EPFL · Wetenschap

Tiny Drones Powered by Sound Waves

EPFL engineers have developed acoustic cavities that convert sound waves into directional thrust, enabling small robots and ultralight aerial vehicles to move without onboard actuators or electronics. This innovation harnesses the physics of Helmholtz resonance to create miniature, sound-powered machines.

Researchers at EPFL's MicroBioRobotic Systems (MICROBS) Lab have created hollow structures that act as miniature, sound-powered machines by converting sound waves into directional thrust. Unlike previous methods that used sound to levitate objects, these devices generate their own propulsive force. The innovation, published in Science Advances, involves fabricating hollow, round, or bell-shaped cavities. When sound waves excite the air within these cavities, the oscillating air is expelled as a concentrated jet, creating an imbalance that generates thrust.

These sound-powered cavities can be constructed from various materials, including 3D-printing plastics, polymers, and glass. At the centimeter scale, the team built miniature boats with multiple cavities, each tuned to a different audible frequency. By altering the sound frequency from a speaker, researchers could control the boats' movement, steering, and even program autonomous navigation.

Using 3D nanoprinting, the team also created 'microfliers'—ultralight flying vehicles with microscopic cavities integrated into their polymer structures. These microfliers operate at ultrasonic frequencies. One design, weighing only 150 micrograms, used its cavities for direct upward thrust, while another combined cavities with tiny blades to achieve stable, helicopter-like lift.

The reliance on hollow cavities rather than motors or gears allows for extreme miniaturization and lightweight designs, compatible with various 3D-printing methods. Future applications could involve integrating multiple sound-responsive structures into a single device, enabling specific parts to move or bend in response to different sound frequencies, potentially leading to shape-changing aerodynamic robots.

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