Colette Veillas

Surface plasmon resonance hydrogen sensor using an optical fibre

An optical fibre surface plasmon resonance (SPR) sensor has been developed for the detection of hydrogen leakages. A thin palladium layer deposited on the bare core of a multimode fibre was used as the transducer. In this device, modification of the SPR is due to variation in the complex permittivity of palladium in contact with gaseous hydrogen. This effect is enhanced by using selective injection of high-order modes in the fibre via a collimated beam with non-normal incidence on the input end of the fibre. Measurements of concentrations as low as 0.8% of hydrogen in pure nitrogen have been found to be possible. The response time varies between 3 s for pure hydrogen and 300 s for the lowest concentrations. Such a large range can be explained by the two different crystallographic phases of the palladium-hydrogen system. Moreover, the response of the sensor is dependent on the length of the sensing area. In preliminary experiments, it has been possible to split the sensing area in order to achieve a two-point detection device.

Fibre gratings for hydrogen sensing

Liquid hydrogen has been intensively used in aerospace applications for the past 40 years and is of great interest for future automotive applications. Following major explosive risks due to the use of hydrogen in air, several studies were carried out in order to develop optical fibre sensors for the detection of hydrogen leakage. This paper aims at the presentation of new hydrogen sensors based on the use of fibre Bragg gratings (FBG) and long period gratings (LPG) coated by palladium nanolayers. The sensing principle based on the palladium–hydrogen interaction is presented, as well as experimental results. It is shown that both techniques could be used for hydrogen sensing but with a sensitivity enhanced by a factor up to 500 when using a LPG sensor. FBG sensors appear to be pure strain sensors and LPG sensors are mainly based on the coupling between the cladding modes and evanescent or surface plasmon waves. Preliminary results obtained with an in-fibre Mach–Zehnder interferometer configuration with in-series LPG sensors are also presented. They show potential interest to compensate for the thermal sensitivity of the fibre gratings.

Gaseous hydrogen leakage optical fibre detection system

Liquid hydrogen has been intensively used in aerospace applications during the past forty years and is of great interest for fuel cells technologies and future automotive applications. Following upon major explosive risks due to the use of hydrogen in air, previous studies were carried out in our laboratory in order to develop optical fiber sensors for the detection of hydrogen leakage. This communication is aimed towards a prototype optical fiber system designed for the detection of gaseous hydrogen leakage near the conecting flanges of the liquid hydrogen pipes on the test bench of the engine Vulcain of the rocket ARIANE V. Depending on the configuration, the prototype sensor provides a two-level alarm signal and the detection of gaseous hydrogen leakage is possible for concentrations lower than the lower explosive limit in air (between 0.1 and 4%) with alarm response times lower than 10 seconds in a wide range of temperatures between -35°C and 300°C. The sensing principle based on palladium-hydrogen interaction is presented as well as the detection system composed of an optical fiber probe and an optoelectronic device.

Condensation phenomenon detection through surface plasmon resonance

The aim of this work is to optically detect the condensation of acetone vapor on an aluminum plate cooled down in a two-phase environment (liquid/vapor). Sub-micron period aluminum based diffraction gratings with appropriate properties, exhibiting a highly sensitive plasmonic response, were successfully used for condensation experiments. A shift in the plasmonic wavelength resonance has been measured when acetone condensation on the aluminum surface takes place due to a change of the surrounding medium close to the surface, demonstrating that the surface modification occurs at the very beginning of the condensation phenomenon. This paper presents important steps in comprehending the incipience of condensate droplet and frost nucleation (since both mechanisms are similar) and thus to control the phenomenon by using an optimized engineered surface.