Evaluation Engineering - 7

U.S. Army

added facilities are Naval
Base Norfolk, VA; Joint Base
Pearl Harbor-Hickam, HI;
Joint Base San Antonio, TX;
the National Training Center
(NTC), Fort Irwin, CA; Fort
Hood, TX; Camp Pendleton,
CA; and Tinker Air Force Base,
OK. These seven facilities in
the second round of 5G study
facilities, referred to the DoD
as its Tranche 2 selection of research facilities, combine with
the earlier five 5G research
facilities for a total of 12 locations for 5G research.
The increased data demands of 5G systems compared to earlier cellular
wireless communications generations is pushing the use of
frequency spectrum well into
the millimeter-wave frequency
range, at and above 24 GHz. In
addition to connecting billions
of people via wireless communications, 5G networks will
connect many things, many
sensors known as Internet of
Things (IoT) devices. Military
bases selected by the DoD earlier for 5G research chores, as
part of the Tranche 1 choice
of research facilities, are the
Joint Base Lewis-McChord,
WA; Hill Air Force Base, UT;
Naval Base San Diego, CA;
Marine Corps Logistics Base
Albany, GA; and Nellis Air
Force Base, NV. All the bases
feature analysis and testing
capabilities in areas needed to

explore phenomena at higher
frequencies and wider bandwidths, and the capabilities
to explore the performance
levels of the latest wireless
communications infrastructure equipment.
Although civilian users
are looking forward to the
availability of 5G systems,
it is expected that the technology will play major roles
in both military and civilian applications. The DoD is
already issuing requests for
prototype proposals from
industry partners in key areas, including for ship-wide
and pier communications at
the Naval Station Norfolk, for
enhancing aircraft mission
readiness at Joint Base Pearl
Harbor-Hickam, and for wireless communications for forward operating bases (FOBs)
and tactical operations centers (FOCs) at the NTC at Fort
Irwin and Fort Hood, TX and
for FOBs and TOCs at Camp
Pendleton, CA.

Army Studies Energy
Levels for Hot Electrons
High-energy or "hot" electrons
have been of interest for some
time in many fields because
of their potential for accelerating electronic reactions.
But to learn more about how
to put hot electrons to work,
researchers needed a practical measurement approach to

measure the energy levels of
those and other charge carriers. Fortunately, recent studies performed by scientists at
the University of Michigan
and Purdue University as
part of the Department
o f D e f e n s e 's ( D o D 's)
Multidisciplinary University
Research Initiatives program
and published in the journal
Science provided details on
the direct measurements of
the energy levels and energy
distributions of hot electrons.
The energy distribution
of hot electrons was measured by a scanning tunneling microscope integrated
with lasers and other optical
components. Such measurements can provide insights
on the efficiencies of different energy sources, such as
motion-driven generators and
solar panels. The research was

U.S. Marine Corps

funded by the Army Research
Office (ARO), part of the U.S.
Army Combat Capabilities
Development Command 's
Army Research Laboratory
(ARL). Hot electrons can be
generated by shining a certain type of light on metal
nanostructures, typically
composed of gold- or silverbased metals, to excite surface
plasmons, producing energy
for different applications as
needed (see the figure). The
research team created hot
electrons by shining a laser

onto a 13-nm-thick gold film
with ridges designed to resonate at the frequency of the
incident light.
"This multidisciplinary basic research effort sheds light
on a unique way to measure
the energy of charge carriers,"
said Dr. Chakrapani Varanasi,
an ARO program manager,
who supported this study.
"These results are expected
to play a crucial role in developing future applications in
energy conversion, photocatalysis and photodetectors,
for instance, that are of great
interest to the Department of
Defense." Dr. Edgar Meyhofer,
a professor of mechanical
engineering at University of
Michigan, who co-led the research along with professors
Pramod Sangi-Reddy and
Vladimir Shalaev, explained:
"If you wanted to employ
light to split
water into
hydrogen
and oxygen,
you can use
hot charge
carriers because electrons that
a r e mor e
energetic
ca n more
readily participate in the reaction and
drive the reaction faster."
"Measuring energy distribution means quantifying how
many electrons are available
at a certain amount of energy,"
said Harsha Reddy, a doctoral
candidate in Purdue's School
of Electrical and Computer
Engineering and co-lead author on this paper. "That crucial piece of information was
lacking for expanding the use
of hot electrons."

JULY 2020 EVALUATIONENGINEERING.COM

7
http://www.EVALUATIONENGINEERING.COM
Evaluation Engineering

Table of Contents for the Digital Edition of Evaluation Engineering
