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: Mehdi Bozorgi

المصدر: IET Microwaves, Antennas & Propagation, Vol 18, Iss 2, Pp 106-115 (2024)

مصطلحات موضوعية: electromagnetic field theory, electromagnetic wave propagation, electromagnetic wave scattering, scattering, wave functions, Telecommunication, TK5101-6720, Electricity and magnetism, QC501-766

الوصف: Abstract A simple yet efficient solution to the problem of transverse electric (TE) scattering by a two‐dimensional right trapezoidal groove placed in a perfect electric conductor (PEC) surface is presented. Using superposition of plane waves and applying the Neumann boundary condition at the groove walls, the transverse magnetic field is expressed as the sums of infinite series of waveguide modes. Considering the equivalent magnetic current on the aperture, a Fredlholm's integral equation with logarithmic singular kernel is extracted and then discretised by a collocation method based on a piecewise constant approximant. The extracted linear system of equations can be easily solved by the matrix methods for the unknown coefficients. Numerous examples are presented to verify the results and show the ability of the proposed method. Finally, this method is employed to examine the effect of the groove parameters and incidence angle on the scattering signatures.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1751-8725Test; https://doaj.org/toc/1751-8733Test

الوصول الحر: https://doaj.org/article/709d636709c544e8b7c53763a7507e35Test

المؤلفون: Liang, Yuwang, Zhou, Fengxi, Cao, Xiaolin, Wang, Liye, Zhu, Shunwang, Zhou, Zhixiong

المصدر: Journal of Vibration & Control; Jan2024, Vol. 30 Issue 1/2, p354-365, 12p

مصطلحات موضوعية: ELASTIC waves, PLANE wavefronts, TIME-domain analysis, ELASTIC wave propagation, ELASTIC scattering, BOUNDARY element methods, TRENCHES, FINITE element method

مستخلص: In this paper, the scattering and vibration isolation of elastic waves from the open trench are analyzed and discussed in the time domain using the scaled boundary finite element method (SBFEM). Based on the theory of soil-structure interaction, the site with an open trench is decomposed into a near-field system and an infinite far-field system. The quadtree domain decomposition technique is employed for SBFEM mesh discretization of the near-field. The far-field is rigorously modeled by the displacement unit impulse response matrix. The obliquely plane elastic wave from the far-field is converted into a traction force acting on the near/far-field boundary. The time-space domain numerical model is established for elastic wave propagation in half-space with an open trench. Finally, through numerical examples to verify the effectiveness of the method of this paper, and parametric analyze the effect law of the incidence angle and the trench depth, etc., on the vibration isolation performance. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Vibration & Control is the property of Sage Publications, Ltd. 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: Kosulnikov, S., Cuesta, F. S., Wang, X., Tretyakov, S. A.

المساهمون: Department of Electronics and Nanoengineering, Sergei Tretiakov Group, Karlsruhe Institute of Technology, Aalto-yliopisto, Aalto University

مصطلحات موضوعية: Electromagnetic diffraction, Harmonic analysis, Impedance, Metasurfaces, Millimeter wave propagation, Optimization, Reflection, Scattering, Substrates, Surface impedance

الوصف: openaire: EC/H2020/871464/EU//ARIADNE ; Active development is taking place in reconfigurable and static metasurfaces that control and optimize reflections. However, existing designs typically only optimize reflections from the metasurface panels, neglecting interference with reflections originating from supporting walls and nearby objects. In this study, we investigate how engineering the metasurface properties can modify the total scattering pattern, enabling the modification and optimization of reflections from significantly larger illuminated areas than the metasurface panel. To accomplish this, a general design approach is developed to create periodical metasurfaces with controlled reflection phase and amplitude for all propagating Floquet harmonics. By combining metasurface reflections with those from the surrounding walls, the total scattering can be manipulated. The study demonstrates how appropriately designed metasurfaces can modify reflections from surrounding walls, enhancing the functionalities of metasurfaces. These findings are intended to facilitate advancements in engineering and optimizing wave propagation channels, particularly for millimeter-wave communications. ; Peer reviewed

