المؤلفون: Roja, Vadlamudi, D., Sriram Kumar

المصدر: International Journal of Microwave & Wireless Technologies; Dec2023, Vol. 15 Issue 10, p1789-1800, 12p

مصطلحات موضوعية: RADIO wave propagation, ANTENNAS (Electronics), PATH analysis (Statistics), WAVE analysis, QUADRATURE amplitude modulation, THEORY of wave motion, SUBSTRATE integrated waveguides

مستخلص: A low-profile slant ±45° polarized antenna for a 4G/5G base station with a dominant path wave propagation model (DPM) is reported in this paper. For dual-polarization and wide impedance bandwidth, the two dipole radiators are crisscrossed and a square metallic ring is integrated with the dipole arms and screwed with the four shorting vias. The antenna operates in Band 40/41/42/43 with strong isolation and low ECC (Envelop Correlation Coefficient). Fabricated antenna results show that the predicted wideband antenna has 13.38% bandwidth in 4G, which is Band 40/41, and 29.33% bandwidth in 5G sub-6 GHz Band 42/43. The antenna has a consistent radiation pattern, a 40 dB XPD (Cross Pol Discrimination), and a beam width of 69.5° ±1.5° in the entire frequency band. Three base station sites were explored to deploy the radiation pattern of a dual-polarized antenna in the 3D EM (Electromagnetic Analysis) tool. To evaluate signal quality, strength, radio network planning, and wave propagation analysis by analyzing antenna performance in real-time scenarios with 64 and 256 QAM (Quadrature Amplitude Modulation) techniques. For the proposed four-stream MIMO (Multiple-Input-Multiple-Output) antenna arrangement at deployed cell sites for 4G/5G base station applications, the maximum downlink and uplink data rates are 3.826/2.8 Mbps and 1044/800 Mbps respectively. [ABSTRACT FROM AUTHOR]

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المؤلفون: Shaokang Li, Wei Su, Yonghao Zhang

المصدر: Journal of Fluid Mechanics; 10/25/2023, Vol. 973, pA35-1-A35-25, 25p

مصطلحات موضوعية: THEORY of wave motion, ACOUSTIC wave propagation, SURFACE forces, DEGREES of freedom, BULK viscosity, SOUND waves

مستخلص: Sound wave propagation in rarefied flows of molecular gases confined in micro-channels is investigated numerically. We first validate the employed kinetic model against the experimental results and then systematically study the gas damping and surface force on the transducer as well as the resonance/anti-resonance in confined space. To quantify the impact of the finite relaxation rates of the translational and internal energies on wave propagation, we examine the roles of bulk viscosity and thermal conductivity in depth over a wide range of rarefactions and oscillation frequencies. It is found that the bulk viscosity only exerts influence on the pressure amplitude and its resonance frequency in the slip regime in high oscillations. In addition, the internal degree of freedom is frozen when the bulk viscosity of a molecular gas is large, resulting in the pressure amplitude of sound waves in the molecular gas being the same as in a monatomic gas. Meanwhile, the thermal conductivity has a limited influence on the pressure amplitude in all the simulated flows. In the case of the thermoacoustic wave, we prove that the Onsager-Casimir reciprocal relation also holds for molecular gases, i.e. the pressure deviation induced by the temperature variation is equal to the heat flux induced by the plate oscillation. Our findings enable an enhanced understanding of sound wave propagation in molecular gases, which may facilitate the design of nano-/micro-scale devices. [ABSTRACT FROM AUTHOR]

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المؤلفون: Schenkel, Francesca, Baer, Christoph, Rolfes, Ilona, Schulz, Christian

المصدر: International Journal of Microwave & Wireless Technologies; Jul2023, Vol. 15 Issue 6, p1001-1011, 11p

مصطلحات موضوعية: CONTINUOUS wave radar, MILLIMETER waves, ELECTROMAGNETIC wave propagation, PLASMA waves, RADAR

