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The possibility of developing a multichannel optical chemical sensor, based on molecularly imprinted polymers (MIPs) and surface plasmon resonance (SPR) in a D-shaped multimode plastic optical fiber (POF), is presented by two cascaded SPR-POF-MIP sensors with different thicknesses of the gold layer. The low cost, the high selectivity and sensitivity of the SPR-POF-MIP platforms and the simple and modular scheme of the optical interrogation layout make this system a potentially suitable on-line multi-diagnostic tool. As a proof of principle, the possibility of simultaneous determination of two important analytes, dibenzyl disulfide (DBDS) and furfural (2-FAL), in power transformer oil was investigated. Their presence gives useful indication of underway corrosive or ageing processes in power transformers, respectively. Preliminarily, the dependence of the performance of the D-shaped optical platform on the gold film thickness has been studied, comparing two platforms with 30 nm and 60 nm thick gold layers. It has been found that the resonance wavelengths are different on platforms with gold layer of different thickness, furthermore when MIPs are present on the gold as receptors, the performances of the platforms are similar in the two considered sensors. Keywords: Cascaded multianalyte detection, Surface plasmon resonance, Dibenzyl disulfide, Furfural (furan-2-carbaldehyde), Molecularly imprinted polymers, Plastic optical fibers

In this paper, frequency dielectric spectroscopy (FDS) and an innovative optical sensor for the detection of 2-furaldehyde (2-FAL) are used to check the degree of ageing of differently processed oil-paper specimens when exposed to thermal stress. The analysis of the trend of moisture content and of 2-FAL concentrations confirms the influence of drying pre-treatment of the specimens on their ageing conditions. FDS elucidated the nature of the drying process of the specimens and the optical sensor correctly assesses a lower 2-FAL production for the vapour phase dried specimens during thermal exposure.

Degradation of electrical insulation due to the oil-paper insulating system is one of the main factors that affect power transformer service life. Although the end of life failure is inevitable, the life of the insulating paper can be maximized through careful monitoring and maintenance. In this paper an optical SPR sensor is reported for high sensitive detection of a chemical marker of the transformers’ insulating paper degradation. Temperature tests were carried out on oil–paper specimens representative of the solid insulating system of transformers, subjected to initial different drying processes and successively exposed to aging temperature. A comparative analysis with standard methods (HPLC—High Performance Liquid Chromatography) confirms that the chemical concentrations detected in oil–paper sampling of different specimens with optical SPR sensors are in good agreement with those measured by standard techniques.

The use of Nanostructured SPR sensors on Plastic Optical Fibers opens new challenges, because in an SPR sensor made by a continuous metal layer, the sensor’s response is basically related to the metal properties at optical frequencies and to the waveguide characteristics. On the other hand, when a Nanostructured SPR sensor is used, the behavior is also related to the geometric parameters of the Nanostructures. Working on them it is potentially possible to tune the sensor’s behavior. In this work the Authors present a numerical investigation in order to evaluate the behavior of two different SPR Nanostructured platforms, made by “long” gold Nanorods, and comparing them to an SPR sensor with a continuous gold layer. The difference between these two Nanostructured platforms is the orientation of the Nanorods, with respect to the light’s propagation direction. The numerical results seem to indicate an increase of the sensitivity, when an SPR Sensor with long Nanorods is used, with respect to the sensor made by a continuous gold film, with some benefits.

This paper reports preliminary results of vibration test carried out on an optical voltage sensor prototype, specially designed for monitoring Voltage parameters in Medium Voltage switchboards. These electrical components, on service, are naturally subjected to environmental noise like mechanical vibrations. Tests were carried out in a laboratory mock up, to critically assess the response of the optical sensor to an applied AC voltage in presence of vibrations. The measured good rejection to vibrations either of the sensor body and of the connecting optical fiber cable, confirmed the suitability of the exploited optical solution for next applications in Medium Voltage substation.

In this work the feasibility of an optical method for an early and high sensitivity detection of chemical agents in oil-filled power transformer is reported. It concerns the assessment of accelerated ageing of transformer insulating systems, primarily constituted of oil, paper and cellulose through an online detection of cellulose degradation by-products. The proposed optical device exploits the Surface Plasmon Resonance (SPR) excitation in a plastic optical fiber (POF) platform. High selectivity is obtained by a joint detection with a Molecularly Imprinted Polymer (MIP) layer, very specific for one of the most significant indicators of the transformer possible failure, furfural, in contact with the SPR active surface. Preliminary results of tests, carried out on calibrated furfural concentration diluted in transformer oil, confirm the feasibility of the proposed optical approach.

