Hypersonic flow-field measurement techniques have been studied for about 50 years. Despite truly remarkable progress with a probe or other device to measure the temperature, pressure or velocity, there are still serio...Hypersonic flow-field measurement techniques have been studied for about 50 years. Despite truly remarkable progress with a probe or other device to measure the temperature, pressure or velocity, there are still serious problems for these "intrusive" techniques. The intrusive measurement techniques introduce unexpected shock waves or flow-field structures, even make the boundary layer transition earlier and show a converse result. In recent years, nonintrusive diagnostics have been in urgent demand to give a more accurate and comprehensive flow-field for hypersonic testing. In this paper, an overview of some advanced nonintrusive measurement techniques such as embedded thermocouples for heat flux measurement, Pressure Sensitive Paint(PSP), Particle Image Velocimetry(PIV), infrared thermographs, and focusing Schlieren system are introduced. All of these techniques are nonintrusive and provide measurement of various parameters such as temperature, static pressure, dynamic pressure, flow velocity and visualization of flow structure, which gives us an exact and direct understanding of the hypersonic flow.展开更多
In this work, the theoretical model of FBG when it is affected by double external variables (temperature and transverse pressure) and triple external variables (temperature, axial strain and transverse pressure) is de...In this work, the theoretical model of FBG when it is affected by double external variables (temperature and transverse pressure) and triple external variables (temperature, axial strain and transverse pressure) is deduced, respectively. The simulated results show that the properties of cross sensitivity would change in a certain regulation with the external effects and fiber parameters. At the same time, some valuable suggestions about how to improve the measurement accuracy are put forward as well.展开更多
The key factor of the sensitivity in the FBG-based pH sensor is analyzed in detail. A multi-thin-layer structure of the gel coated cover was proposed and implemented with a special process. The sensors with the coated...The key factor of the sensitivity in the FBG-based pH sensor is analyzed in detail. A multi-thin-layer structure of the gel coated cover was proposed and implemented with a special process. The sensors with the coated thickness of 420 ~m, 500 ~m, and 580 ~m were built up, respectively. The corresponding spectral shifts of 0.08nm, 0.13nm, and 0.22nm were detected when the pH sensors were soaked in the pH value of 3-9. Meanwhile, the sensor with the gel layer thickness of 580 ~tm was measured in the optimum measurement time period with the pH value changing from 3-12, in which the detected sensitivity of 52pm/pH was achieved in the pH range of 6-12.展开更多
An all-fiber sensor based on a cascaded optical fiber device is proposed and demonstrated, and its sensor head is composed of a core-offset Mach-Zehnder interferometer(MZI) and a long-period fiber grating(LPFG). In th...An all-fiber sensor based on a cascaded optical fiber device is proposed and demonstrated, and its sensor head is composed of a core-offset Mach-Zehnder interferometer(MZI) and a long-period fiber grating(LPFG). In the experiment, two dips shaped by the intermodulation between the interference fringe of MZI and the resonant wavelength of LPFG are monitored. Experimental results show that temperature sensitivities of two dips are 0.060 7 nm/°C and 0.056 3 pm/°C, and the refractive index(RI) sensitivities are –18.025 nm/RIU and –55.06 nm/RIU, respectively. The simultaneous measurement of the temperature and external RI is demonstrated based on the sensitive matrix. Its low fabrication cost, simple configuration and high sensitivity make this sensor have potential applications in chemical and biological sensing.展开更多
A novel fiber Bragg grating(FBG) sensor with simultaneous sensing of displacement and temperature is presented.The FBG is affixed on the cantilever inclinedly.The midpoint of FBG exactly coincides with the zero strain...A novel fiber Bragg grating(FBG) sensor with simultaneous sensing of displacement and temperature is presented.The FBG is affixed on the cantilever inclinedly.The midpoint of FBG exactly coincides with the zero strain layer of a rectangular beam.The vertical displacement can be measured by the broadened bandwidth of FBG as the bandwidth is insensitive to temperature,while the temperature can be measured by the center wavelength shift as the wavelength shift is insensitive to vertical displacement.With 0.1 nm spectral resolution of the analyzer,sensitivities of bandwidth-displacement and center wavelength-temperature are 0.48 nm/mm and 0.05 nm/℃,resolutions are 0.2 mm and 2.0 ℃,and sensing ranges of displacement and temperature are up to 8.5 mm and 45℃ respectively.Experimental results match theoretical analyses very well.展开更多
An all fiber magnetic field sensor with peanut-shape structure based on multimode fiber(MMF) is proposed and experimentally demonstrated. The sensing structure and magnetic fluid(MF) are both encapsulated in capillary...An all fiber magnetic field sensor with peanut-shape structure based on multimode fiber(MMF) is proposed and experimentally demonstrated. The sensing structure and magnetic fluid(MF) are both encapsulated in capillary, and the effective refractive index of MF is affected by surrounding magnetic field strength. The measurement of magnetic field is realized by observing the wavelength drift of interference peak. The transmission spectrum generated by Mach-Zehnder interferometer(MZI) includes core-core mode interference and core-cladding mode interference. Experimental results demonstrate that the core-cladding mode interference is sensitive to magnetic field, and the magnetic field sensitivity is 0.047 8 nm/mT. In addition, two kinds of interference dips are sensitive to temperature, and the sensitivities are 0.060 0 nm/°C and 0.052 6 nm/°C, respectively. So the simultaneous measurement of magnetic field strength and temperature can be achieved based on sensitivity matrix.展开更多
文摘Hypersonic flow-field measurement techniques have been studied for about 50 years. Despite truly remarkable progress with a probe or other device to measure the temperature, pressure or velocity, there are still serious problems for these "intrusive" techniques. The intrusive measurement techniques introduce unexpected shock waves or flow-field structures, even make the boundary layer transition earlier and show a converse result. In recent years, nonintrusive diagnostics have been in urgent demand to give a more accurate and comprehensive flow-field for hypersonic testing. In this paper, an overview of some advanced nonintrusive measurement techniques such as embedded thermocouples for heat flux measurement, Pressure Sensitive Paint(PSP), Particle Image Velocimetry(PIV), infrared thermographs, and focusing Schlieren system are introduced. All of these techniques are nonintrusive and provide measurement of various parameters such as temperature, static pressure, dynamic pressure, flow velocity and visualization of flow structure, which gives us an exact and direct understanding of the hypersonic flow.
