Ammonia sensing system based on wavelength modulation spectroscopy

Abstract

A sensing system in the near infrared region has been developed for ammonia sensing based on the wavelength modulation spectroscopy (WMS) principle. The WMS is a rather sensitive technique for detecting atomic/molecular species, presenting the advantage that it can be used in the near-infrared region by using the optical telecommunications technology. In this technique, the laser wavelength and intensity were modulated by applying a sine wave signal through the injection current, which allowed the shift of the detection bandwidth to higher frequencies where laser intensity noise was typically lower. Two multi-pass cells based on free space light propagation with 160 cm and 16 cm of optical path length were used, allowing the redundancy operation and technology validation. This system used a diode laser with an emission wavelength at 1512.21 nm, where NH 3 has a strong absorption line. The control of the NH 3 gas sensing system, as well as acquisition, processing and data presentation was performed.

Hydrogen gas sensors based on electrostatically spray deposited nickel oxide thin film structures

“…In the current research, nickel oxide thin films were deposited on glass substrates employing a locally-made ESD system [17]. It was essentially made up of a precursor solution, an electrostatic HV-DC power supply, a precursor atomization nozzle assembly, and a temperature-controlled hot plate heater.…”

ECOAL Project—Delivering Solutions for Integrated Monitoring of Coal-Related Fires Supported on Optical Fiber Sensing Technology

“…The integration and analysis of the results obtained in the project [3][4][5][6][7][8][9] allowed for the study of the dynamics and evolution pathways of the combustion process within the coal waste pile, as well as the identification of potential hazards to the environment and human health. In addition, the acquired knowledge and experience enable system optimization, opening up its widespread application in other self-burning coal waste piles as well as in other similar environments, such as coal storage piles.…”

“…Several techniques with such a purpose have been developed over the years; the most successful one is the so-called Wavelength Modulation Spectroscopy (WMS). It is a rather sensitive technique for detecting atomic/molecular species, with the advantage that it can be implemented in the near-infrared region by considering optical telecommunications technology [6].…”

“…It happens when light radiation interacts with molecular species and is represented by the Beer-Lambert Law [6,43,44]:…”

“…The absorption coefficient is ɛ , where is the gas concentration and the specific absorptivity of the gas [6,43,44]. A typical experimental configuration of WMS is composed by a DFB laser diode, which is wavelength-tuneable, a function generator, a gas chamber, a photodetector ,and a lock-in amplifier, as illustrated in Figure 3.…”