Comparison of Mid-IR LED-Based and MEMS Hotplate-Based Photoacoustic CO2 Sensors

The focus of this work is the development of two types of low-cost photoacoustic (PA) CO2 sensors, the first was made from mid-infrared (mid-IR) light emitting diode (LED) and the second was made from micro-electro-mechanical system (MEMS) hotplate. Both sensors use MEMS microphones for the detection of the generated acoustic signal. These sensors have advantages of low power consumption, small size and low cost. Analyses of results from both sensors show that temperature change (within−20°C–50°C range) affects their signal amplitude and sensitivities. Results also show that the absence of buffer gas in the cell reduces the PA signal amplitude. Furthermore, comparison of results from the sensors indicate that the LED sensor is more sensitive by about one order of magnitude while the hotplate sensor, which is less expensive, has a better noise performance. This is the first time that such comparison is done and it is important because it reveals the advantages and limitations of these sensors. The findings is vital for determining which sensor will be suitable for certain applications, considering the cost.