北京正负电子对撞机重大改造工程超导腔恒温器静态热负荷分析

北京正负电子对撞机重大改造工程(BEPCII)采用了频率为500 MHz的单cell超导纯铌腔作为加速腔.通过有限元分析的方法对超导腔恒温器各部件进行热模拟和分析,并将模拟分析结果与超导腔的水平测试结果进行比较验证,确认数值分析结果为可信的,且得出对备用超导腔恒温器设计、加工和运行具有指导意义的结果.     

钽酸锂单晶材料的横向场激励特性

用(yxl)-16.51°切型的钽酸锂(LiTaO3)加工制作两个电极在同一基板平面的横向场激励器件来验证该材料的横向场激励特性.理论上用扩展的Christoffel-Bechmann方法计算了LiTaO3材料的横向场激励机电耦合系数,其c模式值最大为37.9%.实验结果表明在空气中横向场激励在5.257MHz频率附近引起了一个明显的谐振主峰,谐振处阻抗为727ω;在液体中由于液体模拟电极的作用而形成了厚度场激励,使其在5.695MHz附近产生了另外一个谐振主峰.通过对声波相速度和谐振频率的计算也验证了实验结果.     

(10～3000)MHz电压基准

中国计量科学研究院研制的（10－3000）MHz电压基准，于199年6月通过国家鉴定，1986年被原国家计量局正式批准为国家基准。该基准建立在功率替代的原理上，又采用了测热技术，在电磁场扰动的影响等理论上和技术上都有新的突破和独创，技术指标达到国际先进水平，荣获1981年度国家科委发明四等奖。该基准的技术指标为：测量范围：（0．1－2）V频率范围：（10－3000）MHz测量不确定度（3a）：1000MHz02％2000MHz0．5％3000MHz0．7％1986年，该基准与德国技术物理研究院（PTB）进行射频电压国际比对，PTB是国际计量局（BIPM）组织的射…     

27.12 MHz基片偏压在调控磁控溅射离子能量中的作用研究

在基片上施加射频偏压,调控入射离子能量特性,可以有效地控制薄膜生长与性能。常用的13.56 MHz射频基片偏压具有入射离子能量呈展宽发散分布、较强的高能离子轰击作用问题。为解决这些问题,本文通过提高射频偏压频率的方法,采用拒斥场能量分析技术,研究了27.12 MHz射频基片偏压对磁控溅射基片表面离子能量分布特性和离子通量密度性能的影响。结果表明,27.12 MHz射频基片偏压可以有效降低高能离子密度,提高低能离子密度,使离子能量更集中分布,从而降低高能离子对基片的轰击作用。离子能量分布特性的变化与基片偏压频率提高导致的离子渡越鞘层时间τ_i延长、离子与中性基团碰撞几率增大有关。碰撞几率增大使高能离子比例降低、低能离子比例增大,离子能量分布变窄,离子能量的发散降低。因此,提高基片射频偏压频率,可以降低离子能量的发散和高能离子对基片产生的不利作用。     

27.12 MHz基片偏压在调控磁控溅射离子能量中的作用研究北大核心CSCD

在基片上施加射频偏压,调控入射离子能量特性,可以有效地控制薄膜生长与性能。常用的13.56 MHz射频基片偏压具有入射离子能量呈展宽发散分布、较强的高能离子轰击作用问题。为解决这些问题,本文通过提高射频偏压频率的方法,采用拒斥场能量分析技术,研究了27.12 MHz射频基片偏压对磁控溅射基片表面离子能量分布特性和离子通量密度性能的影响。结果表明,27.12 MHz射频基片偏压可以有效降低高能离子密度,提高低能离子密度,使离子能量更集中分布,从而降低高能离子对基片的轰击作用。离子能量分布特性的变化与基片偏压频率提高导致的离子渡越鞘层时间τi延长、离子与中性基团碰撞几率增大有关。碰撞几率增大使高能离子比例降低、低能离子比例增大,离子能量分布变窄,离子能量的发散降低。因此,提高基片射频偏压频率,可以降低离子能量的发散和高能离子对基片产生的不利作用。     

GTEM室内场强分布的计算分析

本文深入研究了近年来在电磁兼容测量及场强测量中广泛应用的吉赫横电磁室（ＧＴＥＭ），讨论了室内场分布的计算机算法，给出了６ｍ室的计算与测量实例。计算结果与测量结果符合较好。     

