Driss Lahem

Hybrid fiber gratings coated with a catalytic sensitive layer for hydrogen sensing in air

Using hydrogen as fuel presents a potential risk of explosion and requires low cost and efficient leak sensors. We present here a hybrid sensor configuration consisting of a long period fiber grating (LPFG) and a superimposed uniform fiber Bragg grating (FBG). Both gratings are covered with a sensitive layer made of WO(3) doped with Pt on which H(2) undergoes an exothermic reaction. The released heat increases the temperature around the gratings. In this configuration, the LPFG favors the exothermic reaction thanks to a light coupling to the sensitive layer while the FBG reflects the temperature change linked to the hydrogen concentration. Our sensor is very fast and suitable to detect low hydrogen concentrations in air whatever the relative humidity level and for temperatures down to -50 degrees C, which is without equivalent for other hydrogen optical sensors reported so far.

Catalytic Fiber Bragg Grating Sensor for Hydrogen Leak Detection in Air

The explosion risk linked to the use of hydrogen as fuel requires low-cost and efficient sensors. We present here a multipoint in-fiber sensor capable of hydrogen leak detection in air as low as 1% concentration with a response time smaller than a few seconds. Our solution makes use of fiber Bragg gratings (FBGs) covered by a catalytic sensitive layer made of a ceramic doped with noble metal which, in turn, induces a temperature elevation around the FBGs in the presence of hydrogen in air.

Silicon-on-Insulator (SOI) Ring Resonator-Based Integrated Optical Hydrogen Sensor

We demonstrate a novel, highly sensitive integrated hydrogen sensor based on a silicon ring resonator on the silicon-on-insulator platform. The hydrogen sensitive element in the sensor structure is a platinum-doped tungsten oxide catalytic coating. The catalytic combustion of hydrogen in air leads to a local temperature rise in the ring resonator. The resulting thermo-optic effect shifts the ring resonator resonance. Resonance wavelength shifts higher than a nanometer are measured for hydrogen concentrations below the 4% lower explosion limit. A potentially tunable sensitivity of around 480 pm shift per %H2 is achieved at an operating temperature of about 40degC.

A Formaldehyde Sensor Based on Molecularly-Imprinted Polymer on a TiO2 Nanotube Array

Today, significant attention has been brought to the development of sensitive, specific, cheap, and reliable sensors for real-time monitoring. Molecular imprinting technology is a versatile and promising technology for practical applications in many areas, particularly chemical sensors. Here, we present a chemical sensor for detecting formaldehyde, a toxic common indoor pollutant gas. Polypyrrole-based molecularly-imprinted polymer (PPy-based MIP) is employed as the sensing recognition layer and synthesized on a titanium dioxide nanotube array (TiO2-NTA) for increasing its surface-to-volume ratio, thereby improving the sensor performance. Our sensor selectively detects formaldehyde in the parts per million (ppm) range at room temperature. It also shows a long-term stability and small fluctuation to humidity variations. These are attributed to the thin fishnet-like structure of the PPy-based MIP on the highly-ordered and vertically-aligned TiO2-NTA.

Mild steel corrosion in chloride environment: effect of surface preparation and influence of inorganic inhibitors

Abstract The aim of the present work is to study the effect of surface mild steel preparation on its electrochemical behaviour in neutral chloride solution without and with an inorganic inhibitor. Various surface preparations are examined: alkaline degreasing, acid pickling and polishing. Open circuit potential measurements and potentiodynamic polarisations are used as corrosion monitoring techniques. The effect of chloride concentration is evaluated. The ability of inorganic inhibitors (Na2MoO4, NaNO2, Na2WO4 and Na2VO3) to stabilise the passive state of steel in chloride containing solutions is assessed by electrochemical and surface analysis techniques. The results reveal that, among the four inhibitors studied, the sodium molybdate is the best environmentally friendly corrosion inorganic inhibitor for steel.

