually revealed the propagation of a stress wave. Critically, the stress strength in the upper cavity increased by 66–83% under the action of the upper charge, which was conducive to the breaking of the upper rock mass and the generation of a new free surface. Therefore, the rock mass in the bottom cavity can be readily broken and discharged. Ultimately, field applications were executed in a rock tunnel. Compared with a conventional cutting pattern, the proposed innovative cutting pattern can prominently increase the cycle advance and hole utilization and greatly reduce the unit consumption of explosives and detonators. This research confirms the usability of the innovative wedge cutting pattern with hole-inner delay in deep-hole blasting driving of rock tunnels.

Adaptive impact analysis in flexible multibody systems based on hierarchically refined IGA models

AbstractUsually, detailed impact simulation models within flexible multibody systems have to be set up manually rather than being generated automatically. This is because the process requires prior knowledge of the time and location of the impact, as well as the element resolution within the contact area. If the penalty method is used to determine the occurring contact forces, the corresponding penalty factor also needs to be determined manually. This work, however, presents an adaptive algorithm to simulate impacts within flexible multibody systems fully automatically using reduced isogeometric analysis models, the floating frame of reference formulation, and quasistatic contact models for an efficient but still accurate simulation. The adaptive algorithm detects impacts in the system, determines the contact locations on the bodies, refines the contact area, and determines the penalty factor, and therefore automatically simulates impacts. The work shows how to automatically simulate impacts in flexible multibody systems without user action or prior knowledge of impact location and size. The first application example simulates significant elastodynamic effects within a long flexible rod. The goal is to validate the algorithm by preserving the wave propagation and energy of the system. The second application example simulates the impacts of two flexible double pendulums. This setup is a suitable benchmark for the complete adaptive impact analysis procedure as the flexible double pendulums undergo large rigid body motions.

Recent Advances in Electromagnetic Metamaterials and Metasurfaces for Polarization Manipulation

Abstract Polarization is an important characteristic of electromagnetic waves that has been exploited in many areas of wave manipulations. While effective control of polarization is highly demanded in various applications, traditional polarization converters have drawbacks such as large volume, narrow operating frequency band, low efficiency, and high losses, hindering themselves from practical applications. Metamaterials and metasurfaces are recently developed artificially structured electromagnetic materials constructed by three- or two-dimensional arrays of meta-atoms with tailored electromagnetic responses, exhibit great potential in controlling the propagation of electromagnetic waves and are highly suitable for flexible control of polarization. Here, we review the recent developments in the field of electromagnetic metamaterials and metasurface for polarization manipulation, focusing on their operation principles and practical applications. We discussed the research progress of chiral metamaterials and anisotropic metasurfaces, and also summarized the achievements of metasurfaces for comprehensive manipulation polarization and phase in recent years. We further summarize the recent achievements on the diversified polarization manipulation functions of metasurfaces. Finally, we discuss reconfigurable metasurfaces that can dynamically control the polarizaiton and wavefronts of electromagnetic waves, including not only electrically reconfigurable metasurfaces with constitutional meta-atoms locally tuned by external stimuli, but also time-modulated metasurfaces exploiting the temporal dimension by applying dynamic switching of the coding sequences. Finally, we look forward to the possible future directions and existing challenges in this rapidly developing field.

Characterization of cracking-healing cycle of asphalt mixture based on air-coupled second harmonic measurement using Duffing-van der pol oscillator

Second harmonic generation (SHG) technique using Rayleigh surface wave has been successfully attempted for the non-destruction evaluation of asphalt mixture during the self-healing process. The air-coupled transducer placement is desirable for the convenient implementation of SHG for the large-scale detection. Nevertheless, the pronounced attenuation of ultrasonic wave by air-coupled propagation will cause the second harmonic induced by microcracks to be barely detectable, particularly under the influence of inevitable noise. In this study, a novel approach by combining Duffing oscillator and van der pol equation is developed to identify and quantify the second harmonic in noise-contained signals based on the phase trajectory and periodic trajectory area exponent. The multi-physics finite element model is first established to simulate the air-asphalt propagation of Rayleigh waves, and proof-of-concept numerical simulations are carried out to estimate the second harmonic amplitude of noise-contaminated signals. The air-coupled SHG experiments are conducted, and the approach of the Duffing-van der pol oscillator is applied to extract the second harmonic in experimental data, and the self-healing behavior of asphalt mixture is analyzed through the variation of the nonlinear parameter of SHG measurements. The results indicate that the contactless SHG method combined with the Duffing-van der pol oscillator can effectively realize the convenient and reliable estimation of the nonlinear ultrasonic signal during the cycle of asphalt deterioration and healing, which is important for the property characterization of asphalt mixture considering its high attenuation to the ultrasonic waves.

