Time-reversal focusing of elastic waves in inhomogeneous media: an application to an elastic-wave landmine detection system

2005 ◽  
Author(s):  
Pelham D. Norville ◽  
Waymond R. Scott, Jr.
Keyword(s):  
Elastic Wave ◽  
Time Reversal ◽  
Elastic Waves ◽  
Detection System ◽  
Inhomogeneous Media ◽  
Landmine Detection

scholarly journals Numerical Modelling and Optimization of Two-Dimensional Phononic Band Gaps in Elastic Metamaterials with Square Inclusions

2021 ◽  
Vol 11 (7) ◽  
pp. 3124
Author(s):  
Alya Alhammadi ◽  
Jin-You Lu ◽  
Mahra Almheiri ◽  
Fatima Alzaabi ◽  
Zineb Matouk ◽  
...  
Keyword(s):  
Elastic Wave ◽  
Tungsten Carbide ◽  
Composite Structure ◽  
Elastic Waves ◽  
Wave Attenuation ◽  
Low Frequency ◽  
Filling Fraction ◽  
Carbide Composite ◽  
Elastic Metamaterials ◽  
Tungsten Carbide Composite

A numerical simulation study on elastic wave propagation of a phononic composite structure consisting of epoxy and tungsten carbide is presented for low-frequency elastic wave attenuation applications. The calculated dispersion curves of the epoxy/tungsten carbide composite show that the propagation of elastic waves is prohibited inside the periodic structure over a frequency range. To achieve a wide bandgap, the elastic composite structure can be optimized by changing its dimensions and arrangement, including size, number, and rotation angle of square inclusions. The simulation results show that increasing the number of inclusions and the filling fraction of the unit cell significantly broaden the phononic bandgap compared to other geometric tunings. Additionally, a nonmonotonic relationship between the bandwidth and filling fraction of the composite was found, and this relationship results from spacing among inclusions and inclusion sizes causing different effects on Bragg scatterings and localized resonances of elastic waves. Moreover, the calculated transmission spectra of the epoxy/tungsten carbide composite structure verify its low-frequency bandgap behavior.

A CALIBRATED MODEL SEISMIC SYSTEM

Geophysics ◽  
1972 ◽  
Vol 37 (3) ◽  
pp. 445-455 ◽  
Author(s):  
C. N. G. Dampney ◽  
B. B. Mohanty ◽  
G. F. West
Keyword(s):  
Wave Propagation ◽  
Elastic Wave ◽  
Elastic Waves ◽  
Critical Examination ◽  
Two Dimensional ◽  
Linear Filtering ◽  
Analog Model ◽  
Basic Assumptions ◽  
Electronic Circuitry ◽  
Seismic System

Simple electronic circuitry and axially polarized ceramic transducers are employed to generate and detect elastic waves in a two‐dimensional analog model. The absence of reverberation and the basic simplicity. of construction underlie the advantages of this system. If the form of the fundamental wavelet in the model itself, as modified by the linear filtering effects of the remainder of the system, can be found, then calibration is achieved. This permits direct comparison of theoretical and experimental seismograms for a given model if its impulse response is known. A technique is developed for calibration and verified by comparing Lamb’s theoretical and experimental seismograms for elastic wave propagation over the edge of a half plate. This comparison also allows a critical examination of the basic assumptions inherent in a model seismic system.

Reverse Time Migration of Elastic Waves Using the Pseudospectral Time-Domain Method

2018 ◽  
Vol 26 (01) ◽  
pp. 1750033 ◽  
Author(s):  
Jiangang Xie ◽  
Mingwei Zhuang ◽  
Zichao Guo ◽  
Hai Liu ◽  
Qing Huo Liu
Keyword(s):  
Elastic Wave ◽  
Time Domain ◽  
Elastic Waves ◽  
Sampling Rate ◽  
Fdtd Method ◽  
Time Domain Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Domain Method

Reverse time migration (RTM), especially that for elastic waves, consumes massive computation resources which limit its wide applications in industry. We suggest to use the pseudospectral time-domain (PSTD) method in elastic wave RTM. RTM using PSTD can significantly reduce the computational requirements compared with RTM using the traditional finite difference time domain method (FDTD). In addition to the advantage of low sampling rate with high accuracy, the PSTD method also eliminates the periodicity (or wraparound) limitation caused by fast Fourier transform in the conventional pseudospectral method. To achieve accurate results, the PSTD method needs only about half the spatial sampling rate of the twelfth-order FDTD method. Thus, the PSTD method can save up to 87.5% storage memory and 90% computation time over the twelfth-order FDTD method. We implement RTM using PSTD for elastic wave equations and accelerate it by Open Multi-Processing technology. To keep the computational load balance in parallel computation, we design a new PML layout which merges the PML in both ends of an axis together. The efficiency and imaging quality of the proposed RTM is verified by imaging on 2D and 3D models.

