Miniature Low-Cost Carbon Dioxide Sensor for Mobile Devices

We present our recent advances on developing a miniature sensor for carbon dioxide that may be used in mobile devices. Until now, limiting factors for the implementation of gas sensors in mobile devices, such as smartphones, include their production costs and large size, which is associated with the comparatively poor sensitivity. To overcome these constraints, we employ a photoacoustic-based infrared detection technology to gauge the light intensity of a mid-infrared LED. The photoacoustic detector mainly consists of a commercially available microphone inside a hermetically sealed, carbon dioxide filled cell. 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. Because of the high sensitivity of our device, the overall size can be reduced to a level where it is compatible with standard IC sockets. Gas measurements were performed that demonstrate the suitability of the sensor. While providing high sensitivity, the influence of humidity on the sensor signal is insignificant and influences due to temperature shifts may be compensated for.