وصف الملف: application/pdf

العلاقة: info:eu-repo/grantAgreement/EC/H2020/871464/EU//ARIADNE; IEEE Transactions on Antennas and Propagation; Kosulnikov, S, Cuesta, F S, Wang, X & Tretyakov, S A 2024, ' Molding of Reflection and Scattering from Uniform Walls Using Space-Periodic Metasurfaces ', IEEE Transactions on Antennas and Propagation, vol. 72, no. 3, pp. 2992-2997 . https://doi.org/10.1109/TAP.2024.3355208Test; PURE UUID: 31598292-a15a-43df-b5ec-c0a9e8b2f586; PURE ITEMURL: https://research.aalto.fi/en/publications/31598292-a15a-43df-b5ec-c0a9e8b2f586Test; PURE LINK: http://www.scopus.com/inward/record.url?scp=85183958526&partnerID=8YFLogxKTest; PURE FILEURL: https://research.aalto.fi/files/142410647/Molding_of_Reflection_and_Scattering_From_Uniform_Walls_Using_Space-Periodic_Metasurfaces.pdfTest; https://aaltodoc.aalto.fi/handle/123456789/126888Test; URN:NBN:fi:aalto-202403062523

الإتاحة: https://doi.org/10.1109/TAP.2024.3355208Test
https://aaltodoc.aalto.fi/handle/123456789/126888Test

المؤلفون: Li, L, Fromme, P

المساهمون: Su, Zhongqing, Peters, Kara J, Ricci, Fabrizio, Rizzo, Piervincenzo

المصدر: In: Su, Zhongqing and Peters, Kara J and Ricci, Fabrizio and Rizzo, Piervincenzo, (eds.) Proceedings Volume 12951: Health Monitoring of Structural and Biological Systems XVIII. (pp. p. 1295116). SPIE: Bellingham, WA, USA. (2024)

مصطلحات موضوعية: Finite element methods, Waveguides, Scattering, Aluminum, Structural health monitoring, Transducers, Nondestructive evaluation, Wave propagation

الوصف: Low frequency guided waves have been used to develop Structural Health Monitoring (SHM) for the early detection of fatigue cracks in metallic aircraft structures. The scattering and mode conversion of guided waves at part-thickness defects was investigated to quantify the sensitivity for defect detection and the potential for the development of a baseline-free SHM methodology employing mode-converted guided waves. Finite Element Analysis (FEA) and experimental validation were conducted to investigate the mode converted scattering from the S0 to the A0 Lamb wave mode at part-thickness crack-like defects in an aluminum plate. A piezoelectric (PZT) transducer was experimentally used as a plate edge excitation for the S0 mode and the out-of-plane displacement was measured using a laser vibrometer. Good agreement between the FEA and experimental results was obtained and the influence of defect depth and length was investigated and quantified.

وصف الملف: text

العلاقة: https://discovery.ucl.ac.uk/id/eprint/10193309/1/1295116.pdfTest; https://discovery.ucl.ac.uk/id/eprint/10193309Test/

الإتاحة: https://discovery.ucl.ac.uk/id/eprint/10193309/1/1295116.pdfTest
https://discovery.ucl.ac.uk/id/eprint/10193309Test/

المؤلفون: Golub, Mikhail V.¹ (AUTHOR) m_golub@inbox.ru, Doroshenko, Olga V.¹ (AUTHOR) oldorosh@mail.ru, Fomenko, Sergey I.¹ (AUTHOR) sfom@yandex.ru, Wang, Yanzheng² (AUTHOR) yzwangzju@gmail.com, Zhang, Chuanzeng² (AUTHOR) c.zhang@uni-siegen.de

المصدر: International Journal of Solids & Structures. Mar2021, Vol. 212, p1-22. 22p.

