11 research outputs found
Wavelength response of a surface plasmon resonance palladium-coated optical fiber sensor for hydrogen detection
No full textAn optical fiber using palladium as sensitive layer is characterized in the range of 450 to 900 nm. The sensitive layer is deposited on the outside of a multimode fiber, after removing the optical cladding. The sensor is based on a measurement technique that uses the surface plasmon resonance effect. A continuous change in output intensity is observed as a function of the hydrogen concentration between 0.5% and 4% H2 by volume in Argon. The response shows that the transmitted intensity can either decrease or increase, depending on the selected wavelength. This behavior is directly related to the change in reflectance upon hydrogenation between the polarization s and p. The loading time is 30 s and the unloading time is 90 s in a mix of argon and 10% of oxygen. The detectors show a good reproducibility.DelftChemTechApplied Science
A reliable, sensitive and fast optical fiber hydrogen sensor based on surface plasmon resonance
No full textWe report for the first time on the experimental response of a Surface Plasmon Resonance fiber optic sensor based on wavelength modulation for hydrogen sensing. This approach of measuring the hydrogen concentration makes the sensor insensitive to intensity fluctuations. The intrinsic fiber sensor developed provides remote sensing and enables the possibility of multi-points sensing. The sensor consists of a multilayer of 35 nm Au / 180 nm SiO2/ Pd deposited on a step- index multimode fiber core. The sensitivity and selectivity of the sensor are optimal at a Pd thickness of 3.75 nm. The sensor is sensitive to a hydrogen concentration ranging between 0.5 and 4% H2 in Ar, with a response time less than 15 s.ChemE/Chemical EngineeringApplied Science
A distributed optical fiber sensor for hydrogen detection based on Pd, and Mg alloys
No full textAn optical fiber containing structured hydrogen sensing points, consisting of Palladium and/or Magnesium alloys is proposed and characterized. The sensitive layer is deposited on the outside of a multimode fiber, after removing the optical cladding. The sensor is based on a measurement technique which uses the Surface Plasmon Resonance effect. Compared to previous work1 which was performed at a single wavelength of 670nm, this study was done in the range of 450 to 900nm. A continuous change in intensity is observed as a function of the hydrogen concentration between 0.5% and 4% H2 in Ar. The response shows that the intensity transmitted can either decrease or increase, depending on the selected wavelength. The response time and the reproducibility of the detectors are also discussed. From our experiments and optical simulations we conclude that Pd covered indicator layers based on Mg alloys, such as Mg-Ti, would be even more advantageous compare to Pd layers thanks to their lower hydrogen equilibrium pressures. We will demonstrate an extended sensitivity range by juxtaposing different materials over a fiber section, having different hydrogen equilibrium pressures.DCT/O&O groepApplied Science
Optimization of Pd Surface Plasmon Resonance sensors for hydrogen detection
No full textA design to optimize a fiber optic Surface Plasmon Resonance (SPR) sensor using Palladium as a sensitive layer for hydrogen detection is presented. In this approach, the sensitive layer is deposited on the core of a multimode fiber, after removing the optical cladding. The light is injected in the fiber with a given wavelength and all fiber modes are equally excited. The intensity modulation at the fiber output is measured to estimate the presence of hydrogen absorbed by the Pd, and consequently the Hydrogen concentration in the environment. The sensor response depends on both the Transverse Magnetic (TM) polarization (magnetic field perpendicular to incidence plane) and the Transverse Electric (TE) polarization (electric field perpendicular to incidence plane). The response for the Transverse Electric polarization is opposite with respect to the Transverse Magnetic polarization. The objective here is to optimize the Pd-SPR hydrogen sensor design in order to increase its sensitivity. We introduce an analysis of the sensor response as a function of the Pd thickness. Finally, a new design based on a multilayer system is proposed to enhance the SP ’effect’.Chemical EngineeringApplied Science
Fiber optic Surface Plasmon Resonance sensor based on wavelength modulation for hydrogen sensing
No full textA new design of a fiber optic Surface Plasmon Resonance (SPR) sensor using Palladium as a sensitive layer for hydrogen detection is presented. In this approach, a transducer layer is deposited on the outside of a multimode fiber, after removing the optical cladding. The transducer layer is a multilayer stack made of a Silver, a Silica and a Palladium layer. The spectral modulation of the light transmitted by the fiber allows to detect the presence of hydrogen in the environment. The sensor is only sensitive to the Transverse Magnetic polarized light and the Traverse Electric polarized light can be used therefore as a reference signal. A more reliable response is expected for the fiber SPR hydrogen sensor based on spectral modulation instead of on intensity modulation. The multilayer thickness defines the sensor performance. The silica thickness tunes the resonant wavelength, whereas the Silver and Palladium thickness determine the sensor sensitivity. In an optimal configuration (NA = 0.22, 100 ?m core radius and transducer length = 1 cm), the resonant wavelength is shifted over 17.6 nm at a concentration of 4% Hydrogen in Argon for the case of the 35 nm Silver/ 100 nm Silica/ 3 nm palladium multilayer.ChemE/Chemical EngineeringApplied Science
