A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be use...A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.展开更多
For the measurement of vertical profiles of sound speed in the sea using laser excited Brillouin scattering, a high resolution measurement of Brillouin frequency shift is required. In this work, a molecular absorption...For the measurement of vertical profiles of sound speed in the sea using laser excited Brillouin scattering, a high resolution measurement of Brillouin frequency shift is required. In this work, a molecular absorption cell was selected as the frequency shift discriminator and several kinds of absorption gases were tried. It was found that the strong line (#1095) of 127 I 2 at 18783.3297 cm -1 and two absorption lines of 129 I 2 located at the two sides of the #1095 line of 127 I 2 could be used as frequency shift discriminator to detect the changes of the Brillouin frequency shift. This selection is the best one within the range from 532.0131 nm to 532.5154 nm. But it is not perfect and there is a lot of work to do before its practical application.展开更多
An efficient and accurate method for solving the two-dimensional Helmholtz equation in domains exterior to elongated obstacles is developed in this paper.The method is based on the so called transformed field expansio...An efficient and accurate method for solving the two-dimensional Helmholtz equation in domains exterior to elongated obstacles is developed in this paper.The method is based on the so called transformed field expansion(TFE) coupled with a spectral-Galerkin solver for elliptical domain using Mathieu functions.Numerical results are presented to show the accuracy and stability of the proposed method.展开更多
We propose the trench-assisted multimode fiber(TA-OM4)as a novel sensing fiber in forward Brillouin scattering(FBS)-based temperature sensor,due to its higher temperature sensitivity,better bending resistance and lowe...We propose the trench-assisted multimode fiber(TA-OM4)as a novel sensing fiber in forward Brillouin scattering(FBS)-based temperature sensor,due to its higher temperature sensitivity,better bending resistance and lower propagation loss,compared with the single mode fiber(SMF)and other sensing fibers.The FBS effect and acousto-optic interaction in TA-OM4 are the first time to be demonstrated and characterized at 1550 nm theoretically and experimentally.A 2.0 km long TA-OM4 is put into an oven to measure its temperature sensitivity,which can reach up to 80.3 kHz/℃,exceeding 53%of SMF(52.4 kHz/℃).The simulated and experimental results verify that the TA-OM4 may be a good candidate as the sensing fiber for the FBS-based temperature sensor.展开更多
Based on the Fermi's golden rule and the theory of Boltzmann collision term approximation, a physically-based model for hole scattering rate(SR) in strained Si1-x Gex/(100)Si was presented, which takes into accoun...Based on the Fermi's golden rule and the theory of Boltzmann collision term approximation, a physically-based model for hole scattering rate(SR) in strained Si1-x Gex/(100)Si was presented, which takes into account a variety of scattering mechanisms,including ionized impurity, acoustic phonon, non-polar optical phonon and alloy disorder scattering. It is indicated that the SRs of acoustic phonon and non-polar optical phonon decrease under the strain, and the total SR in strained Si1-x Gex/(100)Si also decreases obviously with increasing Ge fraction(x). Moreover, the total SR continues to show a constant tendency when x is less than 0.3. In comparison with bulk Si, the total SR of strained Si1-x Gex/(100) Si decreases by about 58%.展开更多
Most of the materials used in engineered cementitious composite are fine in size to achieve ductile nature.Stone slurry powder(SSP)is an inert material obtained from stone industries as by-product which may cause haza...Most of the materials used in engineered cementitious composite are fine in size to achieve ductile nature.Stone slurry powder(SSP)is an inert material obtained from stone industries as by-product which may cause hazardous impact on environment.In this research work,partial replacement of silica sand(SS)and fine sand(FS)by SSP with different contents(25%and 50%each)for making engineered cementitious composite has been explored.The performance was evaluated on the basis of strength,tensile strain,mid span deflection capacity,ultra-sonic pulse velocity and microstructure.Mechanical strength was found to be increased at 25%SSP in both replacements;whereas,strength decreased slightly at 50%replacement.Tensile strain,mid span deflection and quality of concrete were enhanced with increase in SSP content.Using SSP formed denser cementitious composite can help to save the natural resources and contribute in making green cementitious composite.展开更多
The hole mobility of strained silicon along the <110> orientation on (001) Si1?xGex is obtained by solving collision term in the Boltzmann transport equation. The analytical model is proposed that considers the ...The hole mobility of strained silicon along the <110> orientation on (001) Si1?xGex is obtained by solving collision term in the Boltzmann transport equation. The analytical model is proposed that considers the effect of strain-induced splitting at valence band valleys in silicon, doping dependence and three scattering mechanisms, i.e., ionized impurity scattering, acoustic phonon scattering and non-polar optical phonon scattering. The hole occupancy at top band indicates a non-monotonic variation under biaxial tensile strain at low temperature (77 K). What's more, a non-monotonic variation of hole mobility at room temperature (300 K) is presented. Compared with the room temperature hole mobility, the low temperature hole mobility is affected greatly by ionized impurity scattering at lower impurity concentration. At the same time, the room temperature hole mobility is lower than that of electron with the same germanium content and doping concentration. If the parameters are correctly chosen, the model can also be used to calculate the hole mobility of other crystal faces with arbitrary orientation. So, it lays a useful foundation for strained silicon devices and circuits.展开更多
基金the Fundamental Research Foundation of Harbin Engineering University, (grant number HEUF 04017)
文摘A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.
