The selective precise remote manipulation of micrometric objects both in vivo and vitro open some outstanding perspectives e.g. in medecine for noninvasive surgery, in micro-robotics for microrobots propulsion or in microbiology for cells and microorganisms contactless manipulation, organization and mechanical properties testing. Our team has designed 2 new types of microtweezers: some holographic single beam tweezers based on spiraling interdigitated transducers enabling the precise selective manipulation and organization of microparticles and cells [A20, A25, A28, A33], and some reconfigurable tweezers based on IDTs arrays and inverse filter enabling real time adative field synthesis  [A12, A13, A14]. 

In many applications, the vision can be perturbated by the presence of droplets, snow/ice or dust on optical surfaces. After working for more than ten years on the physics of droplets displacement induced by Surface Acoustic Waves (SAWs) [A3, A7, A35, A39], our team recently funded a startup commericalizing an integrated solution (Cleardrop technology) based on ultrasonic SAWs to clean optical windows. Indeed, these "nano-earthquakes" propagating at the surface of the subtrate are adsorbed by the water droplets lying on the surface provoking their displacement through two nonlinear effects called the acoustic radiation force and acoustic streaming. Note that the droplet displacement is promoted by some low frequency (in the 100Hz range) vibrations of the drop free surface, whose origin was elucidated recently in ref [A39].

Besides experimental developments, our team has worked on nonlinear acoustics theory and in particular on the acoustic radiation force [A9, A19] and acoutic streaming [A30, A32, A34]. On acoustic streaming, our work include a study of the acoustic streaming produced by acoustical vortices [A9] and a simplified formulation of the source term for the numerical simulation of acoustic streaming [A19] with reduced computational cost. On the acoustic radiation force, our work include (i) an angular spectrum based formulation of the acoustic radiation torque  [A30], (ii) an extension to the unsteady regime [A32] of Gork'ov's formula and (iii) a unification of different formulation of the acoustic radiation forcea and torque exerted on a particle by an arbitrary incident wavefield [A34].

The presence of partially wetting microparticles at the interface between two fluids can drastically modify the mechanical properties of these interfaces and lead to some unexpected behaviors. First, we demonstrated that pushing a liquid finger inside a tube covered with particles enables the tailored synthesis of cylindrical bubbles encapsulated in a monolayer of particles (so-called “armoured bubbles”) [A11, A21], which remain stable even when extracted from the tube. Second, we revisited the Saffman-Taylor instability when particles are adsorbed by the interface between the two fluids [A18]. Finally, we demonstrated that ultra-long lasting (> 1 year) air bubbles resisting drainage, evaporation and nuclei induced bursting can be simply synthesized by replacing surfactants by microparticles and water by a hygroscopic liquid [A36].

Brutal interfacial reconfigurations of fluid interfaces such as the bursting of a soap bubble [A27] can lead to the emission of a characteristic sound. This sound caries out some information on the underlynig physics of this event. In [A27] we were able to model the popping sound emitted by a bursting bubble using the framework of aeroacoustics, and to show this acoustic emission originates mainly from the capillary stresses exerted by the liquid soap film on the air. This work constitutes a proof of concept that the acoustic signature of violent events of physical or biological origin could be used to measure the forces at play during these events.