Passive wireless surface acoustic wave CO2 sensor for geological sequestration sites monitoring

A passive wireless CO₂ sensing system based on surface acoustic wave technology and carbon nanotube nanocomposite was developed. The gas response of the nanocomposite was about 10% resistance increase under pure CO₂. The sensor frequency change was around 0.03% for pure CO₂. With paralyne packaging, the sensor frequency change from relative humidity of 0% to 100% at room temperature decreased from over 0.1% to less than 0.01%. The lowest detection limit of the sensor is 1% gas concentration, with 0.0036% frequency change. Wireless module was tested and showed over one foot transmission distance at preferred parallel orientation.