Tech Briefs Magazine - May 2022 - 13

Q &A
Radar Imaging at Terahertz Frequencies
Professor Kenneth
K. O. and his colleagues
at The University of
Texas at Dallas and
Oklahoma State University
have developed
an innovative and affordable
terahertz imager
microchip that
can enable devices to detect objects and
create images through obstacles that include
fog, smoke, dust, and snow.
Tech Briefs: What got you started
in this area of research?
Professor Kenneth K. O: For 15 years,
my research group has been trying to figure
out new opportunities for the silicon
integrated circuits industry. When we
started, although we were working on
terahertz applications, our main focus
was on radar operating at 77 GHz.
Tech Briefs: What are some
differences between your terahertz
imaging and 77 GHz radar?
O: The fundamental difference is just
the frequency - it's a factor of roughly
five times higher - so the wavelength is
about five times smaller. That means that
an imager with the same form factor can
give five times better resolution by going
to 430 GHz. Our system is essentially made
of pixel arrays of radars running at 430
GHz. But the performance of these pixels
is worse than at 77 GHz. So, in order to
address that problem, we have designed
the chips to work with a reflector. With the
help of the reflector, we can potentially
achieve the same kind of range - about
200 meters - as radar running at 77 GHz.
Tech Briefs: How does it contribute
to power reduction?
O: You can think of it as a lens - it
focuses the signal and sends it to a particular
point in space. Therefore, all the
power that's radiated from a pixel gets
focused to that point instead of being
dispersed as it propagates.
Tech Briefs, May 2022
Tech Briefs: How does your radar
deal with the frequency limits of
CMOS technology?
O: The problem is that we cannot use
CMOS amplifiers to provide gain for the
receivers at terahertz frequencies. So, we
use frequency multiplication to generate
the RF signal and also use a technique
called harmonic mixing to down-convert
the signal without an amplifier in front.
This degrades the sensitivity of the receiver,
so we have to overcome that. Those
are two challenges in going up to higher
frequencies compared to 77-GHz radar.
Tech Briefs: So, you're saying that
you somehow need more gain to
increase the amplitude of the
reflected signal?
O: Yes, that's exactly right. We need to
make sure that the signal we transmit recaches
the target we're trying to detect and
that the signal power level that reaches the
targets is the same as at 77 GHz. The way we
do that is by using the reflector along with
our focal plane array. This reflector gives us
that gain in power and then it reflects back
and once again gives us gain for the receiver.
So, even with the poor sensitivity, we can
still detect the reflected signal.
Tech Briefs: You've said that this
radar can penetrate atmospheric
obstacles like snow and dust and
fog. But those are all particles;
can it penetrate solids?
O: Some. It can penetrate nonconductive
materials like plastic containers. Industrial
applications include monitoring
the dryness of printing on paper and fabrics.
You can also think of industrial settings,
where you have a steam environment.
You need to monitor what's
behind the steam. A really significant
application is to see through smoke and
fire - an amazing application for fire
fighters to help them search for people.
Read the full transcript of this Q&A at
www.techbriefs.com.
www.techbriefs.com
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Tech Briefs Magazine - May 2022

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