磁致伸缩/压电叠层复合材料磁-机-电耦合系数分析

分析和推导了磁致伸缩/压电叠层复合材料的机-电耦合系数、磁-机耦合系数及磁-电耦合系数与磁致伸缩层和压电层性能参数及几何参数之间的关系.进一步分析表明,叠层复合材料低频时的磁电电压系数正比于磁-电耦合系数,谐振时的磁电电压系数正比于磁-电耦合系数与机械品质因素的乘积;磁电电压系数还与复合结构的本征阻抗有关,本征阻抗越大磁电电压系数越大.通过性能差异较大的Terfenol-D和FeNi基弹性合金分别与压电材料PZT5-H和PZT8相互组合构成复合材料的比较分析,进一步阐明了磁电复合材料磁-电耦合系数和机械品 关键词： 磁电效应 磁-机-电耦合系数 磁致伸缩材料 压电材料     

1-3型纳米多铁复合薄膜中电场诱导的磁化研究

运用Landau-Devonshire热力学唯像理论,考虑铁电相和铁磁相的电致伸缩、磁致伸缩效应以及产生于铁电/铁磁和薄膜/基底界面的弹性应力作用,两次重整介电和磁作用系数得到了这种多铁系统在Landau自由能函数下的本征二次方磁电耦合形式,从而研究了外延1-3型纳米多铁复合薄膜中极化、磁化随薄膜厚度、温度的变化以及该薄膜中外加电场诱导的磁化变化.结果表明薄膜平面内的应压力的弛豫使得磁化强度和极化强度随薄膜厚度的增加而减少,外加电场不仅能诱导铁电相极化场翻转,而且由于铁电和铁磁相界面竖直方向的弹性耦合导致 关键词： 多铁 磁电效应 磁致伸缩 薄膜     

TbDyFe薄膜对三明治膜巨磁阻抗效应的影响

将600℃退火后的超磁致伸缩材料(Tb0.27Dy_0.73)_0.3Fe_0.7薄膜作为Ni_80.2Fe_14.1Si_0.2Mn_0.4Mo_5.1三明治膜的基底，制备出四层膜.结果表明：附加的磁致伸缩并没有减小材料的巨磁阻抗(GMI)效应，而由于磁场下磁致伸缩材料的应力效应影响了三明治膜中的各向异性场，使三明治膜的GMI效应增大了4倍.再将制备态的四层膜在280℃下真空退火，退火态四层膜也增大了三明治膜的GMI效应，但可能由于磁致伸缩向磁性层中的扩散，其GMI效应相对于制备态四层膜则有所降低. 关键词： 巨磁阻抗(GMI)效应 三明治膜 TbDyFe薄膜 各向异性场     

压应力对Fe0.81 Ga0.19单晶磁化和磁致伸缩的影响

研究了Fe_0.81Ga_0.19合金单晶沿[100]方向的磁机械效应和磁致伸缩效应.基于Stoner-Wohlfarth模型,通过数值计算获得了在压应力和外磁场联合作用下磁化强度的方向余弦.研究表明,随着压应力的增加,退磁态下合金中的磁各向异性会由三轴各向异性向双轴各向异性转变.这使得合金中 90° 畴的体积分数增加,导致磁致伸缩效应增大. 关键词： FeGa合金 磁机械效应 巨磁致伸缩效应     

Tb0.3Dy0.7Fe2单晶中巨磁致伸缩的逆效应

研究了Terfenol-D材料中巨磁致伸缩的逆效应,即磁机械效应.基于Stoner-Wohlfarth(SW)模型,考虑磁晶各向异性和应力各向异性能,依据自由能极小原理,获得了退磁态下Terfenol-D单晶中磁化强度方向和压应力的关系.采用数值方法求解了平衡条件下的非线性方程组.理论结果表明,Terfenol-D巨磁致伸缩单晶中的磁各向异性取决于磁晶各向异性和应力各向异性之间的竞争.在压应力的作用下,Terfenol-D单晶中的磁各向异性由立方向单轴转变.理论和实验结果的比较表明,存在一个临界压应力,使磁致伸缩效应达到极大值.该理论结果还解释了压应力使得Terfenol-D单晶材料难于磁化和磁致伸缩效应出现极大值的实验事实.理论计算不仅为研究这类问题提供了一个更准确的方法,而且其结果也有助于理解类似材料中的磁化过程. 关键词： Terfenol-D 磁机械效应 巨磁致伸缩效应 磁各向异性     

