With the flick of a switch, engineers from Drexel University’s College of Engineering have created a thin film device that is made by spray coating and can block electromagnetic radiation.
The innovation, made possible by adaptable two-dimensional materials known as MXenes, has the potential to improve the operation of electrical equipment, fortify wireless links, and protect mobile communications from hacking.
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 most recent MXene finding, which was published in Nature Nanotechnology, demonstrates how this shielding may be adjusted by applying a little voltage that is lower than the voltage generated by an alkaline battery.
“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 special substance in that its internal chemical structure can be temporarily changed to allow these electromagnetic waves to pass through. Because it is highly conductive, MXene is ideal for reflecting microwave radiation that could result in static, feedback, or reduce the performance of communications devices.
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. 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.
Yury Gogotsi
This means that a thin layer applied to an electrical device or component prevents them from both releasing electromagnetic waves and allowing them to be pierced by waves from other devices.
The device’s performance can be ensured by removing the possibility of interference from both internal and external sources, but while it is being used for communication, certain waves must be permitted to depart and enter.
“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.”
Using the flow and expulsion of ions to alternately expand and compress the gap between the material’s layers, like an accordion, as well as to change the surface chemistry of MXenes, is the key to evoking the bidirectional tunability of MXene’s shielding feature.
A tiny voltage is supplied to the film, which allows ions to enter or intercalate between the MXene layers, changing the surface charge and causing electrostatic attraction. These changes affect the layer spacing, conductivity, and shielding effectiveness of the material. The MXene layers revert to their initial state as the current is turned off when the ions are deintercalated.
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. Traditional metals like copper and steel are unable to block microwave radiation, but the materials consistently showed the dynamic tunability of shielding efficacy. 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.”
Gogotsi proposes that the MXene shielding could conceal objects from radar or other tracing system detection for security applications. The team also investigated a one-way shielding switch’s potential. This would enable a device to stay hidden and secure from unauthorized access up until it is used.
“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 investigate new MXene-electrolyte pairings and techniques to fine-tune the shielding in order to obtain a better modulation of electromagnetic wave transmission and dynamic adjustment to block radiation at various bandwidths.
