为研制大位移磁致伸缩位移传感器,对扭转超声波在波导丝中的衰减特性进行研究。由于波导丝材料的均一性受拉伸等加工环节的影响,材料的内部变化对检测信号的影响大于超声波在短距离传播的衰减变化。提出的检测方案将永磁体固定在波导丝...为研制大位移磁致伸缩位移传感器,对扭转超声波在波导丝中的衰减特性进行研究。由于波导丝材料的均一性受拉伸等加工环节的影响,材料的内部变化对检测信号的影响大于超声波在短距离传播的衰减变化。提出的检测方案将永磁体固定在波导丝正中间,去掉两端的阻尼,使得向两端传播的超声波受到同样的反射,通过检测两个回波的幅值来测量超声波衰减系数,可以滤除材料不均匀性产生的影响。搭建了磁致伸缩位移传感器实验平台,基于所提实验方法,测得频率为65 k Hz的扭转超声波在线径为0.5 mm且不受拉力作用下的Fe-Ga和Fe-Ni波导丝的衰减系数分别为1.34 d B/m和1.57 d B/m。实验还对比了不同线径Fe-Ga波导丝、不同扭转超声波频率和波导丝在不同拉力作用下的衰减系数变化,结果表明:衰减系数随波导丝线径的增大而增大;衰减系数与扭转超声波的频率呈正相关;衰减系数随波导丝两端拉力的增大先减小后趋于稳定。展开更多
Structural and spin polarization effects of Cr, Fe and Ti elements on electronical properties of alumina have been studied by using of Local spin density approximation within density functional theory. The calculated ...Structural and spin polarization effects of Cr, Fe and Ti elements on electronical properties of alumina have been studied by using of Local spin density approximation within density functional theory. The calculated results indicated that substituting aluminium atoms by these dopants have a significant influence on the structural and electronic properties of α –Al2O3 crystals. Band gap of alumina decreases with the substitution of these impurities. Results show that band gap is different for spin-up and down (spin splitting effect). Among these impurities the effect of Ti on size of the energy gap is small in comparison with Cr and Fe. It is suggested that the origin of electrons spin splitting is appeared from exchange energy of d-states. These results may be useful to obtain a physical beheviour of transition metals for electrons spin polarization in d-states.展开更多
In this paper, we propose a novel structure of quantum waveguide. In this structure we tailored the quantum wire by Gaussian Profile. Thus, the Dirac-Delta function potentials are weighted according to Gaussian distri...In this paper, we propose a novel structure of quantum waveguide. In this structure we tailored the quantum wire by Gaussian Profile. Thus, the Dirac-Delta function potentials are weighted according to Gaussian distribution function. We studied the electronic transmission properties through this tailored quantum waveguide structure. We have assumed that single free-electron channel is incident on the structure and the scattering of electrons is solely from the geometric nature of the problem. We have used the transfer matrix method to study the electron transmission. Coherent Tunneling is achieved through this structure, which is well-defined allowed conduction bands. The electronic conductance spectrum depends on the number of the Dirac delta function potential in the quantum wire. When the number of Dirac delta function potentials in the structure and their strengths are increased, both well defined conductance bands and sharper and narrower forbidden bands are formed. This novel structure has a good defect tolerance. The structure tolerates strength defect and tolerates position defect for the central Dirac delta function in the Gaussian distribution.展开更多
An S-band cavity BPM is designed for a new injector in National Synchrotron Radiation Laboratory. A re-entrant position cavity is tuned to the TM110 mode as position cavity. Cut-through waveguides are used as pickups ...An S-band cavity BPM is designed for a new injector in National Synchrotron Radiation Laboratory. A re-entrant position cavity is tuned to the TM110 mode as position cavity. Cut-through waveguides are used as pickups to suppress the monopole signal. Theoretical resolution of this design is 31 nm. A prototype cavity BPM system is manufactured for off-line cold tests. The wire scanning method is used to calibrate the BPM and estimate the performance of the on-line BPM system. A cross-talk problem has been detected during the cold test. Racetrack cavity BPM design can be used to suppress the cross-talk. With the nonlinear effect being ignored, transform matrix can be used to correct cross-talk. Analysis of cold test results shows that the position resolution of prototype BPM is better than 3 μm.展开更多
