Swiss scholars bet on sound waves to power next gen of small drones

Governments around the world have increased spending on military and defence, prompting the defence industry to develop increasingly sophisticated technologies for use on the battlefield. Drones have cemented their position as a key tool of modern warfare over the past decade, with unmanned systems playing a prominent role in many recent conflicts involving sophisticated military powers.

Researchers at the Swiss Federal Institute of Technology in Lausanne (EPFL) have now taken drone technology a step further by developing tiny vehicles that can use sound waves to generate propulsion through the air and on water, as Swiss media outlets reported.

Researchers achieved this by equipping the vehicles with hollow structures called cavities that convert sound into propulsion. The amount of thrust generated varies depending on the frequency of the sound waves emitted.

The innovation, developed by the MicroBioRobotic Systems Laboratory (Microbs) at EPFL’s Faculty of Engineering Sciences and Technology, relies on circular or bell-shaped hollow structures known as “cavities”.

When sound waves cause the air inside these cavities to vibrate, the oscillating air is expelled as a concentrated jet, while the incoming airflow is more diffuse.

This imbalance generates enough thrust to propel tiny vehicles, according to an EPFL press release detailing research published in the journal Science Advances.

The researchers exploited a phenomenon known as Helmholtz resonance. The effect was first studied by German scientist Hermann von Helmholtz and can be observed by gently blowing across the neck of an empty bottle.

As air is blown through the opening, the air trapped inside the container begins to oscillate, producing a characteristic note.

Microbs researchers used the same principle to build model boats approximately one centimetre long. The boats were equipped with up to three cavities, each tuned to a different frequency and positioned to propel the vessel in a specific direction.

By adjusting the frequency of sound waves emitted by a loudspeaker, the researchers could selectively activate individual cavities to move the boats, navigate around obstacles and even perform autonomous navigation.

Similar experiments have also been conducted using flying microdrones.

Sound-controlled robotic devices

Because the devices rely on hollow cavities rather than conventional motors, gears or magnetic components, they can be made extremely small and lightweight.

In the future, researchers say several sound-sensitive structures could be incorporated into a single flexible device, with each structure responding to a different sound frequency.

“This would allow specific parts of the device to move, bend or vibrate, which could lead to the creation of aerodynamic robotic devices capable of changing shape in response to sound,” said Selman Sakar, director of the EPFL laboratory.

The technology could potentially enable highly miniaturised robotic systems that can be controlled remotely through sound, while eliminating some of the bulky mechanical components traditionally required for propulsion and movement.

Sound waves have also been used in other research to levitate objects in the air, demonstrating the broader potential of acoustic forces for manipulating and controlling small objects.

By Nazrin Sadigova