Sketches of a hammer-impact, spiked-base, shear-wave source

1983 ◽  
Author(s):  
W.P. Hasbrouck
Keyword(s):  
Shear Wave ◽  
Base Shear ◽  
Wave Source ◽  
Hammer Impact

scholarly journals Lorentz force induced shear waves for magnetic resonance elastography applications

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Guillaume Flé ◽  
Guillaume Gilbert ◽  
Pol Grasland-Mongrain ◽  
Guy Cloutier
Keyword(s):  
Magnetic Resonance ◽  
Shear Wave ◽  
Lorentz Force ◽  
Wave Attenuation ◽  
Shear Waves ◽  
Estimation Method ◽  
Biological Tissues ◽  
Magnetic Resonance Elastography ◽  
Motion Generation ◽  
Wave Source

AbstractQuantitative mechanical properties of biological tissues can be mapped using the shear wave elastography technique. This technology has demonstrated a great potential in various organs but shows a limit due to wave attenuation in biological tissues. An option to overcome the inherent loss in shear wave magnitude along the propagation pathway may be to stimulate tissues closer to regions of interest using alternative motion generation techniques. The present study investigated the feasibility of generating shear waves by applying a Lorentz force directly to tissue mimicking samples for magnetic resonance elastography applications. This was done by combining an electrical current with the strong magnetic field of a clinical MRI scanner. The Local Frequency Estimation method was used to assess the real value of the shear modulus of tested phantoms from Lorentz force induced motion. Finite elements modeling of reported experiments showed a consistent behavior but featured wavelengths larger than measured ones. Results suggest the feasibility of a magnetic resonance elastography technique based on the Lorentz force to produce an shear wave source.

scholarly journals Shear Wave Elastography Based on Noise Correlation and Time Reversal

2021 ◽  
Vol 9 ◽  
Author(s):  
Javier Brum ◽  
Nicolás Benech ◽  
Thomas Gallot ◽  
Carlos Negreira
Keyword(s):  
Shear Wave ◽  
Time Reversal ◽  
Shear Waves ◽  
Shear Wave Elastography ◽  
Noise Correlation ◽  
Elasticity Imaging ◽  
Physiological Noise ◽  
Wave Source ◽  
Imaging Device ◽  
Shear Elasticity

Shear wave elastography (SWE) relies on the generation and tracking of coherent shear waves to image the tissue's shear elasticity. Recent technological developments have allowed SWE to be implemented in commercial ultrasound and magnetic resonance imaging systems, quickly becoming a new imaging modality in medicine and biology. However, coherent shear wave tracking sets a limitation to SWE because it either requires ultrafast frame rates (of up to 20 kHz), or alternatively, a phase-lock synchronization between shear wave-source and imaging device. Moreover, there are many applications where coherent shear wave tracking is not possible because scattered waves from tissue’s inhomogeneities, waves coming from muscular activity, heart beating or external vibrations interfere with the coherent shear wave. To overcome these limitations, several authors developed an alternative approach to extract the shear elasticity of tissues from a complex elastic wavefield. To control the wavefield, this approach relies on the analogy between time reversal and seismic noise cross-correlation. By cross-correlating the elastic field at different positions, which can be interpreted as a time reversal experiment performed in the computer, shear waves are virtually focused on any point of the imaging plane. Then, different independent methods can be used to image the shear elasticity, for example, tracking the coherent shear wave as it focuses, measuring the focus size or simply evaluating the amplitude at the focusing point. The main advantage of this approach is its compatibility with low imaging rates modalities, which has led to innovative developments and new challenges in the field of multi-modality elastography. The goal of this short review is to cover the major developments in wave-physics involving shear elasticity imaging using a complex elastic wavefield and its latest applications including slow imaging rate modalities and passive shear elasticity imaging based on physiological noise correlation.

Successful Use of a VSP Shear Wave Source

2005 ◽  
Author(s):  
M.A. Ackers ◽  
V.T. Nagassar ◽  
D.J. Klauza ◽  
T. Hilton
Keyword(s):  
Shear Wave ◽  
Wave Source

The propagation of elastic waves in a certain class of inhomogeneous anisotropic materials. I. The refraction of a horizontally polarized shear wave source

1992 ◽  
Vol 436 (1898) ◽  
pp. 449-478 ◽  
Keyword(s):  
Shear Wave ◽  
Isotropic Material ◽  
Displacement Vector ◽  
Transversely Isotropic ◽  
Constitutive Law ◽  
Coarse Grained ◽  
Wave Source ◽  
Uniform Asymptotic Expansion ◽  
Wide Range ◽  
Steel Welds

This paper is the first in a series of articles describing the refraction and propagation of infinitesimal disturbances in a 'coarse grained’ inhomogeneous anisotropic material which is fused to an isotropic substrate. Here, the basic constitutive law for the material is motivated by applications to the non-destructive evaluation of austenitic steel welds, although it is clear that the phenomena described and the mathematical analysis used is also of interest in geophysics, the study of composite materials and several other areas of continuum mechanics. This work is concerned with the refraction of a horizontally polarized shear wave source at the fusion interface between a homogeneous isotropic material and transversely isotropic material. The latter is inhomogeneous by virtue of the fact that the zonal axis or axis of symmetry of the crystals varies in direction with the distance from the interface. The mathematical boundary-value problem is solved exactly, and, in the highfrequency limit, a uniform asymptotic expansion for the displacement vector is found. It is shown that in this limit, and for a wide range of material constants, the refracted energy which penetrates certain regions of the ‘weld material’ is totally internally reflected. This conclusion is highly significant in the design of inspection procedures for structurally important welds.

