Palladium thin films have been studied as hydrogen sensing materials and applied to variety of optical hydrogen sensors. Recently, tantalum has emerged as an attractive option for hydrogen sensing materials due to its broad sensing range and flexibility in tuning the sensing range by modifying the alloying composition or elements. Following the demand for optical hydrogen sensors for aerospace applications, testing the performance of hydrogen sensing materials is of interest. This work examines the optical response in respect to changing hydrogen concentrations and thermal expansion of palladium-gold (Pd0.65Au0.35) and tantalum-ruthenium (Ta0.97Ru0.03 and Ta0.91Ru0.09) thin films at temperatures similar to a hydrogen combustion engine. Our results suggest that tantalum-ruthenium alloys are suitable for sensing hydrogen from ambient temperatures up to 270°C because its low detection limit (0.01% of hydrogen in the atmosphere) is well below the explosive limit of hydrogen (4% of hydrogen in the atmosphere).
In this paper, the response of a graphene oxide (GO) coated long period grating (LPG) to the change in temperature and in humidity is reported. To create the probe, an improved Hummer’s method was used to synthesis the GO solution used as its basis, allowing coating of functionalized LPG by using a multi-layer dip coating technique. A consistent and stable response of the resonance peak intensity of the GO coated LPG was observed to the change in humidity, achieving a sensitivity of 0.15 dB / %RH with a linear correlation coefficient of 0.9804 over the relative humidity range from 60%RH to 95%RH at room temperature (25 °C). A blue shift of the resonance peak wavelength was recorded when the proposed sensor was exposed to varying temperature conditions from 25 °C to 70 °C and the response was found to be linear with a correlation coefficient of 0.9973. The GO coated LPG humidity sensor probe performed with a good stability and repeatability over a number of test cycles in this initial performance evaluation.
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