文摘For the measurement of vertical profiles of sound speed in the sea using laser excited Brillouin scattering, a high resolution measurement of Brillouin frequency shift is required. In this work, a molecular absorption cell was selected as the frequency shift discriminator and several kinds of absorption gases were tried. It was found that the strong line (#1095) of 127 I 2 at 18783.3297 cm -1 and two absorption lines of 129 I 2 located at the two sides of the #1095 line of 127 I 2 could be used as frequency shift discriminator to detect the changes of the Brillouin frequency shift. This selection is the best one within the range from 532.0131 nm to 532.5154 nm. But it is not perfect and there is a lot of work to do before its practical application.
基金supported in part by NSF grant DMS-0610646supported by AcRF Tier 1 Grant RG58/08+1 种基金Singapore MOE Grant T207B2202Singapore NRF2007IDM-IDM002-010
文摘An efficient and accurate method for solving the two-dimensional Helmholtz equation in domains exterior to elongated obstacles is developed in this paper.The method is based on the so called transformed field expansion(TFE) coupled with a spectral-Galerkin solver for elliptical domain using Mathieu functions.Numerical results are presented to show the accuracy and stability of the proposed method.
基金supported in part by the National Natural Foundation of China(Nos. 61875086, 61377086)the Aerospace Science Foundation of China (No.2016ZD52042)Nanjing University of Aeronautics and Astronautics Ph. D. short-term visiting scholar project (No.190901DF08)
文摘We propose the trench-assisted multimode fiber(TA-OM4)as a novel sensing fiber in forward Brillouin scattering(FBS)-based temperature sensor,due to its higher temperature sensitivity,better bending resistance and lower propagation loss,compared with the single mode fiber(SMF)and other sensing fibers.The FBS effect and acousto-optic interaction in TA-OM4 are the first time to be demonstrated and characterized at 1550 nm theoretically and experimentally.A 2.0 km long TA-OM4 is put into an oven to measure its temperature sensitivity,which can reach up to 80.3 kHz/℃,exceeding 53%of SMF(52.4 kHz/℃).The simulated and experimental results verify that the TA-OM4 may be a good candidate as the sensing fiber for the FBS-based temperature sensor.
基金Project(JY0300122503)supported by the Research Fund for the Doctoral Program of Higher Education of ChinaProject(P140c090303110c0904)supported by NLAIC Research Fund,ChinaProjects(K5051225014,7214608503)supported by the Fundamental Research Funds for the Central Universities,China
文摘Based on the Fermi's golden rule and the theory of Boltzmann collision term approximation, a physically-based model for hole scattering rate(SR) in strained Si1-x Gex/(100)Si was presented, which takes into account a variety of scattering mechanisms,including ionized impurity, acoustic phonon, non-polar optical phonon and alloy disorder scattering. It is indicated that the SRs of acoustic phonon and non-polar optical phonon decrease under the strain, and the total SR in strained Si1-x Gex/(100)Si also decreases obviously with increasing Ge fraction(x). Moreover, the total SR continues to show a constant tendency when x is less than 0.3. In comparison with bulk Si, the total SR of strained Si1-x Gex/(100) Si decreases by about 58%.
基金Project(F1-17.1/2017-18/MANF-2017-18-HAR-78129)supported by the University Grants Commission New Delhi,India。
文摘Most of the materials used in engineered cementitious composite are fine in size to achieve ductile nature.Stone slurry powder(SSP)is an inert material obtained from stone industries as by-product which may cause hazardous impact on environment.In this research work,partial replacement of silica sand(SS)and fine sand(FS)by SSP with different contents(25%and 50%each)for making engineered cementitious composite has been explored.The performance was evaluated on the basis of strength,tensile strain,mid span deflection capacity,ultra-sonic pulse velocity and microstructure.Mechanical strength was found to be increased at 25%SSP in both replacements;whereas,strength decreased slightly at 50%replacement.Tensile strain,mid span deflection and quality of concrete were enhanced with increase in SSP content.Using SSP formed denser cementitious composite can help to save the natural resources and contribute in making green cementitious composite.
基金supported by the National Ministries and Commissions (Grant Nos. 51308040203, 9140A08060407DZ0103 and 6139801)
文摘The hole mobility of strained silicon along the <110> orientation on (001) Si1?xGex is obtained by solving collision term in the Boltzmann transport equation. The analytical model is proposed that considers the effect of strain-induced splitting at valence band valleys in silicon, doping dependence and three scattering mechanisms, i.e., ionized impurity scattering, acoustic phonon scattering and non-polar optical phonon scattering. The hole occupancy at top band indicates a non-monotonic variation under biaxial tensile strain at low temperature (77 K). What's more, a non-monotonic variation of hole mobility at room temperature (300 K) is presented. Compared with the room temperature hole mobility, the low temperature hole mobility is affected greatly by ionized impurity scattering at lower impurity concentration. At the same time, the room temperature hole mobility is lower than that of electron with the same germanium content and doping concentration. If the parameters are correctly chosen, the model can also be used to calculate the hole mobility of other crystal faces with arbitrary orientation. So, it lays a useful foundation for strained silicon devices and circuits.
