It's neither a bird nor a plane, but a winged microchip as small as a grain of sand that can be carried by the wind as it monitors such things as pollution levels or the spread of airborne diseases.

The tiny microfliers, whose development by engineers at Northwestern University was detailed in an article published by Nature this week, are being billed as the smallest-ever human-made flying structures.

Tiny fliers that can gather information about their surroundings

The devices don't have a motor; engineers were instead inspired by the maple tree's free-falling propeller seeds — technically known as samara fruit. The engineers optimized the aerodynamics of the microfliers so that "as these structures fall through the air, the interaction between the air and those wings cause a rotational motion that creates a very stable, slow-falling velocity," said John A. Rogers, who led the development of the devices.

"That allows these structures to interact for extended periods with ambient wind that really enhances the dispersal process," said the Northwestern professor of materials science and engineering, biomedical engineering and neurological surgery.

The wind would scatter the tiny microchips, which could sense their surrounding environments and collect information. The scientists say they could potentially be used to monitor for contamination, surveil populations or even track diseases.

Their creators foresee microfliers becoming part of "large, distributed collections of miniaturized, wireless electronic devices." In other words, they could look like a swarm.

Although the size and engineering of the microfliers are unique, NPR reported on the development of similar "microdrones" in March. The concept has also found its way to the dystopian science fiction series Black Mirror.

"We think that we beat nature"

But unlike with maple seeds, the engineers needed to slow down the descent of their microfliers to give the devices more time to collect data. Team member Yonggang Huang developed a computer model that calculated the best design that would enable the microfliers to fall slowly and disperse widely.

"This is impossible with trial-and-error experiments," Huang said in a Northwestern news release.

The team also drew inspiration from children's pop-up books for the construction of such tiny devices.

The engineers first created a base and then bonded it to "a slightly stretched rubber substrate," according to the news release. When relaxed, that substrate pops up into a precise three-dimensional shape.

"We think that we beat nature," Rogers said. "At least in the narrow sense that we have been able to build structures that fall with more stable trajectories and at slower terminal velocities than equivalent seeds that you would see from plants or trees."