Electromagnetic damping of elastic waves: Experimental results

1968 ◽  
Vol 5 (4) ◽  
pp. 825-829 ◽  
Author(s):  
F. E. M. Lilley ◽  
C. M. Carmichael
Keyword(s):  
Magnetic Field ◽  
Elastic Wave ◽  
Applied Magnetic Field ◽  
Elastic Waves ◽  
Applied Field ◽  
Eddy Currents ◽  
Electrical Conductor ◽  
Electromagnetic Damping ◽  
The Waves ◽  
The Magnetic Field

The passage of an elastic wave causes straining and translation in the transmitting material. If a magnetic field is applied, and the medium is an electrical conductor, some of the energy of the wave is dissipated by the flow of electrical eddy currents. Usually the amount of energy lost is very small, but it may be greatly increased if the applied field is strongly non-uniform.Laboratory experiments are described which demonstrate this effect for standing elastic waves in a metal bar. The applied magnetic field changes from almost zero to its full strength over a distance which is short compared to the length of the standing wave. The result of this strong non-uniformity is that the energy lost due to the translation of the bar in the field greatly exceeds the energy lost due to the straining of the bar in the field.The dependence of the attenuation of the waves by the magnetic field is investigated for variation in frequency of vibration, bar thickness, and field gradient.

Audible and visual representations of the signals from a seismic landmine detection system

2002 ◽  
Vol 112 (5) ◽  
pp. 2325-2325
Author(s):  
Waymond R. Scott ◽  
Gregg D. Larson ◽  
James S. Martin
Keyword(s):  
Detection System ◽  
Visual Representations ◽  
Landmine Detection

Time reversal enabled elastic wave data communications using sensor arrays

2013 ◽  
Vol 134 (5) ◽  
pp. 3980-3980 ◽  
Author(s):  
Yuanwei Jin ◽  
Yujie Ying ◽  
Deshuang Zhao
Keyword(s):  
Elastic Wave ◽  
Time Reversal ◽  
Sensor Arrays ◽  
Data Communications ◽  
Wave Data

Identification of the interface between acoustic and elastic waves from internal measurements

2020 ◽  
Vol 28 (3) ◽  
pp. 313-322
Author(s):  
Yanli Cui ◽  
Fenglong Qu
Keyword(s):  
Boundary Conditions ◽  
Elastic Wave ◽  
Uniqueness Theorem ◽  
Elastic Waves ◽  
Wave Fields ◽  
Fluid Solid Interaction ◽  
Interaction Problem ◽  
Penetrable Boundary ◽  
Interior Transmission Problem

AbstractConsider the fluid-solid interaction problem for a two-layered non-penetrable cavity. We provide a novel fundamental proof for a uniqueness theorem on the determination of the interface between acoustic and elastic waves from many internal measurements, disregarding the boundary conditions imposed on the exterior non-penetrable boundary. The proof depends on a uniform {H^{1}}-norm boundedness for the elastic wave fields and the construction of the coupled interior transmission problem related to the acoustic and elastic wave fields.

Guiding Solid Elastic Waves to Arbitrary Paths by Isotropic Materials

2013 ◽  
Vol 302 ◽  
pp. 406-409
Author(s):  
Chao Chun Xiang ◽  
Jin Hu
Keyword(s):  
Elastic Wave ◽  
Numerical Simulations ◽  
Elastic Waves ◽  
Wave Beam ◽  
Elastic Beam ◽  
P Waves ◽  
Isotropic Materials ◽  
Engineering Practices ◽  
Incident Cases

As a result of the flexibility provided by the transformation elastodynamics, the impedance-matched condition exists for both S and P waves in perpendicularly incident cases in isotropic materials, thus the isotropic elastic wave beam bender can be designed. In this paper, we explore some characteristics of this bender and show that by assembling the bender units a solid elastic beam can be guided to an arbitrary path, which will provide convenience in engineering practices. Examples are conceived and validated by numerical simulations.

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