A Continuum Approach to the Propagation of Shear Waves in Laminated Wave Guides

1974 ◽  
Vol 41 (1) ◽  
pp. 106-110 ◽  
Author(s):  
Adnan H. Nayfeh ◽  
G. A. Gurtman
Keyword(s):  
Shear Wave ◽  
Shear Waves ◽  
Mixture Theory ◽  
Dispersion Relations ◽  
Approximate Theory ◽  
Continuum Approach ◽  
Polarized Waves ◽  
Transient Solutions ◽  
Wave Guides

We develop a continuum mixture theory to study harmonic and transient shear wave motions in laminated wave guides. Both transversely (SV) and horizontally (SH) polarized waves are considered. Dispersion relations are derived and compared with exact and other approximate theory predictions. Transient solutions for both types of waves are also investigated via the “head-of-the pulse” approximations.

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.

Attenuation and dispersion phenomena of shear waves in anelastic and elastic porous strips

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Parvez Alam ◽  
Suprava Jena ◽  
Irfan Anjum Badruddin ◽  
Tatagar Mohammad Yunus Khan ◽  
Sarfaraz Kamangar
Keyword(s):  
Shear Wave ◽  
Half Space ◽  
Special Functions ◽  
Shear Waves ◽  
Finite Thickness ◽  
Dissipation Factor ◽  
Initial Stresses ◽  
Whittaker Functions ◽  
Content Type ◽  
Attenuation And Dispersion

Purpose This paper aims to study the attenuation and dispersion phenomena of shear waves in anelastic and elastic porous strips. Numerical investigations are performed for the phase and damped velocity profiles of the wave. For numerical computation purposes, water-saturated limestone and kerosene oil saturated sandstone for the first and second porous strips, respectively. Some other peculiarities have been observed and discussed. Design/methodology/approach Dispersion and attenuation characteristic of the shear wave propagations have been studied in an inhomogeneous poro-anelastic strip of finite thickness, which is clamped between an inhomogeneous poroelastic strip of finite thickness and an elastic half-space. Both the strips are initially stressed and the half-space is self-weighted. Analytical methods are used to calculate the interior deformations of the model with the involvement of special functions. The determination of the frequency equation, which includes the Bessel’s and Whittaker functions, has been obtained using the prescribed boundary conditions. Findings Impacts of attenuation coefficient, dissipation factor, inhomogeneities, initial stresses, Biot’s gravity, porosity and thickness ratio parameters on the velocity profile of the wave have been demonstrated through the graphical visuals. These parameters are playing an important role and working as a catalyst in affecting the propagation behaviour of the wave. Originality/value Inclusion of the concept of doubly layered initially stressed inhomogeneous porous structure of elastic and anelastic medium bedded over a self-weighted half-space medium brings a novelty to the existing literature related to the study of shear wave. It may be helpful to geologists, seismologists and structural engineers in the development of theoretical and practical studies.

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.

Dispersion relations for electroelastic shear waves in a periodically layered medium

1990 ◽  
Vol 26 (11) ◽  
pp. 1092-1099 ◽  
Author(s):  
L. P. Zinchuk ◽  
A. N. Podlipenets ◽  
N. A. Shul'ga
Keyword(s):  
Layered Medium ◽  
Shear Waves ◽  
Dispersion Relations

Effect of Anisotropy on Shear Wave Velocity in Wood

2012 ◽  
Vol 535-537 ◽  
pp. 1923-1926
Author(s):  
Jian Ping Zhou ◽  
Jin Xia Liu ◽  
Wen Yang Gao ◽  
Zhi Wen Cui ◽  
Wei Guo Lv ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Radial Direction ◽  
Rotation Angle ◽  
Wood Specimen ◽  
Shear Waves ◽  
Circular Ring ◽  
The Relationship ◽  
Intrinsic Birefringence