مستخلص: This work introduces a method for plasma state supervision, based on a frequency-modulated continuous wave radar sensor and a suitable signal evaluation enabling a continuous supervision method for the plasma state. Highly precise phase evaluation of the signal allows us to detect and visualize smallest changes in the plasma state. Assuming the plasma to act like a frequency-dependent dielectric material, the propagation of the electromagnetic wave depends on the plasma state and hence, also the measured phase. Broadband measurements are carried out at center frequencies of 80 and 140 GHz in a low-pressure plasma. The radar-based setup can be used for a very flexible application, capable for spatially resolved measurements in the plasma bulk. At the same time, the high measurement rate allows for quasi real-time monitoring, so that transient processes in the plasma are recorded. Due to the simple setup, this approach is most suitable for industrial applications to improve process control. The chosen different frequencies will show a change in the influence of the plasma on the electromagnetic wave demonstrating the advantages of multi-frequency approaches in future applications. [ABSTRACT FROM AUTHOR]

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المؤلفون: Huang, J., Porter, R.

المصدر: Journal of Fluid Mechanics; 4/10/2023, Vol. 960, p1-33, 33p

مصطلحات موضوعية: WATER waves, OCEAN energy resources, OCEAN waves, INTEGRAL equations, PROBLEM solving, ELASTIC wave propagation

مستخلص: This paper presents and compares two different approaches to solving the problem of wave propagation across a large finite periodic array of surface-piercing vertical barriers. Both approaches are formulated in terms of a pair of integral equations, one exact and based on a spacing $\delta > 0$ between adjacent barriers and the other approximate and based on a continuum model formally developed by using homogenisation methods for small $\delta$. It is shown that the approximate method is simpler to evaluate than the exact method which requires eigenvalues and eigenmodes related to propagation in an equivalent infinite periodic array of barriers. In both methods, the numerical effort required to solve problems is independent of the size of the array. The comparison between the two methods allows us to draw important conclusions about the validity of homogenisation models of plate array metamaterial devices. The practical interest in this problem stems from the result that for an array of barriers there exists a critical value of radian frequency, $\omega _c$ , dependent on $\delta$ , below which waves propagate through the array and above which it results in wave decay. When $\delta \to 0$ , the critical frequency is given by $\omega _c = \sqrt {g/d}$ , where $d$ is the plate submergence and $g$ is the acceleration due to gravity, which relates to the resonance in narrow channels and is an example of local resonance, studied extensively in metamaterials. The results have implications for proposed schemes to harness energy from ocean waves and other problems related to rainbow trapping and rainbow reflection. [ABSTRACT FROM AUTHOR]

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المؤلفون: Le Bras, Sophie, Gabard, Gwénaël, Bériot, Hadrien

المصدر: Journal of Fluid Mechanics; 12/25/2022, Vol. 953, p1-28, 28p

مصطلحات موضوعية: ACOUSTIC wave propagation, GREEN'S functions, ADJOINT differential equations, COMPRESSIBLE flow, FINITE element method

مستخلص: This paper presents a systematic analysis of direct and adjoint problems for sound propagation with flow. Two scalar propagation operators are considered: the linearised potential equation from Goldstein, and Pierce's equation based on a high-frequency approximation. For both models, the analysis involves compressible base flows, volume sources and surfaces that can be vibrating and/or acoustically lined (using the Myers impedance condition), as well as far-field radiation boundaries. For both models, the direct problems are fully described and adjoint problems are formulated to define tailored Green's functions. These Green's functions are devised to provide an explicit link between the direct problem solutions and the source terms. These adjoint problems and tailored Green's functions are particularly useful and efficient for source localisation problems, or when stochastic distributed sources are involved. The present analysis yields a number of new results, including the adjoint Myers condition for the linearised potential equation, as well as the formulation of the direct and adjoint Myers condition for Pierce's equation. It is also shown how the adjoint problems can be recast in forms that are readily solved using existing simulation tools for the direct problems. Results presented in this paper are obtained using a high-order finite element method. Several test cases serve as validation for the approach using tailored Green's functions. They also illustrate the relative benefits of the two propagation operators. [ABSTRACT FROM AUTHOR]

