Research on the coil-shaped element made of α-Fe2O3 doped MWCNTs for the simultaneous measurement of gas and gap at room temperature

The coil-shaped element based on α-Fe₂O₃ doped multi-walled carbon nanotubes (MWCNTs) is fabricated by sputtering and spraying technology for simultaneously measuring the gap and ethanol vapor at room temperature. The experimental results show that with the increase of spraying time, the gas response properties of MWCNTs-based coil-shaped elements change from p-type to n-type, while the gas response properties of the coil-shaped elements based on α-Fe₂O₃ doped MWCNTs change from n-type to p-type with the increase of mass ratio of α-Fe₂O₃ to MWCNTs. Particularly, the coil-shaped element with a mass ratio of 100 exhibits the highest gas response value and gap sensitivity in the gap range of 0–0.5 mm, the gas response value of impedance amplitude, impedance angle, and resistance is 0.659 %, 0.265 %, and 6.768 % at the ethanol vapor concentration of 5000 ppm, respectively. The absolute/relative gap sensitivity of impedance amplitude and impedance angle is 54,101.8 Ω·mm⁻¹/4.589 %·mm⁻¹ and 2.069°·mm⁻¹/ 5.287 %·mm⁻¹ in the gap range of 0–0.1 mm, respectively. Finally, a signal processing method is proposed for the simultaneous measurement of ethanol vapor concentration and gap. These results lay a foundation for the development of MWCNTs-based sensors and the sensors applied between narrow gaps.