Thomas Gallot - Academia.edu (original) (raw)
Papers by Thomas Gallot
AAS/Division for Planetary Sciences Meeting Abstracts #50, Oct 1, 2018
2013 5th IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), 2013
Seismic interferometry (SI) is a technique used to estimate the Green's function (GF) between two... more Seismic interferometry (SI) is a technique used to estimate the Green's function (GF) between two receivers, as if there were a source at one of the receiver locations. The GF obtained in this way, the interferometric GF (IGF), is estimated here by crosscorrelating the signals from two receivers for many sources and averaging these crosscorrelations over sources. However, in many applications, the conditions needed to recover the exact GF are not met and thus the estimated IGF is inaccurate. For such cases, we improve the IGF by summing lower-rank approximations of the crosscorrelations obtained via the Singular Value Decomposition (SVD), instead of averaging the original crosscorrelations. SVD allows us to enhance low-rank, coherent signals; these are the signals needed to reconstruct the GF. We apply this method to a field dataset where seismic signals from active sources are transformed to simulate passive seismic recordings. In this data set we find that filtering with SVD allows for IGF recovery in cases where standard SI does not.
ABSTRACT To get an insight into the processes underlying dynamic friction that plays an important... more ABSTRACT To get an insight into the processes underlying dynamic friction that plays an important role in seismic sources, we developed a sliding dynamic experiment coupled to ultrafast ultrasonic imaging. This experimental setup permits to observe simultaneously the frictional interface and the waves emitted in the bulk during slipping. We use soft solid sliders made of hydro-organic gel of polymer (PVA), in contact with either glass or sandpaper. In these soft solids, ultrasonic speckle interferometry imaging allows to follow quantitatively the wave field emitted by dynamic friction. Moreover, this imaging method is non-intrusive and well resolved in space and time. It is thus possible to characterise the small scale processes that occurs at the interface during global large scale sliding. We investigate the friction in two different dynamic regimes. In the case of friction on a rough interface (sandpaper), we observe a global behaviour of slow slip events. These slow slip events are correlated with bursts of depinning events occurring at small scale at the interface. In the case of friction on a smooth interface (glass, with an interlayer of sand), ultrasonic imaging reveals that the sliding regime is different and that dynamic rupture propagation prevails. The rupture fronts are propagating at supershear velocity, emitting an elastic Mach wave that is very clearly observed. In this dynamic rupture regime, we add some barriers and present an experimental observation of the effect of barriers on a propagating rupture front.
Proceedings of Meetings on Acoustics, 2012
Multi-wave high resolution imaging methods have been developped in medical imaging. The feasibili... more Multi-wave high resolution imaging methods have been developped in medical imaging. The feasibility of similar methods for geophysical applications has been studied. An interesting configuration is the subsurface imaging in a km scale where a compressional wavefield can be measured between 2 boreholes. A perturbation of this wavefield by shear waves created from the surface could creates a non-linear interaction. In this context, preliminary laboratory scale experiments have been performed in rocks (berea sandstones). The interaction between shear waves and compressional waves has been studied. The shear wave is generated by a shear transducer in the tens of kHz and used as a "localized pump". The localization of this pump is essential for a possible imaging application. The probe is a compressional pulse in the hundreds of kHz range. In this configuration, the delay of the ultrasounds pulse arrival, the time of flight modulation by nonlinear interaction is studied. Fast and slow nonlinear dynamics can be observed in this configuration. This experimental work is in progress.
Frontiers in Physics, 2021
Shear wave elastography (SWE) relies on the generation and tracking of coherent shear waves to im... more 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 wavefie...
Le travail de recherche mene lors de cette these propose d'ameliorer la comprehension et l... more Le travail de recherche mene lors de cette these propose d'ameliorer la comprehension et l'utilisation de champs d'ondes complexes issus de la propagation en milieux reverberants. Dans de tels milieux, la reverberation donne lieu a une repartition spatiale de l'intensite liee a la position de la source. Ce phenomene, appele retro-diffusion coherente, est etudie dans des cavites simples afin de disposer de modeles analytiques permettant de predire les resultats experimentaux de surintensite a la source. Les symetries spatiales jouent aussi un role dans la repartition de l'intensite, role qui est etudie selon la meme approche. La reverberation, aussi complexe soit-elle, contient des informations qui peuvent permettre d'imager le milieu de propagation. Ce principe est utilise pour l'elastographie, l'imagerie de l'elasticite des tissus mous. La problematique et les methodes d'elastographie sont alors presentees puis appliquees a la determination d...