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المؤلفون: Sugimoto, Nobumasa

المصدر: Journal of Fluid Mechanics; 8/25/2022, Vol. 945, p1-36, 36p

مصطلحات موضوعية: ACOUSTIC wave propagation, BOUNDARY layer (Aerodynamics), BOUNDARY value problems, DISPERSION relations, FOURIER series

مستخلص: This paper examines thermoacoustic effects on the propagation of non-planar sound in a circular duct subjected to an axial temperature gradient. Of particular concern are thermoviscous diffusive effects, which are taken into account by the boundary-layer approximation in a framework of the linear theory. For disturbances expanded into Fourier and Fourier–Bessel series in the azimuthal and radial directions, respectively, the pressure in each mode is described by a one-dimensional, dispersive wave equation, if non-diffusive propagation is assumed. When the diffusive effects are included, each radial mode is coupled to the other radial modes through the boundary layer. Focusing on a single azimuthal and radial mode only, the dispersion relation for the propagation along an infinite duct of a uniform gas is first derived. Effects of the temperature gradient are then examined by solving boundary-value problems for a duct of finite length in four typical cases. Assuming that the wall temperature increases exponentially along the duct, eigenfrequencies and decay rates in the lowest axial mode are obtained as well as axial distributions of the sound pressure and the axial velocity in the duct. The frequency and the decay rate increase as the temperature ratio at both ends becomes higher. It is found from the acoustic energy equation that the dispersion combined with the diffusion acts to reduce the damping and that the temperature gradient makes little contribution to the production of the energy. However, it is unveiled that the non-uniformity in temperature yields thermoacoustic sound confinement in the vicinity of the cold end. [ABSTRACT FROM AUTHOR]

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المؤلفون: Giese, Alexandra, Arcone, Steven, Hawley, Robert, Lewis, Gabriel, Wagnon, Patrick

المصدر: Journal of Glaciology; Dec2021, Vol. 67 Issue 266, p1108-1120, 13p

مصطلحات موضوعية: GROUND penetrating radar, DRY ice, ELECTROMAGNETIC wave propagation, GLACIAL melting, GLACIERS

مصطلحات جغرافية: NEPAL

مستخلص: The thickness of a supraglacial layer is critical to the magnitude and time frame of glacier melt. Field-based, short pulse, ground-penetrating radar (GPR) has successfully measured debris thickness during a glacier's melt season, when there is a strong return from the ice–debris interface, but profiling with GPR in the absence of a highly reflective ice interface has not been explored. We investigated the performance of 960 MHz signals over 2 km of transects on Changri Nup Glacier, Nepal, during the post-monsoon. We also performed laboratory experiments to interpret the field data and investigate electromagnetic wave propagation into dry rocky debris. Laboratory tests confirmed wave penetration into the glacier ice and suggest that the ice–debris interface return was missing in field data because of a weak dielectric contrast between solid ice and porous dry debris. We developed a new method to estimate debris thicknesses by applying a statistical approach to volumetric backscatter, and our backscatter-based calculated thickness retrievals gave reasonable agreement with debris depths measured manually in the field (10–40 cm). We conclude that, when melt season profiling is not an option, a remote system near 1 GHz could allow dry debris thickness to be estimated based on volumetric backscatter. [ABSTRACT FROM AUTHOR]

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المؤلفون: Pham, Kim, Mercier, Jean-Francois, Fuster, Daniel, Marigo, Jean-Jacques, Maurel, Agnès

المصدر: Journal of Fluid Mechanics; 1/10/2021, Vol. 906, p1-30, 30p

مصطلحات موضوعية: SOUND wave scattering, NONLINEAR waves, ACOUSTIC wave propagation, SOUND pressure, SPEED of sound, ASYMPTOTIC homogenization

