Quasi-distributed optical fiber hydrogen leakage detecting system based on bus chain topology structure.

Micro-mirror optical fiber hydrogen sensors have the advantages of compact structure and fast demodulation speed. All-optical sensor networks consisting of micro-mirror optical fiber hydrogen sensors are essentially necessary across the hydrogen value chain. A bus chain topology structure hydrogen leakage detecting system based on micro-mirror sensors is proposed and experimentally demonstrated. A compensating optical path with constant power supply is introduced, and the power dissipation scheme is theoretically and experimentally proposed by designating the splitting ratios of the splitters array. By constructing such a network with twenty micro-mirror hydrogen sensors, the system has been experimentally verified with good repeatability and stability under different concentrations of hydrogen. By employing this bus chain topology strategy, a quasi-distributed optical fiber hydrogen leakage detection system with micro-mirror hydrogen sensors array is realized. It will provide a promising solution with high feasibility on multi-point leakage detecting in hydrogen infrastructures.

Improving Pore Characteristics, Mechanical Properties and Thermal Performances of Near-Net Shape Manufacturing Phenolic Resin Aerogels.

Thermally stable high-performance phenolic resin aerogels (PRAs) are of great interest for thermal insulation because of their light weight, fire retardancy and low thermal conductivity. However, the drawbacks of PRA synthesis, such as long processing time, inherent brittleness and significant shrinkage during drying, greatly restrict their wide applications. In this work, PRAs were synthesized at ambient pressure through a near-net shape manufacturing technique, where boron-containing thermosetting phenolic resin (BPR) was introduced into the conventional linear phenolic resin (LPR) to improve the pore characteristics, mechanical properties and thermal performances. Compared with the traditional LPR-synthesized aerogel, the processing time and the linear shrinkage rate during the drying of the PRAs could be significantly reduced, which was attributed to the enhanced rigidity and the unique bimodal pore size distribution. Furthermore, no catastrophic failure and almost no mechanical degradation were observed on the PRAs, even with a compressive strain of up to 60% at temperatures ranging from 25 to 200 °C, indicating low brittleness and excellent thermo-mechanical stability. The PRAs also showed outstanding fire retardancy. On the other hand, the PRAs with a density of 0.194 g/cm3 possessed a high Young's modulus of 12.85 MPa and a low thermal conductivity of 0.038 W/(m·K).

Improved performance of a fiber-optic hydrogen sensor based on a controllable optical heating technology.

A novel, to the best of our knowledge, and compact fiber-optic hydrogen sensor based on light intensity demodulation and controllable optical heating technology is proposed and experimentally investigated. This system employs three photodetectors for optic signal transformation. The first PD is used to receive a little fraction of the amplified spontaneous emission (ASE) for calibration, and the second PD is utilized to detect optic signal reflected by a single mode fiber deposited with WO3-Pd2Pt-Pt composite film. The last PD is utilized to receive the optical power reflected by the short fiber Bragg grating (SFBG) with a central wavelength located in a steep wavelength range (the intensity decreases approximately linearly with the increase of the wavelength) of the ASE light source. A 980 nm laser and proportion integration differentiation (PID) controller were employed to ensure the hydrogen sensitive film working at an operating temperature of 60°C. This sensing system can display a quick response time of 0.4 s toward 10,000 ppm hydrogen in air. In addition, the detection limit of 5 ppm in air can be achieved with this sensing system. The stability of this sensor can be greatly enhanced with a controllable optical heating system, which can greatly promote its potential application in various fields.

Strengthening Mechanism and Damping Properties of SiCf/Al-Mg Composites Prepared by Combining Colloidal Dispersion with a Squeeze Melt Infiltration Process.

