Tech Briefs Magazine - May 2022 - 30

Test & Measurement
Method Measures Temperature Within 3D Objects
This is a completely remote, non-contact way of measuring the thermal properties of materials.
University of Wisconsin, Madison, WI
E
ngineers have remotely determined
the temperature beneath the surface
of certain materials using a new technique
called depth thermography. The
method may be useful in applications
where traditional temperature probes
won't work, like monitoring semiconductor
performance or next-generation
nuclear reactors.
Many temperature sensors measure
thermal radiation, most of which is in
the infrared spectrum, coming off the
surface of an object. The hotter the object,
the more radiation it emits, which
is the basis for devices like thermal imaging
cameras. Depth thermography,
however, goes beyond the surface and
works with a certain class of materials
that are partially transparent to infrared
radiation.
The researchers are able to measure
the spectrum of thermal radiation emitted
from the object and use a sophisticated
algorithm to infer the temperature,
not just on the surface but also underneath
the surface - tens to hundreds of
microns within.
For the project, the team heated a
piece of fused silica (a type of glass)
and analyzed it using a spectrometer.
They then measured temperature readings
from various depths of the sample
using computational tools previously
they previously developed in which the
thermal radiation given off from ob(a)
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An
infrared image of the fused silica window used to test the depth thermography concept. For
the project, the team heated the silica and analyzed it using a spectrometer. They then measured
temperature readings from various depths of the sample. (Photo: Mikhail Kats)
jects composed of multiple materials
was measured. Working backward, they
used the algorithm to determine the
temperature gradient that best fit the
experimental results.
This particular effort was a proof of
concept. In future work, the team hopes
to apply the technique to more complicated
multilayer materials and to apply
machine learning techniques to improve
the process. Eventually, they want
to use depth thermography to measure
semiconductor devices to gain insights
into their temperature distributions as
they operate.
This type of 3D temperature profiling
could also be used to measure and
map clouds of high-temperature gases
and liquids; for example, in molten-salt
nuclear reactors where it's important
to know the temperature of the salt
throughout the volume without having
to use temperature probes that may not
survive at 700 °C.
For more information, contact Mikhail
Kats at mkats@wisc.edu.
Rapid Agent Aerosol Detector for Biological Agents
A highly sensitive trigger enables rapid detection of toxic biological particles suspended in the air.
MIT Lincoln Laboratory, Lexington, MA
A
ny space, enclosed or open, can be
vulnerable to the dispersal of harmful
airborne biological agents. Silent and
near-invisible, these bioagents can sicken
or kill living things before steps can be
taken to mitigate their effects. Venues
where crowds congregate are prime targets
for biowarfare strikes engineered by
terrorists but expanses of fields or forests
could be victimized by an aerial bioattack.
Researchers have developed the Rapid
Agent Aerosol Detector (RAAD), a highly
sensitive and reliable trigger for the
30
U.S. military's early warning system for
biological warfare agents. The trigger is
the key mechanism because its continual
monitoring of the ambient air in a location
picks up the presence of aerosolized
particles that may be threat agents. The
trigger cues the detection system to collect
particle specimens and then initiate
the process to identify particles as potentially
dangerous bioagents.
The RAAD determines the presence of
biological warfare agents through a multistep
process. First, aerosols are pulled
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into the detector by the combined agency
of an aerosol cyclone that uses high-speed
rotation to cull out the small particles,
and an aerodynamic lens that focuses
the particles into a condensed (i.e., enriched)
volume, or beam, of aerosol.
Then, a near-infrared (NIR) laser diode
creates a structured trigger beam that detects
the presence, size, and trajectory of
an individual aerosol particle. If the particle
is large enough to adversely affect the
respiratory tract - roughly 1 to 10 micrometers
- a 266-nanometer ultravolet
Tech Briefs, May 2022
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Tech Briefs Magazine - May 2022

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