مستخلص: Our study concerns the propagation of acoustic waves through a thin screen made of a periodic arrangement of air bubbles in water. The bubbles are oscillators of the Minnaert type whose dynamics is modified by the containment. This nonlinear dynamics is obtained in the time domain using asymptotic analysis and a homogenization technique involving three scales, those being the scale of a bubble, that of the array and eventually that of the wavelength. The resulting effective model is set in the water (the screen has disappeared) and it encapsulates the effect of the screen in a jump of the normal acoustic velocity. The jump is linked to the continuous version of the bubble radius which satisfies an equation of the Rayleigh–Plesset type. This allows us to highlight two important effects. Firstly, a bubble within the array has a much larger radiative damping than an isolated bubble. Secondly it perceives a pressure which differs from the acoustic pressure imposed by the source due to bubble–bubble interactions; it results in a term of mass correction deduced from the Green's function for a Laplace problem which accounts for the bubble arrangement. Our findings are exemplified by numerical experiments of the scattering of a short pulse in the linear and nonlinear regimes. [ABSTRACT FROM AUTHOR]

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المؤلفون: Rienstra, S. W.

المصدر: Journal of Fluid Mechanics; 1/10/2021, Vol. 906, p1-25, 25p

مصطلحات موضوعية: EIGENVALUE equations, ACOUSTIC wave propagation, VORTEX motion, ACOUSTICS, INVISCID flow, WAVENUMBER, SHEAR flow

مستخلص: A slowly varying modes solution of Wentzel–Kramers–Brillouin type is derived for the problem of sound propagation in a slowly varying two-dimensional duct with homentropic inviscid sheared mean flow and acoustically lined walls of slowly varying impedance. The modal shape function and axial wavenumber are described by the Pridmore-Brown eigenvalue equation. The slowly varying modal amplitude is determined in the usual way by an equation resulting from a solvability condition. For a general mean flow, this equation can be solved in the form of an incomplete adiabatic invariant. Due to conservation of specific mean vorticity along streamlines, two simplifications prove possible for a linearly sheared mean flow: (i) an analytically exact approximation for the mean flow, and (ii) a complete adiabatic invariant for the acoustics. For this last configuration some example cases are evaluated numerically, where the Pridmore-Brown eigenvalue problem is solved by a Galerkin projection combined with an efficient nonlinear iteration. [ABSTRACT FROM AUTHOR]

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المؤلفون: Das, Saptarshi, Hobson, Michael P., Feroz, Farhan, Xi Chen, Phadke, Suhas, Goudswaard, Jeroen, Hohl, Detlef

المصدر: Data-Centric Engineering; 2021, Vol. 2, p1-15, 15p

مصطلحات موضوعية: SEISMIC response, COMPUTER algorithms, GAUSSIAN processes, ELASTIC wave propagation, HYPOTHESIS

مستخلص: In passive seismic and microseismic monitoring, identifying and characterizing events in a strong noisy background is a challenging task. Most of the established methods for geophysical inversion are likely to yield many false event detections. The most advanced of these schemes require thousands of computationally demanding forward elasticwave propagation simulations. Here we train and use an ensemble of Gaussian process surrogate meta-models, or proxy emulators, to accelerate the generation of accurate template seismograms from random microseismic event locations. In the presence of multiple microseismic events occurring at different spatial locations with arbitrary amplitude and origin time, and in the presence of noise, an inference algorithm needs to navigate an objective function or likelihood landscape of highly complex shape, perhaps with multiple modes and narrow curving degeneracies. This is a challenging computational task even for state-of-the-art Bayesian sampling algorithms. In this paper, we propose a novel method for detecting multiple microseismic events in a strong noise background using Bayesian inference, in particular, the Multimodal Nested Sampling (MultiNest) algorithm. The method not only provides the posterior samples for the 5D spatio-temporal-amplitude inference for the real microseismic events, by inverting the seismic traces in multiple surface receivers, but also computes the Bayesian evidence or the marginal likelihood that permits hypothesis testing for discriminating true vs. false event detection. [ABSTRACT FROM AUTHOR]

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