Review of the Use of the Optical Fibers for Safety Applications in Tunnels and Car Parks: Pollution Monitoring, Fire and Explosive Gas Detection

Optical fiber sensors bring to measurement systems all the advantages offered by the optical fiber technology. The potential applications for these sensors are numerous and can spread from medical diagnosis to pipe line monitoring passing through geological measurements. This chapter will focus on the applications in road tunnels and undercroft car parks monitoring. It will detail the existing optical fiber sensor methods, commercially available or under development in the field of air quality monitoring, in particular NO2 that is representative of toxic automotive pollution, flaming fire detection and combustible gas leak detection (in particular methane and hydrogen).

Synergistic improvement of inhibitive activity of dicarboxylates in preventing mild steel corrosion in neutral aqueous solution

Abstract The efficiency of dicarboxylate corrosion inhibitors for mild steel in near neutral NaCl solution was studied using electrochemical methods as open circuit potential, potentiodynamic polarisation curves and electrochemical impedance spectroscopy. Surface analysis was carried out to determine the kind of protection afforded by these inhibitors and to establish the inhibition mechanism. The results show that adipate and sebacate are good inhibitors, and their effectiveness is strongly dependent on chloride concentration. In the case of sebacate, the concentration required for inhibition was determined, and it was found that full protection strongly depends on the chloride concentration. Furthermore, it was shown that the mixture of benzotriazole with these dicarboxylates significantly improves the inhibition performance. The combination of these inhibitors exhibits a synergistic protective effect as it leads to higher efficiencies compared to those obtained when used individually.

Novel FBG-based sensor configuration for H2 leak detection in air

The explosion risk linked to the use of hydrogen (H 2 ) as combustible requires low-cost and efficient sensors. We present a multipoint in-fiber sensor capable of H 2 leak detection as low as 1% concentration in air with a response time smaller than a few seconds. Our solution utilizes uniform fiber Bragg gratings (FBGs) surrounded by a catalytic sensitive layer made of a ceramic doped with a noble metal. In the presence of H 2 in air, the sensitive layer undergoes an exothermic reaction and elevates the temperature around the FBGs. The sensor interrogation technique is based on the monitoring of the resonant wavelength shift. In this paper, the performances of the sensor are also discussed.

Hydrogen sensor using fiber gratings covered by a catalytic sensitive layer

In this paper, we present hydrogen sensors based on uniform fiber Bragg gratings and long period fiber gratings covered by a catalytic sensitive layer made of a ceramic doped with noble metal. In presence of hydrogen in air, the sensitive layer has the unique property of being the siege of an exothermic reaction. Hence, for increasing hydrogen concentrations, this chemical reaction leads to an increase of temperature around the fiber gratings, which consequently shifts the resonance wavelength. The sensing mechanism is thus based on the monitoring of the resonance wavelength shift. For both kinds of gratings, the sensor response is linear and without hysteresis between increasing and decreasing hydrogen concentrations. It is also selective and extremely fast. Different experiments obtained on uniform fiber Bragg gratings of different physical lengths and on long period fiber gratings are reported in this paper.

Ultra-low-power chemiresistive microsensor array in a back-end CMOS process towards selective volatile compounds detection and IoT applications

We describe an ultra-low-power volatile compounds microsensor array towards increased selectivity and sensitivity. The chemiresistive transducers are 100 nm-thick interdigitated gold microelectrodes coated with polypyrrole-based polymer. Two sensors arrays were implemented with respectively 3 × 3 and 2 × 2 pixels2, showing a surface per pixel down to 400 × 200 μm2. The fabrication is fully CMOS-compatible and the polymer coating is performed at wafer level by electropolymerization, using a differential pulse method from 1.1 to 1.5 V. The polymer film thickness varies from 1.2 to 1.5 μm. Looking at ammonia detection, a sensitivity up to 80 % at 5 ppm in nitrogen is achieved, while consuming below 20 μW continuously. Finally, temperature and humidity effects are analyzed at 25 and 45 °C, from 45 to 95 % RH. Such devices are very promising for remote environmental monitoring applications requiring low-cost low-power sensors associated with dedicated electronics.