The Journal of the Acoustical Society of America, 2019
Periodic structures exhibit frequency bands where destructive interferences prohibit wave propaga... more Periodic structures exhibit frequency bands where destructive interferences prohibit wave propagation. Such behavior can be useful to mitigate vibrations, in particular when structure lightening is important. Band gap properties can be deduced from Bloch's theory approach, Plane Wave Expansion or Multiple Scattering methods. These methods require a full description of the unit cell geometry and its mechanical properties. In this work we focus on an ideal unit cell geometry to highlight the role of a contrast parameter in the band gap opening process. We consider flexural waves in beams and demonstrate analytically that the contrast parameter fully controls the first Bragg band gap. Numerical simulation and experiments on a beam demonstrator proves that the gap bandwidth is independent of the section geometry: only the flexural rigidity is involved. We propose a semi-analytic model for the central frequency gap that depends on the mass distribution. The established algebraic expressions for the band gap bandwidth and central frequency successfully matches the results in the practical case and can be used to design flexural wave cut-band filters. Finally, symmetry considerations explains the experimental observation of a second band gap, also suitable for vibration mitigation, due to coupling of flexural and compressional waves. Periodic structures exhibit frequency bands where destructive interferences prohibit wave propagation. Such behavior can be useful to mitigate vibrations, in particular when structure lightening is important. Band gap properties can be deduced from Bloch's theory approach, Plane Wave Expansion or Multiple Scattering methods. These methods require a full description of the unit cell geometry and its mechanical properties. In this work we focus on an ideal unit cell geometry to highlight the role of a contrast parameter in the band gap opening process. We consider flexural waves in beams and demonstrate analytically that the contrast parameter fully controls the first Bragg band gap. Numerical simulation and experiments on a beam demonstrator proves that the gap bandwidth is independent of the section geometry: only the flexural rigidity is involved. We propose a semi-analytic model for the central frequency gap that depends on the mass distribution. The established algebraic expressions for the band gap ba...
The Journal of the Acoustical Society of America, 2019
Asteroids and small bodies of the Solar System can be considered as agglomerates of irregular bou... more Asteroids and small bodies of the Solar System can be considered as agglomerates of irregular boulders, therefore cataloged as granular media. Ejections of particles and dust, resulting in a cometary-type plume, can result from impacts on their surface generating waves within these bodies and potentially causing modifications in the rocks distribution. Since no asteroid seismicity data are available, we propose a laboratory scale experiment of impact-induced seismic waves in granular media. Our study focuses on the influence of static compression mimicking pressure variations induced by self-gravity on the asteroid interior. A cubic box (50 x50 x50 cm) filled with different natural and artificial granular matter is impacted with low velocity projectiles (40 to 200 m/s). An array of accelerometers records the resulting wavefield while the box is compressed to understand its dependence with the monitored internal pressure. This study is relevant to understand how asteroids reacts to kinetic energy, as is will be tested at real scale during the Asteroid Impact and Deflection Assessment mission (2022). Asteroids and small bodies of the Solar System can be considered as agglomerates of irregular boulders, therefore cataloged as granular media. Ejections of particles and dust, resulting in a cometary-type plume, can result from impacts on their surface generating waves within these bodies and potentially causing modifications in the rocks distribution. Since no asteroid seismicity data are available, we propose a laboratory scale experiment of impact-induced seismic waves in granular media. Our study focuses on the influence of static compression mimicking pressure variations induced by self-gravity on the asteroid interior. A cubic box (50 x50 x50 cm) filled with different natural and artificial granular matter is impacted with low velocity projectiles (40 to 200 m/s). An array of accelerometers records the resulting wavefield while the box is compressed to understand its dependence with the monitored internal pressure. This study is relevant to understand how asteroids reacts to kinetic energy, as is wi...
