Budget optical sensor offers portable ammonia detection

09 Dec 2020

Aarhus University platform could contribute to reduction of air pollution from agriculture.

Gaseous emissions from agriculture are a factor in global warming, with ammonia from manure storage and application being one significant contributor.

Monitoring these emissions would be more readily achieved with cost-effective and selective gas sensor systems, but optical platforms to detect ammonia have to date been large and expensive.

A team from Aarhus University and DTU Fotonik at the Technical University of Denmark has now developed an integrated and more cost-effective optical ammonia sensor, built around a telecoms photonic integrated circuit (PIC) and a hollow core fiber (HCF) - the first fully integrated ammonia measurement using these two components.

"Our device demonstrates that it is possible to carry out continuous ammonia monitoring for the agricultural sector, and because it is based on mature telecommunications technology, the system can be built at very low cost," said Andreas Hänsel from Aarhus University.

"The system is very compact, and it meets the need for a portable, reliable and above all inexpensive system for detecting ammonia."

As reported in MDPI Photonics, the new sensor's architecture includes a laser source from independent indium-phospide foundry Smart Photonics, with emissions tuned to match the 1522 nanometer absorption line of ammonia.

The gas cell in the device was a commercially available hollow core photonic band gap fiber from NKT Photonics, with the proof-of-concept instrument designed around a fiber length of 1.65 meters. Used together, these components exploit the high technological maturity of InP-based diode lasers and create a sensing system with a small footprint, according to the project.

In trials the new sensor proved able to detect a 5 percent concentration on ammonia gas, and the design is readily adaptable to the detection of lower concentrations by increasing the length of the HCF.

Reduce the environmental impact

The new sensor has been developed as part of the Ecometa project, which has received DKK12.5 million funding from Innovation Fund Denmark and is studying methods and technologies for controlling emissions from agriculture.

An ability to design sensors around commercial mass-produced photonics components, as the new collaboration has done, should ultimately increase the ability of projects like Ecometa to achieve substantive change in the agriculture sector.

"Ecometa is a very relevant research project with great prospects for agriculture," said Kent Myllerup of the project steering committee. "The ability to continuously and cost-effectively track the development in ammonia emissions from agriculture provides completely new opportunities for the industry to experiment on reducing emissions."

The project will run until 2021 and help Denmark to comply with its international commitments for the environment, especially with regard to ammonia.

A new sensor architecture should also be readily adaptable to target other gases that show absorption in near-infrared wavelengths, with several candidate species likely to be detectable. In its published paper, the team indicates that carbon dioxide, methane and nitrogen dioxide, among others, will have detectable concentrations using the same architecture and analogous emitters.

"This new technology takes us one step closer to enabling farmers to monitor their emissions continuously," commented Anders Feilberg of Aarhus University.

"With accurate monitoring of ammonia emissions from sheds and stables, farmers can streamline operations far better. This can allow emissions-based regulation using measured emissions, and significantly reduce the environmental impact of agriculture."