Size-dependent effect on the interaction of surface waves in micropolar thermoelastic medium with dual pore connectivity

This research tackles a critical knowledge gap in Rayleigh surface wave propagation. It offers a comprehensive analysis that surpasses previous limitations. A size-dependent micropolar medium with unique void distributions and thermal effects is considered in this work. The constitutive relations and equations of motion for a nonlocal micropolar thermoelastic medium with double voids (MTMWDV) have been established by using Eringen’s nonlocal elasticity theory. Employing the three-phase-lag thermoelasticity theory (TPLTE), the study utilizes a wave-mode method to derive analytical solutions for Rayleigh waves in a nonlocal MTMWDV. To gain a comprehensive understanding of wave behavior, we solve the characteristic equation and analyze its roots, applying a filter based on the surface wave decay condition. A medium with stress-free and isothermal boundaries is explored through computational simulations to determine the attenuation coefficient and phase velocity. Furthermore, particle motion analysis is conducted to complement the analytical and computational approaches. Moreover, the influence of the nonlocal parameter and various thermoelastic models on these wave phenomena is investigated. The validity of the current mathematical model is confirmed through the derivation of particular scenarios.

Anti-scattering propagation in multiple-bend valley phononic crystals

Abstract Valley topological phononic crystals have attracted wide attention due to the topological properties of their edge states. In general, valley interface states can exist in the interfaces that are constructed by opposite valley topological phases. Here we study the anti-scattering propagation properties of edge states in a single valley phononic crystal. We present that the edge states can exist in different boundary terminations with different band dispersions. The boundary transport behaviors of acoustic waves along the two designed phononic crystals are demonstrated numerically. The results show that the chiral edge states are immune against additional scatterers that preserve the valley pseudospins, but the backscattering can happen when intervalley scattering is included. Nevertheless, the anti-scattering propagation in complex multiple-bend structures can be realized by the smooth transition between the edge states and the valley interface states. Similar to the designed frequency-selective device, more prospective applications can be anticipated in the manipulation of acoustic wave propagation.

Extended finite element method with cell-based smoothing for modeling frictional contact crack-induced acoustic nonlinearity involving distorted mesh

Abstract This study proposes a 2D cell-based smoothed extended finite element method (CS-XFEM) for accurate and efficient simulation of nonlinear ultrasonic wave propagation in solid structures, specifically addressing the effects of frictional contact in cracks. Traditional mesh discretization methods for cracks often suffer from mesh distortion and computational instability owing to their high aspect ratios. To overcome this, CS-XFEM integrates a cell-based smoothing technique into XFEM to model the frictional contact of a crack. A comprehensive numerical example demonstrates the advantages of CS-XFEM. The results show that CS-XFEM exhibits a higher convergence rate and enables a larger critical time increment than XFEM. Specifically, the critical time increment of CS-XFEM was found to be twice that of XFEM, leading to a 50% reduction in the total computational time. These findings confirm that CS-XFEM is an efficient, accurate, and robust numerical method for studying the acoustic nonlinearity induced by crack-induced frictional contact.

PHYSICAL FACTORS OF THE INFLUENCE THE EXPLOSION ON ENCLOSURE GLASS STRUCTURES. OVERVIEW OF TESTING METHODS

The article examines the main physical parameters of an explosive wave, the properties of explosive loads, as well as the peculiarities of the propagation of waves in space and their dynamic influence on enclosing structures, including translucent The considered temporal and spatial conditions under which the formation of the quasi-flat front of the blast wave takes place and the blast loads can be considered as uniformly distributed along the vertical plane. If the distance to the explosive charge exceeds half of the value of the width and height of the structure or its element (provided that the charge is located in the center of the structure or element), then the load on them can be considered approximately averaged by area. The thermophysical factors of influence, which the building structure must withstand, are analyzed. The main differences of explosive and shock effects from static loads, which are taken into account during construction design, are described. The main real-time methods of determining the parameters of the blast wave in real time and the factors of its destructive effect on the elements of the enclosing structures of buildings are considered. The determination of the critical pressure for a specific structure is tied to the determination of the critical distance at which the structure will not withstand the destructive impact of the shock wave. The main real-time methods of determining the blast wave parameters in real time are considered. It was determined that the use of the shock tube method is rational for conducting research in laboratory conditions. The work was carried out with the assistance of the National Research Fund of Ukraine. The materials of the article contain scientific results obtained as part of the implementation of the project No. 208/0172 "Aerodynamics, heat exchange and innovations to increase the energy efficiency of window structures and their use for the reconstruction of war-damaged buildings of Ukraine" of the competition "Science for the reconstruction of Ukraine in the war and post-war periods".

