High sensitivity flexible Lamb-wave humidity sensors with a graphene oxide sensing layer

Abstract

This paper reports high performance flexible Lamb wave humidity sensors with a graphene oxide sensing layer. The devices were fabricated on piezoelectric ZnO thin films deposited on flexible polyimide substrates. Two resonant peaks, namely the zero order antisymmetric (A0) and symmetric (S0) mode Lamb waves, were observed and fitted well with the theoretical analysis and modelling. With graphene oxide microflakes as the sensing layer, the sensing performance of both wave modes was investigated. The humidity sensitivity of the A0 mode is 145.83 ppm per %RH (at humidity 85%RH), higher than that of S0 mode of 89.35 ppm per %RH. For the first time, we have demonstrated that the flexible humidity sensors work as usual without noticeable deterioration in performance even under severe bending conditions up to 1500 με. Also the sensors showed an excellent stability upon repeated bending for thousand times. All the results demonstrated that the Lamb wave flexible humidity sensors have a great potential for application in flexible electronics.

Nanocellulose-assisted dispersion of graphene to fabricate poly(vinyl alcohol)/graphene nanocomposite for humidity sensing

“…In recent years, humidity measurement and monitor have been paid more and more attention for its importance and necessity in many areas such as weather prediction, historic preservation, medical/healthcare product development, industrial manufacturing, agriculture and wearable or mobile electronics [1]. For the requirements of precision, electric hygrometer gains broader concern than the traditional hair hygrometer or psychrometer, due to its sensitivity of electrical signal along with the changing of moisture content in materials.…”

A humidity sensor based on quartz crystal microbalance using graphene oxide as a sensitive layer

“…Therefore, the proposed QCM humidity sensor's sensitivity is much better compared with the reported QCM humidity sensors, and this is attributed to the large specific surface area and hydrophilic nature of the graphene oxide layers. The sensitivity is also related closely to the thickness of graphene oxide layers, and can be significantly enhanced with the increase of graphene oxide layer thickness [9]. As can be seen in Fig.3, the sensitivity of the QCM sensor with GO is high at medium RH values, but low at low RH values, and the linearity of f ∆ and S are also poor, which limited the use of the sensor.…”

“…Although carbon nanotubes and graphene flakes are good sensitive layers owing to their large surface areas, the certain degree of hydrophobicity nature of these carbon nanomaterials have suppressed their positive effects on sensitivity. On the other hand, graphene oxide (GO) flakes are a hydrophilic material beside the common nature of nanomaterials [8], and graphene oxide as a sensitive layer is expected to enhance the sensitivity of QCM humidity sensors significantly as demonstrated by flexible and transparent surface acoustic wave based humidity sensors [9]. Yao et al firstly studied the humidity sensing characteristics of GO on QCM and obtained the relationship between frequency shift and RH [10].…”

Distilling determination of water content in hydraulic oil with a ZnO/glass surface acoustic wave device

“…For this research, only the SAW devices with wavelength of λ = 16 μm were used. Our previous work (Xuan et al 2014(Xuan et al , 2015 has demonstrated the fabricated SAW devices with a wavelength of λ = 16 μm have the Rayleigh wave mode, performed well with resonant frequencies round ~171.7 MHz and have a high sensitivity to humidity. Figure 2b and c are the photo images of the SAW device used for sensing experiments.…”