Air Gun near the Sea Floor as Shear-wave Source?

2015 ◽  
Author(s):  
G.G. Drijkoningen ◽  
D. Dieulangard ◽  
E. Kjos ◽  
M. Holicki
Keyword(s):  
Shear Wave ◽  
Wave Source ◽  
Sea Floor ◽  
Air Gun

Micro-elastography on spheroids using a magnetic pulse as a shear wave source and the impact of cavitation on their mechanical properties

2021 ◽  
Vol 150 (4) ◽  
pp. A31-A31
Author(s):  
Gabrielle Laloy-Borgna ◽  
Thomas Lambin ◽  
Gabrielle Lescoat ◽  
jacqueline ngo ◽  
Magali Perier ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Shear Wave ◽  
Magnetic Pulse ◽  
Wave Source ◽  
The Impact

Near-surface velocities and attenuation at two boreholes near Anza, California, from logging data

1990 ◽  
Vol 80 (4) ◽  
pp. 807-831 ◽  
Author(s):  
Jon B. Fletcher ◽  
Tom Fumal ◽  
Hsi-Ping Liu ◽  
Linda C. Carroll
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Spectral Ratio ◽  
Body Waves ◽  
P Wave ◽  
Wave Source ◽  
Near Surface ◽  
Wave Velocities ◽  
Rock Structure ◽  
Over The Top

Abstract To investigate near-surface site effects in granite rock, we drilled 300-m-deep boreholes at two sites which are collocated with stations from the digital array at Anza, California. The first borehole was sited at station KNW (Keenwild fire station), which is located along a ridge line about 8.7 km east of the San Jacinto Fault zone. Station PFO (Piñon Flat Observatory), chosen for the second site, is another 6 km further to the east of station KNW and is located on a gently sloping hillside. We logged each borehole for P- and S-wave velocities, as well as for crack density and orientation. P waves were generated by striking a plate with a hammer at the surface. A tool consisting of weighted anvils driven by compressed air against end plates along a 3.5-m beam was used to generate shear waves. Signals were recorded downhole with a three-component sensor package at 2.5-m intervals from the surface to 50 m depth, and at 5-m intervals from 50 m depth to the bottom of the hole. Velocities were determined by differencing the measured arrival times of first arrivals or peaks over each interval in depth. Travel times were computed for the first breaks at shallow depths, however, below about 100 m depth, times were computed for the first peaks rather than for first breaks since the first arrival was no longer clearly distinguishable. The KNW site yielded a shear velocity of 1.9 km/sec by only 30 m in depth and reached close to 2.6 km/sec at the bottom of the hole. P-wave velocities at KNW were also high at 5.4 km/sec starting at 120 m depth. The PFO site had similar but slightly higher shear-wave velocities. The bottom-hole shear-wave velocity reached 3.0 km/sec, and the P-wave velocity was 5.4 km/sec. Shear-wave attenuation was computed using both the pulse rise time and spectral ratio methods. At station KNW, attenuation was significant only in an interval between 17.5 and approximately 40 m in depth. Over the top 50 m, attenuation corresponding to a Q of about 8 was obtained. A total T* of 0.004 sec was measured for this interval. Pulse rise times also increased rapidly in this zone. The spectral ratio data for station PFO yields two peaks in attenuation above 50 m. Similar to the attenuation found for station KNW, the peak in attenuation corresponds to a Q of about 11, averaged over the top 50 m. Spectra of the seismic pulses produced by the hammer give good signal between 20 to 80 Hz. Significant motion perpendicular to the polarizations of the first shear-wave arrival was recorded within a few meters of the surface. Apparently, the rock structure is sufficiently complicated that body waves are being converted (SH to SV at oblique incidence) very close to the surface. The presence of these elliptical particle motions within a mere few m of the pure shear-wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not, by itself, a good method for detecting shearwave splitting within the upper few tens of kilometers of the earth's crust. Crack densities and orientations were determined from televiewer records. These records showed cracks with a preferred direction at station KNW and of a greater density than at station PFO. At station PFO, crack densities were smaller and more diffuse in orientation.

scholarly journals Borehole seismoelectric logging using a shear-wave source: Possible application to CO 2 disposal?

2015 ◽  
Vol 33 ◽  
pp. 89-102 ◽  
Author(s):  
Fabio I. Zyserman ◽  
Laurence Jouniaux ◽  
Sheldon Warden ◽  
Stéphane Garambois
Keyword(s):  
Shear Wave ◽  
Wave Source
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