Researchers from Chiba University have developed a novel calibration-free approach that substantially improves the accuracy and detection limits of hydrogen sensing via tunable diode laser absorption spectroscopy (TDLAS). The study was published in the journal Optics and Laser Technology.
Hydrogen detection using tunable diode laser absorption spectroscopy (TDLAS). Deviation of measured concentration (in parts per million) over varying integration times resulting from Allan deviation. Image Credit: Tatsuo Shiina from Chiba University
Hydrogen gas is an attractive energy source with numerous benefits: it is lightweight, storable, energy-dense, and environmentally friendly, generating no pollutants or greenhouse gases compared to fossil fuels. Due to these advantages, hydrogen finds applications across various sectors, such as transportation, construction, power generation, and industry.
However, its high flammability demands effective leak detection and purity assurance methods to enable safe and broad usage. This need has driven the development of trace-gas sensing techniques. Although multiple hydrogen sensing methods exist, none currently provide optimal performance.
Tunable diode laser absorption spectroscopy (TDLAS) has emerged as a promising method for detecting various gases, drawing attention for its non-contact measurement, in situ detection, high selectivity, fast response, low cost, and ability to simultaneously measure multiple components and parameters.
TDLAS utilizes the unique absorption of light at specific wavelengths by gases, creating an absorption line in the spectrum. The gas concentration can be determined by assessing how much laser light is absorbed at this wavelength. However, detecting low hydrogen concentrations with TDLAS remains challenging due to hydrogen’s relatively weak absorption in the infrared range compared to other gases.
To overcome this limitation, a research team in Japan, led by Associate Professor Tatsuo Shiina from the Graduate School of Engineering at Chiba University, developed a novel method for accurately measuring hydrogen gas with TDLAS. The team included Alifu Xiafukaiti and Nofel Lagrosas from Chiba University, Ippei Asahi from Shikoku Research Institute Inc., and Shigeru Yamaguchi from the School of Science at Tokai University.
In this study, we achieved highly sensitive detection of hydrogen gas through meticulous control of pressure and modulation parameters in the TDLAS setup. Additionally, we introduced a calibration-free technique that ensures the adaptability to a wide range of concentrations.
Tatsuo Shiina, Associate Professor, Graduate School of Engineering, Chiba University
In TDLAS, laser light passes through a pressurized gas cell known as a Herriott multipass cell (HMPC) containing the target gas. The laser’s wavelength is modulated around the gas’s target absorption line at a specific frequency to minimize environmental noise. Pressure within the HMPC significantly affects the absorption line width, which in turn influences the modulation parameters in TDLAS.
The researchers analyzed the width of hydrogen’s strongest absorption line at various pressures. Through simulations, they determined the ideal pressure for achieving a broader absorption line width and identified the optimal modulation parameters within this line width.
Their calibration-free approach used the ratio of the first harmonic of the modulated absorption signal to the second harmonic rather than relying solely on the second harmonic signal as conventional TDLAS systems do. They also used a high-pressure gas cell containing pure hydrogen as a reference to fine-tune the modulation parameters of the laser signal.
Using this innovative method, the researchers successfully measured hydrogen concentrations over a broad range from 0.01% to 100%, with 0.01% corresponding to a concentration of 100 parts per million (ppm). Additionally, detection sensitivity improved with extended integration times (the duration for which light absorption is measured).
At an integration time of 0.1 seconds, the minimum detection limit was 0.3% or 30,000 ppm, which improved to 0.0055% or 55 ppm at an integration time of 30 seconds. However, integration times beyond 30 seconds increased the minimum detection limit.
Our system can significantly improve hydrogen detection systems for safety and quality control, facilitating wider adoption of hydrogen fuel. For example, this system can be reliably used for the detection of leakages in hydrogen fuel cell cars.
Tatsuo Shiina, Associate Professor, Graduate School of Engineering, Chiba University
This pioneering technique could play a key role in advancing a sustainable future by supporting the wider adoption of hydrogen as an eco-friendly fuel.
Journal Reference:
Xiafukaiti, A., et al. (2024) Optimization for hydrogen gas quantitative measurement using tunable diode laser absorption spectroscopy. Optics & Laser Technology. doi.org/10.1016/j.optlastec.2024.111587.