EPFL researchers have demonstrated tiny robots that use sound to propel themselves, rather than relying on onboard batteries or motors. Their hollow resonators turn tuned sound into directional air jets: audible tones steer miniature boats, while ultrasound powers separate microflier designs. These are laboratory demonstrations, not consumer-ready robots.
How can sound make a tiny robot move?
The devices use hollow cavities designed to behave as Helmholtz resonators—the same basic acoustic effect that produces a tone when someone blows across a bottle opening. At a cavity’s resonant frequency, the air inside oscillates strongly. In the researchers’ design, that motion forms a concentrated jet of air leaving the cavity, while air entering it is more diffuse. The imbalance creates thrust.
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This differs from using sound waves simply to push or levitate an object. Here, sound activates the resonator, and the resonator produces the device’s own propulsive force. As MICROBS Lab head Selman Sakar put it: “Instead of pushing devices around with sound waves, we have created acoustic resonators that are tuned to harness sound at specific frequencies to generate directional thrust and controlled motion.”
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The resonators can be made from materials including common 3D-printing plastics, rubber-like polymers and glass. For the microfliers, the team used 3D nanoprinting to integrate microscopic cavities into polymer structures.
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What did the researchers demonstrate?
The experiments covered boats and two distinct kinds of microflier. They did not combine every reported feature in one vehicle.
| Demonstration | Sound and actuation | Reported result |
|---|---|---|
| Miniature boats | Audible frequencies selectively activate cavities aimed in different directions. | Movement, steering around obstacles and programmed autonomous navigation; no boat speed or other measurement is specified in the cited announcement. |
| Direct-thrust microflier | Ultrasound activates resonators that generate upward thrust. | One design weighed 150 micrograms, according to EPFL’s 2026 announcement. |
| Blade-driven microflier | Ultrasound activates resonators coupled to tiny blades. | A separate design reached blade speeds of up to 13,000 revolutions per minute, with lift described as stable and helicopter-like. |
The 150-microgram figure belongs to the direct-upward-thrust design; the 13,000-rpm maximum belongs to the blade-driven one. They are separate demonstrations, not specifications for a single craft. EPFL says the boats used audible sound, while the microfliers operated at ultrasonic frequencies, which humans cannot hear.
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How were the boats steered?
The centimeter-scale boats had as many as three cavities. Each cavity was tuned to a different audible frequency and oriented to produce thrust in a particular direction. Changing the frequency played through a speaker selectively activated the corresponding cavity, letting the researchers change the boat’s motion and steer it around obstacles. EPFL also reports programmed autonomous navigation.
This is a way to control motion without putting a conventional motor and its power source aboard the miniature vehicle: the sound comes from outside, and the resonators convert it into directed thrust. The cited announcement does not state the sound intensity required or how the boats perform outside the reported experimental setting.
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What do the results establish—and what remains unknown?
The work establishes that tuned acoustic resonators can generate directional propulsion in small-scale prototypes, including audible-frequency control for boats and ultrasound-driven microflier demonstrations. It does not establish practical readiness for consumer or field use.
The cited EPFL announcement does not provide measured flight duration, travel range, payload capacity, manufacturing yield or cost. It also does not report a safety analysis or define operating-environment limits. Without those details, the prototypes should not be described as ready for medical, environmental or industrial missions.
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The work is reported in Junsun Hwang, Q. Angéloz, A. S. Murugan, H. Lissek and M. S. Sakar, “Acoustic resonators as wireless actuators in air for small-scale robots,” Science Advances 12, issue 33 (2026), DOI 10.1126/sciadv.aef5620. EPFL’s announcement and the lab’s publication listing identify the paper. EPFL’s announcement was published August 14, 2026; the MICROBS Lab publications page lists the work.
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Could this approach lead to smaller or more capable robots?
EPFL describes flexible devices with multiple independently sound-responsive structures as a possible future direction. First author and MICROBS Lab PhD student Junsun Hwang said: “Our concept is compatible with even further miniaturization, enabling advanced designs that push the boundaries of robotics and aeronautics.” That is the researchers’ outlook, not evidence that further miniaturization or a particular application has already been achieved.
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