Exploring Mechanisms for Model‐Dependency of the Stratospheric Response to Arctic Warming

AbstractThe Arctic is estimated to have warmed up to four times faster than the rest of the globe since the 1980s. There is significant interest in understanding the mechanisms by which such warming may impact weather and climate at lower latitudes. One such mechanism is the “stratospheric pathway”; Arctic warming is proposed to induce a wave‐driven weakening of the stratospheric polar vortex, which may subsequently impact large‐scale tropospheric circulation. However, recent comprehensive model studies have found systematic differences in both the magnitude and sign of the stratospheric response to Arctic warming. Using a series of idealized model simulations, we show that this response is sensitive to characteristics of the warming and mean polar vortex strength. In all simulations, imposed polar warming amplifies upward wave propagation from the troposphere, consistent with comprehensive models. However, as polar warming strength and depth increases, the region through which waves can propagate is narrowed, inducing wave breaking and deceleration of the flow in the lower stratosphere. Thus, the mid‐stratosphere is less affected, with reduced sudden stratospheric warming frequency for stronger and deeper warming compared to weaker and shallower warming. We also find that the sign of the stratospheric response depends on the mean strength of the vortex, and that the stratospheric response in turn plays a role in the magnitude of the tropospheric jet response. Our results help explain the spread across multimodel ensembles of comprehensive climate models.

The Phononic Properties and Optimization of 2D Multi-Ligament Honeycombs

Honeycomb structures have attracted much attention for their excellent characteristics of reducing vibration and noise in recent years. In this study, through band analysis of different ligament structures, we aim to optimize the design of a steel structure that can isolate most of the noise in the 1500–5000 Hz range. The present study examines several different chiral structures. We calculate the band gaps of chiral structures under different geometric configurations and identify the variations in band gaps with geometric layouts. It is found that compared to other chiral structures, the triligaments chiral structure exhibits excellent band gap characteristics. The calculation results demonstrate that enhancing axial symmetry while filling central nodes can effectively enhance the structure’s band gap properties. Frequency–response functions of different lattice structures are computed, and the results align with the calculations of band structures. This study then analyzes the influence of the number of periods on the magnitude of vibration attenuation, revealing that under the same number of periods, the wider the band gap of the structure, the greater the vibration attenuation. Both the triligaments chiral structure and the vertical triligaments structure possess ideal band gap widths, effectively suppressing wave propagation. Subsequently, harmonic response analyses and transient wave calculations further validate the accuracy of the band structure and frequency–response curve calculations. Our study results provide a new way to design a sound insulation structure that can isolate noise signals within the frequency range from 1500 to 5000 Hz in engineering.

A three‐dimensional parabolic equation with fast reordered‐alternate direction decomposition in atmosphere duct environment

AbstractIn the design and optimisation of marine wireless communication and navigation systems, a thorough investigation of radio wave propagation characteristics under atmospheric ducting conditions is essential. The authors aim to enhance the efficiency of radio wave propagation loss prediction in marine atmospheric ducting environments, proposing a prediction model based on Fast Reordered‐Alternate Direction Decomposition (FR‐ADD). By approximating the diffraction term into three independent components, exploiting the commutative properties of the Fourier transform to reduce the spatial dimensions, and incorporating a rapid algorithm for the parabolic equation, the model optimises the stepping process and significantly improves computational efficiency. Simulation experiments demonstrate that, in the long‐distance and complex marine ducting environments, the model not only maintains prediction accuracy but also substantially reduces computational load and prediction time, effectively realising over‐the‐horizon propagation prediction. In the experiment of radio wave propagation characteristics in the Yellow and Bohai Seas, the simulation data from the FR‐ADD model showed significant correlation with actual measurements and simulations from the AREPS software, confirming the method's efficiency and practicality.

Analysis of Wave Propagation Across Layered Rock Masses Considering Multiple Reflection Effects

Analysis of Wave Propagation Across Layered Rock Masses Considering Multiple Reflection Effects