Graphene Oxide Dielectric Permittivity at GHz and Its Applications for Wireless Humidity Sensing

Abstract

In this work, the relative dielectric permittivity of graphene oxide (GO), 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 finding is very different to that at a couple of MHz or lower frequency, where the relative dielectric permittivity increases with decreasing humidity. This GO electrical property was used to create a battery-free wireless radio-frequency identification (RFID) humidity sensor by coating printed graphene antenna with the GO layer. The resonance frequency as well as the backscattering phase of such GO/graphene antenna become sensitive to the surrounding humidity and can be detected by the RFID reader. This enables battery-free 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 (IoTs) applications.

Figure 1

(a) Resonator circuit for GO permittivity measurement and (b) Measured (solid lines) and simulated (dashed lines) transmission coefficients (S₂₁) of the samples with/without GO layer for various RH.

Figure 2

(a) Resonance frequency as function of RH and (b) Relative permittivity components and the loss tangent of the GO under various humidity conditions.

Figure 3

(a) Operating principle of the GO based printed graphene RFID sensor system, (b) Printed graphene antenna with a layer of GO on top(the thickness of the GO layer is 15 μm) and (c) The equivalent circuit of the RFID tag.

Figure 4

(a) Measured backscattered signal phases with various humidity as functions of frequency, (b) Enlarged backscattered signal phases at 910 MHz as function of humidity and (c) Enlarged backscattered signal phase at 900 MHz as function of humidity.

Figure 5

SEM view of GO layer on printed graphene RFID antenna on paper substrate. (a) Large view and (b) Enlarged view, layers from top to bottom are GO, printed graphene and paper in sequence.