Ultrason | EPFL Graph Search

L'ultrason est une onde mécanique et élastique, qui se propage au travers de supports fluides, solides, gazeux ou liquides. La gamme de fréquences des ultrasons se situe entre , trop élevées pour être perçues par l'oreille humaine, mais un flux d'ultrasons de très haute intensité, et focalisé, peut être perçu par le corps humain, via d'autres mécanorécepteurs. Le nom vient du fait que leur fréquence est trop élevée pour être audible pour l'oreille humaine (le son est trop aigu : la gamme de fréquences audibles par l'être humain se situe entre 20 et . Ces seuils sont cependant variables avec l'âge), de la même façon que les infrasons désignent les sons dont la fréquence est trop faible pour être perceptible par l'oreille humaine. Lorsque la fréquence est audible pour l'oreille humaine, on parle simplement de « son ». Les ultrasons sont utilisés dans l'industrie ainsi que dans le domaine médical. Domaine ultrasonore Le domaine ultrasonore, c'est-à-dire la g

Wearable Ultrasound Interface for Prosthetic Hand Manipulation

Yifan Liu, Ning Zhang

Ultrasound can non-invasively detect muscle deformations, which has great potential applications in prosthetic hand control. This research developed a miniaturized ultrasound device that could be integrated into a prosthetic hand socket. This compact system included four A-mode ultrasound transducers, a signal processing module, and a prosthetic hand control module. The size of the ultrasound system was 65 * 75 * 25 mm, weighing only 85 g. For the first time, we integrated the ultrasound system into a prosthetic hand socket to evaluate its performance in practical prosthetic hand control. We designed an experiment to perform six commonly used gestures, and the classification accuracy was 95.33% +/- 7.26% for a participant. These experimental results demonstrated the efficacy of the designed prosthetic system based on the miniaturized A-mode ultrasound device, paving the way for an effective HMI system that could be widely used in prosthetic hand control.

SPRINGER INTERNATIONAL PUBLISHING AG2022

Field-based Strategies for Solid-Liquid Separation

Thierry Chappuis

The ever increasing demand for large quantities of bio-engineered pharmaceuticals and the tendency for doses to become larger stimulate the development of more productive and reliable mammalian cell culture technologies. In this context, perfusion bioreactors appear an efficient means to achieve high volumetric productivity and high product concentration. Since large-scale implementation of perfusion is limited by the reliability and scale-up potential of the device used to achieve cell retention, the present work proposes to tackle the problem bottom-up from the fundamentals of physics in order to develop, characterize and model novel particle retention strategies able to overcome the limitations of state-of-the-art systems. The first part of the present thesis focuses on the identification of physical force fields chosen for their ability to drive particles or cells into highly localized regions of a suspension. The ability of ultrasonic, dielectrophoretic and magnetophoretic interactions to make cells levitate over a surface was identified as an innovative way of implementing a Boycott effect (similar to that occurring in inclined sedimentation channels) while maintaining the flow channel in a vertical position. Therefore, inclined settlers were chosen as a reference system and the Ponder-Nakamura-Kuroda theory describing their performance was extended to take into account ultrasonic, dielectrophoretic and magnetic effects. The second part of the work provides deep modeling insight into the mechanisms underlying mammalian cell retention in these new filter implementations. Potentials and limitations are discussed in details. In particular, coupling dielectrophoresis with the Boycott effect proved to be successful in separating polystyrene particles from their moderately electrically conductive suspending medium. However, in highly conductive media, this process was shown to be very sensitive to order-disruptive electrokinetic effects such as ac electroosmosis and electrothermal fluid flow. Heat dissipation is however not specific to dielectrophoresis. This phenomenon is also a known limitation of the ultrasonic or magnetophoretic implementations, in certain conditions. The last part focused its work on the development of magnetophoretically-enhanced sedimentation, which was proposed as a means to partly overcome the heat dissipation problem observed with dielectrophoresis in highly conductive culture media. For such a magnetic approach to work correctly with intrinsically nonmagnetic materials, a paramagnetic suspending medium has to be used. The current implementation proposes to prepare media with fair quantities of gadolinium(III) or dysprosium(III) salts dissolved in them. Using such a paramagnetic buffer, the feasibility of magnetically retaining polystyrene particles could be verified in a vertical separation channel, hence providing first demonstration of the principle. The use of paramagnetic substances in mammalian cell culture media is naturally a matter of concern. The present work addresses this question as well and highlights the feasibility of growing Chinese Hamster Ovary cells in Gd(III)- or Dy(III)-rich environments. In contrast, attempts to develop low electrically conductive culture media failed and replacement of the NaCl content by D-mannitol or glycerol demonstrated severe growth inhibition effects.

EPFL2010

Field-based Strategies for Solid-Liquid Separation

Thierry Chappuis

EPFL2010