Wave Propagation Characteristics Research Articles

Characterization and analysis of attenuation anisotropy in viscoelastic vertical transverse isotropic media

AbstractDue to the intrinsic attenuation of the earth, the study of wave propagation characteristics, considering seismic attenuation plays an important role in high‐precision reservoir prediction. Therefore, we investigate the propagation and reflection characteristics of seismic waves in viscoelastic vertical transverse isotropic media in the complex frequency domain. Specifically, we analyse the response characteristics of velocity, propagation vector and attenuation vector with respect to viscosity media with different attenuation intensities. Furthermore, based on the quasi‐Zoeppritz equation, the variation of reflection coefficient amplitude with offset at different attenuation angles and different attenuation intensities is studied. We also compare the trends in the amplitude variation of reflection coefficients with offset in elastic isotropic, elastic anisotropic and viscoelastic anisotropic media. Due to the complexity of the exact reflection coefficient expression, we first propose the approximate expression of the attenuation–anisotropy parameters and then derive the approximate expression of the reflection coefficient. The numerical simulation results show that the approximate expression of the reflection coefficient is still accurate, even in media with strong anisotropy. Finally, the accuracy evaluations of the reflection coefficient formulas using four typical theory models demonstrate that the approximate reflection coefficient formulas are highly accurate in both weak and strong anisotropic media.

Acoustic shadow zone of the guided wave in a variable thickness plate

This paper calculates the acoustic shadow zone of the guided wave in a variable thickness plate. The variable thickness plate has a wide range of applications in bridges, ships, etc., and the guided wave is often used for its nondestructive testing. The velocity gradient induced by thickness variations will deflect the guided wave towards lower phase velocities. Both frequency and thickness variation play crucial roles in determining the extent of path bending. In particular, the guided wave can undergo reverse propagation at the non-boundary of the plate. This curved propagation path results in an acoustic shadow zone, inaccessible to direct waves. This article calculates and experimentally verifies the curved propagation path of dispersive guided waves. Experiments show that the degree of propagation path bending increases with the increase of frequency in a certain frequency range. On the path that varies along the thickness, the experiment observes an acoustic shadow zone that accounts for nearly 25% of the total path. Additionally, a practical case study involving a guided wave with a curved path is presented. Consideration of the curved path improves the positioning accuracy, offering insights into damage location in variable thickness plates. This research on the propagation path and acoustic shadow zone contributes to advancing the understanding of guided wave propagation characteristics and enhancing their application in nondestructive testing for variable thickness structures.

A Deep-Learning Approach to a Volumetric Radio Environment Map Construction for UAV-Assisted Networks

Providing global coverage for ubiquitous users is a key requirement of the fifth generation (5G) and beyond wireless technologies. This can be achieved by integrating airborne networks, such as unmanned aerial vehicles (UAVs) and satellite networks, with terrestrial networks. However, the deployment of airborne networks in a three-dimensional (3D) or volumetric space requires a new understanding of the propagation channel and its losses in both the areal and altitude dimensions. Despite significant research on radio environment map (REM) construction, much of it has been limited to two-dimensional (2D) contexts. This neglects the altitude-related characteristics of electromagnetic wave propagation and confines REMs to 2D formats, which limits the comprehensive and continuous visualization of propagation environment variation in spatial dimensions. This paper proposes a volumetric REM (VREM) construction approach to compute 3D propagation losses. The proposed approach addresses the limitations of existing approaches by learning the spatial correlation of wireless propagation channel characteristics and visualizing REM in areal and height/altitude dimensions using deep learning models. Specifically, the approach uses two deep learning-based models: volume-to-volume (Vol2Vol) VREM with 3D-generative adversarial networks and sliced VREM with altitude-aware spider-UNets. In both cases, knowledge of the propagation environment and transmitter locations in 3D space is used to capture the spatial and altitude dependency of the propagation channel’s characteristics. We developed the Addis dataset, a large REM dataset comprising 54,000 samples collected from the urban part of Addis Ababa, Ethiopia, to train the proposed models. Each sample of data comprises a 512-meter by 512-meter areal resolution with different 3D obstacles (buildings and terrain), 15 simulated propagation loss maps at every 3-meter altitude resolution, and 80 different 3D transmitter locations. The results of the training and testing of the proposed models reveal that the constructed VREMs are statistically comparable. In particular, the Vol2Vol approach has a minimum L1 loss of 0.01, which further decreases to 0.0084 as the line-of-sight (LoS) probability increases to 0.95.