Journal of Sound and Vibration, 2019
This work aims to provide better physical understanding of Bragg band gap effects in continuously... more This work aims to provide better physical understanding of Bragg band gap effects in continuously periodic corrugated beams for flexural waves. The main outcome is the establishement of original algebraic formulas for the band gap width and central frequency. It is shown that the band gap width and central frequency only depend on a thickness contrast parameter. To do so, a so called two-skins geometry is proposed to approximate the usual solid beam cross section, in order to greatly simplify analytical derivations following the Plane Wave Expansion (PWE) method applied to Euler-Bernoulli theory. Theoretical predictions in the two-skins geometry successfully match the results in the practical case of a solid geometry obtained from both experiments on a beam demonstrator and numerical simulations done by classical PWE (1D Euler and Timoshenko theories) or finite element (3D elasticity theory) methods. The complete set of results is benchmarked in details so that the geometrical approximation is validated and the algebraic formulas are usable as design tools of such notch filters. Moreover, flexural and longitudinal motion coupling due to the non-symetrical thickness profile of the demonstrators leads to an additional band gap that is experimentally identified. A numerical study illustrates the resulting double filtering effect. Potential applications of the background provided by this work can concern Noise,Vibration and Harshness (NVH) engineering, for which metamaterials can be very relevant especially when structure lightening is required.
Journal of Applied Physics, 2015
The nonlinear elastic response of rocks is known to be caused by the rocks' microstructure, parti... more The nonlinear elastic response of rocks is known to be caused by the rocks' microstructure, particularly cracks and fluids. This paper presents a method for characterizing the nonlinearity of rocks in a laboratory scale experiment with a unique configuration. This configuration has been designed to open up the possibility of using the nonlinear characterization of rocks as an imaging tool in the field. In our experiment, we study the nonlinear interaction of two traveling waves: a low-amplitude 500 kHz P-wave probe and a high-amplitude 50 kHz S-wave pump in a room-dry 15 Â 15 Â 3 cm slab of Berea sandstone. Changes in the arrival time of the P-wave probe as it passes through the perturbation created by the traveling S-wave pump were recorded. Waveforms were time gated to simulate a semi-infinite medium. The shear wave phase relative to the P-wave probe signal was varied with resultant changes in the P-wave probe arrival time of up to 100 ns, corresponding to a change in elastic properties of 0.2%. In order to estimate the strain in our sample, we also measured the particle velocity at the sample surface to scale a finite difference linear elastic simulation to estimate the complex strain field in the sample, on the order of 10 À6 , induced by the S-wave pump. We derived a fourth order elastic model to relate the changes in elasticity to the pump strain components. We recover quadratic and cubic nonlinear parameters:b ¼ À872 and d ¼ À1:1 Â 10 10 , respectively, at room-temperature and when particle motions of the pump and probe waves are aligned. Temperature fluctuations are correlated to changes in the recovered values ofb andd, and we find that the nonlinear parameter changes when the particle motions are orthogonal. No evidence of slow dynamics was seen in our measurements. The same experimental configuration, when applied to Lucite and aluminum, produced no measurable nonlinear effects. In summary, a method of selectively determining the local nonlinear characteristics of rock quantitatively has been demonstrated using traveling sound waves. V
SEG Technical Program Expanded Abstracts 2014, 2014
As more and more resources are extracted from unconventional reservoirs, an understanding of the ... more As more and more resources are extracted from unconventional reservoirs, an understanding of the microstructure of reservoir rocks is of increasing importance. Many conventional techniques struggle to sense variations in the micro-structure and pore-fluids of rock samples. The nonlinear coupling of two elastic waves is known to be sensitive to these parameters, however, and so is a natural candidate to improve our understanding of these structures. Here, we develop an experimental technique to sense the nonlinear interaction of two propagating waves: a strong S-wave pump that changes (minutely) the elastic properties of the sample and a weaker P-wave probe that senses those changes. By measuring the delay in the P-wave probe traveltime induced by the S-wave pump, we show that this signal is significant in a Berea sandstone sample and absent in Aluminum and Plexiglass samples. The polarization of the S-wave (particle motion aligned or perpendicular to the P-wave probe) has a large impact on the measured response; this is evidence that the signal we measure is sensitive to the microstructure of the rock. We show that the method is sensitive to fluids by imaging the variations in two specific nonlinear parameters, caused by the introduction of fluid into a Berea sandstone sample.