基金supported by the National Natural Science Foundation of China (No.50876120)the Natural Science Foundation Project of Chongqing, China (No.2010BB2298)
文摘In this work, the theoretical model of FBG when it is affected by double external variables (temperature and transverse pressure) and triple external variables (temperature, axial strain and transverse pressure) is deduced, respectively. The simulated results show that the properties of cross sensitivity would change in a certain regulation with the external effects and fiber parameters. At the same time, some valuable suggestions about how to improve the measurement accuracy are put forward as well.
文摘The key factor of the sensitivity in the FBG-based pH sensor is analyzed in detail. A multi-thin-layer structure of the gel coated cover was proposed and implemented with a special process. The sensors with the coated thickness of 420 ~m, 500 ~m, and 580 ~m were built up, respectively. The corresponding spectral shifts of 0.08nm, 0.13nm, and 0.22nm were detected when the pH sensors were soaked in the pH value of 3-9. Meanwhile, the sensor with the gel layer thickness of 580 ~tm was measured in the optimum measurement time period with the pH value changing from 3-12, in which the detected sensitivity of 52pm/pH was achieved in the pH range of 6-12.
基金supported by the National High Technology Research and Development Program(No.2013AA014200)the National Natural Science Foundation of China(No.61107052)+1 种基金the Natural Science Foundation of Tianjin(No.14JCYBJC16500)the Tianjin University's Science and Technology Development Fund Projects(No.2012)
文摘An all-fiber sensor based on a cascaded optical fiber device is proposed and demonstrated, and its sensor head is composed of a core-offset Mach-Zehnder interferometer(MZI) and a long-period fiber grating(LPFG). In the experiment, two dips shaped by the intermodulation between the interference fringe of MZI and the resonant wavelength of LPFG are monitored. Experimental results show that temperature sensitivities of two dips are 0.060 7 nm/°C and 0.056 3 pm/°C, and the refractive index(RI) sensitivities are –18.025 nm/RIU and –55.06 nm/RIU, respectively. The simultaneous measurement of the temperature and external RI is demonstrated based on the sensitive matrix. Its low fabrication cost, simple configuration and high sensitivity make this sensor have potential applications in chemical and biological sensing.
基金supported by the National High Technology Research and Development Program of China (No.2007AA03Z413)the National Natural Science Foundation of China (No.60727004)+3 种基金the Shaanxi Province "13115" Major Scientific and Technological Innovation Works Special Project (No.708087)the Major Science and Technology Project of Ministry of Education of China (No.Z08119)the Innovation Foundation of the Petro China (No. 2008D-5006-03-08)the Shaanxi Provincial Department of Education Project (No.09JS041)
文摘A novel fiber Bragg grating(FBG) sensor with simultaneous sensing of displacement and temperature is presented.The FBG is affixed on the cantilever inclinedly.The midpoint of FBG exactly coincides with the zero strain layer of a rectangular beam.The vertical displacement can be measured by the broadened bandwidth of FBG as the bandwidth is insensitive to temperature,while the temperature can be measured by the center wavelength shift as the wavelength shift is insensitive to vertical displacement.With 0.1 nm spectral resolution of the analyzer,sensitivities of bandwidth-displacement and center wavelength-temperature are 0.48 nm/mm and 0.05 nm/℃,resolutions are 0.2 mm and 2.0 ℃,and sensing ranges of displacement and temperature are up to 8.5 mm and 45℃ respectively.Experimental results match theoretical analyses very well.
基金supported by the National High Technology Research and Development Program of China(No.2013AA014200)the National Natural Science Foundation of China(No.11444001)the Municipal Natural Science Foundation of Tianjin(No.14JCYBJC16500)
文摘An all fiber magnetic field sensor with peanut-shape structure based on multimode fiber(MMF) is proposed and experimentally demonstrated. The sensing structure and magnetic fluid(MF) are both encapsulated in capillary, and the effective refractive index of MF is affected by surrounding magnetic field strength. The measurement of magnetic field is realized by observing the wavelength drift of interference peak. The transmission spectrum generated by Mach-Zehnder interferometer(MZI) includes core-core mode interference and core-cladding mode interference. Experimental results demonstrate that the core-cladding mode interference is sensitive to magnetic field, and the magnetic field sensitivity is 0.047 8 nm/mT. In addition, two kinds of interference dips are sensitive to temperature, and the sensitivities are 0.060 0 nm/°C and 0.052 6 nm/°C, respectively. So the simultaneous measurement of magnetic field strength and temperature can be achieved based on sensitivity matrix.
