IISc develops and validates low-cost gas sensor
One major objective of the AQM project is the development and validation of a low-cost sensor array system to measure all the parameters necessary for air quality index determination. To that end, the Centre for Nano Science and Engineering (CeNSE) at the Indian Institute of Science just completed the design of its patented nano gas sensors for CO, C02, NO2, and SO2 detection. Furthermore, the packaged sensor also features temperature, pressure and humidity sensors.
Those sensors are fabricated in-house, using a seven-step fabrication process, and later the sensors are characterised and packaged on a single TO-16 pin header. The CeNSE AQM sensors have the following advantages compared to commercially available sensors:
- Lower power consumption: The CeNSE NO2 sensor, for example, only uses 30mW compared to 75-90 mW for a commercially available MEMS sensor.
- Packaged in small size: Seven sensors (four gas sensors and sensors for temperature, pressure and humidity) are part of a 15mm diameter-16 pins configuration, which is half the size of a commercially available MEMS device while also hosting five more sensors.
- Compensation for ambient temperature and humidity with smart algorithms to take care of drifts, whereas typical MEMS sensors do not provide the variations of humidity and temperature for calibration and sensor correction.
- Fast response time of <60 secs with very good cross sensitivity and stability.
The CeNSE calibration facility is having an automated setup to mix gases in different proportions to calibrate each sensor for its performance and also implement algorithms to correct the variations in temperature and humidity. The procedure consists of mixing synthetic air with a known concentration of gas under a controlled flow rate to get a desired parts-per-million (ppm) mixture. The process is controlled via a computer and it can record all parameters including temperature and humidity.
After characterisation, the sensors are packaged and then attached to the Sensor Signal Condition Board (50 mm by 60mm). This sensor board is a four-channel signal conditioning board which can detect sensor current in nano amperes and provide an amplified output for further digital processing. Therefore, we are able to very accurately measure gas concentrations in order to monitor air quality in ppm or micro-/milligram per cubic metre.
Once the the sensor boards are assembled, we will test them in the field and CeNSE will then work on building the prototype “AQM 2.0”, which will house the sensor array and will be able to send the data via WLAN/LORA.