High selectivity, enhanced sensitivity, short response time and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. Since the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of higher aspect ratio, large surface area and, open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence, is described. By modulating the oxygen partial pressure across the equilibrium M/MO proximity line, formation and growth of new oxide surface on an atomic/ submolecular level under conditions of "oxygen deprivation", with exotic morphological features has been achieved in a number of metal oxides that are potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of two model systems, viz., tungsten oxide (WO₃) and titanium oxide (TiO₂).

CEA is interested in radiative transfer induced by hypersonic flow for the study of extern layer ablation phenomena. Material ablation during atmospheric re-entry generally depends on object shape, incidence angle, speed and atmospheric composition at actual altitude. To improve the knowledge of these aero-thermo-chemical phenomena, we use specific instrument inside representative flying object. For this, we must observe the emission of certain chemical components in the shock layer through spectrometric measurements in the visible range. In this paper, we present a characterisation of two commercial spectrometers of Ocean Optics and Avantes trademark. Some tests we made in vibration and acceleration were representative of the different phase of the life cycle of these instruments in a ballistic flight environment. Then, temperature and saturation effects are observed according to the photoelectrical performances of the spectrometer and a transfer function model is proposed. At last, spectrometers have shown they could withstand these harsh environments.

Accurate real time nondestructive modulus measurement is one of the principal requirements in service life monitoring of smart structures. However, most current measurement methods, such as tension and/or compression testing are inappropriate for such applications. For one thing, the force load may damage the casting. For another, the test process is not trivial and inconvenient for real-time modulus monitoring. This paper describes an acoustic-based measurement mechanism using two separated miniature optical sensors. The sensor features miniature size (<500μm), high resolution and accuracy, high temperature and pressure survivability, electromagnetic interference immunity (EMI), electrically non- conductivity, and chemical erosion inertness. This technique offers future potential for real-time measurement for in-service monitoring, particularly in applications involving such environments as high temperatures or high pressure.

Frequently, assessment and monitoring of mechanical (acoustic) vibrations is necessary in large structures. Cost and reliability are major issues for field-deployment. We present a simple, compact and reliable optical accelerometer designed and constructed in our labs, capable of consistent measurement of vibrations in low and intermediate acoustic ranges (few Hz to few kHz). The principle of operation is based on the variation of the optical signal power coupled between singlemode fibers fixed in the optical sensor head. The device sensitivity has a lower limit to accelerations below 1g, and surprising upper value above 180 m/s² (18g).

In this paper, fiber Bragg grating (FBG) sensors are used to monitoring the strain of steel and concrete structure. A designed novel steel slice is introduced to package the used FBG. A shallow rectangular groove is notched on the steel slice. Coated with a thin layer of epoxy, the FBG is fixed and protected on the groove. In order to eliminate to the temperature vibration effect on the wavelength shift of FBG sensors, a FBG temperature sensor is used for temperature compensation. The conventional electrical resistance strain gauges (ERS) are also used to measure the strain for the comparison with the FBG sensors to validate the effectiveness. The experimental shows that the novel FBG stain sensor designed by us can measure the stain of the steel and concrete structure effectively and the results from FBG strain sensor agree well with the results from the resistance strain gauge. The novel FBG strain sensor is simple, smart and fit to use in civil structure health monitoring.

Wind profiling systems are critical for next generation, free space laser communication systems and laser designation systems, which are required to operate in the presence of severe atmospheric turbulence. The precision of the received laser beam depends greatly on the accuracy of estimation of the transversal wind along the laser beam propagation path. Two types of wind profiling techniques are investigated here. One technique is based on the reconstruction of wind velocity information from spatio-temporal intensity scintillation data measured at the optical receiver telescope. For the case of multiple phase-distorting layers located at different distances, the observed intensity scintillation pattern contains intensity spots of different spatial scales. The determination of the wind velocity for each spatial scale allows reconstruction of the wind profile along the entire propagation path. The second technique is based on simultaneous real-time characterization of the transversal wind velocity along the propagation path from the output image streams of a differential nonlinear Zernike wavefront sensor. This sensor consists of an optically addressed spatial light modulator that enables high-speed, high-resolution visualization of wind flow at each distant phase-distorting layer along the propagation path. Both preliminary experimental results and numerical simulation results are shown to validate the performance of the two types of techniques.

