A team of engineers at Northwestern University in Illinois, U.S., has developed a tiny device that can deliver air-dropped payloads such as environmental sensors safely to the ground; they call them “microfliers.” The microfliers’ structure is a solid-state design that works without motors or engines; its complex 3D geometry that enables their success is modeled after seeds found in nature.
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Finding Solutions in Nature
The Northwestern researchers detailed in their article published by Nature, stated that investigations started by studying seeds dispersed by the wind, such as those of maple and sycamore trees. The aerodynamic structure of these seeds enables them to fall to the ground slowly and in a controlled way, to make sure the seed’s “payload” is delivered accurately.
Over billions of years of evolution, nature has refined these seeds’ designs so that their structures function with highly sophisticated aerodynamics. The researchers discovered design concepts from studying these structures that they could apply to platforms for carrying electronics.
The most direct influence on the microfliers’ structure is the tristellateia, common in Madagascar, East Africa, and South Asia. The tristellateia plant’s star-shaped seeds have bladed wings that fall to the ground in a slow spinning motion.
To create the seed-inspired microfliers, the engineers first created models in flat, planar geometries. Then, they bonded those models over a rubber substrate that had been stretched slightly. When the tension was released on the substrate and the rubber relaxed, the models buckled in a controlled motion so that the microfliers’ wings popped up into precisely defined 3D structures.
These structures are about the size of a grain of sand, but they can still deliver payloads such as sensors and other electronics safely to the ground. Each microflier is made up of micro-sized electronic components and their wings. The electronics are the heaviest part, and their extra weight is sited low central to ensure the slow glide to the earth remains steady and smooth.
Microfliers Make Good Environmental Sensors
The stabilized flight that the seed-inspired microflier wings enable makes the device a good candidate for applications as environmental sensors. These tiny devices can be deployed in swarms to gather widely relevant, accurate ecological information.
Air quality monitoring, for example, can gather data on environmental metrics like humidity, temperature, the presence of volatile organic compounds (VOCs) and CO2 in the atmosphere, particulate matter, and other kinds of pollution.
A range of sensor technologies is employed to gather environmental data like this. Automative drones, satellites, and aircraft are employed to take images and other readings such as gas samples. Colorimetric sensors, for example, use image data to determine the molecular make-up of air samples.
Whether in fixed locations or aboard ships, aircraft, and satellites, environmental sensors are limited by the relatively small area they can obtain data from. Modeling is therefore challenging and must integrate multiple sources of environmental data to be effective. As well as pulling information from networks of fixed and vehicle-mounted sensors, air quality monitoring also uses geographic information system (GIS) models and the Sensor Observation Service (SOS) (an online service) to make its analyses.
Impact of Microflier Innovation
The microfliers developed at Northwestern could simplify this process and eventually lead to more environmental monitoring data, leading to better ecological modeling and decision-making. They can be distributed in large-scale collections, accurately covering an expansive area. The researchers also identified possible applications in public policy and population health.
Microfliers were also designed with sophisticated environmental sensors in mind. Researchers claim the structures can be made with electronic, optoelectronic, microfluidic, and microelectromechanical devices included. Ultra-miniaturized technologies that can be added to the microfliers in addition to sensors include power sources, wireless communications antennae, and built-in memory storage.
As environmental sensors, microfliers could have a significant impact in gathering more monitoring data from more possible locations. Dropped from a plane, drone, or high building, the wings bring all of the electronics in a sensor safely to the ground in a controlled flight – giving the sensor enough time to gather the images, or gas analysis data. With a swarm of microfliers all communicating with each other through local, wireless connections, a sensor network could form that can provide more robust and accurate data over a large area. This simple and effective solution would make it easy for researchers, citizens, and policy-makers to obtain information needed to inform their environmental decision-making.
Will We See Microflier Swarms In Our Cities Soon?
The technology developed at Northwestern University could begin a dramatic step-change in the use of sensors for environmental monitoring. The majority of monitoring strategies in use today rely on environmental sensors bulked together in a small number of locations across a fixed area of interest. In the future, microflier-mounted environmental sensors could be deployed in high densities over a large area, forming a wireless network that creates a high-fidelity reading of the area’s ecological state.
References and Further Reading
Kim, B.H. et al. (2021)Three-Dimensional Electronic Microfliers Inspired by Wind-Dispersed Seeds. Nature. [Online]. Available at: https://doi.org/10.1038/s41586-021-03847-y
Rada, E.C., et al. (2012) Perspectives of Low-Cost Sensors Adoption for Air Quality Monitoring. Scientific Bulletin. [Online]. Available at: https://www.scientificbulletin.upb.ro/rev_docs_arhiva/full813_245441.pdf
Institution of Mechanical Engineers. (2021) Winged Microchip Is Smallest Ever Human-Made Flying Device. [Online]. Available at: https://www.imeche.org/news/news-article/winged-microchip-is-smallest-ever-human-made-flying-device