EPFL Researchers 3D-Print Sound-Powered Drones That Hover on Ultrasonic Frequencies

How the sound-powered engine works

Most drones rely on spinning propellers driven by electric motors. A team at EPFL's Microbiorobotic Systems Laboratory took a different route: they built acoustic resonators that harvest energy from sound waves themselves.

The resonators are 3D-printed cavities tuned to specific frequencies. When hit with ultrasonic sound, the air inside oscillates violently and escapes through a nozzle as a focused jet. That jet produces thrust without any moving parts in the engine itself.

Two drone designs proved the concept

The researchers built two microfliers. The first uses three downward-facing resonators and lifts off like a rocket. The second arranges three blade-mounted resonators around a central rotor. When driven at the right frequency, the blades spin at over 12,000 RPM and hold the craft in mid-air.

A third application, a small boat with three tuned resonators, demonstrated directional control. One rear resonator provided thrust while two side resonators steered.

Why this matters for 3D printing

The resonators are complex geometries that would be expensive or impossible to produce by conventional machining. 3D printing made rapid iteration of cavity shapes possible, which was essential for finding shapes that resonated efficiently.

Altitude is still limited. The microfliers hover less than 5 mm off the surface. The boat weighs almost nothing. Scaling to carry a payload will require larger resonators or arrays, which introduces material and resonance challenges.

Still, the proof of concept is solid. Silent, solid-state propulsion could change how small drones are designed, especially for indoor or covert applications where noise gives away position.