On the wave propagation characteristics of functionally graded porous shells

This paper concentrates on the wave propagation characteristics of functionally graded (FG) porous shells. The transversal shear deformation of the shell is taken into consideration by employing a simple higher-ordered shear deformation shell theory. The equations of motion are derived for the proposed model based on Hamilton’s principle. An eigenvalue problem that relates the wave propagation elements is formulated and solved to present the various dispersion relations of FG cylindrical and spherical shells. The effects of porosities, shells’ geometrical parameters, FG material exponent, and wavenumbers on the principal wave propagation frequency and the associated phase velocity are investigated in detail.

Investigation on the propagation characteristics of pressure wave during managed pressure drilling

The small difference between formation pressure and fracture pressure in offshore oil and gas reservoirs poses a huge challenge to drilling. Managed pressure drilling (MPD) technology, as a drilling technique that can accurately control bottomhole pressure, is an effective technique to solve this challenge. In MPD technology, the pressure wave propagation behavior and mechanism in the wellbore induced by wellhead backpressure are crucial for parameter design and efficient application. In this paper, pressure wave propagation characteristics and mechanism in gas-liquid flow were investigated with a new proposed pressure wave velocity model that considers inter-phase mass transfer effect. This new model and its solution algorithm were verified with experimental data in literature. The influence of gas invasion stage, drilling fluid type, drilling fluid density and backpressure on pressure wave propagation characteristics were investigated. Results show that the time for pressure wave induced by wellhead backpressure in the wellbore cannot be ignored in the design of the backpressure value during MPD. This propagation time increases with occurrence of gas invasion. Moreover, the propagation time in water-based drilling fluid is longer than that in oil-based drilling fluid, which is because the interphase mass transfer between invaded gas and oil-based drilling fluid. The influence mechanism of high drilling fluid density and wellhead backpressure on pressure wave propagation characteristics is due to the suppression of gas invasion process. These findings could be used as guides in parameters design and optimization in MPD.

Nonlinear wave propagation in graphene incorporating second strain gradient theory

The exploration of graphene has attracted extensive interest owing to its significant structural and mechanical properties. In this research, we numerically investigate wave propagation in defect-free single-layer graphene, considering its geometrically nonlinear behavior through second-strain gradient elasticity. To capture the geometric nonlinearity, firstly, the nonlinear strain–displacement relations are introduced. The governing equation and associated boundary conditions are derived using Hamilton’s principle. Then, the weak form, including the element matrices, is established. The eigenvalue problem is solved for 2D wave propagation through periodic structures theory. Finally, the dynamical properties such as band structures, mode shapes, energy flow, and wave beaming effects are analyzed. The numerical results reveal that the geometric nonlinearity through the second strain gradient influences the wave propagation characteristics in graphene. The findings are significant and contribute to the understanding of graphene’s dynamic response, with implications for the engineering applications of graphene-based nanostructures.

A modified couple stress model to analyze the effect of size-dependent on thermal interactions in rotating nanobeams whose properties change with temperature

Understanding the behavior of rotating materials and structures on small scales is crucial for many scientific and engineering fields, and such studies play an important role in this regard. This paper aims to propose a novel paradigm for analyzing the vibrational characteristics of thermoelastic nanobeams with diverse physical attributes. The incorporation of size effects in the structural and thermal constitutive relationships involves the consideration of nonlocal elasticity theory (NET) and the modified couple stress (MCS) model, together with the utilization of the Euler–Bernoulli assumptions for thin beams. The work also involves the development of a new non-Fourier thermoelasticity model that incorporates the Moore–Gibson–Thompson (MGT) equation. Furthermore, it was taken into account that the thermal conductivity of the flexible materials is not consistent but rather changes with temperature. Periodic pulse heating was applied to rotating nanobeams, and the behavior of the nanobeams was investigated with respect to thermal, rotational, and length-scale effects. To demonstrate the impact of the distinctive characteristics of the MCS and MGT thermoelastic models on the physical fields, a range of numerical data are presented. The study also investigated the propagation characteristics of thermo-mechanical waves, taking into account aspects such as thermal relaxation time and the influence of temperature change on physical properties. Based on the observed results, including the size impact in the structural and thermal equations can lead to significant disparities when compared to conventional models. The inclusion of the length-scale component in the MCS theory, which increases the rigidity and hardiness of the nanobeam structure, may help to explain the observed effect.

