Researchers at EPFL have created ultralight flying devices that move without motors, gears, or onboard electronics. Instead of relying on traditional hardware, the tiny structures generate thrust by converting sound waves into motion.
How Sound Becomes Lift
The concept is based on Helmholtz resonance, the same acoustic principle behind the familiar tone produced when air moves across a bottle opening. The team designed hollow, 3D-printed cavities with narrow necks that respond strongly at specific frequencies. When tuned sound enters these chambers, the trapped air oscillates and produces a directional jet, creating measurable thrust.
According to the researchers, the effect works across different materials and sizes, from millimeter-scale parts to microscopic structures. The key factors are the resonator's scale and neck geometry, which shape how efficiently sound is transformed into motion.
From Boats to Microfliers
At larger scales, the team demonstrated small boats that could move forward, rotate, and follow curved paths by changing the pitch of the sound they received. Some versions used multiple resonators, each tuned to a different tone, allowing precise steering.
The most striking results came from the smallest devices. Using ultrasound, the scientists built microfliers weighing only a few hundred micrograms. One design rose upward like a miniature rocket, while another used sound-driven jets to spin small blades at high speed and generate lift.
The study, published in Science Advances, shows that acoustic energy can do more than push objects from the outside. It can also activate structures that create their own directional movement. The approach remains experimental, but it opens a path toward compact robots that may one day move, bend, or fly through carefully tuned sound fields. In the future, this could reshape how ultra-small machines are designed for robotics and aeronautics.
