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A calculation model for a tube-sheet under thermal shock loading with the finite element code ANSYS is established in this paper. A three-dimensional finite element model is established to simulate thermal shock process in order to obtain temperature and stress distributions of the structure. The duration time of the thermal shock is taken as about ten seconds and thermal cycling numbers are more than 1000 times for the whole service life of the structure. In order to capture accurate temperature and stress profile of this structure, thermo-mechanical coupling approach and transient thermal analysis is used. Temperature and stress distribution are obtained under the given thermal boundary conditions at different time points and it is also easy to get the stress amplitude of the other points in this structure between any two time points. According to the numerical results, the stress induced by thermal shock changes with time and its magnitude and amplitude cannot be ignored. Strength and fatigue evaluations are also performed according to ASME VIII-2 to ensure its safety.

We present a miniature fiber-optic pressure sensor with a diameter of only 125 mum. The sensor works as an extrinsic Fabry-Peacuterot interferometer and the cavity length can be controlled with a resolution of about several nanometers. Also the sensor sensitivity can be easily adjusted by controlling the sensor gauge length. A passive temperature compensation scheme was used to reduce most of the sensor's temperature dependence. Since the sensor is composed entirely of fused silica, it is reliable, biocompatible, corrosion resistant, and immune to electromagnetic interference and has high-temperature capability

A novel diaphragm-based miniature optical fiber pressure sensor has been shown to work at temperatures up to 700/spl deg/C with a sensitivity of 2.93 nm/psi and a resolution of 0.01 psi (68.9 Pa). A passive temperature compensation scheme was used to reduce the temperature dependence to 0.0076 psi//spl deg/C (52.4 Pa//spl deg/C). The sensor exhibited a linear response in the available testing range from 0 to 200 psi (1.38 MPa), and being composed entirely of fused silica, the sensor's structure is very reliable, corrosion resistant, and immune to electromagnetic interference.

This paper presents a novel fiber optic Fabry-Perot (FP) structure for direct detection of deoxyribonucleic acid (DNA) sequences. The capture DNA is immobilized onto the surface of a silica optical fiber tip by means of the layer-by-layer electrostatic self-assembly (L-b-L ESA) technique. With the FP cavity inside the fiber, the change in optical path length difference (OPD) caused by the immobilization and hybridization can be demodulated. Experimental results demonstrate short (~5 min) response time. In addition, the sensor fabrication is simple and low cost. The signal is stable with high visibility.

Acoustic landmine detection (ALD) is a technique for the detection of buried landmines including non-metal mines. An important issue in ALD is the acoustic excitation of the soil. Laser excitation is promising for complete standoff detection using lasers for excitation and monitoring. Our method is based on a YAG laser at 1.06 um not He-Ne laser or loudspeaker with acoustic excitation and on an erbium fiber laser at 1.54 um not microphone with LDV detection. An analysis is given to show the potential and the inherent limitations of the technique. In the present paper we have tried to answer two questions on locating landmines: (1) too many false alarm; (2) plastic landmine. The answer to the first question is the LDV with an erbium fiber laser at 1.54 um. The second answer is YAG laser at 1.06 um induce acoustic.

Owing to its compactness, lightness, and low cost, laser diodes (LD) play an important role as a coherent source in various fields of technology. Because of the waveguide properties of their active areas, laser diodes generate large divergence-angle beams with elliptically shaped intensity profiles. And the beam of LD has astigmatism. So it is difficult to collimate LD beams effectively. The binary optical elements are small, light, easy to be copied and able to realize multi-purpose integrated, especially suits for the beam shaping of laser diode array. Based on accurate far-field model of high-power laser diode, a design method of binary optical element for laser diode beams, which can correct the astigmatism of the laser beam, has been developed, and the principle and process has been given in detail. The method is simple and practical. The relief surface of the element is of multiphase structure. And its theoretical diffraction efficiency is as high as 95%.

