EPFL Microfliers Fly Using Nothing But 3D-Printed Resonators and Sound

Engineers at EPFL's MicroBioRobotic Systems Lab have built flying drones with no motors, no batteries, and no moving parts. These microfliers rely entirely on 3D-printed acoustic cavities tuned to specific sound frequencies. When exposed to the right pitch, the hollow structures force air out in a concentrated jet, generating enough thrust to lift a 150-microgram vehicle or spin a rotor at 13,000 revolutions per minute.

The trick is Helmholtz resonance, the same physics that produces a tone when you blow across a bottle opening. The EPFL team designed round and bell-shaped cavities that amplify that effect into directional thrust. By positioning multiple cavities at different angles and tuning each to a different frequency, they can steer the device without any onboard electronics.

At the centimeter scale, the researchers built miniature boats with up to three cavities. Changing the speaker frequency activated different cavities, letting the boat pivot around obstacles and follow programmed routes autonomously. At the microscale, they used a 3D nanoprinting technique to embed the cavities directly into polymer airframes. One microflier used its jets like a rocket for vertical thrust. Another combined cavities with tiny blades for stable helicopter-like lift.

The implications are more than a laboratory curiosity. Because these devices contain no motors, gears, or magnetic components, they can be made extremely small and lightweight from common 3D-printing plastics, rubber-like polymers, or even glass. Junsun Hwang, the PhD student who led the work, says the design is compatible with further miniaturization. Lab head Selman Sakar sees a future where a single flexible device contains multiple sound-responsive structures that move, bend, or vibrate independently, creating robots that change shape in response to audio cues.

The research is published in Science Advances. The team's microfliers and sound-powered boats are shown in open-access images credited to EPFL/MICROBS under a CC-BY-SA 4.0 license. There is no commercial product here yet, but the underlying principle is clear: if you can print it and tune it to a frequency, you can make it move without ever installing a motor.