SiC-fiber-reinforced Al-Mg matrix composites with different mass fractions of Mg were fabricated by combining colloidal dispersion with a squeeze melt infiltration process. The microstructure, mechanical and damping properties, and the corresponding mechanisms were investigated. Microstructure analyses found that SiCf/Al-Mg composites presented a homogeneous distribution of SiC fibers, and the relative density was higher than 97% when the mass fraction of Mg was less than 20%; the fiber-matrix interface bonded well, and no obvious reaction occurred at the interface. The SiCf/Al-10Mg composite exhibited the best flexural strength (372 MPa) and elastic modulus (161.7 GPa). The fracture strain of the composites decreased with an increase in the mass fraction of Mg. This could be attributed to the strengthened interfacial bonding due to the introduction of Mg. The damping capacity at RT increased dramatically with an increase in the strain when the strain amplitude was higher than 0.001%, which was better than the alloys with similar composition, demonstrating a positive effect of the SiC fiber on improving the damping capacity of composite; the damping capacity at a temperature beyond 200 °C indicated a monotonic increase tendency with the testing temperature. This could be attributed to the second phase, which formed more strong pinning points and increased the dislocation energy needed to break away from the strong pinning points.

The mitigation potential of synergistic quorum quenching and antibacterial properties for biofilm proliferation and membrane biofouling.

Biofouling has been a persistent problem hindering the application of membranes in water treatment, and quorum quenching has been identified as an effective method for mitigating biofouling, but surface accumulation of live bacteria still induces biofilm secretion, which poses a significant challenge for sustained prevention of membrane biofouling. In this study, we utilized quercetin, a typical flavonoid with the dual functions of quorum quenching and bacterial inactivation, to evaluate its role in preventing biofilm proliferation and against biofouling. Quercetin exhibited excellent antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and the decreased bioactivity was positively correlated with the quercetin concentration, with inhibition rates of 53.1 % and 57.4 %, respectively, at the experimental concentrations. The RT-qPCR results demonstrated that quercetin inhibited AI-2 of E. coli and AGR of S. aureus mediated quorum sensing system, and reduced the expression of genes such as adhesion, virulence, biofilm secretion, and key regulatory proteases. As a result, the bacterial growth cycle was retarded and the biomass and biofilm maturation cycles were alleviated with the synergistic effect of quorum quenching and antibacterial activity. In addition, membrane biofouling was significantly declined in the dynamic operation experiments, dead cells in the biofilm overwhelmingly dominated, and the final normalized water fluxes were increased by more than 49.9 % and 34.5 % for E. coli and S. aureus, respectively. This work demonstrates the potential for mitigating biofouling using protocols that quorum quenching and inactivate bacteria, also provides a unique and long-lasting strategy to alleviate membrane fouling.

Ultrafast deposition of polydopamine for high-performance fiber-reinforced high-temperature ceramic composites.

The low deposition time efficiency and small thickness limit the expansion of polydopamine (PDA) application to fiber-reinforced high-temperature ceramic composites. In this work, the electric field-assisted polymerization (EFAP) route was developed to improve the deposition time efficiency of PDA coating and overcome the thickness limitation. Carbonized polydopamine (C-PDA) coating was used as the interphase of carbon fiber-reinforced ZrB2-based composites (Cf/ZrB2-based composite) to bond rigid fibers and brittle ceramics, where C-PDA coating was prepared by the carbonization of PDA coating. Firstly, uniform and dense PDA coatings were deposited on carbon fibers (Cf) by EFAP. The thickness of PDA coating reached the micron level (over 1800 nm) for the first time. Benefiting from the EFAP route promoting the oxidation process of dopamine (DA) and accelerating the aggregation and in-situ polymerization of DA and its derivatives on the surface of Cf, the deposition rate of PDA coating reached 5589 nm/h, which was 3 orders of magnitude higher than that of the traditional self-polymerization process. By adjusting the EFAP parameters (e.g. DA-concentration, current, and deposition time), the thickness of PDA coating could be conveniently designed from nano-scale to micro-scale. Then, PDA coating was pyrolyzed to obtain C-PDA coating. C-PDA coating was well bonded on Cf without visible cross-sticking among neighboring fibers. C-PDA coating presented a layered structure and the thickness of C-PDA coating could be designed by controlling the thickness of PDA. C-PDA coating was used as the interfacial phase of the Cf/ZrB2-based composite, which ensured that the composite possessed good load-bearing capacity and thermal stability. Moreover, extraordinary damage resistance of the composite was achieved, with work of fracture up to 9936 ± 548 J/m2 at room temperature and 19,082 ± 3458 J/m2 at 1800 °C. The current work provides a high time efficiency processing route for depositing PDA coating on carbon fibers and demonstrates the attractive potential of PDA coating in fiber-reinforced high-temperature ceramic composites.

