Chronic hepatitis is accompanied by progressive deposit of hepatic fibrosis, which may lead to cirrhosis. Evaluation of liver fibrosis is, thus, of great clinical interest and, up to now, has been assessed with liver biopsy. This work aims to evaluate a new noninvasive device to quantify liver fibrosis: the shear elasticity probe or fibroscan. This device is based on one-dimensional (1-D) transient elastography, a technique that uses both ultrasound (US) (5 MHz) and low-frequency (50 Hz) elastic waves, whose propagation velocity is directly related to elasticity. The intra- and interoperator reproducibility of the technique, as well as its ability to quantify liver fibrosis, were evaluated in 106 patients with chronic hepatitis C. Liver elasticity measurements were reproducible (standardized coefficient of variation: 3%), operator-independent and well correlated (partial correlation coefficient = 0.71, p /= F2) and with cirrhosis ( = F4), respectively. The Fibroscan is a noninvasive, painless, rapid and objective method to quantify liver fibrosis.

Transient elastography: a new noninvasive method for assessment of hepatic fibrosis

This article reviews acoustic microfiuidics: the use of acoustic fields, principally ultrasonics, for application in microfiuidics. Although acoustics is a classical field, its promising, and indeed perplexing, capabilities in powerfully manipulating both fluids and particles within those fluids on the microscale to nanoscale has revived interest in it. The bewildering state of the literature and ample jargon from decades of research is reorganized and presented in the context of models derived from first principles. This hopefully will make the area accessible for researchers with experience in materials science, fluid mechanics, or dynamics. The abundance of interesting phenomena arising from nonlinear interactions in ultrasound that easily appear at these small scales is considered, especially in surface acoustic wave devices that are simple to fabricate with planar lithography techniques common in microfluidics, along with the many applications in microfluidics and nanofluidics that appear through the literature.

/pdf/microscale-acoustofluidics-microfluidics-driven-via-5bet39j13p.pdf

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

Surface waves in topological states of quantum matter exhibit unique protection from backscattering induced by disorders, making them ideal carriers for both classical and quantum information. Topological matters for electrons and photons are largely limited by the range of bulk properties, and the associated performance trade-offs. In contrast, phononic metamaterials provide access to a much wider range of material properties. Here we demonstrate numerically a phononic topological metamaterial in an elastic-wave analogue of the quantum spin Hall effect. A dual-scale phononic crystal slab is used to support two effective spins for phonons over a broad bandwidth, and strong spin-orbit coupling is realized by breaking spatial mirror symmetry. By preserving the spin polarization with an external load or spatial symmetry, phononic edge states are shown to be robust against scattering from discrete defects as well as disorders in the continuum, demonstrating topological protection for phonons in both static and time-dependent regimes.

https://academicworks.cuny.edu/cgi/viewcontent.cgi?article=1016&context=qc_pubs

Topologically protected elastic waves in phononic metamaterials

The in vivo assessment of the biomechanical properties of the skeletal muscle is a complex issue because the muscle is an anisotropic, viscoelastic and dynamic medium. In this article, these mechanical properties are characterized for the brachialis muscle in vivo using a noninvasive ultrasound-based technique. This supersonic shear imaging technique combines an ultra-fast ultrasonic system and the remote generation of transient mechanical forces into tissue via the radiation force of focused ultrasonic beams. Such an ultrasonic radiation force is induced deep within the muscle by a conventional ultrasonic probe and the resulting shear waves are then imaged with the same probe (5 MHz) at an ultra-fast framerate (up to 5000 frames/s). Local tissue velocity maps are obtained with a conventional speckle tracking technique and provide a full movie of the shear wave propagation through the entire muscle. Shear wave group velocities are then estimated using a time of flight algorithm. This approach provides a complete set of quantitative and in vivo parameters describing the muscle's mechanical properties as a function of active voluntary contraction as well as passive extension of healthy volunteers. Anisotropic properties are also estimated by tilting the probe head with respects to the main muscular fibers direction. Finally, the dispersion of the shear waves is studied for these different configurations and shear modulus and shear viscosity are quantitatively assessed assuming the viscoelastic Voigt's model. (E-mail: jl.gennisson@espci.fr)

Viscoelastic and anisotropic mechanical properties of in vivo muscle tissue assessed by supersonic shear imaging.

Important tissue parameters such as elasticity can be deduced from the study of the propagation of low frequency shear waves. A new method for measuring the shear velocity in soft tissues is presented in this paper. Unlike conventional transient elastography in which the ultrasonic transducer and the low frequency vibrator are two separated parts, the new method relies on a probe that associates the vibrator and the transducer, which is built on the axis of the vibrator. This setup is easy to use. The low frequency shear wave is driven by the transducer itself that acts as a piston while it is used in pulse echo mode to acquire ultrasonic lines. The results obtained with the new method are in good agreement with those obtained with the conventional one.

