An optically transparent half-wavelength microwave antenna made by layering monolayer graphene onto glass has been created by a group at Aoyama Gakuin University (Kanagawa, Japan). The antenna could be used, for example, as a transparent wireless-communications antenna that would simply be part of an architectural window, an automotive window, eyeglasses, or other glass surface. While indium tin oxide (ITO)-based transparent microwave windows have previously been fabricated, the researchers say that their graphene version removes the need to use indium, which is a rare-earth metal.
The antenna itself is actually rather small: 10.7 × 1.0 mm. It includes a gold-film coplanar waveguide (CPW) at the edge of the window connected by a gold-film transmission line to the graphene antenna itself. To create the device, graphene was first grown on a copper foil via low-pressure chemical-vapor deposition—the graphene was then transferred to the experimental 1-mm-thick, 20 × 20 mm square synthetic quartz substrate. The shape of the antenna and CPW were then patterned using standard photolithographic techniques. Monolayer graphene has a visible absorption of only around 2%, so is highly transparent. Measured reflection minima at the operational microwave frequencies, as well as the detection of the 20.7 GHz operating microwave radiation, showed that the antenna was working well, with about 90% of the microwave power reaching the antenna elements. The researchers are now working on integrating the antenna into optoelectronic devices. Reference: S. Kosuga et al., Appl. Phys. Lett. (2017); http://dx.doi.org/10.1063/1.4984956.
