There is today ample evidence that fiber Bragg gratings (FBGs) distributed along a railway track can provide robust axle counting and bring numerous assets compared to competing technologies in this practical environment. This work brings two relevant originalities with respect to the state-of-the-art solutions. First, a study of the strain distribution in the rail cross-section is performed to determine the sensitivity according to the charge and the position on the rail. Secondly, the technology is deployed along the rail track as a smart object where the sensor head is composed of four FBG wavelength-division-multiplexed in a single telecommunication-grade optical fiber and interrogated by a miniaturized read-out device. Two FBGs ensure the detection of the train direction and another two bring the required redundancy to reach a safety integrity level (SIL) 4. The read-out unit has been specifically developed for the application and contains a vertical-cavity surface-emitting laser (VCSEL) and a photodiode driven by a high-speed microprocessor unit that processes the data and communicates the useful information, i.e., the number of axles. On-field tests confirm that the proposed approach makes the installation process easier while it democratizes the technology.
Plasmonic tilted fiber Bragg gratings (TFBGs) are very efficient for fast, accurate, and minimally invasive biosensing. Their transmitted amplitude spectrum is a dense comb of narrowband cladding mode resonances (full width at half maximum < 1 nm) that is usually demodulated using highly resolved (wavelength resolution < 10 pm) devices. This work demonstrates the possibility of using a coarsely resolved spectrometer (166 pm) to read out the amplitude spectrum of a gold-coated TFBG. A refined analysis of the spectral content has allowed us to develop signal processing that provides a refractometric sensitivity of 2656 nm/RIU. This is a fivefold improvement compared to previously reported read-out techniques. Biosensing has then been successfully implemented with gold-coated TFBGs implemented in reflection mode for the detection of insulin, with specific antibodies grafted on the gold surface. Our experimental work is a first step toward the industrialization of the FBG technology, as it opens the door to fast parallel biosensing, profiting from the multiple sensing channels (up to 64) of the interrogator and its high processing speed (repetition rate up to 3 kHz).
This paper reports on the development of a smart elastic textile band containing pre-strained fiber Bragg gratings (FBG) that was specifically designed with the ambition to dynamically measure the position of the backbone. To this aim, the textile band is 700 mm long and 60 mm wide. A piece of standard single-mode optical fiber, in which four fiber Bragg gratings were inscribed, is sewn on the band. Each FBG is glued on a 3D-printed pad in a pre-strained way, allowing the detection of FBG compression in addition to elongation. Measurements were performed on this sensing elastic band and the resulting sensitivity is a Bragg wavelength shift of 12 pm per mm of textile elongation. Validation tests were also carried out to highlight the sensitivity to compression and to show that the sensing system is capable of repeatability in a dynamic environment.
Despite an increasing number of studies and the apparent simplicity of these model systems, the mechanisms of the growth of metal nanoparticles in a polymer matrix and, in particular, that of gold nanoparticles is still not fully understood. Usually, reported results concern global (ca. surface-averaged) measurements. Furthermore, the optical properties of plasmonic nanocomposites are difficult to investigate when the metal volume fraction is very low, typically less than 1%. This is especially true in the case of gold for which the localized plasmon resonance is less sharp than in the case of silver and, therefore, less easy to probe. In this article, the optical properties of gold-doped nanocomposites have been studied at the (sub)micrometer scale using spatially resolved spectroscopic ellipsometry. At low gold volume fraction, the thermal annealing of the composite leading to the in situ growth of the gold nanoparticles induces a local inhomogeneity of the Ψ and Δ ellipsometric images that can be analyzed in terms of heterogeneity of the gold fraction. Spectroscopic imaging ellipsometry confirms the existence of gold-depleted regions in the vicinity of the largest gold particles.
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