Acoustic scattering by a semi-infinite angular sector with impedance boundary conditions, II: the far-field asymptotics

2020 ◽  
Vol 85 (1) ◽  
pp. 87-112
Author(s):  
Mikhail A Lyalinov
Keyword(s):  
Acoustic Scattering ◽  
Scattered Wave ◽  
Careful Study ◽  
Far Field ◽  
Impedance Boundary ◽  
Transition Zones ◽  
Sommerfeld Integral ◽  
Asymptotic Evaluation ◽  
Plane Incident Wave ◽  
The Waves

Abstract This work is a natural continuation of our recent study devoted to the scattering of a plane incident wave by a semi-infinite impedance sector. We develop an approach that enables us to compute different components in the far-field asymptotics. The method is based on the Sommerfeld integral representation of the scattered wave field, on the careful study of singularities of the integrand and on the asymptotic evaluation of the integral by means of the saddle point technique. In this way, we describe the waves reflected from the sector, diffracted by its edges or scattered by the vertex as well as the surface waves. Discussion of the far-field in the so-called singular directions (or in the transition zones) is also addressed.

scholarly journals Meta-neural-network for real-time and passive deep-learning-based object recognition

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Jingkai Weng ◽  
Yujiang Ding ◽  
Chengbo Hu ◽  
Xue-Feng Zhu ◽  
Bin Liang ◽  
...  
Keyword(s):  
Neural Network ◽  
Deep Learning ◽  
Real Time ◽  
Acoustic Scattering ◽  
Scattered Wave ◽  
Disease Diagnosis ◽  
Great Success ◽  
Destructive Testing ◽  
Unit Cells ◽  
Handwritten Digit

AbstractAnalyzing scattered wave to recognize object is of fundamental significance in wave physics. Recently-emerged deep learning technique achieved great success in interpreting wave field such as in ultrasound non-destructive testing and disease diagnosis, but conventionally need time-consuming computer postprocessing or bulky-sized diffractive elements. Here we theoretically propose and experimentally demonstrate a purely-passive and small-footprint meta-neural-network for real-time recognizing complicated objects by analyzing acoustic scattering. We prove meta-neural-network mimics a standard neural network despite its compactness, thanks to unique capability of its metamaterial unit-cells (dubbed meta-neurons) to produce deep-subwavelength phase shift as training parameters. The resulting device exhibits the “intelligence” to perform desired tasks with potential to overcome the current limitations, showcased by two distinctive examples of handwritten digit recognition and discerning misaligned orbital-angular-momentum vortices. Our mechanism opens the route to new metamaterial-based deep-learning paradigms and enable conceptual devices automatically analyzing signals, with far-reaching implications for acoustics and related fields.

Full Aperture Reconstruction of the Acoustic Far-Field Pattern from Few Measurements

2012 ◽  
Vol 11 (2) ◽  
pp. 647-659 ◽  
Author(s):  
Hélène Barucq ◽  
Chokri Bekkey ◽  
Rabia Djellouli
Keyword(s):  
Total Variation ◽  
Acoustic Scattering ◽  
Numerical Procedure ◽  
Field Pattern ◽  
Far Field ◽  
Exact Representation ◽  
Scattering Problems ◽  
Reconstruction Procedure ◽  
The Stability ◽  
Far Field Pattern

AbstractWe propose a numerical procedure to extend to full aperture the acoustic far-field pattern (FFP) when measured in only few observation angles. The reconstruction procedure is a multi-step technique that combines a total variation regularized iterative method with the standard Tikhonov regularized pseudo-inversion. The proposed approach distinguishes itself from existing solution methodologies by using an exact representation of the total variation which is crucial for the stability and robustness of Newton algorithms. We present numerical results in the case of two-dimensional acoustic scattering problems to illustrate the potential of the proposed procedure for reconstructing the full aperture of the FFP from very few noisy data such as backscattering synthetic measurements.

scholarly journals Stern waves with vorticity

2002 ◽  
Vol 43 (3) ◽  
pp. 321-332 ◽  
Author(s):  
Y. Kang ◽  
J.-M. Vanden-Broeck
Keyword(s):  
Integral Equation ◽  
Numerical Solutions ◽  
Free Surface Flow ◽  
Integral Equation Method ◽  
Surface Flow ◽  
Boundary Integral ◽  
Analytical Relation ◽  
Far Field ◽  
Two Dimensional ◽  
The Waves

AbstractSteady two-dimensional free surface flow past a semi-infinite flat plate is considered. The vorticity in the flow is assumed to be constant. For large values of the Froude number F, an analytical relation between F, the vorticity parameter ω and the steepness s of the waves in the far field is derived. In addition numerical solutions are calculated by a boundary integral equation method.

scholarly journals Far-field and near-field directionality in acoustic scattering

2020 ◽  
Vol 22 (8) ◽  
pp. 083016 ◽  
Author(s):  
Lei Wei ◽  
Francisco J Rodríguez-Fortuño
Keyword(s):  
Near Field ◽  
Acoustic Scattering ◽  
Far Field

Acoustic scattering by a finite nonlinear elastic plate. I Primary, secondary and combination resonances

1987 ◽  
Vol 414 (1846) ◽  
pp. 237-253 ◽  
Keyword(s):  
Incident Wave ◽  
Elastic Plate ◽  
Scattered Field ◽  
Acoustic Waves ◽  
Multiple Scales ◽  
Acoustic Scattering ◽  
Scattered Wave ◽  
Thin Elastic Plate ◽  
Finite Width ◽  
Wave Angle

A thin elastic plate of finite width is irradiated by time-harmonic acoustic waves. The fluid is assumed light compared with the plate mass, and the forcing term is of sufficient amplitude to necessitate the inclusion of a nonlinear term (due to mid-plane stretching) in the plate equation. The order-one scattered field is determined by the method of multiple scales when the forcing frequency approaches a free oscillation frequency (eigenfrequency) of the plate. This solution is shown to agree with previous work, for the linear problem, and can be multivalued for particular values of the plate-fluid parameters. The scattered wave may also exhibit jumps in its amplitude and phase angle as it varies with frequency, incident-wave angle or incident-wave amplitude. The non-linear term further allows the possibility of secondary and combination resonances. These are investigated and the scattered field is shown to contain terms of different frequencies to those of the incident waves. Multivalued solutions and the associated jump phenomenon are again found for these resonant cases.

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