Engineers have added a new capability to electronic microchips: flight. About the size of a grain of sand, the new flying microchip (microflier) does not have a motor or engine. Instead, it catches flight on the wind — much like a maple tree’s propeller seed — and spins like a helicopter through the air toward the ground. The microfliers also can be packed with ultra-miniaturized technology including sensors, power sources, antennas for wireless communication, and embedded memory to store data.
By studying maple trees and other types of wind-dispersed seeds, the engineers optimized the microflier’s aerodynamics to ensure that when dropped at a high elevation, it falls at a slow velocity in a controlled manner. This behavior stabilizes its flight, ensures dispersal over a broad area, and increases the amount of time it interacts with the air, making it ideal for monitoring air pollution and airborne disease.
To design the microfliers, the team studied the aerodynamics of a number of plants’ seeds, drawing its 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.
The team designed and built many different types of microfliers, including one with three wings, optimized to similar shapes and angles as the wings on a tristellateia seed. To pinpoint the most ideal structure, full-scale computational modeling was done of how the air flows around the device to mimic the tristellateia seed’s slow, controlled rotation.
Based on this modeling, the team then built and tested structures in the lab, using advanced methods for imaging and quantifying patterns of flow. The resulting structures can be formed across a wide variety of sizes and shapes.
To manufacture the devices, the team drew inspiration from another familiar novelty: a child’s pop-up book. The team first fabricated precursors to flying structures in flat, planar geometries. Then, they bonded these precursors onto a slightly stretched rubber substrate. When the stretched substrate is relaxed, a controlled buckling process occurs that causes the wings to “pop up” into precisely defined three-dimensional forms.
The microfliers comprise two parts: 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. The weight of the electronics is distributed low in the center of the microflier to prevent it from losing control and chaotically tumbling to the ground.
In demonstrated examples, the team included 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 team outfitted one device 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.
Large numbers of devices could be dropped from a plane or building and broadly dispersed to monitor environmental remediation efforts after a chemical spill or to track levels of air pollution at various altitudes.
The physically transient electronics systems use degradable polymers, compostable conductors, and dissolvable integrated circuit chips that naturally vanish into environmentally benign end products when exposed to water.
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