At the EPFL, micro-drones have been developed that can be moved without a motor or battery.No motors, no batteries, no electronics on board, just small cavities that convert sound waves into thrust: this is the surprising propulsion technology for drones, developed at the Laboratory for Micro-Biorobotic Systems (Microbs) at the Swiss Federal Institute of Technology Lausanne (EPFL). It was recently presented in the journal Science Advances.
The principle is simple: the movement is generated by sounds. “By choosing the frequency, we can control the movements of a micro-object,” explains the director of the laboratory, Selman Sakar, to Radio and Television of Italian-speaking Switzerland (RSI).
The applications of acoustic microrobotics are diverse. Sakar sees the most promising in the medical field: “You could build a tiny structure, such as a drug carrier to be swallowed or injected into the body, and then control it with sound waves.”
The Drone in the Lungs
So far, the use of sound-controlled microrobots has been investigated primarily in liquid environments such as blood vessels. EPFL’s robots work in the air and open up interesting research prospects, for example in the lungs. Although its use in patients is still a long way off, there are already collaborations with the University Hospitals of Geneva and Lausanne.
To move the drones using sound, the researchers used the so-called Helmholtz resonance. Behind this name is the phenomenon known to everyone, which was first investigated by the German scientist Hermann von Helmholtz: When you blow gently through the neck of an empty bottle, not only is a sound produced, but the air trapped in the bottle is made to vibrate.
Selman Sakar’s team has recreated this principle – using so-called resonators. They look like small ampoules. “Their shape determines the tone at which the air inside begins to vibrate,” explains the expert. “When that happens, the air is pushed out of the throat and the structure moves in the opposite direction, a bit like a rocket.”
Ultrasound as an Energy Source
To demonstrate the principle, Sakar’s team has built two types of microaircraft. The first combines three resonators on an ultra-light structure and weighs about 150 micrograms, or 0.15 milligrams. The downward-facing openings create the rays that lift it. The second weighs 184 micrograms and uses the resonators to spin a rotor with small blades that can reach 13,000 revolutions per minute.
The energy is supplied by an external device that generates an ultrasound of 40,000 hertz, beyond the human hearing threshold. The robot is thus freed from components that are difficult to miniaturize, starting with the battery. However, the energy supply remains indispensable: it is transferred from the system that generates the acoustic field to the aircraft.
The researchers observed the take-off and hovering in the air under laboratory conditions. But for these objects to be controlled along complex routes, further developments are needed. The system tested so far operates at a single frequency and still offers limited maneuverability.
RSI, Prima Ora, 10/21/2026, 6:00 p.m.; noes
News – Curated by Amanda Scott, Alias Group Creative
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Micro-drones fly through the body thanks to ultrasound
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