Overview
- A peer-reviewed paper in Science Advances reports EPFL MICROBS Lab prototypes that embed propulsion in passive cavities so devices need no motors, batteries, electronics, or gears.
- The effect uses Helmholtz resonance, where sound excites air inside a shaped cavity and forces a concentrated jet out an opening, producing directional thrust.
- Demonstrations included centimeter-scale boats steered by separate frequency-tuned cavities and ultrasonic microfliers that produced lift for a 150-microgram rocket and spun blades up to about 13,000 RPM, though microfliers rose less than 5 millimeters.
- Key limits remain: the devices rely on external speakers or ultrasonic sources for power and control, deliver only small forces so thrust-to-weight is low, and performance is sensitive to local acoustic conditions.
- The team made parts with standard 3D printing and 3D nanoprinting from plastics, polymers, and glass, and researchers say the approach could one day enable battery-free micro-robots for medical or inspection tasks if engineers overcome power, control, and scaling challenges.