无铅陶瓷中的电致伸缩效应

电致伸缩是一个二次方效应,应变正比于极化强度的平方,比例系数称为电致伸缩系数[Qij].一般固体电介质都能产生电致伸缩效应.对立方晶系的材料来说,电致伸缩系数张量为 当外加电场沿方向1时,E2=E3=0,纵向应变为通过测量材料的应变与外加电压的关系Xi～Vi,和极化强度与外电场的关系P1～Ei,就可以求得电致伸缩系数 电致伸缩效应在天文学、光学通信、激光调制等方面有着广泛的应用.与压电效应相比,它具有重复性好,不需极化,无老化问题等优点.电致伸缩是一个二次方效应,一般较小,不易观察到.已经发现,在具有扩散相转变特征的铁电固溶体中,当…     

电致伸缩效应及其应用

一、电致伸缩效应 电致伸缩(electrostriction)效应是一种机电耦合效应.它是指当外电场作用于电介质上时,所产生的应变正比于电场强度(或极化强度)的平方的现象.由于电致伸缩效应引起的应变与外加电场的方向无关,所以一般固体电介质都能产生电致伸缩效应. 由热力学唯象理论可知,对于晶格点群属于具有对称中心的材料,其应变x与极化强度P的关系为(无外应力时)即应变与极化强度的平方成正比.将x的两个脚标按惯例简化成一个,(1)式改写成 再规定 其中μ=4,5,6,分别对应于k,l的组合为23,13,12.这样,电致伸缩系数山山本来是sl个分量的四阶张量,简…     

YIG和BCVIG中铁磁共振线宽各向异性的可能起因

由于磁弹耦合,应力等效为各向异性场并对磁化强度分布发生影响。借助这一机制阐明了机械抛光的YIG和BCVIG单晶球铁磁共振线宽的各向异性行为,指明机械抛光造成的表面损伤层引起的应力通过磁致伸缩的各向异性使弛豫时间各方向不同,即产生了线宽的各向异性。若损伤层主要由位错组成,按微磁学理论和双磁振子散射模型可得到位错密度、磁致伸缩、磁化强度等与线宽的关系。从测量到的线宽各向异性估算了3μm抛光的YIG的表面层位错密度为5.4×10¹⁰/cm²。该弛豫机制表明,进一步降低多晶小线宽材料的线宽,减小磁致伸缩系数可能是有效途径。 关键词：     

离轴磁场退火后Tb0.3Dy0.7Fe1.95〈110〉取向晶体的磁致伸缩"跳跃"效应

将〈110〉取向Tb_0.3Dy_0.7Fe_1.95合金棒放在与轴向成35°夹角的外磁场中退火处理,研究其在0—30 MPa预压应力σpre作用下的磁致伸缩效应.结果表明,σpre=0条件下的饱和磁致伸缩值λs由退火前的1023×10^-6提高到1650×10^-6;σpre 关键词： 磁致伸缩 磁场退火 磁致伸缩"跳跃"效应     

(La1-xPrx)2/3Sr1/3MnO3系列的磁致伸缩效应研究

用溶胶-凝胶方法制备了一系列的(La_1-xPr_x)_2/3Sr_{1/3MnO3多晶样品,研究了其电磁性能及磁致伸缩效应,发现样品低温下的磁致伸缩主要以线伸缩为主,且在低场下达到饱和,在Pr含量为0.3时达到最大值,约为-90×10^-6.随Pr掺杂含量的逐渐减小,磁致伸缩的饱和场也逐渐减小. 关键词：}     