A novel vacuum-sealed miniature optical fiber sensor for static pressure or acoustic wave measurement is presented. This pressure sensor functions as a diaphragm-based extrinsic Fabry-Perot interferometric (DEFPI) sensor. The sensor can work at high temperatures because of its all-silica structure. In static pressure measurement, the sensor's measurement range can be set up to 15,000psi with different thickness diaphragms. For acoustic applications, the sensor resonant frequency is higher than 600kHz. Evacuation of the sensor's cavity eliminates the thermally induced inner pressure changes (which is a common problem in pressure sensors) and therefore improves the accuracy and repeatability. In addition, the sensor fabrication process is simple, fast, controllable and low cost. This fiber sensor is immune to electromagnetic interference (EMI), and corrosion resistant.

In this paper, a theoretical model of the interferometer using the coaxial structure was established to investigate the temperature effect in measuring the acoustic wave. The experimental result shows that the ratio of the phase shift is 312.5 rad/°C when the Michelson interferometer was used with the 3 meters fiber and the Aluminum as the cylinders. If the maximum amplitude of the signal that can be measured by the system is 10 rad, the temperature variation should be smaller than 0.032°C to keep the system from out of measurement range. Then in a system with measuring time period is 6s for seismic detection, the temperature variation should be smaller than 0.0054°C/s within the measuring period.

Ultra-high temperature measurement is required in many harsh environment applications such as temperature monitoring in combustors and furnaces. This paper presents a novel thermometer, which is capable to measure temperatures above 1000°C with high resolution and accuracy. This sensor functions as a gas thermometer with a fiber optic readout, which will not suffer from blackbody radiation noise. The sensing part has high hardness, good electrical insulation, good wear resistance and does not react with most chemicals. The size of the sensor can be chosen flexibly to satisfy different application requirements. Since no electrical components are involved, the sensor is spark/explosion free and immune to electromagnetic interference (EMI). The sensor structure is simple, easy to fabricate and low cost. Some temperature measurement results in the laboratory are presented.

The mathematical model of a cavity ring-down (CRD) fiber amplified loop gas sensing system is initially proposed. A digital least mean square (LMS) adaptive filter is designed to remove an amplified spontaneous emission (ASE) noise induced by an erbium doped fiber amplifier (EDFA) effectively. The simulation results show that the minimum measurement concentration of 18ppm is obtained.

Monitoring of chemical species is important to a number of industrial and energy related industries. This paper presents a comparison of two fiber optic sensing schemes which are demonstrated for the detection of acetylene and carbon monoxide. The first sensor configuration utilizes the newly developed random hole optical fiber and detects gases entering into the holes in the fiber through the interaction with the evanescent field. The second scheme utilizes a hollow micro-capillary tube based fiber optic sensor system. In both systems, the detection of the chemical species is accomplished by analysis of the infrared absorption spectra produced by the species present in the path of the optical signal. The effect of varying pressure, micro-capillary tube diameter, capillary tube length, and gas species is presented.

Industrial applications using tunable diode laser technology for process gas monitoring are often faced with technical challenges because of dynamic operating conditions in the presence of high particle densities and high temperature. Furthermore, issues related to alignment stability and maintenance requirements must be overcome for industry acceptance of the sensing technology. To address these technical challenges a novel near infrared tunable diode laser system for monitoring CO, H₂O and gas temperature is presented. The system incorporates balanced ratiometric detection and a variable laser power delivery scheme allowing the launch laser power to vary between 2-248 mW while maintaining a constant reference power. Feedback control is used to adjust the level of laser power delivered to the process based on the light transmission through the measurement zone. Results are presented using the system on a 500 kW oxy-fuel pilot furnace with controlled particle injection to simulate industrial conditions in preparation for field test campaign measuring the off-gas of an electric arc (EAF) steel-melting furnace. For the industrial test, monitoring on the EAF process can be considered one of the harshest environments to perform a measurement with particle densities rising above 100 g/Nm³ and temperatures up to 1800°C. In addition, special requirements are needed to integrate the sensor into the process because of the high level of mechanical vibration, high and varying ambient temperatures, EMF interference sources, and protection against flying debris.

