Magneto optic(MO) fiber current sensors utility the Faraday effect of magneto op tic materials to sensing the magnetic(current)fields.The optical fiber sensors(O FS)offer great advantages of simple structure,high reli...Magneto optic(MO) fiber current sensors utility the Faraday effect of magneto op tic materials to sensing the magnetic(current)fields.The optical fiber sensors(O FS)offer great advantages of simple structure,high reliability,high accuracy and sensibility,immunity to electromagnetic interference.They are the most promised method to substitute the conventional current transducers(CTs),much attentions were focused on both domestic and abroad.Magneto optic properties of Faraday se n sing element have much affect on the performance of the optical fiber current se nsor.For used in the sensor system,MO materials with magneto optic characterist i cs of large Faraday rotation(FR)angle θ f ,low temperature sensibility,and suitable saturation field were general demanded. Development of MO materials is one of the most important problems of optical fiber current sensor research. In this paper,one mixed doped Bi substituted yttrium iron garnet crystal BiYb:Y I G, which has large and temperature stable FR angle,was grown from high temperatu re flux.By taking PbO+PbF 2 as the main flux,under the compositions of molar ra tio Y 2O 3:Yb 2O 3:Bi 2O 3:Fe 2O 3:(PbO+PbF 2+B 2O 3+CaCO 3)=7.64:1. 04:1.74:20.78:78:68.8,crystals of quite good quality were grown from melt flux,t he largest one has the size of 22mm×15mm×12mm.Magneto optic proprieties of Fa raday rotation angle and optical absorption spectrum of the BiYb:YIG crystal,expecial ly Y 2.289 Yb 0.246 Bi 0.465 Fe 5O 12 ,in the range of 0.7 1.9 μm waveband were measured.At λ =1.55μm,the BiYb:YIG crystal has special Fa raday rotation angle of -404deg/cm,temperature coefficient 4.2×10 -6 K -1 ,optical absorption coefficient 3.6cm -1 ,and figure of merit 25.8deg/dB . The results indicate that substituted with Bi 3+ can largely improve the Fa raday rotation of rear earth iron garnets.Because Faraday rotation angles of Yb 3Fe 5O 12 and Y 3Fe 5O 12 have opposite temperature dependency,ut ility the compensation effect of mix doped,co doped with some other ions,such a s Yb 3+ ,would decrease the temperature dependency of Bi substituted garnet. So the garnet crystal BiYb:YIG has high and temperature stable Faraday rotation an gle,very suitable to be used as Faraday effect materials for high sensibility an d temperature stable Optical fiber current sensors.Using BiYb:YIG as Faraday rot ation cell,a hybrid bulk crystal optical fiber current sensor was proposed and t ests under direct current(DC) and 50Hz alternating current(AC).The performance c haracteristics of the sensors system were:DC measurement,sensibility 0.01A, l inea rity 1.1%;AC measurement,sensibility 9.5A/mV ,accuracy ±1%,linearity 1.1%,dynam ic range 40dB.In conclusion,Faraday effect magneto optic optical fiber current sensors have higher sensibility and accuracy than conventional CTs.展开更多
The crystal of high concentration Nd:YAG was grown by flux method and diode pu mp microcavity laser was studied.High efficiency and frequency solid state lase r was built on research and development.some applications ...The crystal of high concentration Nd:YAG was grown by flux method and diode pu mp microcavity laser was studied.High efficiency and frequency solid state lase r was built on research and development.some applications such as target designa tion,laser radar,rangefinder,CATV etc. In order to maximize pump efficiency and power output,the Nd concentration shoul d be made as high as possible without degrading the gain through concentration q uenching.In crystal grown by Czochraski method.it is difficult to increase the N d concentration over 1.2% because of Nd segregation in the melt (yttrium aluminum garnet),which leads to large nonuniformities in doping.However,by using the f lux met hod growth technique,it is possible to grow uniformly doped crystal as much as 4 % Nd concentration YAG.展开更多