Inductance of rf-wave-heated plasmas

The inductance of rf-wave-heated plasmas is derived. This inductance represents the inductance of fast electrons located in a plateau during their acceleration due to electric field or deceleration due to collisions and electric field. This inductance has been calculated for small electric fields from the two-dimensional Fokker-Planck equation as the flux crossing the surface of critical energy mv(2)(ph)/2 in the velocity space. The new expression may be important for radio-frequency current drive ramp-up, current drive efficiency, current profile control, and so on in tokamaks. This inductance may be incorporated into transport codes that study plasma heating by rf waves.     

Magnetic permeability and microstructure of the Bi,Si oxides-doped NiZnCu ferrite composite material

Bi,Si oxides-doped NiZnCu ferrite composite material has been fabricated with different sintering times. The microstructure of the samples was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The complex permeability has been measured up to 1 GHz by the impedance analyzers. The complex permeability has been simulated based on the magnetic circuit model, and the result was compared with the experimental results. In the low-frequency region, the real part of the permeability of the composite material is lower than the one of non-doped NiZnCu ferrite, on the other hand it is higher than non-doped sample in the high-field region. The peak position of the imaginary part is shifted to higher frequency in the composite material.     

Recovery of Electron Sheath Current in Magnetically Self-Insulated Transmission Lines

Magnetically self-insulated lines operating at high electric field stress have a high percentage of the current flow in an electron sheath adjacent to the cathode. Recovery of the current in this sheath is desirable for efficient power transport. The Sandia National Laboratories HydraMITE accelerator has a magnetically insulated transmission line (MITL) which has a 7.6-? geometric impedance and operates at 4.8 ?, indicating that approximately 40 percent of the current flows in the electron sheath. If this line is terminated in a section of higher impedance line, theory and simulations indicate that the electron sheath current will be lower at the output. This higher impedance section, however, is effectively an inductance across which there is a voltage drop during the rising part of the pulse. An experiment was conducted on the HydraMITE machine in which input and output currents were measured on a section of line which the impedance changed smoothly from 7.6 ? to 20 ?. At the output the electron current was a few percent of the total current. Measurements were made with a range of inductive and resistive loads. The input and output currents were then compared to lumped circuit line simulations to separate losses related to inductance from electron sheath losses. The measurements indicate that a percentage of the electron sheath is recovered which depends on the load impedance and that the recovery is more efficient after the pulse voltage peak where potential drop along the increased impedance line aids retrapping of electrons.     

铁氧体环的导磁率及其品质因数的测量

 初级绕有线圈的铁氧体环形成电感,如果同时在其次级绕有偏磁线圈并加一直流电流,当此电流改变时,铁氧体导磁率会随之改变,绕有线圈的铁氧体环的电感量也就相应改变。加载了铁氧体环谐振腔的谐振阻抗与铁氧体导磁率、品质因数及腔体谐振频率的乘积成正比,而腔体谐振阻抗直接决定其所需功率的大小。讨论了铁氧体环导磁率和品质因数的测量原理,给出了测试装置的具体电路和测量结果。     

Effect of electrode material on impedance spectra of metal-polyethylene structures with carbon nanotubes

The effect of an electrode material on electrical properties of a composite material based on super-high-molecular polyethylene (SHMPE) filled with carbon nanotubes has been studied using impedance spectroscopy. Using the method of replacing the sample by an equivalent electric circuit, it has been found that, depending on the electrode material, a blocking barrier with high active resistance and a space charge region adjacent to it arise in the interface region. It has been shown that the barrier height is controlled by surface electronic states of SHMPE and weakly depends on the electron work function of metal electrodes (Bardeen barrier). The characteristic times of electrical relaxation characterizing bulk and interface regions of the composite under study have been determined.     

