Xiangdong Chen

Subsecond Response of Humidity Sensor Based on Graphene Oxide Quantum Dots

Humidity sensors based on graphene oxide quantum dots (QDs-GO) with rapid response were developed. Results proved that these QD-GO-based sensors exhibit a subsecond response. The effect of film thickness on response time was discussed. The possible theory of intersection density was proposed to explain the rapid response behavior of QD-GO based humidity sensors. This letter demonstrated that QD-GO based sensors may have various applications, such as human breath monitoring.

PDMS-Coated Piezoresistive NEMS Diaphragm for Chloroform Vapor Detection

A polydimethylsiloxane (PDMS)-coated nanoelectromechanical systems diaphragm embedded with silicon nanowires (SiNWs) is proposed for chloroform vapor detection at room temperature. The PDMS film swells and leads to the deformation of micro-diaphragm when it is exposed to vapor. The SiNWs are connected in a Wheatstone bridge which is used to transform the deformation into a measurable output voltage. This sensor provides good linearity, sensitivity, and repeatability. The sensitivity of our sensor for chloroform vapor detection is 1.41 μV/V/ppm, while the power consumption is as low as 2 μW.

A QCM Humidity Sensors Based on GO/Nafion Composite Films With Enhanced Sensitivity

A novel humidity sensor was made of quartz crystal microbalance and graphene oxide (GO)/Nafion nanocomposites. The humidity sensing properties of the sensor, such as sensitivity, stability, humidity hysteresis, dynamic response, and recovery, were investigated by monitoring changes in both resonant frequency and impedance spectrum. The results of the investigation showed the introduction of GO in Nafion matrix significantly enhanced sensitivity of the humidity sensors and maintained higher stability. Possible interpretation is that the introduction of GO sheets improves the hydrophilic property and mechanical property of GO/Nafion nanocomposites due to unique properties of GO. Meanwhile, the sensors based on GO/Nafion nanocomposite films exhibited a narrow humidity hysteresis.

Ultra-High Sensitivity Humidity Sensor Based on MoS 2 /Ag Composite Films

Novel capacitance-type humidity sensors based on MoS2/Ag composite films with a simple preparation method were proposed. The sensing characteristics of sensors against relative humidity were investigated, and the test results demonstrated that the humidity sensitivity of the MoS2/Ag-based sensors was significantly Enhanced, which is ten times that of the pure MoS2-based humidity sensors. Meanwhile, this kind of sensors exhibited fast response speed capable of detecting the human breath. Furthermore, complex impedance spectroscopy was discussed to understand the sensing mechanisms of MoS2/Ag-based sensors.

A Novel PQCR-L Circuit for Inductive Sensing and Its Application in Displacement Detection

A novel circuit for inductive sensing that was constructed using a quartz crystal resonator and an inductance element in series was proposed. Resonant frequency expression of equivalent model of the circuit was derived. The experimental results of the resonant frequency responses versus inductance changes of the circuit were coincident with the theoretical derivation, which proved that resonant frequency of the circuit could be tuned by inductance element. A quartz crystal inductive displacement sensor utilizing a planar spiral inductor was developed based on the earlier theories. The measurement results of the displacement sensor exhibited a highly sensitive response of 1 Hz/μm in the wide distance range 0-2000 μm and a good stability with 0.043-Hz standard deviation of the output frequency. Furthermore, the fundamental frequency dependence of quartz crystal inductive displacement sensor was also discussed. The experimental results showed that the maximum sensing range of the sensor with 10-MHz fundamental frequency was 18 mm. The best advantage of the proposed method in this paper was the convenient implementation of a high-sensitivity inductive sensor with stable digital frequency output.

A High-Stability Quartz Crystal Resonator Humidity Sensor Based on Tuning Capacitor

In this paper, a quartz crystal resonator (QCR) with high quality factor and a humidity-sensitive capacitor were combined to fabricate a high-sensitivity and good-stability humidity sensor. Through the humidity sensor, the perturbation of the humidity-sensitive capacitor which was caused by different humidity levels could be transformed into the deviation of the resonant frequency of the QCR. The expression between the resonant frequency of the sensor and relative humidity was derived. The test curve of the resonant frequency responses of the sensor versus relative humidity changes was measured and showed a similar trend to the theoretical result. In addition, the influences of different sensitive materials on the sensor performance have also been researched. And the humidity sensors exhibited a high sensitivity (116.2 Hz/%RH) and a good stability with 0.038-Hz standard deviation of the output frequency in the range of 11.13%RH–97.3%RH. The properties of humidity hysteresis as well as response and recovery have also been investigated.

A High-Sensitive Humidity Sensor Based on Water-Soluble Composite Material of Fullerene and Graphene Oxide

Fullerenes (C60) exhibits many advantageous properties but its poor solubility seriously restricts its applications. In this paper, C60 is dissolved in graphene oxide (GO) aqueous solution homogenously. This water-soluble composite material of GO/C60 is used for making a capacitive humidity sensor. This sensor shows a sensitivity of three times larger than that of the sensor based on C60 film. The possible reason is that C60 is uniformly adsorbed on the surface of GO, thus reducing the agglomeration of C60. This is supported by TEM, FTIR, and complex impedance test.

Humidity-Sensitive Properties of TiO 2 Nanorods Grown Between Electrodes on Au Interdigital Electrode Substrate

In this paper, the coralloid TiO2 nanorods were fabricated directly between electrodes on the Au interdigital electrodes via a hydrothermal method. The TiO2 nanorods were characterized using X-ray diffraction and scanning electron microscopy. Results indicated that the TiO2 nanorods have good sensitivity for humidity, including at low humidity level, and response time is momentary. This paper discusses the mechanism that probably caused the improved performance of the TiO2 nanorods by studying its electrical property through a complex impedance analysis method.