This paper presents a novel intrinsic fiber optic Fabry-Perot (FP) structure with a micrometric diameter tip. With the FP cavity inside the fiber, the change in optical path length difference (OPD) caused by the environment can be demodulated. With such a tiny protrusion, the sensor can be inserted into micron size cells for intracellular measurements. This label-free detection method is very useful in biological areas such as DNA hybridization detection. It provides a valuable tool for intracellular studies that have applications ranging from medicine to national security. In addition, the fabrication is simple including only cleaving, splicing, and etching. The signal is stable with high visibility. Last but not the least, the structure shows great promise for reduction to nanometric size. Once this goal is achieved, the sensor can be inserted into most cells with minimal invasiveness.

The authors present a label-free method for direct detection of deoxyribonucleic acid (DNA) sequences. The capture DNA is immobilized onto the surface of a silica optical fiber tip by means of the layer-by-layer electrostatic self-assembly technique. Hybridization of target DNA with complementary capture DNA increases the optical thickness of the fiber tip. This phenomenon can be detected by demodulation of the spectrum of a Fabry-Perot cavity fabricated in the optical fiber. Experimental results demonstrate sequence specificity and sensitivity to nanogram quantities of target DNA sequences with short (similar to 5 min) hybridization time. (c) 2006 American Institute of Physics.

Fiber optic extrinsic Fabry-Perot interferometric (EFPI) sensors are widely used in dynamic pressure measurements because of their inherent advantages including small size, light weight, high sensitivity, high frequency response, electrical passivity, electromagnetic interference immunity (EMI), and single-point measurement. However, small fluctuations of background pressure could shift the operating point of the sensor in an unpredictable way, which introduces a nonlinear response in dynamic pressure measurements. In this paper, we present a novel open structure only 125 μm in diameter to eliminate the operating point dependence on background pressure fluctuations. The essential element is a piece of hollow fiber, which connects a standard telecommunication fiber and another hollow fiber with a smaller inside diameter to form a Fabry-Perot cavity. The structure is open to the environment by a small hole, which allows gas exchange between the sensor cavity and the ambient atmosphere. On the other hand, the sensor is capable of responding to acoustic pressure because of the slow gas exchange through the small hole. In addition, this all fused silica structure features high temperature stability, good linearity, and high repeatability.

This paper presents a label-free method for direct detection of deoxyribonucleic acid (DNA) sequences using layer-by-layer electrostatic self-assembly (L-b-L ESA) technique. The sensor features sequence specificity, cost efficiency, speed, and ease of use.

An all fused silica based pressure sensor with a 125/spl mu/m diameter is presented. A Fabry-Perot interferometer is formed at the fiber tip. It offers biocompatibility, miniature size, high sensitivity, EMI immunity, and low cost.

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.

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 (

New miniature extrinsic Fabry-Perot interferometric (MEFPI) optical fiber sensors with a size of 125μm in diameter are presented, which are ideal for applications where the operation space is highly restricted. The temperature sensor can work up to 800°C with a sensitivity of 0.46nm/°C. The pressure sensor exhibited a sensitivity of about 0.36nm/psi. The sensitivities of the pressure and temperature sensor can be controlled with high precision during fabrication. In addition, their Fabry-Perot cavity lengths can be controlled with a resolution of several nanometers, which provides excellent flexibility in sensor design and signal demodulation. The sensors are composed entirely of fused silica, which is very reliable, biocompatible, corrosion resistant and immune to electromagnetic interference (EMI).

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.

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.

We present a novel method for measuring the frequency response of a diaphragm-based optical fiber Fabry-Perot interferometric pressure sensor. The impulse response of the sensor to the radiation pressure generated by an excimer laser pulse is measured. The Fourier transform of the impulse response yields the frequency response of the pressure sensor. Experimental results show that it is a convenient and efficient method for measurement of the frequency response of diaphragm-based pressure sensors.