مصطلحات موضوعية: *PHONONIC crystals, *ELASTIC wave propagation, *BOUNDARY element methods, *ELASTIC waves

مستخلص: In the present study, the scattering of plane elastic waves by multiple periodic arrays of interface strip-like cracks is investigated. The boundary-value problem is solved using the boundary integral equation method. The convergence of the proposed method is demonstrated for both multiple cracks and multiple periodic arrays of cracks. It is shown that the introduction of periodic arrays of strip-like interface cracks into a layered periodic structure leads to the formation of additional band-gaps in frequency ranges corresponding to pass-bands for the same structure without cracks. The influences of the positions of cracks and their widths on wave transmission through the layered phononic crystal with cracks are studied and compared for several lattices. It is revealed that the introduction of interface cracks may lead to the formation of extra band-gaps and pass-bands. Also, the effects of wave localization and the resonance scattering are investigated for a better understanding of the revealed wave phenomena. [ABSTRACT FROM AUTHOR]

المؤلفون: Miao, Yang, Pedersen, Troels, Gan, Mingming, Vinogradov, Evgenii, Oestges, Claude

المصدر: IEEE Transactions on Antennas & Propagation. Jan2019, Vol. 67 Issue 1, p484-494. 11p.

مصطلحات موضوعية: RADIO wave propagation, ANTENNAS (Electronics), PREDICTION models, RAY tracing, GRAPH theory

مستخلص: This paper proposes a hybrid modeling approach for the prediction of the room-to-room radio propagation channel. The model combines ray tracing (RT) with the propagation graph (PG). The PG vertices are obtained at each room by RT with the assumption that the receive antenna (or transmit antenna) virtually locates on the surface of the separating wall between the two rooms. Rays transmitted from one room to the other through the separating wall are deterministically calculated by Snell’s law of refraction. Predictions by the proposed model are compared with the measurement data from an office-to-office scenario. The results show that the proposed modeling works with the simplest parameter settings, i.e., assuming no propagation from the room containing receive antenna to the room containing transmit antenna, RT applied separately in each room only involves mechanism of line of sight and first-order specular reflection. [ABSTRACT FROM AUTHOR]

: Copyright of IEEE Transactions on Antennas & Propagation is the property of IEEE 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: Wang, Zhuang, Wang, Mengnan

المصدر: IEEE Transactions on Antennas & Propagation. Dec2018, Vol. 66 Issue 12, p6476-6481. 6p.

مصطلحات موضوعية: TROPOSPHERIC scatter communication systems, RADIO wave propagation, RECEIVING antennas, TRANSMITTING antennas, AZIMUTH

مستخلص: Microwave over-the-horizon propagation via troposcatter mechanism is a valuable candidate for passive sensing of remote radiation source applications, e.g., electronic reconnaissance. The result from the misalignment between target emitting and the system receiving antenna, the additional deviation losses in azimuthal and elevation angle are indispensable to model the receiving antenna pattern as well as the arrival scattering signal level. Based on the scatter transfer function, the deviation losses are derived assuming Gaussian antenna patterns and verified by existing measured data from the 1950s. Finally, potential application values of the deviation losses in electronic reconnaissance are provided. [ABSTRACT FROM AUTHOR]

: Copyright of IEEE Transactions on Antennas & Propagation is the property of IEEE 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: Toh, A., Capdeville, Y., Chi, W.‐C., Ide, S.

