This story was originally written for and published by Drexel News.
Researchers in the College of Engineering have developed a thin film
device, fabricated by spray coating, that can block electromagnetic
radiation with the flip of a switch. The breakthrough, enabled by versatile
two-dimensional materials called MXenes, could adjust the performance of
electronic devices, strengthen wireless connections and secure mobile
communications against intrusion.
The team, led by
Yury Gogotsi, PhD
, Distinguished University and Bach professor in Drexel’s College of
Engineering, previously demonstrated that the two-dimensional layered MXene
materials, discovered just over a decade ago, when combined with an
electrolyte solution,
can be turned into a potent active shield against electromagnetic
waves
. This latest MXene discovery, reported in
Nature Nanotechnology
, shows how this shielding can be tuned when a small voltage — less than
that produced by an alkaline battery — is applied.
“Dynamic control of electromagnetic wave jamming has been a significant
technological challenge for protecting electronic devices working at
gigahertz frequencies and a variety of other communications technologies,”
Gogotsi said. “As the number of wireless devices being used in industrial
and private sectors has increased by orders of magnitude over the past
decade, the urgency of this challenge has grown accordingly. This is why
our discovery – which would dynamically mitigate the effect of
electromagnetic interference on these devices – could have a broad impact.”
MXene is a unique material in that it is highly conductive – making it
perfectly suited for reflecting microwave radiation that could cause
static, feedback or diminish the performance of communications devices –
but its internal chemical structure can also be temporarily altered to
allow these electromagnetic waves to pass through.
This means that a thin coating on a device or electrical components
prevents them from both emitting electromagnetic waves, as well as being
penetrated by those emitted by other electronics. Eliminating the
possibility of interference from both internal and external sources can
ensure the performance of the device, but some waves must be allowed to
exit and enter when it is being used for communication.
“Without being able to control the ebb and flow of electromagnetic waves
within and around a device, it’s a bit like a leaky faucet – you’re not
really turning off the water and that constant dripping is no good,”
Gogotsi said. “Our shielding ensures the plumbing is tight – so-to-speak –
no electromagnetic radiation is leaking out or getting in until we want to
use the device.”
The key to eliciting bidirectional tunability of MXene’s shielding property
is using the flow and expulsion of ions to alternately expand and compress
the space between material’s layers, like an accordion, as well as to
change the surface chemistry of MXenes.
With a small voltage applied to the film, ions enter – or intercalate –
between the MXene layers altering the charge of their surface and inducing
electrostatic attraction, which serves to change the layer spacing, the
conductivity and shielding efficiency of the material. When the ions are
deintercalated, as the current is switched off, the MXene layers return to
their original state.
The team tested 10 different MXene-electrolyte combinations, applying each
via paint sprayer in a layer about 30 to 100 times thinner than a human
hair. The materials consistently demonstrated the dynamic tunability of
shielding efficiency in blocking microwave radiation, which is impossible
for traditional metals like copper and steel. And the device sustained the
performance through more than 500 charge-discharge cycles.
“These results indicate that the MXene films can convert from
electromagnetic interference shielding to quasi-electromagnetic wave
transmission by electrochemical oxidation of MXenes,” Gogotsi and his
co-authors wrote. “The MXene film can potentially serve as a dynamic EMI
shielding switch.”
For security applications, Gogotsi suggests that the MXene shielding could
hide devices from detection by radar or other tracing systems. The team
also tested the potential of a one-way shielding switch. This would allow a
device to remain undetectable and protected from unauthorized access until
it is deployed for use.
“A one-way switch could open the protection and allow a signal to be sent
or communication to be opened in an emergency or at the required moment,”
Gogotsi said. “This means it could protect communications equipment from
being influenced or tampered with until it is in use. For example, it could
encase the device during transportation or storage and then activate only
when it is ready to be used.”
The next step for Gogotsi’s team is to explore additional MXene-electrolyte
combinations and mechanisms to fine-tune the shielding to achieve a
stronger modulation of electromagnetic wave transmission and dynamic
adjustment to block radiation at a variety of bandwidths.
In addition to Gogotsi, Meikang Han, Danzhen Zhang, Christopher E.
Shuck, Bernard McBride, Teng Zhang, Ruocun Wang and Kateryna Shevchuk
contributed to this research. The research was supported by the
National Science Foundation.
Read the full paper here:
https://www.nature.com/articles/s41565-022-01308-9