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Posted: Oct 25, 2012
Graphene appears to be the most effective material for EMI shielding
(Nanowerk Spotlight) Sensitive electronic devices like cell phones and computers require shielding from electromagnetic interference (EMI). Such shielding – which must be electrically conductive – has traditionally been made of metal, which poses a weight problem in the push to miniaturize and lighten electronics.
In new work, scientists in Korea have now demonstrated that single-layer graphene is an excellent choice of material for high-performance EMI shielding. They found that CVD-synthesized graphene shows more than seven times greater EMI shielding effectiveness (in terms of dB) than gold film of the same thickness.
Reporting their findings in a recent online edition of Nanotechnology ("Electromagnetic interference shielding effectiveness of monolayer graphene"), a team led by Byung Jin Cho, a professor in the Department of Electrical Engineering at the Korea Advanced Institute of Science and Technology (KAIST), suggests the feasibility of manufacturing an ultrathin, transparent, weightless, and flexible EMI shield by a single or a few atomic layers of graphene.
"Besides the first experimental reports on EMI shielding effectiveness of monolayer graphene, we also studied the dominant mechanism of the shielding through modeling," Cho tells Nanowerk. "According to our model, the ideal monolayer graphene can surprisingly shield as much as 97.8% of incident waves; our actual CVD-synthesized graphene can shield about 40%. This finding is significant because it means that graphene is the most effective material for EMI shielding in terms of shielding effectiveness per mass.
There have been experimental reports and theoretical analysis about the shielding effectiveness of graphene. But in these previous works, the researchers used graphene flakes obtained by the reduction of graphene oxide, not a single layer graphene as in this work.
Schematic drawings of the measurement setup for the electromagnetic interference shielding effectiveness of graphene. (a) Waveguide measurement system (frequency range: 2.2-7 GHz) with two waveguide-to-coaxial adapters and a vector network analyzer. The size of the graphene shield in the waveguide is 8.6 cm x 4.3 cm. (b) Measurement setup using a horn antenna, a transverse electromagnetic mode (TEM) cell, and a vector network analyzer. In this measurement, a single frequency of 2 GHz is used. (Reprinted with permission from IOP Publishing)
For accurate assessment of the EMI shielding capability of a graphene layer, the researchers needed a true monolayer graphene over the entire area of the shield. In their experiments, they fabricated a waveguide with a graphene shield measuring 8.6 cm x4.3 cm.
"To have such a high quality and large size graphene sheet with an excellent thickness uniformity is not an easy job," Cho points out. "Another difficulty is to ensure accuracy of the EMI measurement, eliminating interference from all other sources. Our experiment was extremely carefully carried out and we could obtain reliable measurement results."
So far there have been no theoretical studies on the mechanism of EMI shielding of graphene. With the new model developed by the KAIST team, researchers can now predict the EMI shielding effectiveness of graphene for a specific application.
Since graphene has negligible mass and is ultrathin, transparent, and flexible, it will be an excellent choice of EMI shielding material for portable electronic devices, transparent electronics, automobiles, and EMI isolation of 3D integrated circuits, etc.