Séminaire

Mardi 13 Mai 2025 à 11h00.

Controlled acoustic radiation stresses for the manipulation and characterization of soft materials

''
The propagation of acoustic waves in fluids or solids is associated with a flux of momentum that manifests itself when it is transferred to a material interface in a sustained manner. Nonlinear average stresses, known as radiation stresses, are consequently distributed over the interface and can generate a force, a torque or simultaneously both.
We are interested in this phenomenon in order to develop strategies for the contactless manipulation of highly deformable materials. For example, by controlling the propagation wavefronts of focused ultrasonic beams, we have developed ‘acoustical tweezers’ capable of trapping small objects and precisely controlling their position an orientation in free space. As with optical tweezers, this technique delivers a versatile manipulation platform, useful where conventional contact methods are too invasive, lack sensitivity or are non-local. Compared to optical stresses, acoustic stresses are several orders of magnitude stronger, and can be applied deep in soft materials, well beyond light’s penetration depth. We will discuss recent implementations of this approach with solid objects or microbubbles, which offer interesting perspectives for the local mechanical characterization of a range soft materials such as complex fluids and biological tissues, from the microscopic to the macroscopic length scales.

''