Developed at Northwestern University in Illinois, the flying microchips – known as microfliers – are about the size of a grain of sand. Without motors or engines, they fly by catching the wind like a sycamore seed, spinning through the air towards 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 in a slow and controlled way when dropped from height. This behaviour stabilises its flight, ensuring dispersal over a broad area and increasing the amount of time it is in the air, making it ideal for monitoring air pollution and airborne disease.
The microfliers could 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.”
To design the microfliers, the Northwestern team studied the aerodynamics of a number of plants’ seeds, drawing most direct inspiration from the tristellateia plant, a flowering vine with star-shaped seeds. Tristellateia seeds have bladed wings that catch the wind to fall with a slow, rotating spin.
After design, the team first fabricated precursors to flying structures in flat, planar geometries. They then bonded those precursors onto a slightly stretched rubber substrate. When the stretched substrate was relaxed, a controlled buckling process occurred that caused the wings to pop up into precisely defined three-dimensional forms.
The microfliers include two parts – millimetre-sized electronic components and their wings. 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.
In demonstrated examples, Rogers’ team included sensors, a power source that can harvest ambient energy, memory storage and an antenna that can wirelessly transmit data.
Large numbers of devices could be dropped from planes or buildings, dispersing to monitor environmental remediation efforts after a chemical spill, for example, or tracking air pollution levels at various altitudes.
“Most monitoring technologies involve bulk instrumentation designed to collect data locally at a small number of locations across a spatial area of interest,” Rogers said. “We envision a large multiplicity of miniaturised sensors that can be distributed at a high spatial density over large areas, to form a wireless network.”
Addressing potential concerns about electronic litter, Rogers said his team used transient electronics – developed in his own laboratory – that naturally degrade and disappear in ground water over time.
The research was published in Nature.
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