Papers by Keyword: Fiber Optic

Abstract: We have designed a magneto-optical sensor based on fiber Bragg grating (FBG) and Metglas 2605CO (Fe₆₇Co₁₈B₁₄Si₁) material with magnetostriction coefficient of 35ppm. The FBG sensor is glued between two sheets of Metglas. FBG-based detectors are sensitive to both temperature changes (approximately 10pm/°C) and mechanical stress (approx. 1.15pm). Also due to the thermal expansion of Metglas, it becomes imperative to isolate the joint effects of thermal expansion of Metglas and the FBG temperature drifts. This is achieved by introducing an additional FBG used as a temperature sensor. We have characterized the responses of the sensor in two directions simultaneously: parallel and perpendicular to the direction of the applied magnetic field.

Abstract: In this paper, we report a dual-wavelength temperature sensor based on fiber optic delay. This temperature sensor don’t need to rely on accurate spectrum measurement, but to realize temperature measurement by detecting the variation of delay, which can efficiently reduce the cost and complexity of sensor system. In this dual-wavelength system, one wavelength of light is used as a reference and the other one is used for temperature sensing, so this design can effectively eliminate the negative influences of unstable external environment. The principle of this temperature sensor is theoretically derived, the schematic of sensor system is analyzed and the feasibility of this method is tested in the temperature range of 0°C-80°C. Results indicate that, this temperature sensor is able to achieve temperature measurement in a simple way with low cost.

Abstract: Laser Doppler Velocimetry is an important flow diagnostic methodology used in modern day fluid flow investigations. The present paper describes the design and manufacturing aspects of a novel fibre optic LASER Doppler probe head intended for three dimensional measurements in a complex flow field. The paper particularly concentrates on the tight tolerances required of the various components associated with the probe head to achieve the desired measurement volume. Keywords: Fibre Optic, Laser Doppler, Velocimetry, three-dimensional, complex flow field

Abstract: The theoretical model is got for a new intrinsic Fabry-Perot interferometric fiber pressure sensor structure fabricated by single mode and multimode fibers with different diameters. The pressure response curves are simulated by Matlab software. The analysis results showed that the pressure sensitivity decreased with the diameter of multimode fiber increased at some area, but the sensitivity begins to increase when the diameter value is more than critical point. The high sensitivity can be still got by increasing fiber diameter.

Abstract: The crack is easily generated in the metal structure because of fatigue. It has a strong impact on structural safety. To reduce accident and losses, it is important to detect the local damage such as active crack. The general method to detect the local damage is acoustic-emission technique. But it has the disadvantages of short distance transmission, interfered easily and so on. In this paper, the fiber optic acoustic emission sensor system is designed and developed. A lot of experiments have been done in laboratory. It is shown that the new system has long distance transmission, and has high anti-interference etc. It can meet the demand of local damage detection about the metal structure.

Abstract: In this paper a novel fiber-optic mass flow sensor based on coriolis force is presented. As sensing elements two fiber-optic curvature sensors mounted on elastic rubber tube are used. Rubber tube with sensing elements is excited by stepper motor. Produced system has the option of varying angle and speed of excitation. The bending of the fibers at the sensitive zone on curvature sensor changes the intensity of light traveling through the optical fiber. Curvature sensors are attached to the rubber tube so that they can measure phase difference produced by coriolis force. Mass flow rate is obtained by digital signal processing technique for phase difference detection.

Abstract: The fiber optic dynamic light scattering has become an important technique in applied science for analysing the particle size. This paper reviews these fiber optic dynamic light scattering systems. It analyses the theory of measurement and indicates the structural features of every system. Then this paper discusses the development tendency of the fiber optic dynamic light scatterin systems.

Abstract: An optical fiber remote multiplexed sensing system of methane is designed based on the methane absorption spectroscopy characteristic, by taking the triangular signal to modulate the wavelength of the tunable diode laser. The laser wavelength shift is carried out adaptive adjustment by the built-in gas calibration pond to realize the locking of a methane absorption line. The methane concentration monitoring is realized in the range of 0-100%. The application tests are found in a garbage power generation plant and several coal mine ventilation air methane power generation plants. The results indicate that the monitor has good performances in stability and sensitivity and a long-term precision of 10ppm is achieved. It is possessed of wide application in Clean Development Mechanism (CDM) projects.

Abstract: Fluorescence optical-fiber temperature sensor based on Planck’s law is studied in this paper. Sapphire fiber is adopted as thermal probe. With steady physical chemistry performance, higher melting point, low loss in the waveband of 0.3~0.4 μm , sapphire fiber is very attractive for temperature optical fiber sensing and near infrared energy delivery. Making use of the method of FFT transformation to carry on measurement of fluorescence life time, the measured fluorescence life time can be obtained by tangent value of first non-zero phase angle. This method has virtues such as fast speed, small error and no background interference. Among the detection range from 0 to 450 , the thermometer has an average temperature resolution of 0.4°C .The experimental results show that the temperature measuring system can effectively decrease the influence of instability of light source and intensity variation in measuring channel on measurement results. This system also has advantages of high accuracy, very high temperature resolution, good dynamic response and immunity to the electro-magnetic interference.

Abstract: A new kind of passive underwater acoustic sensor based on fiber Bragg grating is reported. The pressure sensitivity of the sensor is enhanced three orders of magnitude being packaged with polymer material, which is a foundation for underwater acoustic detection. An intensity modulation scheme is adopted to realize high-accuracy detection due to the extra-narrow line-width laser. The experimental results show that the sensor’s noise-limited pressure detection resolution is about 61dB (0dB＝1μPa/ Hz ) at 500 Hz, which satisfies the application of underwater target detection.