المؤلفون: Yisong Zhang¹ yisong.zhang.ee@gmail.com, Smith, Dallin R.² jamesina.simpson@utah.edu, Simpson, Jamesina J.¹ dallinsmith9@gmail.com

المصدر: Applied Computational Electromagnetics Society Journal. Feb2024, Vol. 39 Issue 2, p123-129. 7p.

مصطلحات موضوعية: *ELECTROMAGNETIC wave propagation, *GRID cells, *EARTH (Planet), *ATMOSPHERICS, *PENTAGONS, *IONOSPHERE

مستخلص: A new global 3-D finite-difference timedomain (FDTD) model is introduced to simulate electromagnetic wave propagation around the Earth, including the lithosphere, oceans, atmosphere, and ionosphere regions. This model has several advantages over existing global models, which include grids that follow lines of latitude and longitude and geodesic grids comprised of hexagons and pentagons. The advantages of the new model include: (1) it may be run at the Courant-Friedrichs-Lewy (CFL) time step (as a result, it is termed the Courant-limit model); (2) subgrids may be added to specific regions of the model as needed in a straight-forward manner; and (3) the grid cells do not become infinitely larger as the grid is extended higher in altitude. As a result, this model is a better candidate than the others for investigating electromagnetic phenomena over long time spans of interest and for investigating atmosphere-ionosphere-magnetosphere coupling. The new model is first described and then validated by comparing results for extremely low frequency (ELF) propagation attenuation with corresponding analytical and measurement results reported in the literature. [ABSTRACT FROM AUTHOR]

المؤلفون: Zeng, Hao¹ (AUTHOR), Han, Qiang¹ (AUTHOR), Li, Chunlei¹ (AUTHOR) lichunlei@scut.edu.cn

المصدر: Acta Mechanica. Feb2024, Vol. 235 Issue 2, p1125-1146. 22p.

مصطلحات موضوعية: *CYLINDRICAL shells, *ELASTIC wave propagation, *FIBROUS composites, *LAMINATED materials, *SHAPE memory alloys, *NANOCOMPOSITE materials, *ELASTIC waves, *STRUCTURAL shells

مستخلص: In this paper, dispersion properties of guided waves in multilayer composite cylindrical shells are studied, which is composed of the inner and outer hybrid nanocomposite (MHC) layers and the middle composite core layer reinforced with shape memory alloy (SMA) fibers. According to the Hamiltonian principle and the thermoelastic theory, wave equations of the composite structure at different ambient temperatures are derived and discretized with spectral elements. By combing the thermal effects and the acoustoelastic effects, the modified semi-analytical finite element method is proposed here for the thermo-acoustoelastic effects of wave characteristics in laminated composite shells. The influence of important parameters on the dispersion characteristics of the structure is explored. The results show that the coupling of SMA fiber reinforced composite layer and MHC layers can significantly improve wave propagation characteristics of the composite cylindrical shells. The frequency of modal conversion increases with the increase of CNT volume fraction. Smaller radius-to-thickness ratios are favorable for internal wave propagation in the structure. This work is of great significance for the regulation of elastic wave propagation in multilayered cylindrical shell structures, and provides a valuable guide for the design and optimization of shell structures in engineering applications. [ABSTRACT FROM AUTHOR]

المؤلفون: Kazakov, L. I.¹ (AUTHOR) lev-kazakov@rambler.ru

المصدر: Acoustical Physics. Feb2024, Vol. 70 Issue 1, p39-50. 12p.

مصطلحات موضوعية: *DISTRIBUTION (Probability theory), *ACOUSTIC wave propagation, *LIQUIDS, *SURFACE coatings, *INTEGRAL equations, *BUBBLES

مستخلص: The study considers the possibility of creating a broadband sound-absorbing coating for hydroacoustic measuring tanks and chambers with inertial or soundproof walls, consisting of a layer of viscous liquid with gas bubbles. The coatings are calculated using the well-known theory of sound propagation in a liquid medium with bubbles, as well as the Kramers–Kronig integral dispersion equations. It is shown that the volumetric size distribution function of bubbles should be constant over the entire range of their sizes. A viscous liquid is designed to increase bubble damping to a value on the order of unity that is optimal for coatings by adding viscous losses in the surrounding liquid to small thermal losses. Low-frequency compensating resonators are used in coatings for soundproof walls. Several examples of calculating the acoustic characteristics of coatings are given. [ABSTRACT FROM AUTHOR]

المؤلفون: Bashkatov, V. V.¹ (AUTHOR), Ostrikov, N. N.¹ (AUTHOR) aeroacoustics@tsagi.ru

المصدر: Acoustical Physics. Feb2024, Vol. 70 Issue 1, p9-20. 12p.

