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Vortex wave and plane wave, as two most fundamental forms of wave propagation, are widely applied in various research fields. However, there is currently a lack of basic mechanism to enable arbitrary conversion between them. In this paper, we propose a new paradigm of extremely anisotropic acoustic metasurface (AM) to achieve the efficient conversion from 2D vortex waves with arbitrary orbital angular momentum (OAM) to plane waves. The underlying physics of this conversion process is ensured by the symmetry shift of AM medium parameters and the directional compensation of phase. Moreover, this novel phenomenon is further verified by analytical calculations, numerical demonstrations, and acoustic experiments, and the deflection angle and direction of the converted plane waves are qualitatively and quantitatively confirmed by a simple formula. Our work provides new possibilities for arbitrary manipulation of acoustic vortex, and holds potential applications in acoustic communication and OAM-based devices.

We study the reflection and transmission (R/T) characteristics of inhomogeneous plane waves at the interface between two dissimilar fluid-saturated thermoporoelastic media at arbitrary incidence angles. The R/T behaviors are formulated based on the classic Lord–Shulman (LS) and Green–Lindsay (GL) heat-transfer models as well as a generalized LS model, respectively. The latter results from different values of the Maxwell-Vernotte-Cattaneo relaxation times. These thermoporoelastic models can predict three inhomogeneous longitudinal (P1, P2, and T) waves and one shear (S) wave. We first compare the LS and GL models for the phase velocities and attenuation coefficients of plane waves, where the homogeneous wave has a higher velocity but weaker thermal attenuation than the inhomogeneous wave. Considering the oil–water contact, we investigate R/T coefficients associated with phase angles and energy ratios, which are formulated in terms of incidence and inhomogeneity angles, with the latter having a significant effect on the interference energy. The proposed thermoporoelastic R/T model predicts different energy partitions between the P and S modes, especially at the critical angle and near grazing incidence. We observe the anomalous behavior for an incident P wave with the inhomogeneity angle near the grazing incidence. The energy partition at the critical angle is mainly controlled by relaxation times and boundary conditions. Beyond the critical angle, the energy flux predicted by the Biot poroelastic and LS models vanishes vertically, becoming the opposite for the GL and generalized LS models. The resulting energy flux shows a good agreement with the R/T coefficients, and they are well proven by the conservation of energy, where the results are valuable for the exploration of thermal reservoirs.

In this paper, the system of equations for nonlocal micropolar elastic materials is developed taking into account the assumption that the attenuation functions for the elastic and micropolar material coefficients are different, and applied for harmonic body waves. The dispersion equations of harmonic body waves propagating in a micropolar medium and their cutoff frequencies are obtained in simple form based on the new assumption. The obtained dispersion relations are potentially useful in an inverse problem by fitting the data of elastic and micropolar harmonic waves speed to estimate the elastic and micropolar nonlocal parameters of the medium. Some concerning remarks about the difference between the two-parameter nonlocal theory and the one-parameter nonlocal theory of Eringen are numerically discussed to show the necessary of the developed theory in the problem of wave propagation.

In this study, we have investigated the reflection of plane quasi-P (qP), quasi-SV (qSV) and quasi-SH (qSH) waves at the stress-free boundary of an initially stressed nonlocal triclinic half-space. Closed-form mathematical expressions for the phase velocity, reflection coefficients and energy ratios are derived which provide a comprehensive understanding of wave behavior in this complex medium. The study addresses a significant gap in the literature by analyzing the combined effects of initial stress and nonlocal parameters which have been underexplored in previous research on wave propagation in triclinic media. Our results reveal that the reflection coefficients and energy ratios for the reflected (qP, qSV and qSH) waves are highly sensitive to the incident angle and depend on elastic constants, initial stress, and nonlocal parameters. Numerical computations are performed using Vosges sandstone as the triclinic material and the results are presented graphically. These graphs provide insights into how different material properties and boundary conditions influence wave reflection. For validation, the model is reduced to special cases and compared with pre-established results. The findings of this work contribute advance understanding of wave reflection in anisotropic media and offering potential applications in geophysics, materials science, and seismic analysis.

The Transient Electromagnetic (TEM) method is a critical geophysical technique for subsurface exploration of metal ore bodies, primarily utilizing either loop or grounded transmitters. The Long Offset Transient Electromagnetic (LOTEM) method employs a grounded-source transmitter, relying on a far-source observation mode and plane wave approximation for detection. However, LOTEM’s far-source configuration weakens signal strength, and the plane wave approximation reduces precision, limiting effective detection depth to approximately 1000 m with a comprehensive error of about 15%. Recently, we have developed the grounded-source Short Offset Transient Electromagnetic (SOTEM) method, achieving greater detection depth and accuracy within the 500–2000 m depth range, a crucial interval for mineral resource exploration. This study explores the theoretical framework, instrumentation, data processing, and field applications of SOTEM. Based on a point charge element model, SOTEM accurately computes surface wave effects in EM field calculations, optimized for near-source observation. High-power, high-resolution, wide-bandwidth exploration equipment and an advanced three-dimensional hybrid inversion technique were also developed to enhance the method’s effectiveness. Application of SOTEM to the deep exploration of the Zhou’an Ni-Cu-PGE deposit in Henan Province yielded high-resolution imaging of conductivity structures to about 2.5 km depth. These results, consistent with existing drill data, delineated mineralized ore bodies from surrounding formations, identified zones of mineralization potential, and suggested extensive resource prospects in the region.