文摘为研制大位移磁致伸缩位移传感器,对扭转超声波在波导丝中的衰减特性进行研究。由于波导丝材料的均一性受拉伸等加工环节的影响,材料的内部变化对检测信号的影响大于超声波在短距离传播的衰减变化。提出的检测方案将永磁体固定在波导丝正中间,去掉两端的阻尼,使得向两端传播的超声波受到同样的反射,通过检测两个回波的幅值来测量超声波衰减系数,可以滤除材料不均匀性产生的影响。搭建了磁致伸缩位移传感器实验平台,基于所提实验方法,测得频率为65 k Hz的扭转超声波在线径为0.5 mm且不受拉力作用下的Fe-Ga和Fe-Ni波导丝的衰减系数分别为1.34 d B/m和1.57 d B/m。实验还对比了不同线径Fe-Ga波导丝、不同扭转超声波频率和波导丝在不同拉力作用下的衰减系数变化,结果表明:衰减系数随波导丝线径的增大而增大;衰减系数与扭转超声波的频率呈正相关;衰减系数随波导丝两端拉力的增大先减小后趋于稳定。
文摘Structural and spin polarization effects of Cr, Fe and Ti elements on electronical properties of alumina have been studied by using of Local spin density approximation within density functional theory. The calculated results indicated that substituting aluminium atoms by these dopants have a significant influence on the structural and electronic properties of α –Al2O3 crystals. Band gap of alumina decreases with the substitution of these impurities. Results show that band gap is different for spin-up and down (spin splitting effect). Among these impurities the effect of Ti on size of the energy gap is small in comparison with Cr and Fe. It is suggested that the origin of electrons spin splitting is appeared from exchange energy of d-states. These results may be useful to obtain a physical beheviour of transition metals for electrons spin polarization in d-states.
文摘In this paper, we propose a novel structure of quantum waveguide. In this structure we tailored the quantum wire by Gaussian Profile. Thus, the Dirac-Delta function potentials are weighted according to Gaussian distribution function. We studied the electronic transmission properties through this tailored quantum waveguide structure. We have assumed that single free-electron channel is incident on the structure and the scattering of electrons is solely from the geometric nature of the problem. We have used the transfer matrix method to study the electron transmission. Coherent Tunneling is achieved through this structure, which is well-defined allowed conduction bands. The electronic conductance spectrum depends on the number of the Dirac delta function potential in the quantum wire. When the number of Dirac delta function potentials in the structure and their strengths are increased, both well defined conductance bands and sharper and narrower forbidden bands are formed. This novel structure has a good defect tolerance. The structure tolerates strength defect and tolerates position defect for the central Dirac delta function in the Gaussian distribution.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10875117 and 11005106)National "985 Project" (Grnat No. 173123200402002)+1 种基金China Postdoctoral Science Foundation (Grant No. 20100470853)"the Fundamental Research Funds for the Central Universities"
文摘An S-band cavity BPM is designed for a new injector in National Synchrotron Radiation Laboratory. A re-entrant position cavity is tuned to the TM110 mode as position cavity. Cut-through waveguides are used as pickups to suppress the monopole signal. Theoretical resolution of this design is 31 nm. A prototype cavity BPM system is manufactured for off-line cold tests. The wire scanning method is used to calibrate the BPM and estimate the performance of the on-line BPM system. A cross-talk problem has been detected during the cold test. Racetrack cavity BPM design can be used to suppress the cross-talk. With the nonlinear effect being ignored, transform matrix can be used to correct cross-talk. Analysis of cold test results shows that the position resolution of prototype BPM is better than 3 μm.