مصطلحات موضوعية: *ACOUSTIC wave propagation, *SOUND pressure, *THEORY of wave motion, *SOUND waves, *ACOUSTIC impedance, *NON-uniform flows (Fluid dynamics)

مستخلص: The problem of sound propagation in a cylindrical duct with a uniform flow is considered with nonlinear impedance boundary conditions resulting from the dependence of the impedance of acoustic liners on the sound pressure level. An iterative procedure for solving this problem has been constructed, in which sound propagation is described by an asymptotic solution to the problem of the propagation of sound modes in a cylindrical duct with a uniform flow with a smoothly non-uniform impedance of the walls in the axial direction, and the nonlinear mode of operation of the liners is based on a semiempirical model of a two-layer acoustic liners. It is shown that the constructed iterative algorithm converges within the limits of applicability of the asymptotic solution and diverges beyond them. It is shown that, for the parameters with which the calculations were carried out, the nonlinear effect of the liners operation leads to an increase in sound attenuation compared to a linear solution of a similar problem, and this effect is when sound propagates along rather than against the flow. [ABSTRACT FROM AUTHOR]

المؤلفون: Goncharenko, Yu. Yu.¹ (AUTHOR), Kartsan, I. N.^1,2,3 (AUTHOR) kartsan2003@mail.ru, Zhukov, A. O.^4,5 (AUTHOR)

المصدر: AIP Conference Proceedings. 2024, Vol. 2969 Issue 1, p1-7. 7p.

مصطلحات موضوعية: *SPEECH, *ACOUSTIC wave propagation, *MATHEMATICAL models, *SURFACE of the earth, *RADON transforms, *AUTOMATIC speech recognition, *ACOUSTIC models

مستخلص: The paper proposes a variant of describing the propagation of speech signals under ideal conditions using the mathematical apparatus of Radon in the interests of their subsequent identification. The task of describing the propagation of speech signals has been formulated and it has been shown that the main goal of its solution is to develop a universal mathematical apparatus based on a generalized mathematical model of acoustic wave propagation, which is considered as a spherically symmetric function from the distance to the wave source, described by the Radon transform, which provides automation identification and increases the efficiency of the removal of speech information. The concept of ideal conditions for the propagation of speech signals is described, under which it is necessary to have a point omnidirectional sound source, the constancy of the parameters of acoustic receiving devices, a homogeneous unlimited environment limited only by a flat earth's surface and described by a mathematical model with the Radon transform, where the Fourier transform is understood as the corresponding equivalent norm. A variant of describing the propagation of speech signals under ideal conditions using the mathematical apparatus of Radon is proposed, which makes it possible to identify the received signals, in which all the properties and features of the emitted speech signals that determine their belonging to a fixed object of generation of these signals, propagating under ideal conditions for unlimited distances before registration receiving devices retain all these properties and features. The presence in the database and knowledge of mappings of these properties and features, accumulated and replenished during the execution of applied tasks for the removal of speech information, makes it possible to automate the identification of received signals and fixed objects of their generation. [ABSTRACT FROM AUTHOR]

المؤلفون: Peng, Huichun, Fan, Lijuan, Mei, Jun

المصدر: Journal of Applied Physics; 1/21/2024, Vol. 135 Issue 3, p1-11, 11p

مصطلحات موضوعية: ELASTIC waves, SHEAR waves, OPTIMIZATION algorithms, LONGITUDINAL waves, NONDESTRUCTIVE testing, ELASTIC wave propagation, HOLOGRAPHIC gratings, OPTICAL gratings

مستخلص: Mode coupling and conversion between longitudinal and transverse modes are ubiquitous and universal in elastic waves, presenting a challenge in realistic applications such as nondestructive evaluation and geological exploration, where independent and separate manipulation of each mode is demanded. In this article, we propose a design of elastic metalens that can realize a high-efficiency focusing for the longitudinal wave and a V-shaped converging pattern for the transverse wave at the same time. The metalens is constructed from a metagrating, where each meta-atom has a simple configuration and renders high diffraction efficiency even for large steering angles, enabled by concurrent utilization of grating diffraction theory and advanced optimization algorithms. Interestingly, an arbitrary energy splitting ratio between the reflected longitudinal and transverse waves can be obtained by precisely controlling the coupling strength and conversion efficiency between them, providing improved flexibility and adaptability to various application environments. Two illustrative examples with a sharp focusing effect and tailored conversion efficiency are explicitly demonstrated, with a 50/50 energy splitting ratio between the longitudinal and transverse waves in the first case, and a 70/30 ratio in the second one. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Applied Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Reyes, G., Panayotaros, P., Reyes, J. A.

المصدر: Journal of Applied Physics; 1/14/2024, Vol. 135 Issue 2, p1-12, 12p

مصطلحات موضوعية: CHOLESTERIC liquid crystals, ELECTROMAGNETIC waves, SURFACE waves (Fluids), ELECTROMAGNETIC wave propagation, LIQUID crystals, MAXWELL equations

مستخلص: We study an air–crown glass planar interface that includes a thin layer of a cholesteric liquid crystal doped with silver spheres of nanometer size. We propose a new theoretical model for the propagation of electromagnetic waves through the liquid crystal part and use the Marcuvitz–Schwinger form of the Maxwell equations to compute guided surface wave profiles. The results suggest the presence of anisotropic surface modes with negligible attenuation. The dependence of the surface wave parameters on the liquid crystal layer parameters can be used in liquid crystal-based sensors. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Applied Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Ni, Chun, Xie, Xin, Zhang, Liang

