Scientists Turn Sound Into a New Propulsion System for Tiny Microrobots

Scientists in Switzerland have developed a sound-powered propulsion system for microrobots, using Helmholtz resonators to convert sound into directed air jets. The system allows microrobots to steer and lift small machines, with some versions generating nearly five times their own weight in thrust and others spinning at up to 13,000 revolutions per minute. The study, published in Science Advances, highlights the potential for wireless, energy-efficient propulsion in small robots. The researchers built devices ranging from centimeters to micrometers, demonstrating that sound can be used to propel and steer microboats and flying machines. The work shows that acoustic resonators can be used for active propulsion, offering a new way to power small robots without conventional motors.

• The researchers used 3D-printed cavities, known as Helmholtz resonators, to convert sound into thrust.
• The resonators were tuned to frequencies between 200 hertz and 40 kilohertz, and their geometry and thickness played a key role in performance.
• The team demonstrated that external speakers are not always necessary, as small vibration transducers can send sound through the robot's structure itself.
• The experiments show that the system can be used to guide microboats remotely, with a mean tracking error of just 5.70 millimeters.
• The most striking demonstration was a microflier that used focused ultrasound to generate thrust, achieving a thrust-to-weight ratio of approximately 4.9.
• The microflier weighed only 150 micrograms and could climb 12 millimeters before settling at seven millimeters above its starting position.
• Another version used rapidly spinning rotor blades to generate aerodynamic thrust, spinning at up to 13,000 revolutions per minute.
• The system requires external acoustic hardware to maintain a focused sound field, limiting the robot’s operating area.
• The researchers suggest future multifrequency ultrasonic arrays could allow more independent control of resonators.
• The study highlights the potential for airborne acoustic actuation in small-scale robots, with the concept extending to flexible structures that can bend, vibrate, or change shape.
• The work is a proof-of-concept demonstration rather than a fully autonomous microrobot system.
• The study was published in Science Advances, and the researchers are Tim McMillan, a retired law enforcement executive and co-founder of The Debrief.

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