Influence of the Schottky Junction on the Propagation Characteristics of Shear Horizontal Waves in a Piezoelectric Semiconductor Semi-Infinite Medium

In this paper, a theoretical model of the propagation of a shear horizontal wave in a piezoelectric semiconductor semi-infinite medium is established using the optimized spectral method. First, the basic equations of the piezoelectric semiconductor semi-infinite medium are derived with the consideration of biased electric fields. Then, considering the propagation of a shear horizontal wave in the piezoelectric semiconductor semi-infinite medium, two equivalent mathematical models are established. In the first mathematical model, the Schottky junction is theoretically treated as an electrically imperfect interface, and an interface characteristic length is utilized to describe the interface effect of the Schottky junction. To legitimately confirm the interface characteristic length, a second mathematical model is established, in which the Schottky junction is theoretically treated as an electrical gradient layer. Finally, the dispersion and attenuation curves of shear horizontal waves are numerically calculated using these two mathematical models to discuss the influence of the Schottky junction on the dispersion and attenuation characteristics of shear horizontal waves. Utilizing the equivalence of these two mathematical models and the above numerical results, the numerical value of the interface characteristic length is reliably legitimately confirmed; this value is independent of the thickness of the upper metal layer, the doping concentration of the lower n-type piezoelectric semiconductor substrate, and biasing electric fields. Only the biasing electric field parallel to the Schottky junction can provide an evident influence on the attenuation characteristics of shear horizontal waves and enhance the interface effect of the Schottky junction. Since the second mathematical model is also a validation of our previous mathematical model established through the state transfer equation method, some numerical results calculated using these two mathematical models are compared with those obtained using the previous method to verify the correctness and superiority of the research work presented in this paper. Since these two mathematical models can better calculate the dispersion and attenuation curves of high-frequency waves in micro- and nano-scale piezoelectric semiconductor materials, the establishment of mathematical models and the revelation of physical mechanisms are fundamental to the analysis and optimization of micro-scale resonators, energy harvesters, and amplifications.

Multibolt looseness monitoring of steel structure based on multitask active sensing method and substructure cross-domain transfer learning

Under the influence of service life and the external environment, bolted connections are prone to loosening, which may lead to structural hazards. Thus, it is crucial to carry out real-time monitoring of bolted connections. Based on the active sensing method, previous researchers mainly focused on quantifying the single-bolt looseness, with little focus on locating and quantifying the multibolted connection. This study introduces an innovative approach to monitor multibolt looseness in steel structures. The proposed method utilizes multitask active sensing, incorporating a substructure cross-domain transfer learning technique. A finite-element model of a portal frame structure was first established by ABAQUS software, and the substructure was determined based on the stress wave propagation characteristics. Secondly, the location and degree of bolted connection in the substructure and portal frame structure were monitored using the piezoelectric active sensing method. Monitoring data of the substructure are tagged as the source domain, while data of the portal frame structure are tagged as the target domain. To efficiently decouple the characteristics of loosening, this study extracted multidomain energy and unthresholded multivariate recurrence plots from stress wave signals. These elements were employed to pinpoint the location and assess the degree of looseness. The multibolted connection was then monitored by the adversarial domain adaptation networks. Ultimately, using the target domain’s input, the optimized model was able to precisely detect the location and degree of the multibolted connection step by step. The experimental results demonstrated that the suggested technique has a lot of promise for multibolt looseness monitoring.