The KGd(WO 4) 2[KGW] crystal has a structure belonging to the monoclinic sys tem with space group C 2/ c and with unit cell dimensions a =1.068mm, b =1.043nm, c =0.76nm, β =130°.This crystal is an excellent host...The KGd(WO 4) 2[KGW] crystal has a structure belonging to the monoclinic sys tem with space group C 2/ c and with unit cell dimensions a =1.068mm, b =1.043nm, c =0.76nm, β =130°.This crystal is an excellent host material for solid state lasers.The threshold of the laser oscillations in a Nd 3+ d oped KGW laser crystal is considerable low and has a higher emissive section.T he fluorescent concentration quench effect of the Nd 3+ ion in the KGW crystal may be weakened due to the W O covalent bond,so this crystal has a higher dopi ng concentration of active ion.Furthermore,the absorption band at 808nm of Nd 3+ in the KGW crystal,which has 12nm FWHM,is well matched with the emission w avelength of a laser diode ,a solid state laser pump that is very convenient and popular in laser science and technology today.Therefore the KGW crystal has a l aser emission with higher output and higher efficiency.Scientists of laser techn ology circles are very interested in Yb 3+ doped laser crystals because they have four advanta ges when they are compared with Nd 3+ doped laser crystals.Firstly,their flu orescent lifetimes are three or four times as many as that of Nd 3+ doped la ser crystals,which is beneficial to reserving the energy.Secondly,the heat energ y,which is formed when laser is operating,will be decreased because the pumping band is close to the upper energy level.Not only will the use ratio of energy be increased but also the damage effect to laser properties will be decreased.Thir dly,there is no absorption problems of excite state because the energy level of Yb 3+ is simple.Finally,the higher optical quality crystals are easier to gr ow because the radius of Yb 3+ is closer to that of Gd 3+ .Furthermore,Y b 3+ doped laser crystals can substitute the Ti sapphire for the psec laser .展开更多
Wurtzite strcture gallium nitride, GaN,a direct bandgap semiconductor (3.4 eV at room temperature),is an ideal material for fabrication of blue/green light emit ti ng diodes, laser diodes,and high power integrated cir...Wurtzite strcture gallium nitride, GaN,a direct bandgap semiconductor (3.4 eV at room temperature),is an ideal material for fabrication of blue/green light emit ti ng diodes, laser diodes,and high power integrated circuits.Recent progress in th in film crystal technique has realized the output of blue semiconductor lasers w i th a lifetime of over 10000 hours under continuous wave operation at room tempe r ature.So far GaN and its ternary indium and aluminum alloys are grown almost uni v ersally on foreign substrates with varying lattice mismatches.The mismatch undou btedly results in a significant dislocation density in the grown films.Hence it is necessary to grow single crystal GaN to be used as substrates for improvement of laser diodes.On the other hand,low dimensional GaN materials such as nanocry stalline powder,nanocrystal assembled bulk(nanophase) and nano wires are very u seful in both fundamental mesoscopic research and future development of GaN nano devices.Here we report our main recent progresses on the crystal growth of GaN a nd the preparation of its low dimensional materials.展开更多
为研究液滴撞击不同润湿性加热表面的传热传质问题,基于体积分数(volume of fluid, VOF)方法,分析了壁面润湿性和表面温度对液滴形态及传热特性的作用机理,结果表明:亲水壁面有利于液滴的铺展,疏水壁面则有利于液滴的反弹,随着接触角的...为研究液滴撞击不同润湿性加热表面的传热传质问题,基于体积分数(volume of fluid, VOF)方法,分析了壁面润湿性和表面温度对液滴形态及传热特性的作用机理,结果表明:亲水壁面有利于液滴的铺展,疏水壁面则有利于液滴的反弹,随着接触角的增大,液滴最大铺展因子减小,达最大铺展因子的时间缩短,壁面平均热流密度减小。表面温度对液滴铺展阶段的影响较小,随着表面温度的升高,液滴相变速率加快,壁面平均热流密度增大,表面温度超过临界温度时,产生Leidenfrost现象。展开更多