光子扫描隧道显微镜探测场的数值模拟计算

对光子扫描隧道显微镜（ＰＳＴＭ）的显微成象机理。扫描探测模型做了较为系统的分析和论述。针对具体的探测模型，利用微机编程计算ＰＳＴＭ探测光场的空间分布，并对场分布随扫描控制参量的变化规律进行系统的研究，得到了与实际探测结果一致的分布规律，最终为ＰＳＴＭ的显微成象技术提供了更为具体的理论指导。     

Premo与IHMAN签订合作协议

IHMAN与PREDAN近期宣布签订合作协议，共同开发商业化和营销项目，为西班牙和全球市场提供无线通信模块，工作频率是868MHz和915MHz，适合需要可靠无线连接的场合，最大距离是1km（直线距离）。     

FeZrBCu射频溅射薄膜磁导率和巨磁阻抗效应的研究

采用射频溅射法在单晶硅衬底上制备了（Fe0.88Zr0.07B0.05）97Cu3薄膜样品。X射线衍射结果表明，未经任何后期处理的沉积态薄膜为非晶态结构。在5kHz～13MHz频率范围内，着重研究了沉积态样品的有效磁导率和巨磁阻抗（GMI）效应的变化特性。研究结果表明，样品具有极好的软磁性能和GMI效应，其矫顽力仅为58A／m，饱和磁化强度约为1．15×106A／m，在13MHz的频率下最大巨磁阻抗比达到17％。并发现有效磁导率比随外磁场的变化，在各向异性场仇。0．4kA／m处出现了峰值，GMI效应也在此磁场的位置处出现峰值。这表明GMI效应与磁场诱导的有效磁导率的变化紧密关联。     

偏场下薄膜体声波谐振器频率偏移的摄动分析

为准确预测测量力、热场的薄膜体声波谐振器(FBAR)传感器的灵敏度,采用叠加于有限偏场之上的小增量场理论描述,提出一种摄动与有限元联合求解方法。该方法利用COMSOL有限元软件计算FBAR传感器受外界载荷下其压电层AlN的平均偏置应力,进一步在COMSOL中计算FBAR的谐振频率与相应的振型,将有限元的计算数据代入摄动积分公式中,得到FBAR传感器的频率灵敏度。并以一个圆膜片FBAR为案例,介绍该方法用于计算圆膜片FBAR频率-集中力灵敏度的详细过程。采用摄动与有限元联合求解方法得到的频率灵敏度为41.3 MHz/N,与文献报道的实验结果 50 MHz/N接近,验证了方法的可行性。     

GTEM小室中EUT受试电磁场场分布性能

研究了GTEM小室中EUT受试电磁场的场均匀性和主TEM模特性。在笛卡尔坐标系中建立了加入金属EUT后GTEM小室的三维FDTD模型,计算分析频率达2 GHz。计算了一个“大EUT”和“小EUT”的场分布特性,分析了EUT大小对场分布性能的影响。不仅研究了主分量的场均匀性,还研究了总场强的场均匀性,此外,还给出了各场分量的平均值随频率变化的趋势。研究结果表明:满足“小EUT”条件时,场均匀性良好,而“大EUT”在超出其许可频率后,场均匀性下降;在高频情况下不论是“大EUT”还是“小EUT”交叉极化特性均有所下降,主要表现为纵向场分量的增加。     

三明治结构FeNi/Cu/FeNi多层膜巨磁阻抗效应研究

采用MEMS技术在玻璃基片上制备了三明治结构FeNi/Cu/FeNi多层膜,在1～40 MHz范围内研究了FeNi/Cu/FeNi多层膜中的巨磁阻抗效应特性.当磁场Ha施加在薄膜的长方向时,巨磁阻抗效应随磁场的增加而增加,在某一磁场下达到最大值,然后随磁场的增加而下降到负的巨磁阻抗效应.在频率为5MHz时,巨磁阻抗效应在磁场Ha=800 A/m时达到最大值26.6%.巨磁阻抗效应的最大值及负的巨磁阻抗效应与多层膜中磁各向异性轴的取向及发散有关.另外,当磁场施加在薄膜的短方向时,薄膜表现出负的巨磁阻抗效应,在频率5 MHz、磁场Ha=9600 A/m时,巨磁阻抗效应可达-15.6%.     

Field-modulated conductivity in quasi-one-dimensional molecular conductors

Planar molecular conductors between two carbon nanotubes in a polymer matrix have been created and studied. It is established that the conductivity of the obtained current channel can be modulated by the transverse electric field. A sharp variation of the transverse field can switch off the molecular channel, while the subsequent application of the longitudinal field to the channel switches it on again. In order to explain the observed behavior, it is necessary to consider the micromechanics of molecules in external electric fields.     