Review of Scientific Instruments, 2013
We describe a technique coupling standard rheology and ultrasonic imaging with promising applicat... more We describe a technique coupling standard rheology and ultrasonic imaging with promising applications to characterization of soft materials under shear. Plane wave imaging using an ultrafast scanner allows to follow the local dynamics of fluids sheared between two concentric cylinders with frame rates as high as 10,000 images per second, while simultaneously monitoring the shear rate, shear stress, and viscosity as a function of time. The capacities of this "rheo-ultrasound" instrument are illustrated on two examples: (i) the classical case of the Taylor-Couette instability in a simple viscous fluid and (ii) the unstable shear-banded flow of a non-Newtonian wormlike micellar solution.
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
Ultrafast ultrasonic speckle interferometry, an imaging technique derived from elastography, is u... more Ultrafast ultrasonic speckle interferometry, an imaging technique derived from elastography, is used to follow the dynamic of the interface failure in a friction experiment. Experimental results that characterize two slipping regimes are presented: a slow slip regime associated with depinning events at the interface and a supershear rupture regime associated with the emission of Mach waves fronts. These results are discussed in the light of geophysical observations made at the scale of the Earth on the slip dynamics in active faults.
2011 IEEE International Ultrasonics Symposium, 2011
ABSTRACT In previous works the authors developed a method for extracting the shear elasticity of ... more ABSTRACT In previous works the authors developed a method for extracting the shear elasticity of soft tissues from a complex reverberated elastic field using spatiotemporal correlations interpreted in the frame of the time-reversal symmetry: Time Reversal Elastography (TRE). By measuring the shear wavelength from the focal width as the wave converges the shear elasticity can be obtained. The feasibility of TRE as an imaging technique has already been shown, in vivo, in bi-layer mediums (e.g. belly muscle - liver). In this work the authors take a step forward and demonstrate its feasibility as a quantitative imaging technique by detecting a 10 mm diameter inclusion embedded in a softer medium. As a result the inclusion is clearly detected using TRE despite the low contrast between background and inclusion. A general quantitative agreement within 10% in the shear wave speed estimation was found between TRE and independent transient elastography measurements.
AAS/Division for Planetary Sciences Meeting Abstracts #50, Oct 1, 2018
2013 5th IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), 2013
Seismic interferometry (SI) is a technique used to estimate the Green's function (GF) between two... more Seismic interferometry (SI) is a technique used to estimate the Green's function (GF) between two receivers, as if there were a source at one of the receiver locations. The GF obtained in this way, the interferometric GF (IGF), is estimated here by crosscorrelating the signals from two receivers for many sources and averaging these crosscorrelations over sources. However, in many applications, the conditions needed to recover the exact GF are not met and thus the estimated IGF is inaccurate. For such cases, we improve the IGF by summing lower-rank approximations of the crosscorrelations obtained via the Singular Value Decomposition (SVD), instead of averaging the original crosscorrelations. SVD allows us to enhance low-rank, coherent signals; these are the signals needed to reconstruct the GF. We apply this method to a field dataset where seismic signals from active sources are transformed to simulate passive seismic recordings. In this data set we find that filtering with SVD allows for IGF recovery in cases where standard SI does not.
ABSTRACT To get an insight into the processes underlying dynamic friction that plays an important... more ABSTRACT To get an insight into the processes underlying dynamic friction that plays an important role in seismic sources, we developed a sliding dynamic experiment coupled to ultrafast ultrasonic imaging. This experimental setup permits to observe simultaneously the frictional interface and the waves emitted in the bulk during slipping. We use soft solid sliders made of hydro-organic gel of polymer (PVA), in contact with either glass or sandpaper. In these soft solids, ultrasonic speckle interferometry imaging allows to follow quantitatively the wave field emitted by dynamic friction. Moreover, this imaging method is non-intrusive and well resolved in space and time. It is thus possible to characterise the small scale processes that occurs at the interface during global large scale sliding. We investigate the friction in two different dynamic regimes. In the case of friction on a rough interface (sandpaper), we observe a global behaviour of slow slip events. These slow slip events are correlated with bursts of depinning events occurring at small scale at the interface. In the case of friction on a smooth interface (glass, with an interlayer of sand), ultrasonic imaging reveals that the sliding regime is different and that dynamic rupture propagation prevails. The rupture fronts are propagating at supershear velocity, emitting an elastic Mach wave that is very clearly observed. In this dynamic rupture regime, we add some barriers and present an experimental observation of the effect of barriers on a propagating rupture front.
