三维洞穴环天线的耦合计算

在离子回旋共振加热中,对具有较复杂边界条件的洞穴环天线,通常为了简化计算忽略环天线水平分量的影响,按二维天线模型进行处理.给出了一种三维天线模型的详细计算过程,该模型与实际天线更加吻合,其计算结果可供洞穴环天线设计时参考. 关键词： 洞穴环 波加热 三维模型     

HIRFL新B1聚束器频率微调系统的设计及稳定性分析

 频率自动调谐系统是聚束器的重要组成部分之一。频率调谐系统成功的研制和投入使用达到了使谐振腔体的固有谐振频率在22～54 MHz的范围内自动稳定在输入信号频率上的目的,频率自动微调系统达到了±5×10^-6的频率稳定度,解决了由于腔体失谐所造成的高频电压滑落的问题,由此在腔体的加速缝隙间得到稳定的高频电压,保证了聚束器系统的高质量可靠运行。     

亚千赫兹精度的腔增强分子饱和吸收光谱

饱和吸收光谱法常被用于原子和分子跃迁的亚多普勒测量。光学谐振腔除了可增强有效吸收光程,还能够增加腔内的激光功率来饱和非常弱的分子振转跃迁.本文利用精细度达120000的谐振腔,通过腔增强光谱、腔衰荡光谱、噪声免疫腔增强光外差分子光谱这三种不同的腔增强方法,测量1.4μm处的C_2H_2分子兰姆凹陷.采用不同的腔增强方法确定吸收谱线中心,均给出了亚千赫兹的统计不确定度.并分析比较了不同方法的灵敏度和精度,噪声免疫腔增强光外差分子光谱是最灵敏的方法,但如果期望利用它实现亚千赫兹精度的计量应用,还需要对该方法中的系统误差进行更多的研究.     

Interaction of Love waves with coupled cavity modes in a 2D holey phononic crystal

The interaction of Love waves with square array of pillars deposited on a cavity defined in a 2D holey phononic crystal is numerically investigated using Finite Element Method. First, the existence of SH surface modes is demonstrated separately for phononic crystals that consist of square arrayed holes, or rectangular arrayed Ni pillars, respectively in, or on, a SiO₂ film deposited on a ST-cut quartz substrate. The coupling between SH modes and torsional mode in pillars induces a transmission dip that occurs at a frequency located in the range of the band-gap of the holey phononic crystal. Second, a cavity is constructed by removing lines of holes in the holey phononic crystal and results in a transmission peak that matches the dip. The optimal geometrical parameters enable us to create a coupling of the cavity mode and the localized pillar mode by introducing lines of pillars into the cavity, which significantly improved the efficiency of the cavity without increasing the crystal size. The obtained results will pave the way to implement advanced designs of high-performance electroacoustic sensors based on coupling modes in phononic crystals.     

Junction configurations and their impacts on Cu(In,Ga)Se2 based solar cells performances

One dimension solar cells simulator package (SCAPS) is used to study the possibility of carrying out thin CIGS solar cells with high and stable efficiency. In the first step, we modified the conventional ZnO:B/i-ZnO/CdS/SDL/CIGS/Mo structure by substituting the SDL layer with the P?+?layer, having a wide bandgap from 1 to l.12?eV. Then, we simulated the J-V characteristics of this new structure and showed how the electrical parameters are affected. Conversion efficiency of 18.46% is founded by using 1.1?μm of P?+?layer thickness. Secondly, we analyze the effect of increase thickness and doping density of CIGS, CdS and P?+?layers on the electric parameters of this new structure. We show that only the short-circuit current density (J_SC) and efficiency are improved, reaching respectively 34.68?mA/cm² and 18.85%, with increasing of the acceptors density. Finally, we introduced 10?nm of various electron reflectors at the CIGS/Mo interface in the new structure to reduce the recombination of minority carriers at the back contact. High conversion efficiency of 23.34% and better stability are obtained when wide band-gap BSF is used.     