A technique to precisely control the cavity length in fiber optic extrinsic Fabry-Perot interferometric structures by CO/sub 2/ laser is described. The white light monitored laser bonding system can achieve a 3 nm cavity control resolution.

Pressure measurements at various locations of a gas turbine engine are highly desirable to improve the operational performance and reliability. However, measurement of dynamic pressure (1psi (6.9kPa) variation superimposed on the static bias) in the operating environment of the engine, where temperatures might exceed 600°C and pressures might exceed 100psi (690kPa), is a great challenge to currently available sensors. To meet these requirements, a novel type of fiber optic engine pressure sensor has been developed. This pressure sensor functions as a diaphragm-based extrinsic Fabry-Perot interferometric (EFPI) sensor. The structure of the sensor head, composed entirely of fused silica, allows a much higher operating temperature to be achieved in conjunction with a low temperature dependence. The sensor head and the fiber tail have been packaged in a metal fitting connected to a piece of metal extension tubing, which improves the mechanical strength of the sensor and facilitates easy sensor installation. The sensor exhibited very good performance in an engine field test, demonstrating not only that the sensors' package is robust enough for engine operation, but also that its performance is consistent with that of a commercial Kulite sensor.

In this paper, we present a miniature fiber optic pressure sensor. The sensor is extrinsic Fabry-Perot interferometer (EFPI) based with its FP cavity directly fabricated on the tip of the fiber by fusion splicing and chemical etching. The processes are simple, with no other materials but silica fibers involved. The sensor has the same dimension as the fiber itself, only 125μm in diameter. The length of the FP cavity and the interference pattern will change in response to ambient pressure variation. The signal is demodulated by tracing the spectrum shift. Sensitivity can be adjusted for different applications with low or high pressure range. Prototype sensors were fabricated and tested for static response. Dynamic measurements were performed in a turbine engine. Theoretical and experimental analysis of the sensor response are also presented.

This paper describes the effort in developing a sapphire temperature prototype sensor for coal gasifier applications. The sensor is tested in laboratory to 1600 degree C and demonstrated 0.47% accuracy with respect to full measurement range. The efforts on sensor prototype development ranging from sensor probe packaging at each level, sensor electronics, LED modulation to remote data access are addressed.

A self-compensating fiber optic flow sensor system based on the principle of broadband white-light interferometers and cantilever beam bending is described. The fiber optic sensor system uses two fiber ferrule sensors that are bonded on either side of a cantilever beam to measure the flow rate by monitoring the air-gap changes caused by the bending of the cantilever beam. Cross sensitivity of the temperature and pressure dependence of the sensor can be compensated for automatically. The prototype sensor system was constructed, laboratory characterized, and field tested. The results from the field testing have demonstrated high resolution, repeatability, and stability for on-line detection of the flow rates of fluids. (C) 2004 Optical Society of America. National Petroleum Technology Laboratory U.S. Department of Energy Chevron Texaco Research & Technology Company

In this paper, we present a novel design of a fiber optic flow sensor system for single-phase fluid flow detection. This new system is based on the principle of broadband interferometry and cantilever beam bending. The fiber optic sensor system utilizes two fiber ferrule sensors that are bonded on both sides of a cantilever beam. The flow rate can be determined by monitoring the air gap changes caused by bending of the cantilever beam. Cross-sensitivity of the temperature and pressure dependence of the sensor can be compensated for automatically. The prototype sensor system was fabricated and tested on the lab-scale with preliminary evaluations completed. Field-testing was performed in the indoor and outdoor flow loops of Tulsa University in Tulsa, Okalahoma. Both the lab-scale and field-testing results verified that the designed flow sensor system could measure the single-phase fluid flow rate with high resolution and repeatability by compensating the thermal and pressure effects of the environment. The outdoor field-testing demonstrated the feasibility of the designed fiber optic flow sensor for single-phase fluid flow rate measurements in the oil fields.

