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. 2009;9(9):7431-44.
doi: 10.3390/s90907431. Epub 2009 Sep 16.

A Capacitive Humidity Sensor Based on Multi-Wall Carbon Nanotubes (MWCNTs)

Wei-Ping Chen  1 , Zhen-Gang Zhao, Xiao-Wei Liu, Zhong-Xin Zhang, Chun-Guang Suo
Affiliations

A Capacitive Humidity Sensor Based on Multi-Wall Carbon Nanotubes (MWCNTs)

Wei-Ping Chen et al. Sensors (Basel). 2009.

Abstract

A new type of capacitive humidity sensor is introduced in this paper. The sensor consists of two plate electrodes coated with MWCNT films and four pieces of isolating medium at the four corners of the sensor. According to capillary condensation, the capacitance signal of the sensor is sensitive to relative humidity (RH), which could be transformed to voltage signal by a capacitance to voltage converter circuit. The sensor is tested using different saturated saline solutions at the ambient temperature of 25 °C, which yielded approximately 11% to 97% RH, respectively. The function of the MWCNT films, the effect of electrode distance, the temperature character and the repeatability of the sensor are discussed in this paper.

Keywords: capacitive sensor; capillary condensation; carbon nanotubes (CNTs); humidity sensor.

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Figures

Figure 1.
Figure 1.
Detailed structure feature (a) and schematic diagram (b) of the capacitive humidity sensor.
Figure 2.
Figure 2.
SEM image of MWCNTs-SiO2 films.
Figure 3.
Figure 3.
Kelvin radius at different RH.
Figure 4.
Figure 4.
Schematic diagram of the capacitance to voltage converter circuit.
Figure 5.
Figure 5.
Schematic diagram of switch demodulator and low-pass filter.
Figure 6.
Figure 6.
Layout (a) and photograph (b) of the circuit chip.
Figure 7.
Figure 7.
Capacitance sensitivity to RH.
Figure 8.
Figure 8.
Simulation curve and measured curve of voltage to RH.
Figure 9.
Figure 9.
Comparison of the response of the CNT sensor and Cu-plates sensor.
Figure 10.
Figure 10.
Voltage signal responses of the sensors with different plate distances.
Figure 11.
Figure 11.
Repeatable responses of the sensor during four cycles between 11% and 86% RH.
Figure 12.
Figure 12.
Time of adsorption and desorption procedure.
Figure 13.
Figure 13.
temperature characters of the sensor.
See this image and copyright information in PMC

References

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