A team of physicists led by Philippe Lambin from the Université de Namur in Belgium has found that a graphene plane can provide an effective absorbent shield against microwaves. The scientists demonstrated that the conductivity of several graphene layers grows when thin polymer spacers separate them. Maximum microwave absorption in the Ka communications band between 26.5 and 40 GHz is achieved with six graphene planes separated by layers of poly-methyl methacrylate (PMMA), a transparent plastic also known as acrylic glass.
A single layer of graphene can absorb up to 25% of incident microwave radiation. With a multilayer graphene/PMMA arrangement, the absorption rises to 50%. This can be explained by analysing the transmission and reflection of a plane wave at the interface between two dielectric media, when the interface contains a thin conducting layer. In this way, the researchers were able to optimise their graphene-PMMA structures for maximum absorption, with the results confirmed by electromagnetic testing.
The team has found that the static conductivity of graphene is close to the value which relates the magnetic and electric fields in any electromagnetic radiation propagating in air. This coincidence makes graphene an ideal material for absorbing radio waves, thus protecting sensitive electronic devices.