Microfluidic techniques developed since the year 2000 have now matured to provide a unique tool to produce large amounts of microbubbles that are not only finely tuned in size, but that can also be embedded in tiny microfabricated structures.In the present proposal, we plan to take advantage of these novel microfabrication techniques to develop two innovative acoustic applications. These applications, which were out of reach without current techniques, are based on the use of microbubbles with a huge acoustic resonance. The project is structured in two parts that only differ in the way bubbles are embedded in microfluidic environments:1) Arrays of bubbles: Acoustic LaserThis first part is the development of an acoustic laser, based on microbubbles trapped in a microfluidic circuit. To obtain the conditions for an acoustic laser, arrays of microbubbles will be designed so that they bubbles pulsate in phase, reemitting their energy coherently. The applications are novel systems for high ultrasonic emission power, or meta-materials that store vibration energy.2) Mobile “armoured” bubbles: swimming micro-robots remotely powered by ultrasoundThe second part is the conception of ultrasonically activated microswimming devices, with microbubbles embedded within freely moving objects. Their application is to behave as carriers, such as drug carriers, activated at a distance, or to be active tracers that enhance mixing. Microswimmers are mechanical analogues to RFID devices (where electromagnetic vibration is converted into current), here sound is converted into motion at small scales.Both parts include the same three complementary steps: step 1 is the 3D microfabrication of the geometry where bubbles are embedded, step 2 is their ultrasonic activation, and then step 3 is the optimisation of their resonance by a study of individual resonators.