爆磁压缩装置经组合功率调节系统产生高电压的实验研究

 介绍了以爆磁压缩装置为脉冲功率能源,经变压器和爆炸金属丝断路开关组合功率调节系统,在电阻负载上产生高电压的实验研究。实验结果为：在100W 水电阻负载两端得到了约800kV的高电压脉冲,脉宽约100ns。此项工作拓宽了爆磁压缩装置的应用范围。     

负载回路电感对低阻抗脉冲形成线输出波形的影响

 介绍了一个基于带状脉冲形成线的低阻抗实验平台,针对该平台设计了两种不同类型结构的匹配负载,并分别进行了实验研究,得到了不同的输出脉冲波形,发现轨道结构的水负载具有很低的负载回路电感,适于作为低阻抗脉冲形成线的匹配负载。实验结果表明：在开关电感一定的情况下,负载回路电感是影响低阻抗形成线输出波形的决定性因素。对于0.5 Ω的带状脉冲形成线,只有将负载回路电感控制在30 nH以内,才能获得波形较好的输出脉冲,高压实验结果也验证了此结论。利用数值模拟的方法,分析了负载回路电感对不同阻抗形成线输出波形的影响,结果表明：随着形成线阻抗的增加,负载回路电感对波形的影响越来越小。     

Continuing Studies of Plasma Erosion Switches for Power Conditioning on Multiterawatt Pulsed Power Accelerators

Recent PITHON experiments with plasma erosion switches (PES) have extended the range of operation of the switches by about 50 percent, in terms of closed time and charge passing through the switch. The quantity of charge passed through the switch has been increased to as much as 35 mC. Currents as large as 1 MA and voltages as great as 1.8 MV have been switched off to be diverted to a downstream load. The impedance of the erosion switch can be described as having three stages: 1) essentially zero impedance, 2) a transitional opening phase, and 3) an impedance which is very large (greater than 5 ?) in comparson with the subohm downstream load. Current diagnostics, consisting of Rogowski coils and segmented shunts, have been successfully developed to monitor the current which propagates to the load region. These monitors have measured rise times as short as 38 ns and slew rates as great as 1014 A/s at the load. With wire array loads, the pulse conditioning of the switch has been observed to reduce the magnitude of the current losses in the feed which are present when no switch is used. Correlations have been made between the switch closed time, voltage, current, and power with the feed inductance and the generator power injected into the magnetic insulated transmission line (MITL).     

高功率宽谱开关振荡器

采用1/4波长开关同轴谐振器技术路线,开展了高功率宽谱微波产生及耦合输出技术研究。设计振荡器工作在200 MHz,低阻抗1/4波长同轴传输线与传输线一端的环形多通道气体火花开关构成谐振器,耦合器由集中电容和分布电感构成,实现宽谱微波的能量提取。通过数值模拟研究了振荡器的振荡及耦合输出过程,分析了高压脉冲馈入方式、谐振器阻抗特性及开关齿槽结构对环形开关导通特性的影响。数值模拟和实验结果证明,采用直馈方式、高阻结构和齿槽结构有利于形成开关多通道导通,并提高开关导通的稳定性。在输出电压为500 kV的Marx脉冲功率源平台上构建了高功率宽谱微波产生实验装置,实验得到的宽谱微波振荡频率为195 MHz,辐射因子约150 kV,频谱带宽约30%。     

基于阻抗模拟的等效电磁参数研究

为能够较好的计算混合介质等效复介电常数和复磁导率, 提出了一种基于等效电路理论的阻抗模拟方法.导出了材料的电磁参数与材料容抗、感抗之间的对应关系, 并建立了能够较完整、精确地刻画实际复合材料的模型.通过求解混合介质的等效阻抗, 进一步反演其等效电磁参数.将计算结果与经典理论公式以及基于有限差分的数值方法进行了比较, 结果都符合得很好, 说明该方法可以用于计算材料的等效电磁参数.另外, 引入薄膜层结构来刻画表面效应等因素, 使得计算结果更加符合实验结果, 弥补了经典公式在这方面的不足, 同时也体现了该方法在刻画实际模型时所具有的优势. 关键词： 等效电磁参数 阻抗模拟 等效电路 混合介质