Piezoelectric bimorph optical-fiber sensor

We propose and demonstrate a novel high-voltage optical-fiber sensor. This sensor consists of an emitting fiber, a receiving fiber, and a piezoelectric bimorph transducer. The emitting fiber is fixed in a base, whereas the receiving fiber is mounted on the free end of the piezoelectric bimorph transducer. When a voltage is applied to the piezoelectric bimorph transducer, its free end is displaced over a distance delta. The displacement induces a loss in the optical coupling between the emitting and the receiving fiber. The voltage can be measured by monitoring the coupling loss.     

Optical-fiber sensor using tailored porous sol-gel fiber core

A new concept in optical-fiber chemical sensors, the active fiber core optical sensor (AFCOS), is presented. In this sensor, the fiber core acts as a transducer. The sensitivity of an AFCOS sensor is compared with that of an active coating [evanescent wave (EW)] based optical-fiber sensor. Requirements for a fiber core to act as a chemical sensor are discussed. Novel techniques for making a porous sol-gel silica fiber, doping chemical reagents into the fiber, and constructing a chemical sensor using the porous fiber as a transducer have been developed. The microstructure of the fabricated sol-gel silica fiber and the effect of the fiber's microstructure on the capability of the porous sol-gel silica fiber for guiding light are discussed. A humidity sensor employing a CoCl/sub 2/-doped porous sol-gel fiber as a transducer has been constructed as an example. The test results for the humidity sensor verified a theoretical analysis indicating that an optical-fiber chemical sensor using an active fiber core as a transducer has a much higher sensitivity than that of an EW-based sensor.     

A Fiber-Optic Sensor for Monitoring Trace Ammonia in High-Temperature Gas Samples With a ${hbox{CuCl}}_{2}$-Doped Porous Silica Optical Fiber as a Transducer

An optical fiber chemical sensor for detecting/monitoring trace ammonia in high-temperature gas streams has been developed. This sensor uses a ${hbox{CuCl}}_{2}$-doped porous silica optical fiber, prepared via a previously reported sol-gel process, as a transducer. Trace ammonia in a gas sample diffuses into the porous fiber to react with the doped agent to form a ${hbox{Cu}}^{2+}$-ammonia complex. The concentration of the ${hbox{Cu}}^{2+}$ -ammonia complex inside the porous silica optical fiber is proportional to ammonia concentration in the gas sample, to which the sensing porous silica fiber is exposed. Therefore, ammonia concentration in the gas sample can be detected through detecting the optical absorption signal of the formed ${hbox{Cu}}^{2+}$-ammonia complex inside the fiber by using a fiber-optic UV/Vis absorption spectrometric method. This sensor can be used to reversibly monitor trace ammonia in a gas sample at an elevated temperature up to 450 $^{circ}$C in the tested range. A detection limit of 0.24 ppmv ammonia in an air gas sample was achieved when the sensor was tested at a temperature of 450 $^{circ}$ C.      

An optical fiber chemical sensor for mercury ions based on a porphyrin dimer

The synthesis of a novel fluoroionophore, 5-p-[[4-(10',15',20'-triphenyl-5'-porphinato) phenyloxyl]-1-butyloxyl]phenyl-10,15,20-triphenylporphine (DTPP), and its application for preparation of a Hg(II)-sensitive optical fiber chemical sensor are described. The response of the sensor is based on the fluorescence quenching of DTPP by coordination with Hg(II). The porphyrin dimer-based sensor shows a linear response toward Hg(II) in the concentration range 5.2 x 10(-7)-3.1 x 10(-4) mol x L(-1), with a working pH range from 2.4 to 8.0. The sensor shows excellent selectivity for Hg(II) over transition metal cations including Cd(II), Co(II), Cu(II), Ni(II), Pb(II), Zn(II), and Fe(III). As a sensing agent, the porphyrin dimer shows obviously better fluorescence response characteristics toward Hg(II) compared to porphyrin monomer or metalloporphyrin. The effect of the composition of the sensor membrane was studied, and the experimental conditions were optimized. The sensor has been used for determination of Hg(II) in water samples.     