Influence of Lithology on the Characteristics of Wave Propagation and Dynamic Response in Rocky Slope Sites Subject to Blasting Load Via the Discrete Element Method

Abstract To investigate the dynamic response and attenuation law of rock slope sites subjected to blasting, three lithological numerical models, including slate (hard rock), tuff (relatively soft rock), and shale (soft rock), are established by using MatDEM. By analyzing the wave field, velocity, and acceleration response of the models and their Fourier spectrum, combined with stress and energy analysis, their dynamic response characteristics are investigated. The results show that blasting waves propagate from near field to far field in a circular arc, and the attenuation effect of waves in soft rock is less than that in hard rock. The influence of lithology on the dynamic response of the ground surface and bedrock is different. Blasting waves mainly affect the dynamic response in the near-field area of the blasting source. In addition, the dynamic amplification effect of slopes is as follows: hard rock > relatively soft rock > soft rock. The slope surface has an elevation attenuation effect. A dynamic amplification effect appears in the slope interior within the relative elevation (0.75, 1.0). The Fourier spectrum has an obvious predominant frequency, and that of the slope crest and interior is less than that of the slope surface. Moreover, the total energy generated by the rocky sites gradually changes into kinetic energy, gravitational potential energy, elastic potential energy, and heat. Energy-based analysis shows that the attenuation effect of blasting waves in hard rock is larger than that in soft rock overall. This work can provide a reference for revealing the blasting vibration effect of rock sites.

Frequency-selective coherent propagating spin waves induced by localized perpendicular magnetic anisotropy nanofilm stack

Magnonics has long been hailed as a promising technology poised to overcome the heat dissipation challenges in traditional electronic devices. With the escalating integration level of magnon devices, the demand arises for lower external field excitation conditions, coupled with enhanced coherence and frequency-selective excitation characteristics. In this proposal, we suggest introducing a localized perpendicular magnetic anisotropy nanofilm stack into the spin-wave transmission channel to finely regulate the propagation characteristics of spin waves. This adjustment can be achieved by altering the width and period of the stack in both horizontal and vertical dimensions. Additionally, the optimal transmission characteristics of spin waves are achieved at low frequencies (1–1.67 GHz) and in the presence of small magnetic fields (0–20 mT). Frequency-selective spin waves with triggering stability can effectively prevent signal folding resulting from changes in microwave power within the range of −30 to 0 dBm. At 1.08 GHz, the group velocity of frequency-selective spin waves can be increased by up to 2.86 times. This innovative method of regulating spin waves presents a potential alternative pathway for the development of future magnonic circuits.

Robustness of partially coherent vortex beams to the impact of dynamic Kolmogorov kind of turbulence

The wave propagation characteristics of Gaussian-Schell model vortex beams passing through a dynamic Kolmogorov type of turbulence are analyzed at the laboratory level. The effect of a rotating pseudo-random phase plate, which simulates Kolmogorov-type atmospheric turbulence, on the Gaussian-Schell model beams carrying twist phase is characterized by calculating the scintillation index and intensity line profiles. Our analysis proves the resilience of Gaussian-Schell model vortex beams to the impact of dynamic turbulence. Simulation studies are further used to validate the experimental results. Because of the resemblance between our investigation conditions and real-world atmospheric turbulence, these findings have potential applications in free-space communication systems.

Analysis and modeling of radio propagation fading characteristics in tunnel construction

With the development of underground rail transit, the concept of intelligent tunnel construction has been proposed and promoted. High-quality networking during tunnel construction is a prerequisite for this, making it highly urgent to establish networking during tunnel construction. When studying intra-tunnel networking, it is necessary to consider the propagation characteristics of radio waves in the tunnel. In this paper, according to the actual needs of engineering in tunnel construction and the characteristics of tunnel scenes, an improved ray tracing method is proposed, which considers the type and installation position of antennas, transceiver frequency band and power in channel modeling, and proposes a field strength calculation method under different coordinate systems according to the characteristics of straight and curved segments during tunnel construction. In addition, the propagation characteristics of radio waves in dynamic tunnel construction scenarios are quantitatively analyzed. In this paper, by establishing antenna diagram, two-dimensional and three-dimensional models of tunnels, the computer simulation method is applied to compare with the improved algorithm, and the results have good consistency, in addition, the improved algorithm does not require a lot of modeling work in the early stage, and has high applicability and portability. Not only that, this paper also makes actual measurements of the subway under construction in Zhengzhou, China in different scenarios, and verifies the effectiveness of the method.

