Research On Sensing Mechamisn Of Capacitive Type Cnt Gas/humidity Sensor

The carbon nanotube (CNT: carbon nanotube) has been catching broad attention since its discovery by Iijima from Japan in 1991. Mount of theories and experimental research demonstrate that the CNT has some excellent properties arising from its special nano structure, such as huge surface-volume ratio, good performance on absorption, stable chemistry, and also special electrical property. It is the excellent properties above-mentioned that make CNT a good candidate for kinds of sensors. By research, it is found that the sensor with CNT as sensing material is of high sensitivity and fast responding, making it have potential application.This paper was carried out on the sensing mechanism of SiO2-CNT film with low concentration of MWNT(multi-wall carbon nanotube) based on capacitive response to gas concentration. The absorption curve of gas after capillary concentration in porous sensitive film was acquired based Dubinin-Radushkevich equation of Soviet Russia academician Dubinin on gas adsorption in porous carbon. The dielectric property of multi-phase composite was studied with dielectric theory, including the expression of dielectric constant with absorption volume of gas and modifying the expression. Meanwhile, the diffusion of gas in the film was also researched and responding time was obtained.The theory was improved by the following experiment. The porous films of SiO2-CNT with different concentration of CNT were fabricated and also tested in different frequencies. It is shown from the result of the study that there is obvious interfacial polarization in low frequency sector (from 100Hz to 1MHz) for the sensing film. The absorption curve was obtained in different frequency. And the effect of slenderness ratio of CNT on sensing property was studied. For sensors with the same concentration of CNT, the capacitance of the ones with CNT of little slenderness ratio(30) is much more than those with CNT of big slenderness ratio (100). It was discovered that sensors with 1wt% CNT had excellent linearity.