Carbon dioxide sensor for mobile devices: A novel approach for low-power consuming, highly sensitive NDIR sensors

In this work, a miniature sensor for carbon dioxide is presented. Until now, limiting factors for the implementation of gas sensors in smartphones include their production costs, large size and the comparatively poor sensitivity. A small-scale sensor for carbon dioxide suitable for integration in a smartphone is introduced that overcomes these constraints. The sensor components are low-cost, low-power consuming only. As light source a mid-infrared LED is employed and to gauge the light intensity a photoacoustic detector consisting of a commercially available microphone inside a hermetically sealed carbon dioxide cell is used. To save space and minimize intensity losses, a novel waveguide is used to direct the LED radiation to the detector. The waveguide simultaneously forms the measuring chamber. At the same time, because of the high sensitivity of our detector, the overall size can be reduced to a level where it is compatible with standard IC sockets. Gas measurements were performed that emphasize the suitability of the sensor. While providing high sensitivity, the influence of cross-sensitivities to humidity are insignificant and influences due to temperature shifts may be compensated for.