An Autonomous Sensor and Telemetry System for Low-Level pCO(2) Measurements in Seawater

The measurement of low-level dissolved CO(2) using a fiber-optic sensor is described. The sensor, based on the Severinghaus CO(2) electrode principle, consists of a CO(2)-sensitive bicarbonate buffer solution containing the pH-sensitive fluorescent dye carboxy-SNAFL-1 immobilized at the end of an optical fiber using a gas-permeable membrane. The sensor is used in a ratiometric mode and has a reversible working dynamic range between 200 and 1000 ppm pCO(2) and a sensitivity ±1 ppm. Results are presented for the sensor calibration, effects of temperature, and response time characteristics. An integrated measurement system with electrooptic and data acquisition modules coupled to a satellite transmission system was tested in Vineyard Sound, MA, and data are presented that demonstrate continuous monitoring of pCO(2) in surface seawater.     

Oxygen optrode for use in a fiber-optic glucose biosensor

An optical fiber oxygen sensor, based on the dynamic quenching of the luminescence of tris(1,10-phenanthroline)-ruthenium(II) cation by molecular oxygen, is presented. The complex is adsorbed onto silica gel, incorporated in a silicone matrix possessing a high oxygen permeability, and placed at the tip of the optical fiber. Oxygen has been monitored continuously in the 0-750 Torr range, with the detection limit being as low as 0.7 Torr. The device has been applied to the development of a fast responding and highly sensitive fiber-optic glucose biosensor based on this highly sensitive oxygen transducer. The sensor relates oxygen consumption (as a result of enzymatic oxidation) to glucose concentration. The enzyme is immobilized on the surface of the oxygen optrode; carbon black is used as an optical isolation in order to prevent ambient light and sample fluorescence to interfere. Measurements have been performed in a flow-through cell in air-equilibrated glucose standard solutions of pH 7.0. The effects of enzyme immobilization procedures (including enzyme immobilization on carbon black) as to response times (around 6 min), analytical ranges (0.06-1 mM glucose), reproducibility in sensor construction, and long-term stability have been studied as well.     

A Fiber Optic Ultrasonic System to Monitor the Cure of Epoxy

A fiber optic ultrasonic system is described which monitors the cure of an epoxy resin. Ultrasound is generated using a high-power optical fiber to deliver high-energy pulses of light to the prepared surface of an aluminum mold that contains the curing epoxy resin. The generated ultrasound is detected using a local fiber optic ultrasound sensor embedded in the curing epoxy resin. The system was used to measure the ultrasonic signal velocity and ultrasonic attenuation throughout the cure of a neat epoxy resin at room temperature. Similar measurements also were performed using a piezoelectric transducer for ultrasound generation and an embedded fiber optic sensor for detection, which provided verification of the results using the complete fiber optic system. The complete fiber optic system demonstrated adequate sensitivity throughout the entire cure to measure the ultrasonic signal velocity and ultrasonic attenuation.     

Direct detection of S-nitrosothiols using planar amperometric nitric oxide sensor modified with polymeric films containing catalytic copper species

The direct amperometric detection of S-nitrosothiol species (RSNOs) is realized by modifying a previously reported amperometric nitric oxide gas sensor with thin hydrophilic polyurethane films containing catalytic Cu(II)/(I) sites. Catalytic Cu(II)/(I)-mediated decomposition of S-nitrosothiols generates NO(g) in the thin polymeric film at the distal tip of the NO sensor. Three different species are examined to create the catalytic layer: (1) a lipophilic Cu(II)-ligand complex; (2) Cu(II)-phosphate salt; and (3) small (3-microm) metallic Cu(0) particles. All three catalytic layers yield reversible amperometric response in proportion to the concentration of S-nitrosothiols (e.g., nitrosocysteine, nitrosoglutathione, S-nitroso-N-acetylcysteine, S-nitrosoalbumin) present in the aqueous test solution. Sensitivity toward the different RSNO species is dependent on the respective catalytic rates of decomposition of the RSNO species by reactive Cu(I), accessibility of the species into the polyurethane layer containing the catalyst, the level of reducing agents (ascorbate) used in solution to help generate reactive Cu(I) species, and the concentration of metal ion complexing agents present in the test solution (e.g., EDTA). Under optimized conditions, all RSNO species can be detected at < or =1 microM levels, with sensor lifetimes of at least 10 days for the sensors based on Cu(II)-phosphate and Cu0 particles. It is further shown that the new RSNO sensors can be used to assess the "NO-generating" ability of fresh blood samples by effectively detecting the total level of reactive RSNO species present in such samples.     

