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Measure What Matters – Sense CO2 to Improve Air Quality in Smart Homes and Smart Buildings

We are an indoor generation, spending most of our time in cars, plains, trains or buildings. The level of CO2 indoor has a severe impact on our wellbeing and performance.  The health impact can range from headaches, drowsiness, and poor concentration that could lead to reduced productivity to the undetected build-up of airborne viruses, such as Covid-19.

The demand for this sensing capability is immense. A recent 2021 market forecast projects the advanced CO2 sensors market to grow by USD 258.87 million during 2021-2025 at a CAGR of over 7% during the forecast period. The growth of the global construction market is one of the major factors driving the market.

System designers have choices for the CO2 sensing technology used in their sensors. Two common choices are non-dispersive infrared (NDIR) sensors and sensors that estimate the concentration of carbon dioxide or eCO2 sensors

NDIR sensors consist of an IR light source, a sample chamber, a spectral filter, and reference and absorption IR detectors. As a result, they are relatively large and expensive. In spite of making accurate CO2 measurements, their form factor makes them difficult to integrate and unsuitable for installation in small internet of things (IoT) devices or smart home components.

Unlike the NDIR sensor, eCO2 sensors can be smaller but they do not perform real-time measurements. Instead, they use algorithms to calculate an equivalent CO2 value. Based on many assumptions, the estimated values do not necessarily improve the air quality at the right moment, resulting in the climate control system consuming an unnecessarily large amount of energy.

Using its extensive microelectromechanical system (MEMS) technology, Infineon has developed a new CO2 sensor based on photoacoustic spectroscopy (PAS) that addresses the shortcomings of existing CO2 sensors. In the PAS sensor (see Figure 1), pulses of light from an infrared source pass through an optical filter tuned specifically to the CO2 absorption wavelength of λ= 4.2 µm. The CO2 molecules inside the measurement chamber absorb the filtered light, causing the molecules to vibrate and generate a pressure wave with each pulse. Detecting the pressure change generated by the CO2 molecules within the sensor cavity, the sensor’s microcontroller converts the output into a CO2 concentration reading.

CO2 sensor diagram
Fig 1

Incorporating an acoustic detector, similar to an internal microphone, Infineon’s XENSIVTM PAS CO2 sensor achieves size and cost benefits compared to NDIR sensors, without compromising performance.

In addition to integrating a photoacoustic transducer with a detector, infrared source, and optical filter on a small PCB, the 14 x 13.8 x 7.5 mm3 XENSIV™ CO2 sensor contains a microcontroller for on-board signal processing, sophisticated algorithms, and a MOSFET for operating the infrared source (see Figure 2). To achieve the highest performance of the detector, the PAS sensor design had to minimize system noise. This required isolating the MEMS detector from external noise so that only the pressure change originating from the CO2 molecules in the chamber is detected. To do this, the absorption chamber is acoustically isolated from external noise to provide accurate CO2 sensing information and minimize the impact of noise. This results in the sensor achieving accurate and robust performance of ±30 ppm ±3% of reading.

Fig 2

The integrated microcontroller in the XENSIV™ PAS CO2 sensor performs ppm calculations as well as providing advanced compensation and configuration algorithms for high performance CO2 sensing.

The PAS CO2 kits are now available. Showing how fast and easy the sensor is to use, the kits demonstrate plug & play CO2 measurements in ppm readout for indoor air quality monitoring. A complete suite of product evaluation boards (PAS CO2 evaluation board, Arduino-based Shield2Go board), software libraries, and comprehensive documentation, including application notes, will also be available soon to support customers and accelerate the design-to-market time of the PAS CO2 sensor.

While CO2 is a colorless and odorless gas, Infineon’s XENSIV™ PAS CO2 sensor provides an electronic nose to sniff out potential air quality problems. The new sensor is ideal for high-volume, cost-sensitive smart home and building automation applications such as demand-controlled ventilation systems, air purifiers, thermostats, weather stations, and personal assistants. By integrating CO2 measurement into these systems, energy can be saved by an automated air ventilation system, operation only when needed and indoor air quality can be greatly improved, leading to a lower energy bill and a healthier indoor environment. Infineon is making a valuable contribution to enable everyone to track their environment in a smart, easy-to-use and affordable way – for a better and healthier life!

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BiS Team

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