EPFL's 3D-Printed Drones Hover Using Only Sound

Engineers at EPFL have built flying machines that contain no motors, no gears, and no batteries. These microfliers hover using nothing but 3D-printed cavities tuned to ultrasonic sound waves.

The team in EPFL's MicroBioRobotic Systems Lab published their findings in Science Advances this month. Their approach starts with a familiar phenomenon: blow across a bottle neck and the air inside resonates. The researchers turned that same physics into a propulsion system.

How the cavities work

Each microflier carries hollow, bell-shaped cavities machined into its structure. When a speaker emits sound at the cavity's resonant frequency, the air inside oscillates and escapes as a concentrated jet. The incoming air is more diffuse, so the net effect is thrust. No spinning blades, no magnetic coils, no combustion.

The cavities can be 3D-printed from standard plastics, rubber-like polymers, or glass. That makes the whole vehicle cheap to produce and trivial to scale down.

Two designs, two flight modes

The researchers built centimeter-scale boats first. Each boat carried up to three cavities, each tuned to a different audible frequency. By shifting the speaker tone, they could activate individual cavities to steer around obstacles or run pre-programmed routes.

The flying versions pushed the concept further. One 150-microgram flier used three downward-facing cavities as a rocket engine, lifting straight up. A second design attached cavities to tiny blades. The blades spun at 13,000 rpm, giving the craft stable helicopter-like lift. Both were powered at ultrasonic frequencies, so they operate in near silence.

Why this matters

Most micro-drones today rely on tiny brushless motors that wear out, need precise assembly, and draw power from limited batteries. The EPFL system replaces all of that with a passive structure. The vehicle becomes a mechanical transducer, simpler and potentially longer-lived than anything with moving parts.

The researchers note that multiple cavities on a single flexible body could respond to different frequencies, letting a device change shape or bend in flight. That points toward morphing aerial robots that adapt without motors or wiring.

The work is still at laboratory scale. Altitude is currently under five millimeters for the fliers, and the boats weigh almost nothing. But the principle is proven. Scaling up to carry a useful payload is the next hurdle, and if the team clears it, acoustic propulsion could find its way into surveillance, inspection, and search-and-rescue hardware where silence and simplicity matter.