Stabilization of an embedded fiber optic Fabry-Perot sensor forultrasound detection

A method is proposed to stabilize an intrinsic fiber optic Fabry-Perot interferometric sensor embedded in a solid material for the purpose of detecting ultrasound. Without stabilization the interferometer drifts out of quadrature due to the presence of low-frequency dynamic strains. Stabilization is achieved by using active homodyne stabilization which tunes the laser frequency to maintain quadrature. A control loop shifts the laser frequency by 10 GHz at rates less than 25 Hz in order to compensate for induced drifts. The stabilization procedure was tested for a sensor embedded in an epoxy plate. Ultrasonic pulses, generated by a 5 MHz piezoelectric transducer, were detected with the embedded fiber sensor stabilized in the presence of applied low frequency strains. Improvements in sensitivity which result from stabilization are demonstrated. Additionally, a simulated acoustic emission signal, generated by a lead pencil break (Hsu-Neilson source), was detected with the sensor stabilized in the presence of dynamic strains     

Erbium Fiber Laser Accelerometer

A new form of fiber accelerometer based on an erbium fiber laser sensor is presented. The transducer is a unique shape derived by an automated finite element analysis design optimization program and is constructed using stereolithography     

Silicon nanowires-based fluorescence sensor for Cu(II)

Si nanowires (SiNWs) were covalently modified by fluorescence ligand, N-(quinoline-8-yl)-2-(3-triethoxysilyl-propylamino)-acetamide (QlOEt) and finally formed an optical sensor to realize a highly sensitive and selective detection for Cu(II). The QlOEt-modified SiNWs sensor has sensitivity for Cu(II) down to 10(-8) M, which is more sensitive than QlOEt alone. Metal ions interferences have no observable effect on the sensitivity and selectivity of QlOEt-modified SiNWs sensor. The SiNWs-based fluorescence sensor is reversible by addition of acid to replace Cu(II). The sensing mechanisms of QlOEt-modified SiNWs to Cu(II) and the rationale for the increase in sensitivity and selectivity of QlOEt-modified SiNWs over QlOEt on Cu(II) are discussed. The current sensor structure may be extendable to other chemo- and biosensors, and even to nanosensors for direct detection of specific materials in intracellular environment.     

Coupling fiber optics to a permeation liquid membrane for heavy metal sensor development

We present the first sensing system for metal ions based on the combination of separation/preconcentration by a permeation liquid membrane (PLM) and fluorescence detection with an optical fiber. As a model, a system for the detection of Cu(II) ions was developed. The wall of a polypropylene hollow fiber serves as support for the permeable liquid membrane. The lumen of the fiber contains the strip solution in which Cu(II) is accumulated. Calcein, a fluorochromic dye, acts as stripping agent and at the same time as metal indicator. The quenching of the calcein fluorescence upon metal accumulation in the strip phase is detected with a multimode optical fiber, which is incorporated into the lumen. Fluorescence is excited with a blue LED and detected with a photon counter. Taking advantage of the high selectivity and sensitivity of PLM preconcentration, a detection limit for Cu(II) of approximately 50 nM was achieved. Among five tested heavy metal ions, Pb(II) was the only major interfering species. The incorporation of small silica optical fibers into the polypropylene capillary allows for real-time monitoring of the Cu(II) accumulation process.     

