Winged microchip is smallest-ever human-made flying structure
The size of a grain of sand, dispersed microfliers could monitor air pollution, airborne disease and environmental contamination

Date:
September 22, 2021
Source:
Northwestern University
Summary:
By studying the aerodynamics of wind-dispersed seeds, researcher
developed a flying microchip (or 'microflier') that catches
the wind and passively flies through the air. Packed with
ultra-miniaturized technology, including sensors and wireless
communication capabilities, these microfliers could be used to
monitor air pollution, airborne disease and more.



FULL STORY ========================================================================== Northwestern University engineers have added a new capability to
electronic microchips: flight.


========================================================================== About the size of a grain of sand, the new flying microchip (or
"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.

By studying maple trees and other types of wind-dispersed seeds, the
engineers optimized the microflier's aerodynamics to ensure that it
-- when dropped at a high elevation -- 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.

As the smallest-ever human-made flying structures, these microfliers also
can be packed with ultra-miniaturized technology, including sensors,
power sources, antennas for wireless communication and embedded memory
to store data.

The research is featured on the cover of the Sept. 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,"
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." A pioneer
in bioelectronics, Rogers is the Louis Simpson and Kimberly Querrey
Professor of Materials Science and Engineering, Biomedical Engineering
and Neurological Surgery in the McCormick School of Engineeringand
Feinberg School of Medicineand director of the Querrey Simpson Institute
for Bioelectronics.

Yonggang Huang, the Jan and Marcia Achenbach Professor of Mechanical Engineering at McCormick, led the study's theoretical work.



==========================================================================
'We think we that beat nature' Most people have watched a maple leaf's
whirling propeller seed spin through the air and gently land on the
sidewalk. This is just one example of how nature has evolved clever, sophisticated methods to increase the survival of various plants. By
ensuring that seeds are widely dispersed, otherwise sedentary plants
and trees can propagate their species over vast distances to populate
broad areas.

"Evolution was likely the driving force for the sophisticated aerodynamic properties exhibited by many classes of seeds," Rogers said. "These
biological structures are designed to fall slowly and in a controlled
manner, so they can interact with wind patterns for the longest-possible
period of time. This feature maximizes lateral distribution via
purely passive, airborne mechanisms." To design the microfliers,
the Northwestern 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.

Rogers and his 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, Huang led full-scale computational modeling of how
the air flows around the device to mimic the tristellateia seed's slow, controlled rotation.



========================================================================== Based on this modeling, Rogers' group then built and tested structures in
the lab, using advanced methods for imaging and quantifying patterns of
flow in collaborations with Leonardo Chamorro, an associate professor of mechanical engineering at the University of Illinois at Urbana-Champaign.

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

"We think that we beat nature," Rogers said. "At least in the narrow
sense that we have been able to build structures that fall with more
stable trajectories and at slower terminal velocities than equivalent
seeds that you would see from plants or trees. We also were able to
build these helicopter flying structures at sizes much smaller than
those found in nature. That's important because device miniaturization represents the dominating development trajectory in the electronics
industry, where sensors, radios, batteries and other components can be constructed in ever smaller dimensions." From plants to pop-up books
To manufacture the devices, Rogers' team drew inspiration from another
familiar novelty: a child's pop-up book.

His 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.

"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."
Packed with promise 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, Rogers' team included sensors, a power source
that can harvest ambient energy, memory storage and an antenna that can wirelessly transfer data to a smart phone, tablet or computer.

In the lab, Rogers' group 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.

Rogers imagines that 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.

"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 miniaturized sensors that can be distributed at a high spatial density
over large areas, to form a wireless network." Disappearing act But
what about all the electronic litter? Rogers has a plan for that. His
lab alreadydevelops transient electronicsthat can harmlessly dissolve in
water after they are no longer needed -- as demonstrated in recent work
on bioresorbable pacemakers.Now his team is using the same materials and techniques to build microfliers that naturally degrade and disappear in
ground water over time.

"We fabricate such physically transient electronics systems using
degradable polymers, compostable conductors and dissolvable integrated
circuit chips that naturally vanish into environmentally benign end
products when exposed to water," Roger said. "We recognize that recovery
of large collections of microfliers might be difficult. To address this concern, these environmentally resorbable versions dissolve naturally
and harmlessly." The study, "Three-dimensional electronic microfliers
inspired by wind-dispersed seeds," was supported by the Querrey Simpson Institute for Bioelectronics at Northwestern University. In addition
to Rogers and Huang, co-corresponding authors include Leonardo Chamorro
of the University of Illinois and Yihui Zhang of Tsinghua University in
China. The paper's first authors are Bong Hoon Kim of Soongsil University
in Korea, Kan Li of Huazhong University of Science and Technology in China
and Jin-Tae Kim and Yoonseok Park, both in Rogers' lab at Northwestern.

Video of Microflier: https://www.youtube.com/watch?v=x6gB1hKjDys ========================================================================== Story Source: Materials provided by Northwestern_University. Original
written by Amanda Morris. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Kim, B.H., Li, K., Kim, JT. et al. Three-dimensional electronic
microfliers inspired by wind-dispersed seeds. Nature, 2021 DOI:
10.1038/ s41586-021-03847-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210922121815.htm

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