Fiber Optical Hydrogen Sensor Based on WO3-Pd2Pt-Pt Nanocomposite Films.

In this paper, WO3-Pd2Pt-Pt nanocomposite films were deposited on a single mode fiber as the hydrogen sensing material, which changes its reflectivity under different hydrogen concentration. The reflectivity variation was probed and converted to an electric signal by a pair of balanced InGaAs photoelectric detectors. In addition, the performance of the WO3-Pd2Pt-Pt composite film was investigated under different optical powers, and the irrigating power was optimized at 5 mW. With the irrigation of this optical power, the hydrogen sensitive film exhibits quick response toward 100 ppm hydrogen in air atmosphere at a room temperature of 25 °C. The experimental results demonstrate a high resolution at 5 parts per million (ppm) within a wide range from 100 to 5000 ppm in air. This simple and compact sensing system can detect hydrogen concentrations far below the explosion limit and provide early alert for hydrogen leakage, showing great potential in hydrogen-related applications.

Hypersensitive H2 sensor based on polymer planar Bragg gratings coated with Pt-loaded WO3-SiO2: erratum.

We present an erratum to our Letter [Opt. Lett.45, 3601 (2020)OPLEDP0146-959210.1364/OL.395341]. Labeling errors in two figures and an incorrect sentence are revised. The corrections have no influence on the conclusions of the original Letter.

Hypersensitive H2 sensor based on polymer planar Bragg gratings coated with Pt-loaded WO3-SiO2.

This Letter demonstrates a novel, to the best of our knowledge, hydrogen sensor based on a polymer planar Bragg grating coated with Pt-loaded WO3-SiO2. The reflected Bragg signal shows a distinct peak splitting correlated to substrate anisotropies originating from the injection molding process. Especially at low H2 concentrations, both sensing peaks exhibit an outstanding response to the heat generated by the exothermic reaction between hydrogen molecules and coating. Thereby, a hydrogen volume ratio of 50 ppm leads to a Bragg wavelength shift of -37pm, which yields an outstandingly low detection limit of only 5 ppm H2 in air. Thus, functionalized polymer planar Bragg gratings are eminently suitable for H2 leak detection applications.

Polar-groups-modified polyimide based on a fiber Bragg grating for relative humidity sensors.

In this work, the effect of the polar groups modified polyimide fiber Bragg grating relative humidity sensor was studied. Polyimide films containing different polar groups were deposited on fiber Bragg gratings by an impregnating method to form different relative humidity (RH) sensors. The experimental results show that the addition of a carboxyl group and a hydroxyl group in the synthesis could improve the humidity sensitivity (2.28 and 1.59 times, respectively) from 35% RH-95% RH. The sensor based on modified polyimide still has good linear response to humidity and temperature. In addition, the sensors containing a carboxyl group and a hydroxyl group can shorten the response time of the humidity sensor and improve the stability of the sensor at the same time.

High-temperature Mechanical Properties and Their Influence Mechanisms of ZrC-Modified C-SiC Ceramic Matrix Composites up to 1600 °C.

In order to understand the influence of the mechanisms of ZrC nanoparticles on the high-temperature mechanical properties of C-SiC ceramic matrix composites, the mechanical properties were measured from room temperature (RT) to 1600 °C under vacuum. The microstructures features were characterized by scanning electron microscopy. In comparison with the composites without ZrC nanoparticles, the ZrC-modified composite presented better mechanical properties at all temperatures, indicating that the mechanical properties could be improved by the ZrC nanoparticles. The ZrC nanoparticles could reduce the residual silicon and improve the microstructure integrity of composite. Furthermore, the variation of flexural strength and the flexural modulus showed an asynchronous trend with the increase of temperature. The flexural strength reached the maximum value at 1200 °C, but the highest elastic modulus was obtained at 800 °C. The strength increase was ascribed to the decrease of the thermally-induced residual stresses. The degradation of mechanical properties was observed at 1600 °C because of the microstructure deterioration and the formation of strongly bonded fiber-matrix interface. Therefore, it is concluded that the high temperature mechanical properties under vacuum were related to the consisting phase, the matrix microstructure, and the thermally-induced residual stresses.

