•Humidity sensitive membrane (HSM) is a key factor that decides the performance of an optical fiber humidity sensor.•The wavelength shift of the optical fiber F-P humidity sensor coated with ...polyimide HSM, was expressed as the function of ambient humidity.•The sensitivity of optical fiber sensors is mainly decided by the adsorption equilibrium constant.•For polyimide HSMs, the measured data show that the adsorptions obey the Langmuir isotherm model.
An optical fiber Fabry–Perot humidity sensor was constructed by coating a foamed polyimide (PI) membrane on the end of a multimode fiber. This sensor had a sensitivity of 0.164 nm/%RH in the humidity range of 20–95% RH. Through building refractive index (RI) and volume expansion models of the PI humidity sensitive membrane (HSM), the relationship between the volume fraction of absorbed water in the PI HSM upon and ambient humidity was investigated and the quantitative relationship between the sensor’s sensitivity and adsorption kinetics of the PI HSM determined.
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For the prism based SPR glucose sensors, glucose sensitive membrane (GSM) is a key factor that decides the performance of sensor. GSM consists of glucose oxidase (GOD) and matrix material (for ...example, polyacrylamide gel, PAM). As the prism based SPR glucose sensor coated with GSM is put in the glucose solution, some glucose and dissolved oxygen can diffuse into the GSM and produce by-products, then the by-products will change the refractive index (RI) of GSM and cause the spectrum shift of SPR sensor. In this paper, our proposes are to build the quantitative relationships among the resonance angle of SPR sensor, the RI of GSM, the concentration of glucose in GSM and the concentration of glucose in solution, and then to provide an efficient research method for the GSM of optical sensors. Firstly, we have reported the fabrication and characterization of GSM which is made of immobilized GOD on SiO2 nanoparticles and polyacrylamide gel. Secondly, we have finished a serial of SPR sensing experiments and obtained the resonance spectra of SPR sensors coated with pure PAM gel film, with free GOD@PAMfilm, and with immobilized GOD@PAM film in PBS solution, respectively, also displayed their variation relationship of resonance angle with the concentration of glucose in PBS solution. Thirdly, we have investigated the effects of solution pH and the content of immobilized GOD on the performance of the sensor, and obtained the optimum solution pH and the optimum content of GOD. Finally, we have related the resonance angle of SPR sensor and the RI of GSM by the combination of SPR experiment data and theoretical simulation, related the RI of GSM and the concentration of glucose in GSM according to Gladstone-Dale mixing rule, related the concentration of glucose in GSM and the concentration of glucose in solution by using the adsorption isotherm model of GSM.
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A novel fiber-optic refractive index (RI) and temperature sensor based on a multimode-single-mode-multimode fiber (MMF-SMF-MMF) structure coated with graphene-metal hybrid films was proposed and ...investigated. The surface plasmon resonance (SPR)-based RI sensitivity is improved by the addition of the graphene layer above or below the gold coating of the fiber and then further enhanced with the addition of gold-silver core-shell nanoparticles (Au@Ag NPs). Furthermore, the surface of graphene-Au-Au@Ag NPs film was modified with polydimethylsiloxane (PDMS) for temperature sensing, achieving a high sensitivity of −1.02 nm/°C with good repeatability. This new structure with graphene-gold-Au@Ag NPs-PDMS hybrid films shows applications in many fields, including environmental protection, clean energy, and nano-medicine.
In this work, we have proposed a novel long-range surface plasmon resonance (LRSPR) sensor with sharp reflection spectrum, which consists of a glass prism, a (A/B)4-type waveguide-coupled layer and a ...metal layer. To reveal its sharp reflection spectrum perfectly, we have simulated the effects of all factors of this LRSPR sensor on the reflection spectrum, and finally presented the optimal parameters of the LRSPR sensor with sharp reflection spectrum.
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An improved glucose sensitive membrane (GSM) is prepared by immobilizing glucose oxidase (GOD) onto a mixture of silica mesocellular foams (SiMCFs) and SiO
2
nanoparticles (SiNPs) and then trapping ...it in a polyvinyl alcohol (PVA) gel. The membrane is coated onto a gold-glass sheet to create a surface plasmon resonance (SPR) sensor. A series of experiments are conducted to determine the optimized parameters of the proposed GSM. For a GSM with a component ratio of SiMCFs: SiNPs = 7: 3 (mass rate), the resonance angle of the sensor decreases from 68.57° to 63.36°, and the average sensitivity is 0.026°/(mg/dL) in a glucose concentration range of 0 mg/dL‒200 mg/dL. For a GSM with a component ratio of SiMCFs: SiNPs = 5: 5 (mass rate), the resonance angle of the sensor decreases from 67.93° to 63.50°, and the sensitivity is 0.028°/(mg/dL) in a glucose concentration range of 0 mg/dL‒160 mg/dL. These data suggest that the sensor proposed in this study is more sensitive and has a broader measurement range compared with those reported in the literature to date.