Innovative fiber optic sensor for hydrogen detection
No full textA new design of a fiber optic sensor using Palladium as a sensitive layer is presented. In this new configuration, a transducer layer is deposited on a multimode fiber (without the optical cladding). The transducer layer is a multilayer stack based on a silver, a silica and a Pd layer. The spectral modulation of the light transmitted by the fiber allows to detect hydrogen. The sensor is only sensitive to the Transverse Magnetic polarized light and the Transverse Electric polarized light can be used as a reference signal. The multilayer thickness defines the sensor performance. The Silica thickness tunes the resonant wavelength, whereas the silver and Pd thickness determines the sensor sensitivity. We present some results obtained for different multilayer Pd configuration
Surface water availability and cattle herding practices shape the human-wildlife interface at the edge of a protected area
No full textPresented at the 9th international wildlife ranching symposium: wildlife - the key to prosperity for rural communities, held on 12-16 September 2016 at Hotel Safari & the Safari Court, Windhoek, Namibia in conjuction with the IUCN 2nd African Buffalo Symposium.Spatial and temporal partitioning of key resources promotes species coexistence. On the edge of unfenced protected areas, livestock and wild herbivores share foraging and watering resources. We investigated whether effective resource partitioning was maintained in African savannas as surface water availability declined during the dry season. We quantified avoidance between African elephant (Loxodonta Africana), African buffalo (Syncerus caffer) and cattle (Bos taurus & indicus) at multiple scales using habitat selection models with GPS relocation data according to seasonal changes in surface water distribution on the eastern fringe of Hwange National Park, Zimbabwe. The range and duration of cattle incursions into the protected area varied seasonally by shifting from consistent selection of open habitats close to water pans during the rainy season to the less predictable selection of areas far away from the now dried up water pans at the end of the dry season. During the rainy and cold dry season, buffalo successfully avoid cattle at large (overlap<3%) and fine spatial scales. By the end of the dry season, buffalo herds, which are restricted to the vicinity of water, still avoid the boundary of the protected area but tolerate higher overlap with cattle (10%) and do not avoid them as strongly at fine scales. Elephant home-ranges overlap extensively with cattle (15-68%) throughout the year but elephant avoid cattle by staying away from the boundary during the day and getting closer to it at night. As the dry season advances, elephant bulls range closer to the boundary especially at night and may even make excursions into the communal land in their search of forage. Synthesis: Wild herbivores strongly avoid livestock and people at the boundary of a protected area as long as their foraging and drinking resources allow. In the advent of a drought, artificial water provisioning and cattle husbandry determine the level of avoidance and may be used to mitigate disease transmission and crop-raiding
Water and cattle shape habitat selection by wild herbivores at the edge of a protected area
No full textUnderstanding the spatiotemporal dynamics of human‐wildlife interfaces is important for the sustainable management of protected areas and wildlife conservation. We investigated the drivers of domestic and wild herbivore habitat selection at the edge of an unfenced protected area adjacent to Hwange National Park, Zimbabwe. We used GPS data to quantify the movement patterns of elephant bulls, buffalo and cattle at multiple scales and according to seasonal changes of surface water availability. Cattle, elephant and buffalo prefer open grassland habitats found close to water but elephant and buffalo avoid cattle differently. During the rainy season, cattle enter the protected area daily; buffalo avoid cattle completely at the home range scale, whereas elephant bulls avoid cattle at finer scales by favoring temporal niche shift. Elephant bulls avoid direct encounters with cattle (or people) during the day but come closer to the boundary and to water at night when cattle are kept in enclosures close to the homesteads. During the dry season, when cattle range further into the protected area in search of forage, buffalo and cattle spatial overlap increases as water dependence takes precedence over avoidance. Elephant bulls range closer to the boundary at night and increase the number of excursions into the Communal Area. Cattle herding creates a buffer zone between wildlife areas and human settlements because wild herbivores strongly avoid livestock and people. However, avoidance only lasts as long as resources are abundant. Our study suggests that long‐term planning of both artificial water provisioning and traditional cattle herding practices could help maintaining spatial segregation and thus mitigate conservation conflicts such as pathogen transmission, crop raiding or livestock depredation
