Engineers in EPFL’s MICROBS Lab have 3D-printed hollow cavities that convert sound waves into thrust. The cavities power miniature boats and ultralight drones that have no onboard actuators or electronics. One microflier weighs just 150 micrograms.
Sound waves at specific frequencies make the air inside these cavities oscillate and force it out as a concentrated jet. The incoming air is more diffuse, so the imbalance creates propulsion. “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,” says lab head Selman Sakar. “Our work shows the feasibility of transforming a simple, cleverly designed mechanical piece into robotic matter.”
Researchers built centimeter-scale boats equipped with up to three cavities, each tuned to a different audible frequency and positioned to push in a particular direction. Changing a speaker’s frequency selectively activates the cavities to move the boats, steer them around obstacles, and program them for autonomous navigation.
Using a 3D nanoprinting technique, the team built microfliers with three microscopic cavities integrated into their polymer structures. These fly on ultrasonic frequencies people can’t hear. One 150-microgram design generates direct upward thrust like a rocket. Another combines the cavities with tiny blades that spin at speeds of up to 13,000 revolutions per minute for helicopter-like aerodynamic lift.
The sound-powered cavities can be made from common 3D-printing plastics, rubber-like polymers, and glass. “Our concept is compatible with even further miniaturization, enabling advanced designs that push the boundaries of robotics and aeronautics,” says first author and MICROBS Lab PhD student Junsun Hwang. Sakar said several sound-responsive structures could be built into a single flexible device, each reacting to a different frequency. “This would allow specific parts of the device to move, bend or vibrate, potentially leading to aerodynamic robotic devices that can change shape in response to sound,” he says.
Source: actu.epfl.ch
