Dispersed microfliers, the size of a grain of sand, could monitor air pollution, airborne disease, and environmental contamination.
Electronic microchips now have a new capability: flight, thanks to Northwestern University engineers.
The new flying microchip (or “microflier”) is about the size of a grain of sand and lacks a motor or engine. Instead, it takes to the air like a maple tree’s propeller seed and spins through the air like a helicopter toward the ground.
Engineers optimized the microflier’s aerodynamics by studying maple trees and other types of wind-dispersed seeds to ensure that it falls at a slow and controlled speed when dropped from a high altitude. This behavior stabilizes its flight, ensures dispersion over a large area, and extends the time it spends in the air, making it ideal for monitoring air pollution and disease.
These microfliers can be packed with ultra-miniaturized technology, such as sensors, power sources, antennas for wireless communication, and embedded memory to store data, as they are the smallest human-made flying structures ever.
The study is featured on the cover of Nature on September 23, 2021.
John A. Rogers is a pioneer in bioelectronics and the director of the Querrey Simpson Institute for Bioelectronics. He is the Louis Simpson and Kimberly Querrey Professor of Materials Science and Engineering, Biomedical Engineering, and Neurological Surgery in the McCormick School of Engineering and Feinberg School of Medicine. The study’s theoretical work was led by Yonggang Huang, the Jan and Marcia Achenbach Professor of Mechanical Engineering at McCormick.
‘We think that we beat nature’
The whirling propeller seed of a maple leaf has been seen by most people spinning through the air and gently landing on the sidewalk. This is just one example of how nature has devised ingenious, sophisticated strategies to help plants survive. Otherwise sedentary plants and trees can propagate their species over vast distances and populate large areas by ensuring that seeds are widely dispersed.
The Northwestern team studied the aerodynamics of a variety of plant seeds to create the microfliers, with the tristellateia plant, a flowering vine with star-shaped seeds, providing the most direct inspiration. Seeds of Tristellateia have bladed wings that catch the wind and fall in a slow, rotating spin.
Rogers and his team created a variety of microfliers, including one with three wings that were optimized to resemble the shapes and angles of tristellateia seed wings. Huang led full-scale computational modeling of how air flows around the device to mimic the tristellateia seed’s slow, controlled rotation in order to pinpoint the most ideal structure.
In collaboration with Leonardo Chamorro, an associate professor of mechanical engineering at the University of Illinois at Urbana-Champaign, Rogers’ group then built and tested structures in the lab using advanced methods for imaging and quantifying flow patterns.
The resulting structures can be made in a wide range of sizes and shapes, with some possessing properties that rival those of nature.
“We think that we beat nature. 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. We also were able to build these helicopter flying structures at sizes much smaller than those found in nature. That’s important because device miniaturization represents the dominating development trajectory in the electronics industry, where sensors, radios, batteries and other components can be constructed in ever smaller dimensions.”John A. Rogers