Wake-field characteristics of a high-intensity, multibunched beam

A systematic experimental study on the wake-field characteristics of a high-intensity, multibunched electron beam was carried out in detail at the primary electron section of the KEK positron generator linac. The observed energy spectrum, which indicated the energy variation of one bunch from another, was explained fairly well by the multibunch effect of a longitudinal wake field; the importance of introducing a self-wake loss and a bunch-length effect into calculations of the energy loss due to a longitudinal wake field is noted. On the other hand, a transverse motion of each bunch, showing a peculiar behavior when the transverse instability occurred, was in good agreement with the results of a numerical calculation based on a multibunch version of Wilson's two-particle model. In both cases, the wake field for our cavity was estimated using a computer code called TBCI.     

Dielectric Properties and Hysteresis Loops of a Ferroelectric Nanoparticle System Described by the Transverse Ising Model

In this work, we use the effective field theory based on the probability distribution method to investigate the longitudinal and transverse polarizations, susceptibility, pyroelectric coefficient, and the hysteresis behavior of a ferroelectric cubic nanowire. The effects of the core–shell exchange interaction and the core–shell transverse fields on the longitudinal and transverse polarizations, the susceptibility, the pyroelectric coefficient, and the hysteresis loops of the system are examined. Some characteristic phenomena are found in the thermal variations, depending on the physical parameters in the shell and in the core.     

Acoustic impedance measurements of transverse and longitudinal sound in superfluid3He

We report on simultaneous acoustic impedance measurements of transverse and longitudinal sound at 61 MHz and pressures of 15.6, 10.5, and 8.0 bar.     

A study of ultrasonic velocity and attenuation on polycrystalline Ni-Zn ferrites

Polycrystalline NiZn ferrites with different grain sizes (1.2 (Am to 10.2 (Am) were prepared by the usual ceramic method. The magnetic properties were measured at room temperature. The ultrasonic velocity and attenuation were measured on Ni-Zn ferrite by using the pulse transmission method at 1 MHz, in the temperature range 300–600 K. The velocity was found to be slightly sample dependent at room temperature and decreased with increasing temperature, except near the Curie temperature, T _c ,where a small anomaly was observed. The longitudinal attenuation (α ₁ )at room temperature was found to be more sample dependent. The temperature variation of ultrasonic longitudinal attenuation exhibited a broad maximum around 400 K and a sharp maximum just below Curie temperature ( T _c ).The above observations were carried out in the demagnetized state. The application of a 380 mT magnetic field allowed us to reach the saturated state of the sample at all the measuring temperatures. The anomaly observed in the thermal variation of velocities (longitudinal and transverse) and attenuation has been qualitatively explained with the help of the temperature variation of the magneto-crystalline anisotropy constant.     

Spatial correlation properties of focused partially coherent vortex beams

The spatial correlation properties in the geometrical focal region of a converging, partially coherent vortex wave field are analyzed. Expressions are derived for a pair of points on the axis of symmetry and for a pair of points in the focal plane. It is found that the longitudinal and transverse coherence lengths in the focal region change with the variation of the topological charge and the normalized coherence length of the vortex field. In addition, the degree of coherence is shown to possess phase singularities.     

Nonparaxial propagation of spirally polarized optical beams

The free-propagation features of light beams whose transverse electric field lines are logarithmic spirals (namely, spirally polarized beams) are investigated in both the paraxial and the nonparaxial regime. The complete propagated electric field is considered, and some general properties are obtained regardless of the specific transverse distribution. Simple and significant analytical results are obtained when the transverse intensity profile is chosen as that pertinent to an axially symmetric Laguerre-Gaussian beam of order 1 (namely, spirally polarized donut beams). In particular, it is found that for such beams, the propagated longitudinal electric field can be expressed as a simple superposition of elegant Laguerre-Gaussian beams. Numerical results are presented for different values of the beam parameters and are compared with recently obtained experimental results.     

Magnetization ringing in the B phase of superfluid3He

We study theoretically the ringing of magnetization in superfluid³He-B for two configurations: the ringing in the Leggett configuration in the presence of a transverse field and the longitudinal ringing in the parallel plate configuration. It is shown that the time variation of the magnetization is described in terms of three distinct ringing frequencies in these general configurations.