Investigations of Different Ion Intercalations on the Performance of FBG Hydrogen Sensors Based on Pt/MoO3.

α-MoO3 has been used as a hydrogen sensing material due to its excellent properties and unique crystalline layer structure. However, the low repeatability of α-MoO3 based hydrogen sensor restricts its practical application. In this paper, the effect of intercalated ion species and the amount in α-MoO3 is experimentally investigated and discussed. It is concluded that the repeatability of the sensor depends on the radius of intercalated ions and amount of ionic bonds. The optimal ion species is Na+ and the optimal amount of precursor is 1 mmol.

High-sensitivity fiber optic hydrogen sensor in air by optimizing a self-referenced demodulating method.

Self-referenced demodulating methods of fiber optic hydrogen sensors based on WO3-Pd2Pt-Pt composite film are studied in this paper. By employing the proper baseline intensity as sensing parameters, fluctuations of the sensing signal of the hydrogen sensor can be obviously depressed, and sensitivity can be greatly improved. Experimental results show that the resolution of the hydrogen sensor can reach 3 parts per million (ppm) when the hydrogen concentration is lower than 1000 ppm. Additionally, the hydrogen sensor shows better sensitivity toward lower concentrations of hydrogen, enabling a hydrogen threshold down to 10 ppm in air at room temperature. To the best of our knowledge, this is the lowest threshold reported for an optical hydrogen sensor operated at room temperature in air. Moreover, the sensor has good repeatability during hydrogen response. This work proposes a simple and novel method to improve the performance of fiber optic hydrogen sensors, which can greatly promote their potential application in various fields.

Ultrahigh Conductive Copper/Large Flake Size Graphene Heterostructure Thin-Film with Remarkable Electromagnetic Interference Shielding Effectiveness.

To guarantee the normal operation of next generation portable electronics and wearable devices, together with avoiding electromagnetic wave pollution, it is urgent to find a material possessing flexibility, ultrahigh conductive, and superb electromagnetic interference shielding effectiveness (EMI SE) simultaneously. In this work, inspired by a building bricks toy with the interlock system, we design and fabricate a copper/large flake size graphene (Cu/LG) composite thin film (≈8.8 µm) in the light of high temperature annealing of a large flake size graphene oxide film followed by magnetron sputtering of copper. The obtained Cu/LG thin-film shows ultrahigh thermal conductivity of over 1932.73 (±63.07) W m-1 K-1 and excellent electrical conductivity of 5.88 (±0.29) × 106 S m-1 . Significantly, it also exhibits a remarkably high EMI SE of over 52 dB at the frequency of 1-18 GHz. The largest EMI SE value of 63.29 dB, accorded at 1 GHz, is enough to obstruct and absorb 99.99995% of incident radiation. To the best of knowledge, this is the highest EMI SE performance reported so far in such thin thickness of graphene-based materials. These outstanding properties make Cu/LG film a promising alternative building block for power electronics, microprocessors, and flexible electronics.

Ultra-Weak Fiber Bragg Grating Sensing Network Coated with Sensitive Material for Multi-Parameter Measurements.

A multi-parameter measurement system based on ultra-weak fiber Bragg grating (UFBG) array with sensitive material was proposed and experimentally demonstrated. The UFBG array interrogation principle is time division multiplex technology with two semiconductor optical amplifiers as timing units. Experimental results showed that the performance of the proposed UFBG system is almost equal to that of traditional FBG, while the UFBG array system has obvious superiority with potential multiplexing ability for multi-point and multi-parameter measurement. The system experimented on a 144 UFBG array with the reflectivity of UFBG ~0.04% for the four target parameters: hydrogen, humidity, temperature and salinity. Moreover, a uniform solution was customized to divide the cross-sensitivity between temperature and other target parameters. It is expected that this scheme will be capable of handling thousands of multi-parameter sensors in a single fiber.