A potential way to produce large amounts of hydrogen for energy needs is the thermal breakdown of sulfuric acid (H₂SO₄) to oxygen, water, and sulfur dioxide (SO₂). The sulfur dioxide can then be reacted with iodide to produce hydrogen iodide and ultimately hydrogen. In order to maximize the efficiency of the process it would be ideal to make in situ measurements of SO₃, SO₂, H₂SO₄, and water in the process stream in order to maximize the efficiency of the system. Fourier transform infrared (FT-IR) spectroscopy is well suited to detection of these gas phase species as they all contain strong infrared modes in the 900 to 3000 wavenumber region, 11 to 3.3 μm. However, the reactive nature of the gases and the high temperatures at which the reactions are run, 650 to 800 °C, makes standard implementation of FT-IR in process monitoring challenging. This is because the infrared detection most be done in a stand off mode and typical window and cell materials used for infrared monitoring will break down under these extreme conditions. This paper presents modifications to typically FT-IR window materials to allow them to be more robust in the environment of interest and gasket materials that can withstand both high temperatures and the oxidative conditions. Infrared spectra of SO₂, SO₃, and H₂SO₄ at elevated temperatures obtained with our system and the quantitative results are presented.

In this paper, the long period grating (LPG) with a metal outer clad is analyzed. The transfer constant of core mode and cladding mode were derived from numerical method. The complex refractive index of the metal outer clad make the transfer constant to be a complex number. The imaginary part of the transfer constant is representing the loss during the wave's transmission. Theoretical analysis shows that the core mode's loss caused by metal clad is can be ignored when the radius of the clad is 62.5um. The complex refractive index make larger resonance wavelength shift than the refractive index without imaginary part.

We present the quasi-distributed temperature measurement results in a selective catalytic reduction unit of a power plant by using a frequency-division-multiplexing optical fiber measurement system with eight intrinsic Fabry-Perot interferometric fiber sensors along a single fiber. The sensor was constructed by splicing a section of multimode fiber between single mode fibers. A high resolution swept laser interrogator was used to measure the spectrogram of the reflected light from the sensors, which contains multiple frequency components in wave number domain corresponding to sensors with different cavity lengths. The temperatures were measured by estimating the optical path length of each Fabry-Perot interferometer. Field test results show that the proposed technology can potentially be used in applications of multi-point high temperature sensing.

As a clean, reliable, and comparatively inexpensive alternative to fossil fuels, geothermal electricity generation could provide energy for fifty years or more if properly managed. Real-time and remote measurement of some key parameters of the geothermal well as well as their temporal and spatial variations can provide critical information to improve plant efficiency and optimize plant operation to accommodate a resource that is declining with time. A hermetically sealed single mode fiber extrinsic Fabry-Perot interferometric (EFPI) sensor was developed for in-situ monitoring the temperature of geothermal wells. The amplified spontaneous emission of an erbium doped fiber amplifier was investigated as the broadband source to interrogate the fiber EFPI temperature sensor. Real-time compensation of the source spectrum distortion was investigated to improve the measurement accuracy and extend the sensor lifetime.

Sensor technology is one of three major pillars of the modern information technology. With the extensive application of sensor, the dependability of the sensor is paid more and more attention. The development of sensor faults diagnose technology offers strong guarantee for using the sensor reliably. In this paper, the application of combining the wavelet and BP neural networks to sensors failure detection is studied, and a novel diagnosis method based on discrete wavelet transform and BP neural network was proposed to detect and identify sensor abrupt fault. Since wavelet transform can accurately localize sensor signal characteristics both in time and frequency domain, it is very suitable for non-stationary signal analysis. After discrete wavelet transform analysis for sensor output, eigenvector of energy changing rate was extracted, and classification of sensor fault was conducted by using BP neural network. The proposed method does not need construction of sensor model and measurement of sensor input. Hence redundant data can be reduced by omitting some wavelet coefficients and the capability of fault detection can be improved. Sensor fault diagnosis is simulated by the computer. Through a large amount of simulated examples it indicates that the sensors fault diagnosis method based on the theory of wavelet has characteristic such as good sensitivity, high accuracy rate and robust ability to overcome noise. Simulation results proved the effectiveness of this method.

