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Sensors 2001, 1(6), 193-205; doi:10.3390/s10600193

A Carbon Nanotube-based Sensor for CO2 Monitoring

 and *
Department of Electrical Engineering & Materials Research Institute, 208 Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802, USA
* Author to whom correspondence should be addressed.
Received: 8 October 2001 / Accepted: 17 October 2001 / Published: 2 November 2001
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A carbon dioxide (CO2) sensor is fabricated by depositing a thin layer of a multiwall carbon nanotube (MWNT) – silicon dioxide (SiO2) composite upon a planar inductorcapacitor resonant circuit. By tracking the resonant frequency of the sensor the complex permittivity of the coating material can be determined. It is shown that the permittivity of MWNTs changes linearly in response to CO2 concentration, enabling monitoring of ambient CO2 levels. The passive sensor is remotely monitored with a loop antenna, enabling measurements from within opaque, sealed containers. Experimental results show the response of the sensor is linear, reversible with no hysteresis between increasing and decreasing CO2 concentrations, and with a response time of approximately 45 s. An array of three such sensors, comprised of an uncoated, SiO2 coated, and a MWNT-SiO2 coated sensors is used to self-calibrate the measurement for operation in a variable humidity and temperature environment. Using the sensor array CO2 levels can be measured in a variable humidity and temperature environment to a ± 3% accuracy.
Keywords: Carbon dioxide; carbon nanotube; resonant circuit; wireless; remote query Carbon dioxide; carbon nanotube; resonant circuit; wireless; remote query
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Ong, K.G.; Grimes, C.A. A Carbon Nanotube-based Sensor for CO2 Monitoring. Sensors 2001, 1, 193-205.

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