Optical Fiber Grating Hydrogen Sensors: A Review.

In terms of hydrogen sensing and detection, optical fiber hydrogen sensors have been a research issue due to their intrinsic safety and good anti-electromagnetic interference. Among these sensors, hydrogen sensors consisting of fiber grating coated with sensitive materials have attracted intensive research interests due to their good reliability and distributed measurements. This review paper mainly focuses on optical fiber hydrogen sensors associated with fiber gratings and various materials. Their configurations and sensing performances proposed by different groups worldwide are reviewed, compared and discussed in this paper. Meanwhile, the challenges for fiber grating hydrogen sensors are also addressed.

Ultra-high sensitive optical fiber hydrogen sensor using self-referenced demodulation method and WO3-Pd2Pt-Pt composite film.

A novel fiber optic hydrogen concentration detection platform with significantly enhanced performance is proposed and demonstrated in this paper. The hydrogen sensing probe was prepared by depositing WO3-Pd2Pt-Pt composite film on the fiber tip of two Bragg gratings paired with high-low reflectivity. At a room temperature of 25°C, the hydrogen sensor has a significant response towards 10 ppm hydrogen in nitrogen atmosphere, and may detect tens of ppb hydrogen changes when the hydrogen concentration is between 10~60 ppm. Besides, the proposed system shows quick response when the hydrogen concentration is above 40 ppm. Moreover, the hydrogen sensor shows good repeatability during the hydrogen response. This work proposes a new concept to develop hydrogen sensing technology with ultra-high sensitivity, which can significantly promote its potential application in various fields, especially for ultra-low hydrogen detection in oxygen-free environment.

Water photolysis effect on the long-term stability of a fiber optic hydrogen sensor with Pt/WO3.

One of the technological challenges for hydrogen sensors is long-term stability and reliability. In this article, the UV-light irradiation was introduced into the hydrogen sensing process based on water photolysis effect of Pt/WO3. Ascribing to that, fiber optic hydrogen sensor with Pt/WO3 nanosheets as the sensing element was demonstrated with significantly improved performance of stability. Under UV irradiation, the hydrogen sensor exhibits higher sensitivity and resolution together with a smaller error range than that without UV irradiation. The enhanced performance could be attributed to the effective decomposition of water produced in the hydrogen sensing process due to the water photolysis effect of Pt/WO3. The influence of the water on stability was evaluated using experimental results, and the UV irradiation to remove water was analysed by theoretical and FT-IR spectra. This work provides new strategy of UV-light irradiation to promote the long-term stability of hydrogen sensor using Pt/WO3 as the sensing element.

Sagnac interferometer hydrogen sensor based on panda fiber with Pt-loaded WO3/SiO2 coating.

A highly sensitive optical fiber Sagnac interferometer hydrogen sensor is proposed and demonstrated. The device is fabricated by inserting a segment of panda fiber coated with Pt-loaded WO3/SiO2 into a Sagnac interferometer loop. When Pt/WO3 film is exposed to hydrogen, the exothermic reaction raises the temperature of the panda fiber, resulting in the resonant wavelength shift of the interferometer, and the resonant dip obtained has a large extinction ratio of ∼25 dB and a narrow linewidth of 2.5 nm. Such a device responds fast to hydrogen, exhibits a high sensitivity of -7.877 nm/% (vol. %) within the range of 0%-1.0% and is robust, low cost, and easy to fabricate.

Novel polyimide coated fiber Bragg grating sensing network for relative humidity measurements.

A novel relative humidity (RH) sensing network based on ultra-weak fiber Bragg gratings (FBGs) is proposed and demonstrated. Experiment is demonstrated on a 5 serial ultra-weak FBGs sensing network chopped from a fiber array with 1124 FBGs. Experimental results show that the corresponding RH sensitivity varies from 1.134 to 1.832 pm/%RH when ambient environmental RH changes from 23.8%RH to 83.4%RH. The low-reflectance FBGs and time-division multiplexing (TDM) technology makes it possible to multiplex thousands of RH sensors in single optical fiber.