Effects of spin polarization on the propagation of surface waves on a quantum plasma half-space

The study explores the wave propagation characteristics of surface plasma waves in a semi-bounded plasma, incorporating the influence of spin polarization arising from spin mismatch. The formulated plasma model integrates the density correlation effect via Bohm's potential force, Fermi pressure employing Fermi-Dirac statistics, and the exchange potential. These factors are considered in spin-polarized form and interconnected through the spin polarization index κ. We derive a dispersion relation for surface plasma waves, delineating the propagation features of the configured wave mode. Our findings indicate that an increase in spin polarization among electron populations results in a decrease in the phase velocity of surface plasma waves compared to the usual electron-ion quantum plasma. Moreover, an increase in the exchange potential contributes to a decrease in the phase speed. However, the ratio of plasmon to Fermi energy leads to an increase in the phase velocity of surface plasma waves in a spin-polarized quantum plasma. We provide a comparative analysis of our work with an earlier model based on the gold–air interface, revealing that our model facilitates the propagation of surface plasma waves with higher frequencies across the wave vector. This study highlights the significance of quantum effects for electrostatic surface plasma waves in dense metallic plasmas at room temperature, with implications for signal transmission in metallic waveguides observed in a recent study [Guo et al., “Excitation of graphene magneto-plasmons in terahertz range and giant Kerr rotation,” J. Appl. Phys. 125(1), 013102 (2019)] and some of the references therein.

Characteristics of the electromagnetic wave propagation in magnetized plasma sheath and practical method for blackout mitigation

“Magnetic window” is considered as an effective method to solve the communication blackout issue. COMSOL software package based on the finite element method is utilized to simulate the propagation of right-handed circularly polarized wave in the magnetized plasma sheath. We assume a double Gaussian model of electron density and an exponential attenuation model of magnetic field. The propagation characteristics of right-handed circularly polarized wave are analyzed by the observation of the reflected, transmitted and loss coefficient. The numerical results show that the propagation of right-handed circularly polarized wave in the magnetized plasma sheath varies for different incident angles, collision frequencies, non-uniform magnetic fields and non-uniform plasma densities. We notice that reducing the wave frequency can meet the propagation conditions of whistle mode in the weak magnetized plasma sheath. And the transmittance of whistle mode is less affected by the variation of the electron density and the collision frequency. It can be used as a communication window.

Experimental investigation of Rayleigh wave propagation in a locally resonant metamaterial layer resting on an elastic half-space

In this experimental investigation, we explore the propagation characteristics of surface Rayleigh waves in a Locally Resonant Metamaterial (LRM) layer positioned on an elastic half-space. The study focuses on characterizing the dispersion and attenuation properties of these waves and validating analytical and numerical models of the LRM. For practical purposes, we utilize a thin-plate sample and construct the LRM layer, featuring multiple rows of sub-wavelength resonators, by machining the resonators at one edge of the plate. Employing a piezoelectric transducer coupled to the plate and a laser vibrometer, we actuate and receive the surface-like waves propagating at the plate edge. Two resonant layer configurations, comprising 3 and 5 rows of resonators, corresponding to heights of ∼0.6λh and λh, where λh represents the reference wavelength of Rayleigh waves, are examined. The experimental observations reveal the hybridization of the fundamental surface mode at the resonant frequency of the embedded resonators, leading to the creation of a low-frequency bandgap. This bandgap, attributed to the local resonance mechanism, exhibits a remarkable attenuation of surface wave amplitudes. To support our experimental findings, we conduct both analytical and numerical studies. These analyses demonstrate the confinement of the lowest-order surface mode within the frequency ranges proximate to the resonators’ resonance. The insights gained from this experimental study contribute to the advancement of strategies for mitigating surface waves through the application of resonant metamaterials and metastructures.