The purpose of this paper is to present a novel three-layer adaptive multisensor data fusion system, which is appropriate to the harsh environment. In order to overcome the noise in the data collected by the sensors in the harsh environment, the first layer of the system is the data pretreatment layer. In this layer, the data collected by the sensor array is denoised by the wavelet threshold algorithm, which provides reliable data to the next data fusion Layer. Taking use of the good error tolerance and self-studying performance of NN (neural network), the data from the first layer is fused by the second layer--- data fusion layer based on NN. The third layer is the feedback layer, in which the output signal is feedback to the second layer. The adaptive algorithm will adjust the weights of the units in the NN, which implements the adaptive ability of the whole system. The experimental results presented in the paper indicate that the system proposed here implements data fusion effectively, its fusion precision is improved compared with the traditional fusion system, and has many advantages like strong adaptive ability, high SNR (signal-to-noise ratio) and low distortion, etc.

Pressure sensors are the key elements for industrial monitoring and control systems to lower equipment maintenance cost, improve fuel economy, reduce atmospheric pollution, and provide a safer workplace. However, the testing environment is usually harsh. For example, inside the turbine engine, temperatures might exceed 600°C and pressures might exceed 100psi (690kPa), where most current available sensors cannot survive. Moreover, due to the restricted space for installation, miniature size of the sensor is highly desirable. To meet these requirements, a novel type of all fused silica optic fiber tip pressure sensor with a 125μm diameter was developed. It is a diaphragm based pressure sensor in which a Fabry-Perot interferometer is constructed by the end face of an optical fiber and the surface of a diaphragm connected by a short piece of hollow fiber. The FP cavity length and the interference pattern will change according to ambient pressure variation. Its main improvement with respect to previously developed optical sensors, such as those utilizing techniques of wet etching, anodic bonding and sol-gel bonding, is the fact that no chemical method is needed during the cavity fabrication. Its dynamic pressure performance was verified in a turbine engine field test, demonstrating not only that it can safely and reliably function near the fan of a turbine engine for more than two hours, but also that its performance is consistent with that of a commercial Kulite sensor.

A general analysis of an inserted LPG in air-clad PCF for temperature and strain measurement is presented. The temperature and strain can be detected simultaneously by matrix inversion. The maximum temperature errors are 3^oC and 0.8^oC in the temperature ranges from 35^oC to 50^oC and 90^oC to 120oC, respectively. The corresponding maximum strain errors are 250με and 135με in the strain range from 0 to 3000με respectively.

In the present paper, two materials, aluminum and iron, were prepared on the optical fiber core to monitor the corrosive behavior of the materials in the marine environment. X-ray diffraction proved the metallic film forming on the core. The reason of initial drop of optical sensing curve was researched and measured. The scanning electron microscope observed the appearances of aluminum and iron materials on the core and certificated the analytical results.

A novel evolutionary algorithm called dynamic multi-swarm particle swarm optimizer (DMS-PSO) is used to improve the performance of fiber Bragg grating (FBG) sensors in a wavelength division multiplexed (WDM) network. Simulation results show that the root-mean-square (RMS) value of the Bragg wavelength detection error is 0.8pm when 10 FBGs in the WDM network are completely overlapped in the noisy environment.

An erbium-doped fiber amplifier (EDFA) gain flattening technique using an embedded long period grating (ELPG) is proposed. By bending the ELPG, because the different bending curvature yields the different coupling strength, it is used for the dynamic gain flattening despite the different pump power on the EDFA. The flattened gain region of 35nm can be achieved with 1dB ripple.

This article firstly gives out when the phase modulation amplitude is at best value of homodyne demodulation using phase generated carrier, and then presents three methods that can be realized to get the best value. Some differences based on practicality are made among them, and a method which is easy to be implemented by digital circuits, is chosen to be carried out by digital circuits. Also this paper gives out simulation analysis and real experiment results. The error range is from -3.80% to 2.11% with real system. The origins of the error limiting the accuracy are discussed.

In this paper, an on-line down-well crude oil analysis system is presented, which is applied to measurement of the mount of components in down-well oil, water and gas. Instead of full spectrum of oil, the disperse-spectrum-selecting algorithm was presented to simplify the design of conventional spectrum analysis system. By the disperse-spectrum-selecting algorithm, the system can be designed in small size and compact structure, and the experiment results show that the correlation of the model using disperse wavelength is equivalent to the model using the all wavelengths and system measurement accurate reach to 2 percent.

