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Inside Air Monitor Devised as Smartphone Add-On

Gas sensor connected to mobile device
Gas sensor connected to mobile device (VTT Technical Research Centre)

13 August 2015. Engineers in Finland designed a miniaturized system for measuring levels of carbon dioxide and other gases with smartphones to monitor interior air quality for health care needs. The team at VTT Technical Research Centre, an applied research institute in Finland, developed the monitor as an add-on to mobile devices, with a spin-off company now commercializing the technology.

The team from VTT’s optical microspectrometer lab, led by Anna Rissanen, is seeking a solution deployed with mobile devices at many locations that when linked together in a network can provide an accurate reading of air quality in homes and offices. Using smartphones as the base technology makes the monitor device, for example, useful in homes to measure exhaled carbon dioxide as an indicator of sleep quality.

In addition, says Rissanen in a VTT statement, “Many day-to-day issues, such as precision and efficiency in the workplace, can depend on carbon dioxide levels and internal air quality.” She adds that the technology is made possible “due to the spread of the Internet of Things, which enables indirect observations of a range of environmental factors based on data gathered from single sensors or sensor networks.”

The system is based on a miniature gas sensor that employs a form of spectroscopy — analysis of physical properties from interaction with light — to return the presence of gases in the air. In this case, the sensor uses a form of spectroscopy known as a Fabry-Pérot interferometer that analyzes and measures gases by multiple reflections between two closely-spaced silver surfaces. Measurements are made of the beams that penetrate at various light wavelengths to determine the nature of the gas in the air, by matching the readings against known absorption rates of light for carbon dioxide and other substances.

Rissanen, senior scientist Rami Manilla who designed the sensor, and other VTT colleagues described the air monitoring system in a paper in June 2015 at a meeting of the optics and photonics society SPIE. As described in the paper, the sensor is a one-piece device integrated into a cover that fits over the smartphone, with simple control electronics, and two coin-cell batteries for power that transfers data to the smartphone through a Bluetooth connection.

Because the system is based on a simple technology, it lends itself to mass production, and a spin-off company, Spectral Engines in Helsinki, is taking that technology to market. The company is developing sensors with Fabry-Pérot interferometers as stand-alone devices or as original equipment integrated into other companies’ products.

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