Shear elasticity probe for soft tissues with 1-D transient elastography

Elastic waves in solids

Elastic Waves in Solids II

The sensor device for detecting the presence or absence of a liquid (2) at predetermined level (N) in a tank (1) comprises a transmitter transducer (51; 51'; 61), a receiver transducer (52, 52', 62), and electronic means (100) for processing the signals applied to the transmission transducer and delivered by the receiver transducer. In the vicinity of the predetermined level (N) of the tank (1), the device includes a detection plate (50; 50', 60) having at least one face (58) which comes into contact with the liquid (2) when the liquid reaches that level. The detection plate carries the transmitter transducer which is disposed for locally generating Lamb waves in the plate, and the plate also carries the receiver transducer which is disposed for detecting the presence or the absence of Lamb waves transmitted along the plate. The receiver transducer is connected to a high gain amplifier whose output is connected to the transmitter transducer so as to form an oscillating closed loop, with oscillations in the loop being interrupted when the liquid reaches the predetermined level (N).

Sensor device using lamb elastic waves for detecting the presence of a liquid at a predetermined level

It is known that the level of a liquid in a tank can be determined from the measurement of the time of flight of acoustic waves propagating in the atmosphere between the transducer and the surface of the liquid. Unfortunately, the propagation of the waves is affected by any variation (pressure. air motion, temperature) of the atmosphere. In order to reduce the effects of these disturbances, we propose to guide the acoustic waves. We report on experiments performed, in a water tank, with cylindrical tube waveguides (diameters 12-14 m). Two modes of flexion, symmetrical and antisyrmnetrical, have been excited by piezoelectric ceramic transducers (ring. bar). The echo from the reflection at the guide-water interface is easily detected.

http://ieeexplore.ieee.org/iel5/10287/32720/01535961.pdf

A Guided Acoustic Wave Liquid Level Sensor

La comprehension du principe et la definition du domaine de fonctionnement des dispositifs acousto-electroniques decrits dans l’article Dispositifs acousto-electroniques requierent une analyse de la propagation des ondes elastiques dans les solides, isotropes et anisotropes, et de leur generation par effet piezoelectrique. Ces deux points sont examines dans les deux cas principaux qui sont : les ondes planes dans un milieu de dimensions laterales grandes par rapport a celles du faisceau d’ondes elastiques (ondes de volume) ; les ondes guidees par la surface libre d’un milieu semi-infini (ondes de surface). Avant d’aborder ces deux cas, nous decrivons intuitivement les principaux types d’ondes elastiques aptes a se propager dans les solides. Les grandeurs caracteristiques des champs mecanique et electrique associes a ces ondes sont ensuite definies. Puis les relations entre ces grandeurs et les equations d’etat d’un materiau piezoelectrique ainsi que les tableaux des constantes elastiques et piezoelectriques des principaux cristaux sont presentes. La propagation des ondes de volume aboutit a la caracterisation d’un cristal par une surface des lenteurs et aussi par un coefficient de couplage electromecanique si ce cristal est piezoelectrique. Leur generation se fait a l’aide d’une plaquette piezoelectrique. Cette plaquette, comme tout transducteur piezoelectrique, se presente comme un dispositif a une entree electrique et a deux sorties elastiques (on dit aussi acoustiques) dont une seule est, en general, utilisee. La puissance acoustique qu’elle emet est naturellement fonction du coefficient de couplage electromecanique. Pour la propagation des ondes guidees, principalement des ondes de surface ( ondes de Rayleigh ), l’analyse est plus complexe que celle relative aux ondes de volume puisqu’elle impose la prise en compte de conditions aux limites mecaniques et electriques, si le cristal est piezoelectrique. La notion de permittivite de surface en simplifie l’approche. Les ondes guidees par une plaque, appelees ondes de Lamb, et par une couche, appelees ondes de Love, sont presentees bien qu’elles ne donnent lieu a des applications que dans le domaine des capteurs. La generation des ondes de Rayleigh par transducteurs a electrodes interdigitees est exposee a l’aide de la methode de la reponse impulsionnelle. Nota : La presentation des dispositifs acousto-electronique, c’est-a-dire des composants electroniques a ondes elastiques, fait donc l’objet d’un deuxieme article Dispositifs acousto-electroniques .

Eugene Dieulesaint

Papers

Elastic waves in solids

Elastic Waves in Solids II

Sensor device using lamb elastic waves for detecting the presence of a liquid at a predetermined level

A Guided Acoustic Wave Liquid Level Sensor

Propagation et génération des ondes élastiques