Tech Briefs Magazine - September 2021 - 37

Wearable Sensors Detect Gas Leaks
The ultra-compact, wearable hologram sensor immediately notifies the user of volatile
gas detection.
Pohang University of Science and Technology, Korea
G
as accidents - such as toxic gas
leakage in factories, carbon mon -
oxide leakage of boilers, or toxic gas
suffocation during manhole cleaning
- continue to claim lives and cause
injuries. Developing a sensor that can
quickly detect toxic gases or biochemicals
is still an important issue in public
health, environmental monitoring, and
military sectors. A research team has
developed an inexpensive, ultra-compact,
wearable hologram sensor that
immediately notifies the user of vol -
atile gas detection.
The researchers integrated a metasurface
with a gas-reactive liquid crystal
optical modulator to develop a sensor
that provides an immediate visual holographic
alarm when harmful gases are
detected. Conventional gas sensing de -
vices are not widely used due to their
high manufacturing cost. In addition,
commercial gas sensors have limitations
in that they are difficult to use and have
poor portability and reaction speed.
To solve these issues, the team utilized
the metasurface - an optical device
known to have an " invisible cloak " effect
by making visible objects disappear by
controlling the refractive index of light.
The metasurface is especially used to
transmit two-way holograms or 3D video
images by freely controlling light.
Using the metasurface,
the team
developed a gas sensor that can float a
holographic image alarm in space in just
a few seconds by using the polarization
control of transmitted light that transforms
due to the change in orientation
of liquid crystal molecules in the liquid
crystal layer inside the sensor device
when exposed to gas. Moreover, the gas
sensor requires no support from external
mechanical or electronic devices,
unlike other conventional commercial
gas sensors.
The researchers used isopropyl alcohol
as the target hazardous gas known as
a toxic substance that can cause stomach
pain, headache, dizziness, and even
leukemia. The sensor was confirmed to
detect even the minute amount of about
200 ppm of gas. In an actual experiment
using a board marker - a volatile gas
source in our daily life - a visual holoTech
Briefs, September 2021
Cov
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37
graphic alarm popped up instantaneously
the moment the marker was brought
to the sensor.
A one-step nano composite printing
method was developed to produce the
flexible, wearable gas sensor. The metasurface
structure, which was previously
processed on a hard substrate, was
designed to enable rapid production
with a single-step nanocasting process

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Tech Briefs Magazine - September 2021

Table of Contents for the Digital Edition of Tech Briefs Magazine - September 2021

Tech Briefs Magazine - September 2021 - Intro
Tech Briefs Magazine - September 2021 - Sponsor
Tech Briefs Magazine - September 2021 - Cov1
Tech Briefs Magazine - September 2021 - Cov2
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Tech Briefs Magazine - September 2021 - 24A
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Tech Briefs Magazine - September 2021 - Cov3
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Tech Briefs Magazine - September 2021 - PIT-Cov1
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