Fabrication,characterization and sensing properties of Cu(II) ion imprinted sol–gel thin film on QCM

Cu(II)-molecularly imprinted sol–gel films (Cu(II)-MISGF), coated on a quartz crystal microbalance (QCM) chip, were fabricated using a sol–gel procedure. Co-hydrolysis and co-condensation of Cu(II) (templates), 3-aminopropyltrimethoxysilane (APTS, functional monomer) and tetraethoxysilane (TEOS, cross-linking agent) were performed with acid and base catalysis. The properties of the Cu(II)-MISGF were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and the electrochemical methods of cyclic voltammetry (CV). Microstructural observations revealed that the acid-catalyzed system yielded more mechanically stable thin films. A combined Cu(II)-MISGF-QCM with flow injection analysis (FIA) method was utilized to investigate the sensing performance of the Cu(II)-MISGF, with special emphasis on the most important properties of sensitivity, selectivity and response time. The Cu(II)-MISGF-QCM sensor, at a TEOS/APTS molar ratio of 10, exhibited excellent selectivity and rapidly responded to Cu(II) ions.     

Optical temperature sensor using Eu3+-doped fluoride glass

A thermooptical temperature sensor suitable for low temperatures is proposed. Eu3+-doped fluoride glass can be used as a thermooptical transducer, since its optical absorption intensity for the (7)F1-(7)F6 transition, which occurs at 2.2 microm, is modulated by temperature. Temperature resolving power is confirmed to be 0.5 K in the 77-150 K range using a Eu 3+-doped fluoride fiber. The applicable temperature range and resolving power are varied with the doping content of the Eu3+ ion.     

Electrodeposition of Cu from acidic sulphate solutions in the presence of polyethylene glycol and chloride ions

A surface-enhanced Raman scattering (SERS) spectroelectrochemical investigation has been carried out during Cu electrodeposition from an acidic sulphate solution in the presence of Polyethylene glycol (PEG) and chloride ions. PEG-related bands are clearly visible at the open circuit potential (OCP) and during the electroplating process, showing that the polymer is stably adsorbed on the Cu surface in a wide cathodic potential window. Our experimental range was limitated by the occurrence of fluorescence at potentials more cathodic then − 200 mV versus Ag/AgCl, indicating the formation of fluorescent species by electrodic reaction. A tentative reactivity scheme for PEG is provided. The co-adsorption of chloride and sulphate species from copper (II) sulphate and sulphuric acid was highlighted as well.     

Direct Interfacial Excitation from TiO2 to Cu(II) Nanoclusters Enables Cathodic Photoresponse for Hydrogen Evolution under Visible-Light Irradiation

The titanium dioxide (TiO₂) photocatalyst is only active under UV irradiation due to its wide-gap nature. A novel excitation pathway denoted as interfacial charge transfer (IFCT) has been reported to activate copper(II) oxide nanoclusters-loaded TiO₂ powder (Cu(II)/TiO₂) under visible-light irradiation for only organic decomposition (downhill reaction) so far. Here, the photoelectrochemical study shows that the Cu(II)/TiO₂ electrode exhibits a cathodic photoresponse under visible-light and UV irradiation. It originates from H₂ evolution on the Cu(II)/TiO₂ electrode, while O₂ evolution takes place on the anodic side. Based on the concept of IFCT, a direct excitation of electrons from the valence band of TiO₂ to Cu(II) clusters initiates the reaction. This is the first demonstration of a direct interfacial excitation-induced cathodic photoresponse for water splitting without any addition of a sacrificial agent. This study is expected to contribute to the development of abundant visible-light-active photocathode materials for fuel production (uphill reaction).     