المصدر: Geophysical Research Letters; 4/28/2023, Vol. 50 Issue 8, p1-9, 9p

مصطلحات موضوعية: FAULT zones, EARTHQUAKE zones, ELASTIC wave propagation, TREMOR, SEISMOMETERS, OCEAN bottom, EARTHQUAKES, SUBDUCTION zones, PALEOSEISMOLOGY

مستخلص: Tremors are a type of slow earthquake with long‐duration signals compared to ordinary earthquakes. The long signals have been considered to solely reflect their long source process. However, here, we provide evidence suggesting that the source processes of tremors are not always long. We refer to these observations as short‐duration tremors. They were recorded by ocean‐bottom seismometers placed very close to the source. Although these tremors exhibit a short‐duration signal when recorded near the source, they exhibit a typical long‐duration signal elsewhere. Our numerical simulations demonstrate that the features can be captured by considering a strongly scattering medium around their source. One such structure could be small low‐velocity inclusions distributed around the seismic source. The inclusions may represent the seismic expression of geologically detected aquifers in tremor source regions. Furthermore, this medium could be embedded along the slow earthquake fault zone and play a critical role in their source process. Plain Language Summary: At least two types of earthquakes occur in shallow subduction zones: ordinary earthquakes and tremors. Tremors are known to exhibit long signal duration compared to ordinary earthquakes. To date, tremors' long‐duration signal has been solely interpreted by their source process. Here, we discovered tremors that exhibit short duration signals when recorded close from the source which we referred to as "short‐duration tremors". They suggest that tremors' source process is not always long and structural effects may partially form the typical long‐duration signals. We performed numerical simulations on elastic wave propagation and demonstrated that the observations can be qualitatively reproduced by assuming a strongly scattering material surrounding the seismic source. On the other hand, it has been reported based on ocean bottom drilling project that tremor source region may consist of patchily distributed aquifers. The inclusions in our model may be the seismic expressions of the geologically detected aquifers. Further, such a structure could be embedded along the slow‐earthquake fault zone and play a key role in their source process. Key Points: Short‐duration tremors in ocean‐bottom seismometer records suggest that the source process of tremors is not always longShort‐duration tremors can be interpreted by placing a strongly scattering medium around their sourceSuch a medium embedded along the slow earthquake fault zone could play a key role in the tremor source process [ABSTRACT FROM AUTHOR]

: Copyright of Geophysical Research Letters is the property of Wiley-Blackwell 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: Poulier, P.-L.¹ (AUTHOR) poulier@mps.mpg.de, Fournier, D.¹ (AUTHOR), Gizon, L.^1,2 (AUTHOR), Duvall, T. L.¹ (AUTHOR)

المصدر: Astronomy & Astrophysics / Astronomie et Astrophysique. Nov2020, Vol. 643, p1-13. 13p.

مصطلحات موضوعية: *SOLAR granulation, *ACOUSTIC wave propagation, *WAVE packets, *BORN approximation, *SOUND waves, *ACOUSTIC models

مستخلص: Context. The frequencies, lifetimes, and eigenfunctions of solar acoustic waves are affected by turbulent convection, which is random in space and in time. Since the correlation time of solar granulation and the periods of acoustic waves (∼5 min) are similar, the medium in which the waves propagate cannot a priori be assumed to be time independent. Aims. We compare various effective-medium solutions with numerical solutions in order to identify the approximations that can be used in helioseismology. For the sake of simplicity, the medium is one dimensional. Methods. We consider the Keller approximation, the second-order Born approximation, and spatial homogenization to obtain theoretical values for the effective wave speed and attenuation (averaged over the realizations of the medium). Numerically, we computed the first and second statistical moments of the wave field over many thousands of realizations of the medium (finite-amplitude sound-speed perturbations are limited to a 30 Mm band and have a zero mean). Results. The effective wave speed is reduced for both the theories and the simulations. The attenuation of the coherent wave field and the wave speed are best described by the Keller theory. The numerical simulations reveal the presence of coda waves, trailing the ballistic wave packet. These late arrival waves are due to multiple scattering and are easily seen in the second moment of the wave field. Conclusions. We find that the effective wave speed can be calculated, numerically and theoretically, using a single snapshot of the random medium (frozen medium); however, the attenuation is underestimated in the frozen medium compared to the time-dependent medium. Multiple scattering cannot be ignored when modeling acoustic wave propagation through solar granulation. [ABSTRACT FROM AUTHOR]