Mobile Nitrogenous Gas Sensor for Air Quality, Breeding, and Farming applications – M3GA

To meet the selectivity and resolution requirements, the technology chosen in this project is a spectroscopy system based QCL (Quantum Cascade Lasers) laser source emitting in the mid infrared spectral band (i.e. 4 to 10 µm). The measurement of N2O requires the development of a QCL source in the 4.5 - 4.6 µm spectral bands or 7.5 – 8 µm range while NH3 measurement requires to develop a QCL source in the 9 – 10 µm spectral band. To monitor these chemicals,
several commercial tools based on optical detection are nowadays available but, when the tools can meet the performance requirements, their costs are prohibitive and the size inadequate for some of the applications mentioned below (particularly for field deployment).
In the M3GA project, significant size and cost reduction will be achieved by miniaturizing some key components, such as the optical assembly: in fact, it could combine the lasers beams or the detection chamber directly onto a planar substrate by means of MEMS/IC technologies.

MirSense has studied, designed and realized quantum cascade laser arrays by micro technology steps on InP substrates. The emission wavelengths of the array are close to 9µm (wave number ~ 1111cm-1), with an experimentally validated tunable range of 54cm-1. This makes it possible to cover the absorption spectral range of ammonia (NH3) and nitrous oxide (N2O).
The design of the sensor initially imagined as a hollow microcavity where the infrared light was to be guided and absorbed by the gases led to a production deadlock due to excessive propagation losses of the order of 7dB / cm. A new sensor design from segmented guides, where the gas light interaction is increased tenfold by the splitting of the guide, has reduced propagation losses to 1dB / cm. The fabrication of silicon substrate sensors by micro technology steps has been performed, but has not produced functional components for light injection and
gas detection.
- In parallel, the design and manufacture of a wavelength multiplexer on a silicon substrate has been realized. Optical performance has been achieved and qualified to allow integration with the QCL laser and wavelength multiplexing in a single multi-gas sensor.

Although the project did not allow the realization of prototypes to evaluate the measurement of gas in agricultural environments (field or buildings of breeding) its interest remains to facilitate the traceability of the polluting gases such as N2O and NH3 and to allow the production conditions adjustment or the preventive means to reduce their productions. What for livestock would improve animal comfort and for agriculture in the field to reduce input and its impact on the environment.

The published articles about array wavelength grating (AWG) for the mid-infrared show the latest Ge / SiGe20% AWG performance for the wavelength range of the M3GA project. The performance limitations due to the material are shown by the AWG characterization curves.

The objective of M3GA project is the development of a novel miniaturized tool to measure trace concentrations of nitrous oxide (N2O) and ammonia (NH3) in the air on to be used to monitor and manage of ventilation in livestock buildings or to monitor emissions from agriculture. The control of N2O and NH3 emissions from agriculture is becoming a great challenge for the next years: in France agriculture and farming account for more than 90% of the N2O and NH3 emissions. If the monitoring of nitrous gasses is to become more and more important for farming and agriculture, the detection of these species in traces can meet the requirements of several other application areas from the quality control of indoor and outdoor air to the monitoring of industrial emissions.
The measurement unit requires the development of a multi-gas sensor to detect concentrations ranging from 0.1 to 3 ppmv for N2O and 1 ppbv to 35 ppmv for NH3. Existing solutions (electrochemical sensor or semiconductor) can satisfy the criteria of compactness and portability but they have the disadvantage of being sensitive to other pollutants such oxidizing agents (ozone, nitrogen monoxide, ... ) and therefore being poorly selective especially to N2O.
To meet the selectivity and resolution, the technology chosen is a spectroscopy system based QCL (Quantum Cascade Lasers) laser source emitting in the mid-infrared spectral band (i.e. 4 to 10 µm). The measurement of N2O requires the development of a QCL source in the 4.5 - 4.6 µm spectral bands or 7.5 – 8 µm range while NH3 measurement requires develop a QCL source in the 9 – 10 µm spectral band. To monitor these chemicals, several commercial tools based on optical detection are nowadays available but, when the tools can meet the performance requirements, their costs are prohibitive and the size inadequate for field deployment.
In M3GA significant size and cost reduction will be achieved by miniaturizing some key components, such as the optical assembly to combine the lasers beams or the detection chamber, directly onto a planar substrate by means of MEMS/IC technologies. If the use of these technologies drives miniaturization and fab cost reduction it can also confer higher robustness both during the assembling and during the product lifetime.
These miniaturized devices will be assembled with suitable electronics and fluidic interconnects, provided with a specific hardware and software units to manage the whole system. The whole modules are designed and realized to be compact enough to be portable, but also equipped with an autonomous data control system and communication. This property of mobility is necessary for mapping the air quality over large areas (eg. fields).
To tune the working parameters and to assess the full operability of the system, a first series of tests will be carried out in lab conditions replicating environmental conditions similar to field test.
Finally, the sensor device will be evaluated in two application scenario: outdoor (cultivated fields / poultry farm open yard) and indoor (poultry livestock building). In these tests, the prototype performances will be compared to those of classical measurement methods for the two kinds of environments.