RESUMO
Carbon-based materials, such as graphene, exhibit interesting physical properties and have been recently investigated in sensing applications. In this paper, a novel technique for glucose concentration correlation with the resonant frequency of a microwave resonator is performed. The resonator exploits the variation of the electrical properties of graphene at radio frequency (RF). The described approach is based on the variation in transmission coefficient resonating frequency of a microstrip ring resonator modified with a graphene film. The graphene film is doctor-bladed on the ring resonator and functionalised in order to detect glucose. When a drop with a given concentration is deposited on the graphene film, the resonance peak is shifted. The graphene film is modelled with a lumped element analysis. Several prototypes are realised on Rogers Kappa substrate and their transmission coefficient measured for different concentrations of glucose. Results show a good correlation between the frequency shift and the concentration applied on the film.
RESUMO
In this work, an enhanced tunable microwave phase shifter is presented. The phase shifter consists of three short circuited stubs and a tapered line. The stubs are connected to graphene pads. Graphene's tunable conductivity is varied by a DC voltage. This in turn causes a reactance variation at the input of the tapered line, which causes a phase variation. The physical parameters of the stubs are optimized for a maximum reactance variation by the help of analytical models, circuit and full wave simulations. Measurements of an optimized prototype are performed and a dynamic phase variation of 59∘ is obtained with an amplitude variation of less than 1 dB.