针对传统电机输出端口单一的问题,提出一种新型多端口盘式永磁电机(multi-port disk permanent magnet motor,MDPMM)。首先,介绍该电机的结构及工作原理;其次,针对该电机环形弧线定子周向端部使其漏磁和磁场分布较为复杂的问题,引入磁...针对传统电机输出端口单一的问题,提出一种新型多端口盘式永磁电机(multi-port disk permanent magnet motor,MDPMM)。首先,介绍该电机的结构及工作原理;其次,针对该电机环形弧线定子周向端部使其漏磁和磁场分布较为复杂的问题,引入磁通分布系数,对受环形弧线定子端部影响的区域建立等效磁网络模型,计算各等效磁阻,解析该区域漏磁系数表达式;最后,考虑永磁体电流密度等效,建立环形弧线定子及对应盘式转子区域的分区域解析模型,运用等效磁化强度法推导该区域气隙磁场解析式,并采用许−克变换分析定子齿槽结构对气隙磁场的影响。研究结果表明:该电机可以同时实现双盘式转子和行星轮转子多自由度动力输出;受环形弧线定子端部截面影响和未受影响的2种磁路的气隙漏磁系数计算值分别为1.263、1.167,有限元仿真值分别为1.375、1.222,计算值和仿真值的相对误差分别为8.15%、4.50%;2种磁路的平均气隙磁密计算值分别为0.481、0.492,有限元仿真值分别为0.497、0.503,计算值和仿真值的相对误差分别为3.22%、2.19%,满足工程计算精度要求。展开更多
文摘Magneto optic(MO) fiber current sensors utility the Faraday effect of magneto op tic materials to sensing the magnetic(current)fields.The optical fiber sensors(O FS)offer great advantages of simple structure,high reliability,high accuracy and sensibility,immunity to electromagnetic interference.They are the most promised method to substitute the conventional current transducers(CTs),much attentions were focused on both domestic and abroad.Magneto optic properties of Faraday se n sing element have much affect on the performance of the optical fiber current se nsor.For used in the sensor system,MO materials with magneto optic characterist i cs of large Faraday rotation(FR)angle θ f ,low temperature sensibility,and suitable saturation field were general demanded. Development of MO materials is one of the most important problems of optical fiber current sensor research. In this paper,one mixed doped Bi substituted yttrium iron garnet crystal BiYb:Y I G, which has large and temperature stable FR angle,was grown from high temperatu re flux.By taking PbO+PbF 2 as the main flux,under the compositions of molar ra tio Y 2O 3:Yb 2O 3:Bi 2O 3:Fe 2O 3:(PbO+PbF 2+B 2O 3+CaCO 3)=7.64:1. 04:1.74:20.78:78:68.8,crystals of quite good quality were grown from melt flux,t he largest one has the size of 22mm×15mm×12mm.Magneto optic proprieties of Fa raday rotation angle and optical absorption spectrum of the BiYb:YIG crystal,expecial ly Y 2.289 Yb 0.246 Bi 0.465 Fe 5O 12 ,in the range of 0.7 1.9 μm waveband were measured.At λ =1.55μm,the BiYb:YIG crystal has special Fa raday rotation angle of -404deg/cm,temperature coefficient 4.2×10 -6 K -1 ,optical absorption coefficient 3.6cm -1 ,and figure of merit 25.8deg/dB . The results indicate that substituted with Bi 3+ can largely improve the Fa raday rotation of rear earth iron garnets.Because Faraday rotation angles of Yb 3Fe 5O 12 and Y 3Fe 5O 12 have opposite temperature dependency,ut ility the compensation effect of mix doped,co doped with some other ions,such a s Yb 3+ ,would decrease the temperature dependency of Bi substituted garnet. So the garnet crystal BiYb:YIG has high and temperature stable Faraday rotation an gle,very suitable to be used as Faraday effect materials for high sensibility an d temperature stable Optical fiber current sensors.Using BiYb:YIG as Faraday rot ation cell,a hybrid bulk crystal optical fiber current sensor was proposed and t ests under direct current(DC) and 50Hz alternating current(AC).The performance c haracteristics of the sensors system were:DC measurement,sensibility 0.01A, l inea rity 1.1%;AC measurement,sensibility 9.5A/mV ,accuracy ±1%,linearity 1.1%,dynam ic range 40dB.In conclusion,Faraday effect magneto optic optical fiber current sensors have higher sensibility and accuracy than conventional CTs.
文摘The crystal of high concentration Nd:YAG was grown by flux method and diode pu mp microcavity laser was studied.High efficiency and frequency solid state lase r was built on research and development.some applications such as target designa tion,laser radar,rangefinder,CATV etc. In order to maximize pump efficiency and power output,the Nd concentration shoul d be made as high as possible without degrading the gain through concentration q uenching.In crystal grown by Czochraski method.it is difficult to increase the N d concentration over 1.2% because of Nd segregation in the melt (yttrium aluminum garnet),which leads to large nonuniformities in doping.However,by using the f lux met hod growth technique,it is possible to grow uniformly doped crystal as much as 4 % Nd concentration YAG.