An improved glucose-sensitive membrane (GSM) was prepared by immobilizing glucose oxidases (GODs) onto silica mesocellular foams and trapping them in a polyacrylamide gel. This gel was then coated on ...a gold/glass sheet to realize surface plasmon resonance (SPR) sensors. A series of sensing experiments was conducted to obtain the optimized parameters with the improved GSM. The experimental results showed that the improved SPR glucose sensor has a sensitivity of 0.0135 degree/(mg/dL) and a linear range of 0-160 mg/dL. This linear range is twice that obtained with the GSM by immobilizing GODs on SiO 2 nanoparticles.
To detect perimeter intrusion accurately and quickly, a stream computing technology was used to improve real-time data processing in perimeter intrusion detection systems. Based on the traditional ...density-based spatial clustering of applications with noise (T-DBSCAN) algorithm, which depends on manual adjustments of neighborhood parameters, an adaptive parameters DBSCAN (AP-DBSCAN) method that can achieve unsupervised calculations was proposed. The proposed AP-DBSCAN method was implemented on a Spark Streaming platform to deal with the problems of data stream collection and real-time analysis, as well as judging and identifying the different types of intrusion. A number of sensing and processing experiments were finished and the experimental data indicated that the proposed AP-DBSCAN method on the Spark Streaming platform exhibited a fine calibration capacity for the adaptive parameters and the same accuracy as the T-DBSCAN method without the artificial setting of neighborhood parameters, in addition to achieving good performances in the perimeter intrusion detection systems.
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Large-scale distributed fiber Bragg grating (FBG) sensor networks have a wide range of applications. However, serious crosstalk could occur in a near-identical serial FBG sensor network because of ...multiple reflections. Since crosstalk cannot be observed directly and separately from signal, experimental investigation of crosstalk is challenging. In this work, we point out the similarity and symmetry between crosstalk and ghost gratings, and by way of measuring the spectrum of ghost gratings, we experimentally study the characteristics of crosstalk in a serial array of 3010 near-identical FBGs using a commercial FBG sensor interrogation system. We show that ghost gratings drop much more rapidly in power as one goes downstream, and they are more homogeneous in spectral distribution than real gratings. The peak wavelengths of real gratings vary within ±100 pm while the peak wavelengths of the ghost gratings they generate vary within ±20 pm only. Spectral ripples are observed for ghost gratings and real gratings severely affected by crosstalk. These ripples reduce the FBG wavelength reading accuracy to ±5 pm. The work constitutes the first experimental study on crosstalk in large-scale FBG arrays.
The detection of early corrosion is a key issue to mitigate the damage induced by metal corrosion. This paper presents a corrosion sensor for steel based on an iron film-coated optical fiber ...polarizer. The polarizer is fabricated by sputtering a Fe-C film on a side-polished single mode fiber. The new fabricated polarizer shows highly birefringence, indicated by the difference of the transmission between the TE and TM modes, as well as the extinction ratio (ER). A series of simulations has been performed based on two models. The influences of the parameters of the sensor fabrication, the surrounding media, and film composition on the ER ratio and leakage are studied by the simulations. The accelerated corrosion experiments by immersing the polarizer into NaCl solution show that the polarizers become weakly birefringent after exposure. The results show that the ER and measured optical power decrease gradually during the corrosion process. The proposed polarizer can be used for monitoring the early stage of steel corrosion by building the relationship between the corrosion status and the polarization characteristics.
By fixing two FBGs on the surface of a rotating shaft along the direction of ± 45° and using dynamic wavelength demodulation technology, we propose an optical fiber sensing system to monitor the ...driving torque and torsion angle of the rotating shaft. In theory, the dependence relation of the dynamic difference of central wavelengths on the torque and torsion angle of the rotating shaft has been deduced. To verify an optical fiber sensing system, a series of sensing experiments have been completed and the measured data are approximately consistent with the theoretical analysis. The difference of two central wavelengths can be expressed as the sum of two parts: a "DC" part and a harmonic "AC" part. The driving torque or torsion angle is linear with the "DC" part of the difference of two central wavelengths, the harmonic "AC" part, meaning the torsion angle vibration, illustrates that periodic vibration torque may be caused by inhomogeneous centrifugal forces or inhomogeneous additional torques produced by the driving system and the load.
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