These tiny drones are powered by sound

When you blow air across the neck of a bottle, you're not just producing a pleasant tone: you're also demonstrating a phenomenon called Helmholtz resonance. This occurs when airflow passing across an opening causes air trapped inside a cavity (like a glass bottle) to oscillate back and forth. At certain frequencies, these oscillations become much stronger, producing the familiar humming sound. Now, researchers in the MicroBioRobotic Systems ( MICROBS) Lab in EPFL's School of Engineering have harnessed the physics behind this phenomenon to build hollow structures that act as miniature, sound-powered machines. The innovation has been published in Science Advances.