Listening for pollution

The world’s first micro-sensor to measure air quality by ‘listening’ to the acoustic frequency of carbon dioxide has been developed by a Scandinavian consortium.

The Mascot micro-machined sensor analyses the specific resonance frequencies of gases, which change depending on the molecular mass of the gas. It has been designed to provide an early-warning system and will alert a ventilation system if oxygen levels fall too low. The acoustic resonator on the sensor’s chip can detect the signature frequency of CO2 in a volume of gas smaller than one microlitre.

The technology was developed by Norwegian and Swedish research institutes and SMEs, including Norway’s Sensonor which co-ordinated the EU-funded project.

Per Gloersen, Sensonor’s R&D co-ordinator, said that the Mascot sensor’s main benefits lay in its high-energy efficiency. He said that conventional chemical sensors are notorious for their poor long-term stability, particularly their sensitivity which, with prolonged exposure to the gas, can alter slightly over time.

According to Gloersen, the Mascot sensor will be far more stable.

‘We wanted to design a sensor that can be used for 10 years with-out deteriorating,’ he said. ‘It had to be consistently accurate and robust.’

The sensor is designed to specifically detect CO2, but Gloersen said that it could be calibrated to detect a variety of different gases. One of the technology’s main applications is to be used in car air-conditioning units.

The sensor would be connected to sophisticated electronics and continuously monitor the CO2 content of the car’s cabin. If the sensor detected an unhealthy level of the gas it would activate a switch and bring air in from outside.

In the same way, if the air outside the vehicle is full of pollutants and low oxygen levels, the system would decide to switch to just re-circulating the air.

‘This system is important for indoor air quality and climate applications,’ said Gloersen. ‘It only takes a few minutes in heavy traffic before the level of CO2 in cars becomes uncomfortable, but the dangerous aspect is that the gas is completely odourless.’

Gloersen also foresees the sensor as being useful in monitoring leakages from CO 2 -powered air-conditioning systems, as manufacturers move away from potentially environmentally unfriendly Freon-powered systems. As the operating pressure for CO 2 systems is far higher than when using Freons, there is a greater risk of a gas leakage.

The consortium’s Swedish partners are looking to use the technology in medical applications, particularly diagnostics. It is thought that the sensor could monitor patients suffering from respiratory conditions such as asthma or sleep apnea, and it is claimed that monitoring the exact amount of exhaled CO2 in a patient’s room would provide doctors with far greater precision than any existing techniques.

Gloersen said that the group is currently in discussion with a number of industrial partners, and suggested that the sensor could be commercialised within the next one to three years.