From: Princeton University, Engineering School
November 3, 2021 -- Princeton
researchers have taken a step toward developing a type of antenna array that
could coat an airplane's wings, function as a skin patch transmitting signals
to medical implants, or cover a room as wallpaper that communicates with internet
of things (IoT) devices.
The technology, which could enable many
uses of emerging 5G and 6G wireless networks, is based on large-area
electronics, a way of fabricating electronic circuits on thin, flexible
materials. The researchers described its development in a paper published Oct.
7 in Nature Electronics.
The approach overcomes limitations of
conventional silicon semiconductors, which can operate at the high radio
frequencies needed for 5G applications, but can only be made up to a few
centimeters wide, and are difficult to assemble into the large arrays required
for enhanced communication with low-power devices.
"To achieve these large dimensions,
people have tried discrete integration of hundreds of little microchips. But
that's not practical -- it's not low-cost, it's not reliable, it's not scalable
on a wireless systems level," said senior study author Naveen Verma, a
professor of electrical and computer engineering and director of Princeton's
Keller Center for Innovation in Engineering Education.
"What you want is a technology that
can natively scale to these big dimensions. Well, we have a technology like
that -- it's the one that we use for our displays" such as computer
monitors and liquid-crystal display (LCD) televisions, said Verma. These use
thin-film transistor technology, which Verma and colleagues adapted for use in
wireless signaling.
The researchers used zinc-oxide
thin-film transistors to create a 1-foot-long (30-centimeter) row of three
antennas, in a setup known as a phased array. Phased antenna arrays can
transmit narrow-beam signals that can be digitally programmed to achieve
desired frequencies and directions. Each antenna in the array emits a signal
with a specified time delay from its neighbors, and the constructive and destructive
interference between these signals add up to a focused electromagnetic beam --
akin to the interference between ripples created by water droplets in a pond.
A single antenna broadcasts a fixed
signal in all directions, "but a phased array can electrically scan the
beam to different directions, so you can do point-to-point wireless
communication," said lead study author Can Wu, a postdoctoral researcher
at Stanford University who completed a Ph.D. in electrical and computer
engineering at Princeton earlier this year.
Phased array antennas have been used for
decades in long-distance communication systems such as radar systems,
satellites, and cellular networks, but the technology developed by the
Princeton team could bring new flexibility to phased arrays and enable them to
operate at a different range of radio frequencies than previous systems.
"Large-area electronics is a thin
film technology, so we can build circuits on a flexible substrate over a span
of meters, and we can monolithically integrate all the components into a sheet
that has the form factor of a piece of paper," said Wu.
In the study, the team fabricated the
transistors and other components on a glass substrate, but a similar process
could be used to create circuits on flexible plastic, said Wu.
This type of antenna system could be
installed almost anywhere. When used like wallpaper in a room, it could enable
quick, secure and energy-efficient communication with a distributed network of
IoT devices such as temperature or motion sensors.
Having an antenna that's a flexible
surface could also be beneficial for satellites, which are launched in a
compact format and unfold as they reach orbit, and a large area could be
advantageous for long-distance communication with aircraft.
"With an airplane, because its
distance is so far, you lose a lot of the signal power, and you want to be able
to communicate with high sensitivity. The wings are a fairly large area, so if
you have a single point receiver on that wing it doesn't help too much, but if
you can expand the amount of area that's capturing the signal by a factor of a
hundred or a thousand, you can reduce your signal power and increase the
sensitivity of your radio," said Verma.
In addition to Wu and Verma, the paper's
coauthors, all from the Department of Electrical and Computer Engineering, were
Ph.D. graduates Yoni Mehlman (2020) and Tiffany Moy (2017); graduate students
Prakhar Kumar and Yue Ma; postdoctoral research associate Hongyang Jia;
professor emeritus and senior scholar Sigurd Wagner; and James Sturm, the
Stephen R. Forrest Professor in Electrical Engineering.
The work was supported in part by the
Defense Advanced Research Projects Agency's Center for Brain-Inspired Computing
and by Princeton's Program in Plasma Science and Technology. The research also
utilized cleanroom facilities at the Princeton Institute for the Science and
Technology of Materials.
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