  Graphene oxide relative dielectric permittivity, both its real and imaginary
parts, have been measured under various humidity conditions at GHz. It is
demonstrated that the relative dielectric permittivity increases with
increasing humidity due to water uptake. This electrical property of graphene
oxide was used to create a battery-free wireless radio-frequency identification
(RFID) humidity sensor by coating printed graphene antenna with the graphene
oxide layer. The resonance frequency as well as the backscattering phase of
such graphene oxide/graphene antenna become sensitive to the surrounding
humidity and can be detected by the RFID reader. This enables batteryless
wireless monitoring of the local humidity with digital identification attached
to any location or item and paves the way for low-cost efficient sensors for
Internet of Things applications.