Proceedings of Meetings on Acoustics, 2012
Multi-wave high resolution imaging methods have been developped in medical imaging. The feasibili... more Multi-wave high resolution imaging methods have been developped in medical imaging. The feasibility of similar methods for geophysical applications has been studied. An interesting configuration is the subsurface imaging in a km scale where a compressional wavefield can be measured between 2 boreholes. A perturbation of this wavefield by shear waves created from the surface could creates a non-linear interaction. In this context, preliminary laboratory scale experiments have been performed in rocks (berea sandstones). The interaction between shear waves and compressional waves has been studied. The shear wave is generated by a shear transducer in the tens of kHz and used as a "localized pump". The localization of this pump is essential for a possible imaging application. The probe is a compressional pulse in the hundreds of kHz range. In this configuration, the delay of the ultrasounds pulse arrival, the time of flight modulation by nonlinear interaction is studied. Fast and slow nonlinear dynamics can be observed in this configuration. This experimental work is in progress.
Frontiers in Physics, 2021
Shear wave elastography (SWE) relies on the generation and tracking of coherent shear waves to im... more 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 wavefie...
Le travail de recherche mene lors de cette these propose d'ameliorer la comprehension et l... more Le travail de recherche mene lors de cette these propose d'ameliorer la comprehension et l'utilisation de champs d'ondes complexes issus de la propagation en milieux reverberants. Dans de tels milieux, la reverberation donne lieu a une repartition spatiale de l'intensite liee a la position de la source. Ce phenomene, appele retro-diffusion coherente, est etudie dans des cavites simples afin de disposer de modeles analytiques permettant de predire les resultats experimentaux de surintensite a la source. Les symetries spatiales jouent aussi un role dans la repartition de l'intensite, role qui est etudie selon la meme approche. La reverberation, aussi complexe soit-elle, contient des informations qui peuvent permettre d'imager le milieu de propagation. Ce principe est utilise pour l'elastographie, l'imagerie de l'elasticite des tissus mous. La problematique et les methodes d'elastographie sont alors presentees puis appliquees a la determination d...
The Journal of the Acoustical Society of America, 2019
Periodic structures exhibit frequency bands where destructive interferences prohibit wave propaga... more Periodic structures exhibit frequency bands where destructive interferences prohibit wave propagation. Such behavior can be useful to mitigate vibrations, in particular when structure lightening is important. Band gap properties can be deduced from Bloch's theory approach, Plane Wave Expansion or Multiple Scattering methods. These methods require a full description of the unit cell geometry and its mechanical properties. In this work we focus on an ideal unit cell geometry to highlight the role of a contrast parameter in the band gap opening process. We consider flexural waves in beams and demonstrate analytically that the contrast parameter fully controls the first Bragg band gap. Numerical simulation and experiments on a beam demonstrator proves that the gap bandwidth is independent of the section geometry: only the flexural rigidity is involved. We propose a semi-analytic model for the central frequency gap that depends on the mass distribution. The established algebraic expressions for the band gap bandwidth and central frequency successfully matches the results in the practical case and can be used to design flexural wave cut-band filters. Finally, symmetry considerations explains the experimental observation of a second band gap, also suitable for vibration mitigation, due to coupling of flexural and compressional waves. Periodic structures exhibit frequency bands where destructive interferences prohibit wave propagation. Such behavior can be useful to mitigate vibrations, in particular when structure lightening is important. Band gap properties can be deduced from Bloch's theory approach, Plane Wave Expansion or Multiple Scattering methods. These methods require a full description of the unit cell geometry and its mechanical properties. In this work we focus on an ideal unit cell geometry to highlight the role of a contrast parameter in the band gap opening process. We consider flexural waves in beams and demonstrate analytically that the contrast parameter fully controls the first Bragg band gap. Numerical simulation and experiments on a beam demonstrator proves that the gap bandwidth is independent of the section geometry: only the flexural rigidity is involved. We propose a semi-analytic model for the central frequency gap that depends on the mass distribution. The established algebraic expressions for the band gap ba...