Increasing the efficiency of oil production operations requires improved sensors to supply critical information such as mixed‐phase fluid flow, pressure and temperature measurements within the down‐hole oil environment. In order to provide robust and reliable fiber optic temperature sensors capable of operating in the harsh down‐hole oil environment, where temperatures might exceed 250 °C and pressures might reach 20,000 psi (140 Mpa), a novel type of fiber optic temperature sensor has been developed. This temperature sensor functions as an EFPI (extrinsic Fabry‐Perot interferometric) sensor. One unique contribution of this work is that the glass tubing used is a borosilicate glass with a relatively high coefficient of thermal expansion (CTE) and long gauge length, allowing a much higher sensitivity to be achieved, without hysteresis. The sensor structure utilizes a dual tubing design (tubing within a tubing) to allow pressure isolation. An LED light beam is used as the signal interrogation source to remotely interrogate the sensor which may be located tens of thousands of meters away, connected by an optical fiber. A white‐light interferometer measurement system is utilized to process the returned interference signal and to precisely determine the length of the Fabry‐Perot interferometric cavity. Another unique feature of this work is that the sensor has been packaged with a specially developed hermetic protection process to prevent water penetration and to improve the mechanical integrity of the sensor. This protection process has allowed the successful hydraulic deployment of fiber optic sensors through 3 mm ID stainless steel tubing into a functioning oil well. Data on the resolution, repeatability and pressure sensitivity are presented.

An all-fused-silica pressure sensor fabricated directly onto a fiber tip of 125 microm diameter is described. Simple fabrication steps include only cleaving and fusion splicing. Because no chemical processes are involved, the fabrication is easy, safe, and cost effective. Issues in sensor design and loss analysis are discussed. The sensor has been tested for static pressure response, showing a sensitivity of 2.2 nm/psi, a resolution of 0.01 psi (68.9 Pa), a hysteresis of 0.025%, and capability of operation at temperatures up to 600 deegrees C. This miniature sensor may be suitable for medical diagnostics, environmental monitoring, and other industrial applications.

We present a miniature diaphragm-based Fabry-Perot (F-P) interferometric fiber optic sensor fabricated by novel techniques for pressure or acoustic wave measurement that is only approximately 0.32 mm in diameter. By choosing different diaphragm thicknesses and effective diameters, we obtain a sensor measurement range from 5 to 10,000 psi (1 psi = 51.72 Torr) and a frequency response up to 2 MHz. In addition, the sensor's F-P cavity can be set from micrometers to millimeters with a precision of several nanometers. With the all-silica structure, the sensor is reliable, biocompatible, and immune to electromagnetic interference and has high-temperature sensing capability.

A new structure for diaphragm-based extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensors is presented. This structure introduces a through hole in a conventional diaphragm-based EFPI sensor and significantly reduces the effect of operating point drift due to the background pressure and fluctuations. This structure also potentially has high temperature stability.

We describe a fiber optic extrinsic Fabry-Perot interferometer EFPI based temperature sensor that incorporates a pressure isolation fixture. The sensor has high temperature sensitivity and low pressure- induced crosstalk. The detailed analysis and discussion of the sensor design, the signal demodulation algorithm, and the sensor fabrication as well as the sensor performance are presented. © 2005 Society of Photo-Optical

White light interferometry has been used in the sensing area for many years. A novel data processing method for demodulating the information from the interference spectrum of a white light system is presented. Compared with traditional algorithms, both high-resolution and large dynamic range have been achieved with a relatively low-cost system. Details of this arithmetic are discussed. A compact white light interferometric system employing this algorithm has been developed, combined with fiber Fabry-Perot sensors. A60.5-nm stability over 48 hours with a dynamic range on the order of tens of microns has been achieved with this system. The temperature dependence of this system has been analyzed, and a self-compensating data processing approach is adopted. Experimental results demonstrated a 61.5-nm shift in the temperature range of 10 to 45°C. © 2003 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1613958)