Coupled models for propagation of explosive shock waves in cylindrical and spherical geometries

The propagation of shock waves in different geometries is crucial in engineering and scientific applications. A comprehensive model is developed to elucidate the hydrodynamic growth and decay of shock waves in cylindrical and spherical geometries by using the strong shock wave assumption. This model takes into consideration the conservation equations governing mass, momentum, and energy, thereby allowing for an accurate description of the coupled behavior between the piston and shock wave propagation. In contrast to the localized analysis employed in previous self-similar methods, this model incorporates the finite sound wave velocity to introduce the concept of retarded pressure on the piston surface. Consequently, the proposed model offers a multitude of advantages by providing a complete set of dynamic information concerning the trajectories, velocities, and accelerations of both the piston and shock wave. Furthermore, an asymptotic analytical solution is derived to describe the decay of shock waves in cylindrical and spherical geometries. To validate the theoretical analysis and illustrate the propagation characteristics of shock waves in these specific geometries, thorough comparisons are conducted. These findings contribute to the advancement of our understanding of shock wave dynamics in various physical systems, particularly in the field of plasma physics.

Ray Tracing Meets Terahertz: Challenges and Opportunities

It is very likely that the terahertz (THz) spectrum will be used for the operation of the upcoming 6th-generation (6G) wireless communication systems. This article presents a study for the application of ray tracing (RT) for THz channel modeling. Because of the extremely short wavelengths of THz signals, we argue that signal propagation in the THz spectrum can be precisely modeled by employing RT techniques and thus accurate channel models can be obtained in an efficient manner. We first review recent research and standardization activities related with RT-assisted channel modeling which mainly deal with millimeter-wave (mmWave) applications and to a much lesser extent have been applied the THz spectrum. Then, we present the basic THz wave propagation characteristics, including reflection, scattering, penetration, shadowing as well as signal absorption by atmospheric molecules and tiny particles under different weather conditions. The methodologies for the appropriate construction of target scenarios are presented as well as efficient computational methods for the effective RT operation. Finally, various research and development (R&D) challenges related to RT-based channels for future THz communication systems are identified and possible solutions are highlighted.

Analytical study on transverse behaviour of Love-type waves in a corrugated cylindrical composite structure: A perturbation theory

The current study focuses on the analysis of propagation characteristics of Love-type waves in a corrugated composite cylindrical structure, with corrugation at the lateral surface. The corrugated cylindrical structure is comprised of two regions of functional gradient fiber-reinforced material media with distinct radii. The amplitude of corrugation at the outermost lateral surface is assumed to be small. The functional gradients in outer and inner cylindrical layers are generated because of radial variation of the elastic parameters and density. An analytical treatment featuring a perturbation method and Debye Asymptotic Expansion is employed to attain the dispersion relation. The obtained dispersion relation is validated with some established standard and classical results through particular cases. The substantial effects of reinforcement, functional gradients, and corrugation parameters on both phase and group velocities of the Love-type wave have been analyzed extensively with the aid of graphical illustrations, accomplished by numerical computations.

Research on the Optimization of Multibeam Bathymetry Survey Line Layout Based on Simulated Annealing Algorithm

Multibeam bathymetry systems are widely used in water depth measurement, and their principle is based on the propagation characteristics of sound waves in water. The system has multiple advantages, such as high resolution, high accuracy, wide measurement range, automated mapping, and high efficiency. This study is based on the propagation characteristics of sound waves in water and utilizes a multibeam bathymetry system for water depth measurement, focusing on key issues such as coverage width, survey path, and seawater depth. Based on a two-dimensional plane model, the direction of the emitted beams from the measurement vessel and the relationship with seafloor slope angles are considered. The key parameter calculation model of the multibeam bathymetry system is established using the sine theorem and cosine theorem. To enhance the analysis accuracy, the calculation model is extended to three dimensions, incorporating more factors that have a significant impact on the measurement, such as the slope angle along the survey lines and changes in water depth. In practical applications, the survey lines are set to run in a north-south direction, and a greedy algorithm is used to ensure complete coverage of the measurements. Taking into account the complex seafloor topography, the fitted lines are used to represent the seafloor slopes. The multi-objective programming model is transformed into an unconstrained single-objective programming problem for further optimization. By solving the problem using simulated annealing algorithm, the optimized solution provides specific values for the spacing between adjacent survey lines, total track length, missed coverage rate of the surveyed area, and duplicate measurement coverage, enabling the optimal utilization of multibeam bathymetry systems in oceanic surveys.