The Journal of the Acoustical Society of America, 2019
Asteroids and small bodies of the Solar System can be considered as agglomerates of irregular bou... more Asteroids and small bodies of the Solar System can be considered as agglomerates of irregular boulders, therefore cataloged as granular media. Ejections of particles and dust, resulting in a cometary-type plume, can result from impacts on their surface generating waves within these bodies and potentially causing modifications in the rocks distribution. Since no asteroid seismicity data are available, we propose a laboratory scale experiment of impact-induced seismic waves in granular media. Our study focuses on the influence of static compression mimicking pressure variations induced by self-gravity on the asteroid interior. A cubic box (50 x50 x50 cm) filled with different natural and artificial granular matter is impacted with low velocity projectiles (40 to 200 m/s). An array of accelerometers records the resulting wavefield while the box is compressed to understand its dependence with the monitored internal pressure. This study is relevant to understand how asteroids reacts to kinetic energy, as is will be tested at real scale during the Asteroid Impact and Deflection Assessment mission (2022). Asteroids and small bodies of the Solar System can be considered as agglomerates of irregular boulders, therefore cataloged as granular media. Ejections of particles and dust, resulting in a cometary-type plume, can result from impacts on their surface generating waves within these bodies and potentially causing modifications in the rocks distribution. Since no asteroid seismicity data are available, we propose a laboratory scale experiment of impact-induced seismic waves in granular media. Our study focuses on the influence of static compression mimicking pressure variations induced by self-gravity on the asteroid interior. A cubic box (50 x50 x50 cm) filled with different natural and artificial granular matter is impacted with low velocity projectiles (40 to 200 m/s). An array of accelerometers records the resulting wavefield while the box is compressed to understand its dependence with the monitored internal pressure. This study is relevant to understand how asteroids reacts to kinetic energy, as is wi...
Journal of Sound and Vibration, 2019
This work aims to provide better physical understanding of Bragg band gap effects in continuously... more This work aims to provide better physical understanding of Bragg band gap effects in continuously periodic corrugated beams for flexural waves. The main outcome is the establishement of original algebraic formulas for the band gap width and central frequency. It is shown that the band gap width and central frequency only depend on a thickness contrast parameter. To do so, a so called two-skins geometry is proposed to approximate the usual solid beam cross section, in order to greatly simplify analytical derivations following the Plane Wave Expansion (PWE) method applied to Euler-Bernoulli theory. Theoretical predictions in the two-skins geometry successfully match the results in the practical case of a solid geometry obtained from both experiments on a beam demonstrator and numerical simulations done by classical PWE (1D Euler and Timoshenko theories) or finite element (3D elasticity theory) methods. The complete set of results is benchmarked in details so that the geometrical approximation is validated and the algebraic formulas are usable as design tools of such notch filters. Moreover, flexural and longitudinal motion coupling due to the non-symetrical thickness profile of the demonstrators leads to an additional band gap that is experimentally identified. A numerical study illustrates the resulting double filtering effect. Potential applications of the background provided by this work can concern Noise,Vibration and Harshness (NVH) engineering, for which metamaterials can be very relevant especially when structure lightening is required.