This manuscript investigates harmonic plane wave propagation in a time differential Moore–Gibson–Thompson thermoelastic medium. It is noted that six possible plane harmonic waves may propagate at different speeds. Among these, two are transverse waves, while the other four are coupled longitudinal waves. The transverse waves are decoupled, undamped over time, and propagate independently at a speed unaffected by the thermal field. The four longitudinal plane waves exhibit coupling, temporal damping, and dispersion due to the thermal influence of the medium. A longitudinally quasi-elastic wave decays exponentially over time, with its amplitude diminishing to zero as time progresses toward infinity. A stationary quasi-thermal wave also decays exponentially to zero over time. Additionally, there are two possible dilatational quasi-thermal propagating waves with varying rates of time damping, or there could be a single time-harmonic dilatational thermal wave, depending on the time delay value. The problem of surface waves is also discussed for Moore–Gibson–Thompson thermoelasticity. The surface of the half-space is assumed to be traction-free and able to exchange heat freely with the surrounding medium. The dispersion relation for the surface wave is explicitly formulated, and the secular equation is derived. Numerical simulations are carried out for both plane and surface waves within a specified model. The computed results are visually depicted, and a summary analysis of these outcomes is provided.

We obtain the reflection and transmission coefficients for inhomogeneous plane waves incident on a flat interface separating two double-porosity media described by the Biot–Rayleigh model, which takes into account the effect of local fluid flow (LFF). Three longitudinal and one transverse waves are reflected and transmitted, represented by potential functions specified by the propagation and attenuation directions. The continuity of the energy at the interface for sealed and open-boundary conditions yields a system of equations for the coefficients, and the expressions of the energy ratios for the reflected and refracted waves are derived in closed form. Numerical examples showing the magnitude, phase and energy ratio as a function of frequency and incidence angle are carried out to investigate the influence of the inhomogeneity angle, boundary condition, type of incidence wave and LFF effect. The results confirm that the LFF affects the reflection and transmission behaviors for the incident P1 and SV waves, irrespective of whether the interface is open or sealed. The effect causes interference fluxes between different waves, a consequence of energy conservation at the interface. We also perform full-waveform simulations to validate the results.

Deep learning has shown potential as an effective beamformer for improving the image quality of plane wave imaging (PWI). But most existing deep learning methods cannot directly handle the complex in-phase and quadrature (IQ) data. And noise in ultrasound signals would significantly damage the performance of regular convolution networks. To address these challenges, we proposed the Complex Pseudo 3D Auto-Correlation Network (CP3AN) which combined complex convolution and pseudo 3D auto-correlation blocks (P3AB) to directly map delayed IQ data from 0° plane wave into PWI pixels. The complex convolution could fully utilize the envelope and phase information of IQ data, while the P3AB used 1D convolution to extract noise in channel and space dimensions, allowing the network to prioritize valid signals with extremely low computational cost. We evaluated the performance of CP3AN through numerical simulations, phantom experiments, and in-vivo experiments, which showed comparable metrics with minimum variance (MV), including contrast (CR), contrast-to-noise ratio (CNR), generalized contrast-to-noise ratio (GCNR), lateral, and axial full-width half maximum (FWHM) at -9.60 dB, 1.12, 0.65, 319 um, and 344 um, respectively. The CP3AN achieved a low computational cost of 0.11 M floating-point operations (FLOPs), significantly lower than the MV or other compared deep learning-based methods. Our proposed method provided a promising solution for improving single-angle PWI imaging, particularly in situations where high frame rates are necessary.

The influence of temperature on the unit cell wave attenuation of 1-D viscoelastic periodic structures is important for the design of phononic structures and mechanical metamaterials with desirable properties, considering the damping provided by viscoelasticity. However, the dispersion of evanescent waves in 1-D viscoelastic phononic structures (VPnSs) with thermal effects has not been reported yet. In this study, it is investigated the complex dispersion diagram of 1-D VPnSs considering an isotropic solid ( i.e., bulk waves, 3-D model, in plane strain condition) and the standard linear solid model for the viscoelastic effect. The unit cell of the VPnS is composed by steel (elastic material) and epoxy (viscoelastic material). The thermal effect is included in terms of the Young’s modulus ( E ) with a temperature ( T ) dependence ( i.e., E ( T )) for epoxy. It is supposed that the unit cell has a uniform temperature along its dimensions, thus there is no heat flux. The extended plane wave expansion, k ( ω , T ) approach, where ω is the frequency and k is the wave number, is derived to obtain the propagating and evanescent modes of the VPnSs for each value of temperature. The temperature influences significantly the unit cell wave attenuation zones and also the evanescent wave modes. Before the glass transition temperature of the epoxy, the wave modes are shifted for lower frequencies, the attenuation bands are decreased, and the unit cell wave attenuation increases with the rise of temperature. Near the glass transition temperature of the epoxy, the wave dispersion behaviour, depending on the temperature, is very different, whereas after the glass transition temperature of epoxy, the wave dispersion behaviour is close. The relevant results can be used for the wave attenuation design of viscoelastic periodic structures with thermal effects.

While using the subway brings people convenient transportation, The low frequency vibration caused by metro is one of the factors that seriously threaten the physical and mental health of human beings and the working environment. Phononic crystals structure and elastic metamaterials have been favored for the past few years because of their excellent low frequency vibration control properties. In this paper, based on local resonance theory, an elastic metamaterial thick plate structure is designed to attenuate low frequency vibration. Through plane wave expansion method and numerical simulation, the dispersion curve and reduced vibration effect of the thick plate structure are simulated and analyzed, and it is proved that the elastic metamateric thick plate structure opens the bend wave band gap range of 36–110 Hz within the limits of lower frequency below 150 Hz. Finally, a kind of new lower frequency vibration isolation thick plate barrier is designed to minish the effect of low-frequency vibration, which has a potential engineering application foreground in the field of low-frequency vibration control and isolation of subway.