文摘The KGd(WO 4) 2[KGW] crystal has a structure belonging to the monoclinic sys tem with space group C 2/ c and with unit cell dimensions a =1.068mm, b =1.043nm, c =0.76nm, β =130°.This crystal is an excellent host material for solid state lasers.The threshold of the laser oscillations in a Nd 3+ d oped KGW laser crystal is considerable low and has a higher emissive section.T he fluorescent concentration quench effect of the Nd 3+ ion in the KGW crystal may be weakened due to the W O covalent bond,so this crystal has a higher dopi ng concentration of active ion.Furthermore,the absorption band at 808nm of Nd 3+ in the KGW crystal,which has 12nm FWHM,is well matched with the emission w avelength of a laser diode ,a solid state laser pump that is very convenient and popular in laser science and technology today.Therefore the KGW crystal has a l aser emission with higher output and higher efficiency.Scientists of laser techn ology circles are very interested in Yb 3+ doped laser crystals because they have four advanta ges when they are compared with Nd 3+ doped laser crystals.Firstly,their flu orescent lifetimes are three or four times as many as that of Nd 3+ doped la ser crystals,which is beneficial to reserving the energy.Secondly,the heat energ y,which is formed when laser is operating,will be decreased because the pumping band is close to the upper energy level.Not only will the use ratio of energy be increased but also the damage effect to laser properties will be decreased.Thir dly,there is no absorption problems of excite state because the energy level of Yb 3+ is simple.Finally,the higher optical quality crystals are easier to gr ow because the radius of Yb 3+ is closer to that of Gd 3+ .Furthermore,Y b 3+ doped laser crystals can substitute the Ti sapphire for the psec laser .
文摘Wurtzite strcture gallium nitride, GaN,a direct bandgap semiconductor (3.4 eV at room temperature),is an ideal material for fabrication of blue/green light emit ti ng diodes, laser diodes,and high power integrated circuits.Recent progress in th in film crystal technique has realized the output of blue semiconductor lasers w i th a lifetime of over 10000 hours under continuous wave operation at room tempe r ature.So far GaN and its ternary indium and aluminum alloys are grown almost uni v ersally on foreign substrates with varying lattice mismatches.The mismatch undou btedly results in a significant dislocation density in the grown films.Hence it is necessary to grow single crystal GaN to be used as substrates for improvement of laser diodes.On the other hand,low dimensional GaN materials such as nanocry stalline powder,nanocrystal assembled bulk(nanophase) and nano wires are very u seful in both fundamental mesoscopic research and future development of GaN nano devices.Here we report our main recent progresses on the crystal growth of GaN a nd the preparation of its low dimensional materials.
文摘为研究液滴撞击不同润湿性加热表面的传热传质问题,基于体积分数(volume of fluid, VOF)方法,分析了壁面润湿性和表面温度对液滴形态及传热特性的作用机理,结果表明:亲水壁面有利于液滴的铺展,疏水壁面则有利于液滴的反弹,随着接触角的增大,液滴最大铺展因子减小,达最大铺展因子的时间缩短,壁面平均热流密度减小。表面温度对液滴铺展阶段的影响较小,随着表面温度的升高,液滴相变速率加快,壁面平均热流密度增大,表面温度超过临界温度时,产生Leidenfrost现象。
文摘针对传统电机输出端口单一的问题,提出一种新型多端口盘式永磁电机(multi-port disk permanent magnet motor,MDPMM)。首先,介绍该电机的结构及工作原理;其次,针对该电机环形弧线定子周向端部使其漏磁和磁场分布较为复杂的问题,引入磁通分布系数,对受环形弧线定子端部影响的区域建立等效磁网络模型,计算各等效磁阻,解析该区域漏磁系数表达式;最后,考虑永磁体电流密度等效,建立环形弧线定子及对应盘式转子区域的分区域解析模型,运用等效磁化强度法推导该区域气隙磁场解析式,并采用许−克变换分析定子齿槽结构对气隙磁场的影响。研究结果表明:该电机可以同时实现双盘式转子和行星轮转子多自由度动力输出;受环形弧线定子端部截面影响和未受影响的2种磁路的气隙漏磁系数计算值分别为1.263、1.167,有限元仿真值分别为1.375、1.222,计算值和仿真值的相对误差分别为8.15%、4.50%;2种磁路的平均气隙磁密计算值分别为0.481、0.492,有限元仿真值分别为0.497、0.503,计算值和仿真值的相对误差分别为3.22%、2.19%,满足工程计算精度要求。