المصدر: Journal of Applied Physics; 11/14/2023, Vol. 134 Issue 18, p1-9, 9p

مصطلحات موضوعية: CURRENT distribution, SURFACE structure, ELECTROMAGNETIC wave propagation, COPLANAR waveguides, UNIT cell, ANTENNAS (Electronics)

مستخلص: Scientific research has shown that the geometric structure of the metasurface has a significant impact on its ability to control the propagation of electromagnetic waves. The control of surface current can be achieved by designing the shape of the metasurface unit cell. In this paper, the traditional metasurface is studied using characteristic mode analysis, and a modified metasurface is proposed, which consists of 4 × 4 hexagonal rings with an asymmetric concave interior. The modified metasurface controls the distribution of surface current by increasing the path of surface current, thus lowering the frequency of modal significance. In addition, due to the special asymmetric concave interior, the frequency difference of different modal currents increases, leading to the expansion of the operating bandwidth of modal currents. A metasurface antenna is fabricated and measured for proof of concept. With a size of 0.69λL × 0.69λL × 0.06λL (λL is the wavelength in free space at the lowest operating frequency), the designed antenna achieves a −10 dB impedance band of 40%, 3 dB axial ratio band of 19.4%, and boresight gain of 8 dBi. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Applied Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Sayed Ahmed, Moustafa¹ (AUTHOR), Ghommem, Mehdi² (AUTHOR), Shahab, Shima¹ (AUTHOR) sshahab@vt.edu

المصدر: Journal of Applied Physics. 9/28/2022, Vol. 132 Issue 12, p1-15. 15p.

مصطلحات موضوعية: *ELASTIC wave propagation, *ACOUSTIC radiators, *PHENOMENOLOGICAL theory (Physics), *PIEZOELECTRIC transducers

مستخلص: Mode couplings associated with elastic wave propagation through three-dimensional multiplex structures, as manifested by asymmetric eigenmodes and dissipation, determine the efficiency of electromechanical structures. As a result, it is critical to predict electroelastic symmetric modes such as thickness expander and radial modes, as well as asymmetric flexural modes, while accounting for material losses. Multiplex electromechanical structures include multi-layered through-wall ultrasound power transfer (TWUPT) systems. Physical processes that support TWUPT include vibrations at a transmitting/acoustic source element, elastic wave propagation through a barrier and coupling layers, piezoelectric transduction of elastic vibrations at a receiving element, and spatial resonances of the transmitting and receiving elements. We investigate mode couplings in an optimized modal TWUPT system, including their physical origins, models used to describe them, and regimes of weak and strong couplings. The system layout optimization is defined in terms of size (volume), operating frequency, and matching circuit load optimization. A computational model is developed and utilized in conjunction with experimental modal characterization to highlight the impact of eigenmode features on optimization results. Several behavioral modes are identified and analyzed. The interaction of symmetric radial and asymmetric flexural modes causes the system damping to increase and the device's overall efficiency to decrease. The electromechanical coupling factor value is likewise reduced as a result of this. Such occurrences are explained by the flow of energy between modes as they interact. The present work also proposes design guidelines to improve the performance of TWUPT systems based on exploiting inherent physical phenomena. [ABSTRACT FROM AUTHOR]

المؤلفون: Yue, Chong-Wang¹ (AUTHOR) ycw1981@163.com, Li, Xiao-Chun² (AUTHOR), Xu, Ji-Shan³ (AUTHOR), Feng, Bo¹ (AUTHOR)

المصدر: Applied Geophysics: Bulletin of Chinese Geophysical Society. Dec2023, Vol. 20 Issue 4, p469-478. 10p.

مصطلحات موضوعية: *ELASTIC wave propagation, *ACOUSTIC wave propagation, *ELASTIC waves, *ROCK deformation, *ROCK properties, *SEDIMENTARY rocks, *QUALITY factor

مستخلص: Because of the viscous properties of rock, a viscoelastic model is closer to the real situation of rock media than an elastic model is. Cracks in the media are common geophysical phenomena. In particular, horizontal cracks are widely developed in the thin interbeds of sedimentary rock. Taking a Cole—Cole viscoelastic medium as the background medium, we compute the frequency-dependent velocities, quality factors, anisotropy coefficients, crack densities, and crack aspect ratios of P- and S-waves based on Hudson's theory. We give the velocity-stress staggered finite-difference equations of the elastic wave propagation in a cylindrical coordinate system for a viscoelastic medium with horizontal cracks and numerically simulate acoustic propagation in the cracked medium with different crack densities and aspect ratios. The simulation results indicate that as the crack density increases outside a borehole the P- and S-wave velocities decrease and their amplitudes increase, in a borehole the P- and S—wave velocities and amplitudes decrease; as the crack aspect ratios increases outside a borehole the P-wave velocities decrease, its amplitudes change little and the S-wave amplitudes and velocities change little, in a borehole the P-wave velocities and amplitudes decrease and the S-wave velocities in a borehole change little, and the S-wave amplitudes decrease. [ABSTRACT FROM AUTHOR]