THE EFFECTS OF CATHODIC POTENTIAL AND CALCAREOUS DEPOSITS ON CORROSION FATIGUE CRACK GROWTH RATE IN SEA WATER FOR TWO OFFSHORE STRUCTURAL STEELS

The effects of cathodic protection potential, corrosion products and stress ratio on corrosion fatigue crack growth rate have been studied on offshore structural steels. These materials were cathodically polarised in seawater and 3% sodium chloride solution at three potentials of -0.8, -1.0 and -1.1 V(SCE). The corrosion fatigue crack growth rate in seawater was greater than that in air and increased with more negative potentials. The maximum acceleration of crack growth rate in seawater was observed at the crack growth plateau which was independent of ΔK. Calcareous deposits precipitated within the cracks resulted in an increase of crack opening level and contributed to a reduction of the corrosion fatigue crack growth rate. Such a corrosion-product-wedging effect could be evaluated by using an effective stress intensity range, ΔK_eff. The estimation of corrosion fatigue crack growth rate in terms of ΔK_eff clarified the effect of hydrogen embrittlement under a cathodic potential. Thus the processes of cracking in seawater at cathodic potentials resulted from mechanical fatigue and hydrogen embrittlement with calcareous deposits reducing the crack growth rate. All these three mechanisms were mutually competitive.     

用于非线性兰姆波检测的高灵敏度宽带光纤光栅传感器

光纤传感器因其灵敏度高,已逐渐应用于超声检测的研究中,但大多数光纤传感器的频带响应范围有限,约为几百k Hz,很难检测到更高频率的信号。所提出的光纤布拉格光栅(Fiber Bragg Grating,FBG)传感器的高频检测范围可以达到4 MHz左右,大大提高了其检测带宽范围。文中将传感器应用于304不锈钢板兰姆波的非线性检测,同时与传统超声换能器的检测结果做对比。实验结果表明,用脉冲波激励信号时,FBG传感器可以检测到钢板兰姆波的基频到五倍频信号,表明FBG在检测兰姆波非线性上是有很大潜力的。     

Selective removal of Cr(VI) ions from aqueous solutions including Cr(VI), Cu(II) and Cd(II) ions by 4-vinly pyridine/2-hydroxyethylmethacrylate monomer mixture grafted poly(ethylene terephthalate) fiber

In this study, a new reactively fibrous adsorbent was prepared by grafting 4-vinly pyridine (4-VP) and 2-hydroxyethylmethacrylate (HEMA) monomer mixture onto poly(ethylene terephthalate) (PET) fibers for removal of Cr(VI), Cu(II) and Cd(II) metal ions from aqueous solution by using batch adsorption method. The influence of various parameters such as graft yield (GY), pH, adsorption time, initial ion concentration and adsorption temperature was investigated. The selectivity of the reactive fiber was also examined. The results show that the adsorbed amount of metal ions followed as given in the order Cr(VI) > Cd(II) > Cu(II). At pH 3, Cr(VI) was removed by 99% while the initial concentration of ions was at 5 mg L⁻¹ and by 94% at 400 mg L⁻¹. It was found that the grafted fiber is more selective for Cr(VI) ions in the mixed solution of Cr(VI)–Cu(II), Cr(VI)–Cd(II) and Cr(VI)–Cu(II)–Cd(II) at pH 3 and it was observed that the grafted fibers are stable and regenerable by acid and base without losing their activity.     

Ion adsorption studies of micro and nano acrylic fibers modified by ethanolamine

Micro and nano polyacrylonitrile fibers were modified to polyacrylonitrile‐monoethanolamine (PAN‐MEA) through reaction PAN with ethanolamine. The modified PAN fiber was prepared by conversion nitrile groups into hydroxyle groups using ethanolamine solution with different concentration under refluxing at 91°C. Modified raw acrylic fibers (RAF) with submicrometer diameters ranging from 120 to 300 nm were produced using electrospinning in N,N‐dimethyl formamide (DMF). The PAN‐MEA micro and nano fibers were examined as chelating material in a series of batch adsorption experiments for removal of Cu (II), Pb (II) and Ni (II) ions. The fiber structure has been investigated by different experimental techniques of characterization such as Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Also, the physical and mechanical properties has been investigated in this study. Nano fibers show adsorption metal ions more than the usual fiber because of high ratio of surface to mass.