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The Good News
2019 February/March
Pg 3 - The Sunshine Express
The team is now planning to build more com-
plex systems and improve efficiency. The work
was made possible, in part, by a collaboration
with the Technical University of Madrid through
the MIT International Science and Technology
Initiatives (MISTI). It was also partially support-
ed by the Institute for Soldier Nanotechnologies,
the Army Research Laboratory, the National
Science Foundation¡¯s Center for Integrated
Quantum Materials, and the Air Force Office of
Scientific Research.
(source: Rob Matheson, MIT News Office,
news.mit.edu)
Ultrafast Schottky Diode
And, although using
these materials to fab-
ricate small devices is
relatively inexpensive,
using them to cover
vast areas, such as
the surfaces of build-
ings and walls, would
be cost-prohibitive.
Researchers have been
trying to fix these
problems for a long
time. But the few flex-
ible rectennas reported
so far operate at low
frequencies and can¡¯t
capture and convert
signals in gigahertz
frequencies, where
most of the relevant
cell phone and Wi-Fi
signals are.
To build their rectifier,
the researchers used
a novel 2-D material
called molybdenum
disulfide (MoS2), which
at three atoms thick
is one of the thinnest
semiconductors in the
world.
In doing so, the team
leveraged a singular
behavior of MoS2:
When exposed to
certain chemicals, the
material¡¯s atoms rear-
range in a way that
acts like a switch, forc-
ing a phase transition
from a semiconductor
to a metallic material.
The resulting structure
is known as a Schottky
diode, which is the
junction of a semicon-
ductor with a metal.
¡°By engineering MoS2
Converting Wi-Fi signals to electricity
with new 2-D materials
January 28, 2019: Imagine a world where smart-
phones, laptops, wearables, and other electronics
are powered without batteries. Researchers from
MIT and elsewhere have taken a step in that direc-
tion, with the first fully flexible device that can
convert energy from Wi-Fi signals into electricity
that could power electronics.
Devices that convert AC electromagnetic waves
into DC electricity are known as ¡°rectennas.¡± The
researchers demonstrate a new kind of rectenna,
described in a study appearing in Nature today,
that uses a flexible radio-frequency (RF) antenna
that captures electromagnetic waves ¡ª including
those carrying Wi-Fi ¡ª as AC waveforms.
The antenna is then connected to a novel device
made out of a two-dimensional semiconductor just
a few atoms thick. The AC signal travels into the
semiconductor, which converts it into a DC voltage
that could be used to power electronic circuits or
recharge batteries.
In this way, the battery-free device passively cap-
tures and transforms ubiquitous Wi-Fi signals into
useful DC power. Moreover, the device is flexible
and can be fabricated in a roll-to-roll process to
cover very large areas.
¡°What if we could develop electronic systems that
we wrap around a bridge or cover an entire high-
way, or the walls of our office and bring electronic
intelligence to everything around us? How do you
provide energy for those electronics?¡± says paper
co-author Tom¨¢s Palacios, a professor in the De-
partment of Electrical Engineering and Computer
Science and director of the MIT/MTL Center for
Graphene Devices and 2D Systems in the Micro-
systems Technology Laboratories. ¡°We have come
up with a new way to power the electronics sys-
tems of the future ¡ª by harvesting Wi-Fi energy in
a way that¡¯s easily integrated in large areas ¡ª to
bring intelligence to every object around us.¡±
Promising early applications for the proposed
rectenna include powering flexible and wearable
electronics, medical devices, and sensors for the
¡°internet of things.¡± Flexible smartphones, for in-
stance, are a hot new market for major tech firms.
In experiments, the researchers¡¯ device can pro-
duce about 40 microwatts of power when exposed
to the typical power levels of Wi-Fi signals (around
150 microwatts). That¡¯s more than enough power
to light up an LED or drive silicon chips.
Another possible application is powering the data
communications of implantable medical devices,
says co-author Jes¨²s Grajal, a researcher at the
Technical University of Madrid. For example, re-
searchers are beginning to develop pills that can
be swallowed by patients and stream health data
back to a computer for diagnostics.
¡°Ideally you don¡¯t want to use batteries to power
these systems, because if they leak lithium, the
patient could die,¡± Grajal says. ¡°It is much better
to harvest energy from the environment to power
up these small labs inside the body and communi-
cate data to external computers.¡±
All rectennas rely on a component known as a
¡°rectifier,¡± which converts the AC input signal into
DC power. Traditional rectennas use either silicon
or gallium arsenide for the rectifier. These materi-
als can cover the Wi-Fi band, but they are rigid.
into a 2-D semiconducting-metallic phase junc-
tion, we built an atomically thin, ultrafast Schottky
diode that simultaneously minimizes the series
resistance and parasitic capacitance,¡± says first
author and EECS postdoc Xu Zhang, who will soon
join Carnegie Mellon University as an assistant
professor.
Parasitic capacitance is an unavoidable situation
in electronics where certain materials store a little
electrical charge, which slows down the circuit.
Lower capacitance, therefore, means increased
rectifier speeds and higher operating frequen-
cies. The parasitic capacitance of the researchers¡¯
Schottky diode is an order of magnitude smaller
than today¡¯s state-of-the-art flexible rectifiers, so
it is much faster at signal conversion and allows it
to capture and convert up to 10 gigahertz of wire-
less signals.
¡°Such a design has allowed a fully flexible device
that is fast enough to cover most of the radio-
frequency bands used by our daily electronics,
including Wi-Fi, Bluetooth, cellular LTE and many
others,¡± Zhang says.
The reported work provides blueprints for other
flexible Wi-Fi-to-electricity devices with substantial
output and efficiency. The maximum output effi-
ciency for the current device stands at 40 percent,
depending on the input power of the Wi-Fi input.
At the typical Wi-Fi power level, the power ef-
ficiency of the MoS2 rectifier is about 30 percent.
For reference, today¡¯s rectennas made from rigid,
more expensive silicon or gallium arsenide achieve
around 50 to 60 percent.
¡°This very nice teamwork from MIT demonstrates
the first real application [of] atomically thin
semiconductors for a flexible rectenna for energy
harvesting,¡± says Philip Kim, a professor of physics
and applied physics at Harvard University whose
research focuses on 2-D materials. ¡°I am amazed
by the innovate approach that the team has set up
to utilize the waste energy from RF power around
us.¡±
There are 15 other paper co-authors from MIT,
Technical University of Madrid, the Army Research
Laboratory, Charles III University of Madrid,
Boston University, and the University of Southern
California.
CDA Announces Colorado¡¯s 2018
Approved Certified Hemp Seed Varieties
BROOMFIELD, CO, Jan 7, 2019: The Colorado
Department of Agriculture (CDA) is announc-
ing that six industrial hemp seed varieties have
passed the 2018 statewide THC validation and
observation trial and are now eligible to be
grown by the members of the Colorado Seed
Growers Association for production of ¡°CDA Ap-
proved Certified Seed.¡±
In 2018, the CDA Approved Certified Hemp seed
program trialed eight varieties of hemp across
Colorado¡¯s diverse growing conditions to vali-
date if they would grow mature plants that test
at or below 0.3% THC concentration on a dry
weight basis.
During 2018, the program approved six new va-
rieties approved to be grown as a class of ¡°CDA
Approved Certified Seed.¡± (continued Pg 4>>)
More Hemp Seeds Available