We report a novel clinometer (or tilt sensor) by using three fiber Bragg gratings (FBGs). It can detect the magnitude as well as the direction of the inclination from the horizontal direction by directly measuring the reflected optical powers of the FBGs, whose bandwidths vary with the inclination. The experimental results show that it is inherently insensitive to temperature, eliminating the need for compensation of temperature, and a tilt angle measurement accuracy of ±0.13° and resolution of 0.02° have been achieved.

The resonant wavelength of long-period fiber gratings (LPFGs) is very sensitive to the ambient refractive index. LPFGs will have many potential applications on biochemistry sensors and environment monitor system. At present, LPFGs chemical sensors can only measure the medium, which has lower refractive index than that of the fiber cladding, however, the detecting range can be greatly enlarged if the LPFGs coated with Langmuir-Blodgett thin film are used. LPFGs will have more extensive applications with the mature of the L-B thin film technology. In this paper, the spectrum performance of the resonant wavelength of LPFGs varying with the changes of the ambient refractive index (1< n < 1.8) is theoretically analyzed. As the ambient index is increased, each resonance wavelength first shifts toward the shorter-wavelength direction and then disappears where the value of n is about 1.45. When the ambient index is larger than that of the cladding (~1.45), the resonance wavelengths reappear at slightly longer wavelength than those measured in ambient air. According to the mode coupling method, the theoretical four-layered fiber model is developed on the relationships among the resonant wavelengths of LPFGs coated with L-B thin film, the refractive index and thickness of the L-B thin film, and ambient refractive index. The shift of the resonant wavelength is calculated through numeric method and is presented graphically.

With the development of industry and agriculture, the environmental pollution becomes more and more serious. Various kinds of poisonous gas are the important pollution sources. Various kinds of poisonous gas, such as the carbon monoxide, sulfureted hydrogen, sulfur dioxide, methane, acetylene are threatening human normal life and production seriously especially today when industry and various kinds of manufacturing industries develop at full speed. The acetylene is a kind of gas with very lively chemical property, extremely apt to burn, resolve and explode, and it is great to destroy things among these poisonous gases. Comparing with other inflammable and explosive gas, the explosion range of the acetylene is heavier. Therefore carrying on monitoring acetylene pollution sources scene in real time, grasping the state of pollution taking place and development in time, have very important meanings. Aim at the above problems, a set of optical fiber detection system of acetylene gas based on the characteristic of spectrum absorption of acetylene is presented in this paper, which has reference channel and is for on-line and real-time detection. In order to eliminate the effect of other factors on measurement precision, the double light sources, double light paths and double cells are used in this system. Because of the use of double wavelength compensating method, this system can eliminate the disturbance in the optical paths, the problem of instability is solved and the measurement precision is greatly enhanced. Some experimental results are presented at the end of this paper.

Wireless sensing is prevalent quickly in these years, and it has many advantages, such as fewer catastrophic failures, conservation of natural resources, improved emergency response, etc. Wireless sensors can be deployed in extremely hostile environment. Since the wireless sensors are energy constrained, many researches have been in progress to solve these problems. In this paper, we proposed a joint source-channel coding scheme to solve energy efficiency of wireless sensors. Firstly, we decomposition information in wavelet domain, then compress it by using multi-scale embedded zerotree wavelet algorithm, and generate a bit stream that can be decompressed in a scalable bit rate. Then, we transmit the bit stream after encoding them with unequal error protection turbo codes to achieve error robust transmission. We transmit multiple bit streams according to some energy strategy, and redundancies to base stations are reduced by only transmitting coarse scale information. Due to the scalability of multi-scale EZW, we can adopt diversified bit rate strategy to save energy of battery powered sensors.

Wireless sensor networks (WSN) have become possible because of the on-going improvements in sensor technology. As the development of WSN, the application area using this technology is growing up. The Structure Health Monitoring (SHM) is the importance one way. Localization detection for sensor nodes is a new research point in the structure monitoring environment. Using signal strength is the common way for localization. However, the whole Wireless Sensor Networks is a power efficient system. One issue in smart sensor networks is achieving efficient operation because of the limited available power. So we must research the relationship between the sensor nodes' deployment and the system's power efficient.