Engineering professor John Rogers and his team at Northwestern drew on inspiration from nature to create the microchips, which are the size of a grain of sand. The chips do not have engine-driven propellers. Instead, their wings catch the wind like maple tree or dandelion seeds; the most direct inspiration came from the star-shaped seeds of the tristellateia plant, a flowering vine.
The research appeared on the cover of the September 23 issue of Nature.
“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, miniaturized electronic devices to sense the environment for contamination monitoring, population surveillance or disease tracking,” Rogers said in a September news release.
“Over the course of billions of years, nature has designed seeds with very sophisticated aerodynamics,” Rogers said. “We borrowed those design concepts, adapted them and applied them to electronic circuit platforms.”
Mechanical engineering professor Yonggang Huang led the theoretical work, using full-scale computational modeling of how the air flows around the device to mimic the tristellateia seed’s slow, controlled rotation.
“The computational modeling allows a rapid design optimization of the fly structures that yields the smallest terminal velocity,” Huang said. “This is impossible with trial-and-error experiments.”
The microfliers include millimeter-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, with the electronics’ weight distributed low in the center of the microflier to ensure stability. In addition, the researchers were able to include sensors, a power source that can harvest ambient energy, memory storage and an antenna that can wirelessly transfer data to a smartphone, tablet or computer.
The researchers developed a fabrication process inspired by children’s pop-up books. First, they created precursors to flying structures in flat, planar geometries. They then bonded the precursors onto a slightly stretched rubber substrate. When the stretched substrate relaxed, a controlled buckling process caused the wings to “pop up” into precisely defined three-dimensional forms.
“This strategy of building 3D structures from 2D precursors is powerful because all existing semiconductor devices are built in planar layouts,” Rogers said. “We can thus exploit the most advanced materials and manufacturing methods used by the consumer electronics industry to make completely standard, flat, chip-like designs. Then, we just transform them into 3D flying shapes by principles that are similar to those of a pop-up book.”