Journal of Applied Physics, 2015
The nonlinear elastic response of rocks is known to be caused by the rocks' microstructure, parti... more The nonlinear elastic response of rocks is known to be caused by the rocks' microstructure, particularly cracks and fluids. This paper presents a method for characterizing the nonlinearity of rocks in a laboratory scale experiment with a unique configuration. This configuration has been designed to open up the possibility of using the nonlinear characterization of rocks as an imaging tool in the field. In our experiment, we study the nonlinear interaction of two traveling waves: a low-amplitude 500 kHz P-wave probe and a high-amplitude 50 kHz S-wave pump in a room-dry 15 Â 15 Â 3 cm slab of Berea sandstone. Changes in the arrival time of the P-wave probe as it passes through the perturbation created by the traveling S-wave pump were recorded. Waveforms were time gated to simulate a semi-infinite medium. The shear wave phase relative to the P-wave probe signal was varied with resultant changes in the P-wave probe arrival time of up to 100 ns, corresponding to a change in elastic properties of 0.2%. In order to estimate the strain in our sample, we also measured the particle velocity at the sample surface to scale a finite difference linear elastic simulation to estimate the complex strain field in the sample, on the order of 10 À6 , induced by the S-wave pump. We derived a fourth order elastic model to relate the changes in elasticity to the pump strain components. We recover quadratic and cubic nonlinear parameters:b ¼ À872 and d ¼ À1:1 Â 10 10 , respectively, at room-temperature and when particle motions of the pump and probe waves are aligned. Temperature fluctuations are correlated to changes in the recovered values ofb andd, and we find that the nonlinear parameter changes when the particle motions are orthogonal. No evidence of slow dynamics was seen in our measurements. The same experimental configuration, when applied to Lucite and aluminum, produced no measurable nonlinear effects. In summary, a method of selectively determining the local nonlinear characteristics of rock quantitatively has been demonstrated using traveling sound waves. V
SEG Technical Program Expanded Abstracts 2014, 2014
As more and more resources are extracted from unconventional reservoirs, an understanding of the ... more As more and more resources are extracted from unconventional reservoirs, an understanding of the microstructure of reservoir rocks is of increasing importance. Many conventional techniques struggle to sense variations in the micro-structure and pore-fluids of rock samples. The nonlinear coupling of two elastic waves is known to be sensitive to these parameters, however, and so is a natural candidate to improve our understanding of these structures. Here, we develop an experimental technique to sense the nonlinear interaction of two propagating waves: a strong S-wave pump that changes (minutely) the elastic properties of the sample and a weaker P-wave probe that senses those changes. By measuring the delay in the P-wave probe traveltime induced by the S-wave pump, we show that this signal is significant in a Berea sandstone sample and absent in Aluminum and Plexiglass samples. The polarization of the S-wave (particle motion aligned or perpendicular to the P-wave probe) has a large impact on the measured response; this is evidence that the signal we measure is sensitive to the microstructure of the rock. We show that the method is sensitive to fluids by imaging the variations in two specific nonlinear parameters, caused by the introduction of fluid into a Berea sandstone sample.
Review of Scientific Instruments, 2013
We describe a technique coupling standard rheology and ultrasonic imaging with promising applicat... more We describe a technique coupling standard rheology and ultrasonic imaging with promising applications to characterization of soft materials under shear. Plane wave imaging using an ultrafast scanner allows to follow the local dynamics of fluids sheared between two concentric cylinders with frame rates as high as 10,000 images per second, while simultaneously monitoring the shear rate, shear stress, and viscosity as a function of time. The capacities of this "rheo-ultrasound" instrument are illustrated on two examples: (i) the classical case of the Taylor-Couette instability in a simple viscous fluid and (ii) the unstable shear-banded flow of a non-Newtonian wormlike micellar solution.
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
Ultrafast ultrasonic speckle interferometry, an imaging technique derived from elastography, is u... more Ultrafast ultrasonic speckle interferometry, an imaging technique derived from elastography, is used to follow the dynamic of the interface failure in a friction experiment. Experimental results that characterize two slipping regimes are presented: a slow slip regime associated with depinning events at the interface and a supershear rupture regime associated with the emission of Mach waves fronts. These results are discussed in the light of geophysical observations made at the scale of the Earth on the slip dynamics in active faults.
2011 IEEE International Ultrasonics Symposium, 2011
ABSTRACT In previous works the authors developed a method for extracting the shear elasticity of ... more ABSTRACT In previous works the authors developed a method for extracting the shear elasticity of soft tissues from a complex reverberated elastic field using spatiotemporal correlations interpreted in the frame of the time-reversal symmetry: Time Reversal Elastography (TRE). By measuring the shear wavelength from the focal width as the wave converges the shear elasticity can be obtained. The feasibility of TRE as an imaging technique has already been shown, in vivo, in bi-layer mediums (e.g. belly muscle - liver). In this work the authors take a step forward and demonstrate its feasibility as a quantitative imaging technique by detecting a 10 mm diameter inclusion embedded in a softer medium. As a result the inclusion is clearly detected using TRE despite the low contrast between background and inclusion. A general quantitative agreement within 10% in the shear wave speed estimation was found between TRE and independent transient elastography measurements.