Flying microchips the size of a sand grain used to monitor air quality

Developed by engineers at Northwestern University, the chips do not have a motor or engine and instead catch flight on the wind. In a similar way to maple tree seeds, the chips use the wind to spin like a helicopter through the air toward the ground.

By studying maple trees and other types of wind-dispersed seeds, the engineers optimised the microflier’s aerodynamics to ensure that it falls at a slow velocity in a controlled manner when dropped at high velocity.

This behaviour stabilises its flight to ensure dispersal over a broad area and increasing the amount of time it interacts with the air, making it ideal for monitoring air pollution and airborne disease.

The engineers believe they are the smallest-ever human-made flying structures and they have been designed so that they can be packed with ultra-miniaturised technology, including sensors, power sources, antennas for wireless communication and embedded memory to store data.

“Our goal was to add winged flight to small-scale electronic systems, with the idea that these capabilities would allow us to distribute highly functional, miniaturised electronic devices to sense the environment for contamination monitoring, population surveillance or disease tracking,” said Northwestern’s John A. Rogers, who led the device’s development.

“We were able to do that using ideas inspired by the biological world. Over the course of billions of years, nature has designed seeds with very sophisticated aerodynamics. We borrowed those design concepts, adapted them and applied them to electronic circuit platforms.”

The team designed and built many different types of microfliers, including one with three wings, optimised to similar shapes and angles as the wings on a tristellateia seed.

To pinpoint the most ideal structure, computational modelling of how the air flows around the device was employed. Based on this modelling, a wide variety of structures in different shapes and sizes were then built and tested in the lab.

“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,” Rogers said.

“We also were able to build these helicopter flying structures at sizes much smaller than those found in nature. That’s important, because device miniaturisation represents the dominating development trajectory in the electronics industry, where sensors, radios, batteries and other components can be constructed in ever smaller dimensions.”

The microfliers are comprised of two parts: millimetre-sized electronic functional components and their wings. As the microflier falls through the air, its wings interact with the air to create a slow, stable rotational motion. The weight of the electronics is distributed low in the centre of the microflier to prevent it from losing control and chaotically tumbling to the ground.

The team has already looked into examples that included sensors; a power source that can harvest ambient energy; memory storage, and an antenna that can wirelessly transfer data to a smart phone, tablet or computer.

One device was outfitted with all of these elements to detect particulates in the air. In another example, they incorporated pH sensors that could be used to monitor water quality and photodetectors to measure sun exposure at different wavelengths.