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

Xianjun Huang,Jijo Abraham,Ting Leng,Rahul Raveendran Nair,Kostya S Novoselov,Zhirun Hu,Thanasis Georgiou

doi:10.1038/s41598-017-16886-1

Xianjun Huang, Jijo Abraham + Show 5 more

Open Access

https://doi.org/10.1038/s41598-017-16886-1

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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.

Highlights

Pristine graphene oxide (GO) has been used in this work, which is a relatively good insulator at room temperature and low humidity
In order to extract the relative permittivity, a calibration circuit with exactly the same parameters was prepared, where GO layer was mimicked by a thin dielectric layer of exactly the same thickness as GO with known relative permittivity
The measurement results clearly reveal that the GO dielectric property changes with the humidity but in a different manner as it does in a couple of MHz or lower frequency

Summary

Introduction

Pristine GO has been used in this work, which is a relatively good insulator at room temperature and low humidity. The ionic conductivity due to the intercalated water increases and GO becomes poorly conductive[6]. We experimentally determine both the real and imaginary parts of the GO relative dielectric permittivity at GHz. The findings in this work are very different to those reported in7,12 – both the real and imaginary parts of the GO relative dielectric permittivity decrease with decreasing humidity, from ∼17 at 100% RH to 12 at 10% RH (the real part of the relative permittivity) and from 6 at 100% RH to 2 at 10% RH (the imaginary part of the relative permittivity). The electrical properties of the GO are used to construct battery-free wireless RFID humidity sensors for Internet of Things (IoTs) applications

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