Tech Briefs Magazine - September 2021 - 30

Communications
Wireless, Wearable Transmitter
The wearable antenna bends, stretches, and compresses without compromising function.
The Pennsylvania State University, University Park
C
urrent research on flexible electronics
is paving the way for wireless sensors
that can be worn on the body and collect a
variety of medical data. But without a similar
flexible transmitting device, these sensors
would require wired connections to
transmit health data.
Like wearable sensors, a wearable transmitter
needs to be safe for use on human
skin, functional at room temperature, and
able to withstand twisting, compression,
and stretching. The flexibility of the transmitter,
though, poses a unique challenge:
When antennas are compressed or
stretched, their resonance frequency (RF)
changes and they transmit radio signals at
wavelengths that may not match those of
the antenna's intended receivers.
Researchers have created a flexible,
wearable transmitter in layers. Building
upon previous work, they fabricated a copper
mesh with a pattern of overlapping,
wavy lines. This mesh makes up the bottom
layer, which touches the skin, and the
top layer, which serves as the radiating element
in the antenna. The top layer creates
a double arch when compressed and
stretches when pulled - and moves
between these stages in an ordered set of
steps. The structured process through
which the antenna mesh arches, flattens,
and stretches improves the overall flexibility
of the layer and reduces RF fluctuations
between the antenna's states.
The bottom mesh layer keeps radio signals
from interacting with the skin. This
implementation, beyond preventing tissue
damage, avoids a loss of energy caused by
tissue degrading the signal. The antenna's
ability to maintain a steady RF also allows
the transmitter to collect energy from
radio waves, potentially lowering energy
consumption from outside sources.
The transmitter, which can send wireless
data at a range of nearly 300 feet, can easily
integrate a number of computer chips or
sensors. With further research, it could
have applications in health monitoring
and clinical treatments as well as energy
generation and storage.
After developing the stretchable antenna
prototype, the researchers analyzed it
30
Cov
The research is paving the way for wireless, wearable health monitoring devices that can collect
and transfer information. (Image: Huanyu Cheng)
The wearable transmitter is designed to compress its top layer in a double arch pattern (shown
here) to respond to movement without compromising signal transmission. (Image: Huanyu Cheng)
to identify new fundamental pathways for
fine-tuning such a device that could be
applied to similar, future research. The
team fabricated an antenna with layers
and a mesh pattern similar to their previous
prototype but lacking the double-arch
compression structure. They measured
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the deformation of the antenna as the
mesh was stretched at different intervals,
then used computer simulations to examine
the relationship between the deformation
and the antenna performance.
To simplify the analysis of the antenna's
radio signal transmission, the re -
Tech Briefs, September 2021

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Tech Briefs Magazine - September 2021

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