The velocities of shear waves propagating along radial direction of birch and elmwood specimens are measured in order to study the effect of anisotropy on shear wave velocity. The relationship between the shear wave velocity and the oscillation direction is examined by rotating an ultrasonic sensor. The results indicate that the effect of anisotropy on shear wave velocity in birch and elmwood specimens is similar to Japanese magnolia specimen. When the oscillation direction of the shear wave corresponds to the certain anisotropic direction of the wood specimen, the shear wave velocity decreases sharply and the relationship between shear wave velocity and rotation angle tends to become discontinuous. The intrinsic birefringence due to the anisotropy of birch and elmwood woods is observed. Their texture anisotropies are strong. In an isotropic nylon, on the contrary, the value of shear wave velocity was similar to a circular ring. This investigation is significant meanings in architectural and civil engineering field.

scholarly journals Insights Into Traumatic Brain Injury From MRI of Harmonic Brain Motion

2019 ◽  
Vol 13 ◽  
pp. 117906951984044 ◽  
Author(s):  
Ruth J Okamoto ◽  
Anthony J Romano ◽  
Curtis L Johnson ◽  
Philip V Bayly
Keyword(s):  
Traumatic Brain Injury ◽  
Wave Propagation ◽  
Brain Injury ◽  
Shear Wave ◽  
Relative Motion ◽  
Vector Fields ◽  
Shear Waves ◽  
Mechanical Deformation ◽  
Minor Role ◽  
The Brain

Measurements of dynamic deformation of the human brain, induced by external harmonic vibration of the skull, were analyzed to illuminate the mechanics of mild traumatic brain injury (TBI). Shear wave propagation velocity vector fields were obtained to illustrate the role of the skull and stiff internal membranes in transmitting motion to the brain. Relative motion between the cerebrum and cerebellum was quantified to assess the vulnerability of connecting structures. Mechanical deformation was quantified throughout the brain to investigate spatial patterns of strain and axonal stretch. Strain magnitude was generally attenuated as shear waves propagated into interior structures of the brain; this attenuation was greater at higher frequencies. Analysis of shear wave propagation direction indicates that the stiff membranes (falx and tentorium) greatly affect brain deformation during imposed skull motion as they serve as sites for both initiation and reflection of shear waves. Relative motion between the cerebellum and cerebrum was small in comparison with the overall motion of both structures, which suggests that such relative motion might play only a minor role in TBI mechanics. Strain magnitudes and the amount of axonal stretch near the bases of sulci were similar to those in other areas of the cortex, and local strain concentrations at the gray-white matter boundary were not observed. We tentatively conclude that observed differences in neuropathological response in these areas might be due to heterogeneity in the response to mechanical deformation rather than heterogeneity of the deformation itself.

Reflection of coupled dilatational and shear waves in the generalized micropolar thermoelastic materials

2020 ◽  
Vol 26 (21-22) ◽  
pp. 1948-1955 ◽  
Author(s):  
Rengsi Lianngenga ◽  
Sanasam S Singh
Keyword(s):  
Wave Propagation ◽  
Free Surface ◽  
Boundary Conditions ◽  
Shear Wave ◽  
Shear Waves ◽  
Energy Ratios ◽  
Micropolar Thermoelasticity ◽  
Incident Waves

The problem of wave propagation in the generalized theory of micropolar thermoelasticity under the Green–Lindsay model has been investigated. We have investigated the reflected dilatational and shear waves due to incident waves at a plane-free surface of generalized micropolar thermoelastic materials. The amplitude and energy ratios corresponding to the reflected coupled dilatational and coupled shear waves are derived using boundary conditions at the free surface. These ratios are also computed numerically for a particular model. Note that there are critical angles for the incident shear wave.