In this work, we report the design, implementation and characterization of SPR sensors in a D-shaped plastic optical fiber (POF), based on thin bilayers of different metals, combined titanium and gold films or palladium and gold films. These optical sensor platforms may be used for monitoring different bio-chemical receptors, particularly those with refractive indexes exceeding the typical values of aqueous phases, like for example polymeric artificial receptors. In this work different configurations have been investigated, which are all appropriate for molecularly imprinted polymers (MIPs) receptors.

Several thin transparent and conductive films composed of conductive oxides (ITO) and metallic ultrathin layers (Ag, Au, Ti) have been deposited on flexible polycarbonate substrate and characterized in terms of optical transmittance, electrical conductivity and electric field screening efficiency. Thin films properties were evaluated with respect to the requirement concerning conductive garments described in Standard IEC 60895 “Live working -Conductive clothing” for workers operating on High Voltage or Ultra High Voltage live lines. Results show that the investigated multilayers could be adopted as facial masks for protection of workers from drift currents and electric field exposure, offering better alternative in electric performances and wearing comfort than previously tested metallic nets.

This work reports preliminary results of characterization of a new optical ceramics-based device for application to Medium Voltage (MV) substations. These optical ceramics, which are based on Kerr effect, offer advantages of high sensitivity to electrical field together with a low cost for the device. Preliminary tests were successfully carried out on a commercially available device using these optical ceramics; it was suitably designed as a synchronization system for MV switchboard.

This paper describes the application of a double-sided approach to assess the spent life fraction of thermal barrier coatings (TBCs) at local positions of ex-service blades with NiCoCrAlY-Re bond coat and EB-PVD TBC. A life prediction code implemented with inverse problem solution routines was applied to determine the mean local temperature. On the single blade, large differences (>150°C) of mean local temperature were estimated between regions just after the cooling holes and far from them. A self-developed portable photostimulated luminescence piezospectroscopy (PLPS) instrument was also applied and the coating spent life fraction was evaluated with a recently proposed PLPS diagnostic parameter. The spent life fractions evaluated from mean local temperature values were in good agreement with those estimated from PLPS measurements. Lower spent life fractions were found in well cooled regions of all blades, while higher spent life fractions were calculated at the hottest positions of the blades, particularly on components coming from a plant with a double number of starts. The results confirm the reliability of the PLPS technique and its diagnostic capability also for NiCoCrAlY-Re bond coats; both local differences on the single component and blade-to-blade variations in coating spent life can be evidenced in a nondestructive way.

The application of a fibre optic sensor for ozone detection in MV switchboard is evaluated. The sensor is based on the differential measure of the absorption in UV and visible spectral bandwidths. The layout exploits the use of an optical retro-reflector, to improve the detection sensitivity. Preliminary tests were performed in comparison with another calibrated system to assess the sensitivity and the linearity of the innovative sensor (0.1-10 ppm). Further results of tests carried out on a laboratory mock-up simulating predischarge phenomena are discussed confirming the compliance of the main features of the assembled system with application requirements.

A fiber-interferometric sensor realized with standard telecommunication components operating at 1550nm is developed to detect acoustic emissions from partial discharges in oilinsulated transformers. Sensor performance is compared with typical electric measurement in realistic harsh environment.

An optical sensor based on surface plasmon waves (SPW) interrogation for chemical sensing has been developed. The optical set-up is fabricated in a compact way by means of a resonant scanner which provides an angularly spread beam incident to the sensing element. The angular position of the excited surface plasmon depends on the chemical species at the surface. The instrument has been tested to detect small variation of refractive index of a liquid mixture in contact with the film.

a previous paper', it develops the concept that both the reference beam and the sensingbeam must be conveyed along the same single -mode polarization -maintaining fiber. In such away a high noise -rejection ratio for any environmental perturbation is obtained2.The above requirements are to be added to the others related to the working conditions

The electronic structure of a single monatomic gold wire is presented for the first time. It has been obtained with state-of-the-art ab-initio full-potential density-functional (DFT) LMTO (linearized muffin-tin orbital) calculations taking into account relativistic effects. For stretched structures in the experimentally accessible range the conduction band is exactly half-filled, whereas the band structures are more complex for the optimized structure. By studying the total energy as a function of unit-cell length and of a possible bond-length alternation we find that the system can lower its total energy by letting the bond lengths alternate leading to a structure containing separated dimers with bond lengths of about 2.5 \AA, largely independent of the stretching. However, first for fairly large unit cells (above roughly 7 \AA), is the total-energy gain upon this dimerization comparable with the energy costs upon stretching. We propose that this together with band-structure effects is the reason for the larger interatomic distances observed in recent experiments. We find also that although spin-orbit couplings lead to significant effects on the band structure, the overall conclusions are not altered, and that finite Au_2, Au_4, and Au_6 chains possess electronic properties very similar to those of the infinite chain., Comment: (14 pages, 5 figures; Elsevier Preprint style elsart.sty)