The winged microchip is the smallest flying structure ever created by man – the size of a grain of sand

The size of a grain of sand, scattered microflyers could monitor air pollution, airborne disease and environmental contamination.

Northwestern University engineers have added a new ability to microchips: theft.

About the size of a grain of sand, the new flying microchip (or “microflier”) has no motor or motor. Instead, it takes flight with the wind – much like the propeller seed of a maple tree – and spins like a helicopter through the air towards the ground.

By studying maple trees and other types of wind-dispersed seeds, engineers optimized the aerodynamics of the microflier to ensure that it – when released at high altitudes – falls at a slow speed in a controlled manner. . This behavior stabilizes its flight, ensures dispersion over a wide area and increases the duration of interaction with the air, making it ideal for monitoring air pollution and airborne diseases.

As the smallest flying structures ever created by humans, these microfliers can also feature ultra-miniaturized technology, including sensors, power sources, antennas for wireless communication, and built-in memory for store data.

The research covers the September 23, 2021 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 detect the environment for contamination monitoring, environmental monitoring. population or disease monitoring, ”said Northwestern’s John. A. Rogers, who led the development of the device. “We were able to do this using ideas inspired by the organic world. Over billions of years, nature has engineered seeds with highly sophisticated aerodynamics. We have borrowed these design concepts, adapted and applied them to electronic circuit platforms.

A pioneer in bioelectronics, Rogers is Louis Simpson and Kimberly Querrey Professor of Materials Science and Engineering, Biomedical Engineering, and Neurological Surgery at the McCormick School of Engineering and the Feinberg School of Medicine and Director of the Querrey Simpson Institute for Bioelectronics. Yonggang Huang, Jan and Marcia Achenbach professor of mechanical engineering at McCormick, led the theoretical work of the study.

“We think we are beating nature”

Most people have seen the seed of a maple leaf’s swirling propeller spin in the air and land softly on the sidewalk. This is just one example of how nature has developed smart and sophisticated methods to increase the survival of various plants. By ensuring that the seeds are widely dispersed, otherwise the sedentary plants and trees can propagate their species over great distances to populate large areas.

“Evolution was probably the driving force behind the sophisticated aerodynamic properties exhibited by many classes of seeds,” said Rogers. “These biological structures are designed to fall slowly and in a controlled manner, so that they can interact with the winds for the longest period of time possible. This feature maximizes lateral distribution via purely passive airborne mechanisms.

To design the microfliers, the Northwestern team studied the aerodynamics of a number of plant seeds, most directly inspired by tristellateia, a flowering vine with star-shaped seeds. The seeds of Tristellateia have bladed wings that catch the wind to fall with a slow, rotating rotation.

Rogers and his team have designed and built many different types of microfliers, including one to three wings, optimized for shapes and angles similar to those of the wings of a tristellateia seed. To identify the most ideal structure, Huang conducted large-scale computer modeling of how air circulates around the device to mimic the slow, controlled rotation of the tristellateia seed.

Based on this modeling, Rogers’ group then built and tested structures in the laboratory, using advanced imaging methods and quantification of flow models in collaboration with Leonardo Chamorro, associate professor of mechanical engineering at the ‘University of Illinois at Urbana-Champaign.

The resulting structures can be formed into a wide variety of sizes and shapes, some with properties that can give nature a run for its money.

“We think we’re beating nature,” Rogers said. “At least in the narrow sense that we were able to build structures that fall with more stable trajectories and at slower terminal velocities than the equivalent seeds you would see from plants or trees. We were also able to build these helicopter flight structures to sizes much smaller than those found in nature. This is important because the miniaturization of devices represents the dominant development trajectory in the electronics industry, where sensors, radios, batteries and other components can be built in ever smaller dimensions.

From plants to pop-up books

To make the devices, the Rogers team took inspiration from another familiar novelty: a pop-up book for children.

His team first fabricated precursors of flying structures in flat and planar geometries. Then they glued these precursors onto a slightly stretched rubber substrate. When the stretched substrate is released, a controlled buckling process occurs that causes the wings to “pop up” into precisely defined three-dimensional shapes.

“This strategy of building 3D structures from 2D precursors is powerful because all existing semiconductor devices are built in planar configurations,” said Rogers. “This allows us to harness the most advanced materials and manufacturing methods used by the consumer electronics industry to create completely standard, flat, chip-like designs. Then we simply turn them into 3D flying shapes using principles similar to a pop-up book.

Packed with the promise

Microfliers are made up of two parts: functional electronic components of millimeter size and their wings. As the microflier falls through the air, its wings interact with the air to create a slow and stable rotational motion. The weight of the electronics is distributed low in the center of the microflier to prevent it from losing control and falling to the ground chaotically.

In demonstrated examples, the Rogers team have included sensors, a power source that can harvest ambient energy, memory storage, and an antenna that can transfer data wirelessly to a smartphone, tablet or tablet. a computer.

In the laboratory, the Rogers group has equipped a device with all these elements to detect particles 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.

Rogers imagines that a large number of devices could be dropped from an airplane or building and widely dispersed to monitor environmental remediation efforts after a chemical spill or to track pollution levels in air at different altitudes.

“Most surveillance technologies involve bulk instrumentation designed to collect data locally at a small number of locations within a spatial area of ​​interest,” Rogers said. “We envision a large multiplicity of miniaturized sensors that can be distributed at high spatial density over large areas, to form a wireless network. “

Disappearance certificate

But what about all electronic waste? Rogers has a plan for this. His lab is already developing transient electronic components that can safely dissolve in water when they’re no longer needed, as recent work on bioabsorbable pacemakers has shown. Now his team uses the same materials and techniques to build microflyers that naturally degrade and disappear into groundwater over time.

“We make such physically transient electronic systems using degradable polymers, compostable conductors and soluble integrated circuit chips that naturally disappear into environmentally friendly end products when exposed to water,” Roger said . “We recognize that retrieving large collections of microfliers could be difficult. To address this concern, these environmentally absorbable versions dissolve naturally and harmlessly.

Reference: “Three-dimensional electronic microfliers inspired by seeds scattered by the wind” by Bong Hoon Kim, Kan Li, Jin-Tae Kim, Yoonseok Park, Hokyung Jang, Xueju Wang, Zhaoqian Xie, Sang Min Won, Hong-Joon Yoon, Geumbee Lee , Woo Jin Jang, Kun Hyuck Lee, Ted S. Chung, Yei Hwan Jung, Seung Yun Heo, Yechan Lee, Juyun Kim, Tengfei Cai, Yeonha Kim, Poom Prasopsukh, Yongjoon Yu, Xinge Yu, Raudel Avila, Haiwen Luan, Honglie Song, Feng Zhu, Ying Zhao, Lin Chen, Seung Ho Han, Jiwoong Kim, Soong Ju Oh, Heon Lee, Chi Hwan Lee, Yonggang Huang, Leonardo P. Chamorro, Yihui Zhang and John A. Rogers, September 22, 2021, Nature.
DOI: 10.1038 / s41586-021-03847-y

The study was supported by the Querrey Simpson Institute for Bioelectronics at Northwestern University. In addition to Rogers and Huang, corresponding authors include Leonardo Chamorro from the University of Illinois and Yihui Zhang from Tsinghua University in China. The first authors of the article are Bong Hoon Kim from Soongsil University in Korea, Kan Li from Huazhong University of Science and Technology in China, and Jin-Tae Kim and Yoonseok Park, both in Rogers’ lab in Northwestern.