The team designed miniature boats with three cavities tuned to different audible frequencies, enabling them to steer the boat in a particular direction by changing the frequency of the sound waves from a speaker. Their 3D-printed microfliers also had three integrated cavities tuned to ultrasonic frequencies, capable of generating upward thrust or aerodynamic lift, similar to a helicopter.

Science Advances, 2026. DOI: 10.1126/sciadv.aef5620.

Cooling without electricity

Standard refrigerators and AC systems operate using the Carnot cycle, relying on electricity-driven compressors to transfer heat via a refrigerant gas from a high-pressure chamber to a lower-pressure chamber. But it’s not an ideal approach, and Albert Einstein and Leo Szilard, among others, have tried to come up with alternatives; the patented Einstein-Szilard refrigerator was an energy-efficient absorption system with no moving parts. The latest breakthrough is a heat-driven, elastocaloric system capable of leveraging waste heat and solar energy for cooling, according to a paper published in the journal Nature Energy.

Elastocaloric cooling systems exploit shape-memory alloys, which heat up when a mechanical load is applied and cool down when that load is released. Such systems still rely on actuators driven by electricity to apply that force. The authors of the Nature Energy paper found a way around that obstacle by coupling two ultra-thin nickel-titanium films. The first is designed to shrink when it heats up, converting thermal energy into mechanical work with no need for an electric motor. That work is then transferred to the second film and produces reversible changes in the crystal structure, generating cold.

This makes it possible to drive solid-state cooling using waste heat and solar energy. Thus far, it is just a demonstration of the feasibility of the approach; the next step is to connect multiple films to increase cooling capacity. If the approach can be scaled up, such systems would be ideal for cooling computer processors, using their own waste heat as a driver, or for cooling sensitive car electronics, drawing on waste heat from the drivetrain.

Nature Energy, 2026. DOI: 10.1038/s41560-026-02122-6.