THE INFLUENCE OF A CRITICAL ANGLE ON AN ORIENTATION OF RADIATION OF A SHEAR WAVE THE ANGLE BEAM PROBE

2019 ◽  
pp. 14-25
Author(s):  
V. N. Danilov
Keyword(s):  
Shear Wave ◽  
Critical Angle ◽  
Asymptotic Expression ◽  
Shear Waves ◽  
Far Field ◽  
Directivity Characteristic ◽  
The Third ◽  
Working Frequency

In a far field it is received asymptotic expression of displacement of the shear waves transmitted in the elastic environment by the angle beam probe in view of features of radiation of such waves under a angle of probe, coming nearer to the third critical. At sufficient remoteness from a critical corner this expression passes in received earlier in geometroacustical approximation. The estimations carried out for steel have shown, that for converters with nominal angles of probe 37 – 40 influence of this critical angle causes increase of an angle of registration of a maximum of the signal, observed earlier experimentally. This feature is influenced as distance up to points of registration of a shear wave, and with working frequency of the angle beam probe and its size piezoplate (width of the directivity characteristic).

Shear‐wave splitting in cross‐hole surveys: Modeling

Geophysics ◽  
1989 ◽  
Vol 54 (1) ◽  
pp. 57-65 ◽  
Author(s):  
Enru Liu ◽  
Stuart Crampin ◽  
David C. Booth
Keyword(s):  
Shear Wave ◽  
Seismic Anisotropy ◽  
Pore Space ◽  
Shear Waves ◽  
Shear Wave Splitting ◽  
Surface Layers ◽  
Near Surface ◽  
Crustal Rocks ◽  
Wave Splitting ◽  
Almost All

Shear‐wave splitting, diagnostic of some form of effective seismic anisotropy, is observed along almost all near‐vertical raypaths through the crust. The splitting is caused by propagation through distributions of stress‐aligned vertical parallel fluid‐filled cracks, microcracks, and preferentially oriented pore space that exist in most crustal rocks. Shear waves have severe interactions with the free surface and may be seriously disturbed by the surface and by near‐surface layers. In principle, cross‐hole surveys (CHSs) should be free of much of the near‐surface interference and could be used for investigating shear waves at higher frequencies and greater resolution along shorter raypaths than is possible with reflection surveys and VSPs. Synthetic seismograms are examined to estimate the effects of vertical cracks on the behavior of shear waves in CHS experiments. The azimuth of the CHS section relative to the strike of the cracks is crucial to the amount of information about seismic anisotropy that can be extracted from such surveys. Interpretation of data from only a few boreholes located at azimuths chosen from other considerations is likely to be difficult and inconclusive. Application to interpreting acoustic events generated by hydraulic pumping is likely to be more successful.

Linear‐transform techniques for processing shear‐wave anisotropy in four‐component seismic data

Geophysics ◽  
1993 ◽  
Vol 58 (2) ◽  
pp. 240-256 ◽  
Author(s):  
Xiang‐Yang Li ◽  
Stuart Crampin
Keyword(s):  
Time Series ◽  
Shear Wave ◽  
Seismic Data ◽  
Shear Waves ◽  
Shear Wave Splitting ◽  
Data Set ◽  
Reflection Data ◽  
Wave Splitting ◽  
Linear Transform ◽  
Zero Offset

Most published techniques for analyzing shear‐wave splitting tend to be computing intensive, and make assumptions, such as the orthogonality of the two split shear waves, which are not necessarily correct. We present a fast linear‐transform technique for analyzing shear‐wave splitting in four‐component (two sources/ two receivers) seismic data, which is flexible and widely applicable. We transform the four‐component data by simple linear transforms so that the complicated shear‐wave motion is linearized in a wide variety of circumstances. This allows various attributes to be measured, including the polarizations of faster split shear waves and the time delays between faster and slower split shear waves, as well as allowing the time series of the faster and slower split shear waves to be separated deterministically. In addition, with minimal assumptions, the geophone orientations can be estimated for zero‐offset verticle seismic profiles (VSPs), and the polarizations of the slower split shear waves can be measured for offset VSPs. The time series of the split shear‐waves can be separated before stack for reflection surveys. The technique has been successfully applied to a number of field VSPs and reflection data sets. Applications to a zero‐offset VSP, an offset VSP, and a reflection data set will be presented to illustrate the technique.

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