一种时间相关吸收光谱技术分析新方法

时间相关吸收光谱技术,如腔衰荡光谱技术(CRDS)和腔衰减相移光谱技术(CAPS),是近三十几年发展起来的一类新型吸收光谱检测技术,它具有探测灵敏度高、响应速度快、不受光源强度起伏变化影响等优点。传统的吸收光谱技术都是基于Lambert-Beer定律,如直接吸收光谱技术(DAS)、波长调制光谱技术(WMS)和腔增强吸收光谱技术(CEAS)等,这类光谱技术在探测物质微弱吸收的时候一旦遇到较强的背景光信号就变得难以测量,而且光源的不稳定性也会对检测带来一定的限制。时间相关吸收光谱技术由于其不受光源强度起伏变化的特点,在很大程度上能够弥补传统吸收光谱技术所存在的缺陷,但其也有自身的局限性。首先在理论上,CRDS和CAPS这两种时间相关吸收光谱技术并不统一,而且在现有光谱理论下,Pulse-CRDS在应用时使用的脉冲光源的脉宽必须远小于谐振腔本身的时间常数,对于长脉宽的脉冲光或者反射率低(小于99.9%)的腔体,现有理论将不再适用;CAPS在应用时光源调制信号必须是周期性的正弦信号或者方波信号,对于其他类型的周期调制信号或者非周期性信号,现有理论并没有涉及。针对上述提到的时间相关吸收光谱技术的局限性,提出了一种新的分析时间相关吸收光谱技术的方法,即利用一阶传递函数,将谐振腔视为一阶传感系统,对时间相关吸收光谱技术理论进行统一解释,在公式推导上证明新方法下的推导结果和现有理论结果的一致性。针对Pulse-CRDS,以高斯脉冲光为例,给出一阶传感理论下的透射光强表达式,并对一系列不同的脉冲宽度γ、谐振腔时间常数τ_real以及从输出信号中拟合而得的时间常数τ_anal进行了模拟仿真。经过分析比较后发现,当γ<0.3τ_real时,τ_anal和τ_real的偏差小于1%;当γ>0.3τ_real时,τ_anal和τ_real的偏差渐渐变大,将不再满足实验条件。为了使Pulse-CRDS在长脉宽脉冲光下也能应用,本文给出了修正函数,使得在脉宽大于腔衰荡时间0.3倍的情况下,经过修正补偿后,衰荡时间的误差小于1%。对于CAPS系统,搭建相应实验平台,LED中心波长选用405 nm,使用方波调制信号,测量不同频率下的入射参考信号与探测信号的相位差和探测信号峰-峰值,通过由一阶传递函数推导而得的相频特性和幅频特性,拟合得到时间常数τ,结果分别为7.24和7.25 μs,残差范围分别为[-0.01, 0.02]和[-0.02, 0.025],两者结果基本一致。实验结果验证了一阶传感系统理论完全适用于时间相关光谱的信号分析,并且一阶传感系统理论还使得时间相关光谱技术的理论得到了统一。     

轨道板中超声兰姆波传播的有限元计算和实验*

该文针对我国高速铁路轨道板缺陷的非接触动态检测问题,研究了空气耦合超声兰姆波在轨道板中的传播规律。首先,给出了轨道板中超声兰姆波的相速度和群速度频散曲线,结果表明:随着频厚积的增加,频散现象越明显,并且A0相速度收敛于Rayleigh波的波速。然后,建立轨道板中波传播的有限元模型,计算得到兰姆波传播的群速度为2220 m/s,且二维傅里叶变换系数的较大值沿Rayleigh波的频散曲线分布。最后,在沪杭高铁嘉兴南站进行了现场测试,以8.8°倾斜角向轨道板激励产生超声兰姆波,激发产生的兰姆波模态群速度为2325 m/s,且二维傅里叶变换分析其系数的较大值沿Rayleigh波的频散曲线分布。有限元计算结果和实验结果均与理论计算结果一致。该研究为后续轨道板缺陷的非接触动态检测提供了理论依据和实验方法。     

Detection of micro solder balls using active thermography and probabilistic neural network

Micro solder ball/bump has been widely used in electronic packaging. It has been challenging to inspect these structures as the solder balls/bumps are often embedded between the component and substrates, especially in flip-chip packaging. In this paper, a detection method for micro solder ball/bump based on the active thermography and the probabilistic neural network is investigated. A VH680 infrared imager is used to capture the thermal image of the test vehicle, SFA10 packages. The temperature curves are processed using moving average technique to remove the peak noise. And the principal component analysis (PCA) is adopted to reconstruct the thermal images. The missed solder balls can be recognized explicitly in the second principal component image. Probabilistic neural network (PNN) is then established to identify the defective bump intelligently. The hot spots corresponding to the solder balls are segmented from the PCA reconstructed image, and statistic parameters are calculated. To characterize the thermal properties of solder bump quantitatively, three representative features are selected and used as the input vector in PNN clustering. The results show that the actual outputs and the expected outputs are consistent in identification of the missed solder balls, and all the bumps were recognized accurately, which demonstrates the viability of the PNN in effective defect inspection in high-density microelectronic packaging.     

Defect effect on tribological behavior of diamond-like carbon films deposited with hydrogen diluted benzene gas in aqueous environment

This study examined the friction and wear behavior of diamond-like carbon (DLC) films deposited from a radio frequency glow discharge using a hydrogen diluted benzene gas mixture. The DLC films were deposited on Si (1 0 0) and polished stainless steel substrates by radio frequency plasma-assisted chemical vapor deposition (r.f.-PACVD) at hydrogen to benzene ratios, or the hydrogen dilution ratio, ranging from 0 to 2.0. The wear test was carried out in both ambient and aqueous environments using a homemade ball-on-disk type wear rig. The stability of the DLC coating in an aqueous environment was improved by diluting the benzene precursor gas with hydrogen, suggesting that hydrogen dilution during the deposition of DLC films suppressed the initiation of defects in the film and improved the adhesion of the coating to the interface.     

C2H2 Overtones Near 12300 cm-1 Revisited with a Very Sensitive Cavity Ring-down Spectrometer

利用单模连续的钛宝石激光器, 构建了一台光腔衰荡光谱仪, 其可探测的最小吸收可达1.8×10^-10/cm. 该光谱仪被用来记录C₂H₂分子在12240～12350 cm^-1的泛频光谱. 与在同一波段测量的已报到的CRDS和激光腔内吸收光谱仪结果比较,本测量同时具有更好的灵敏度和精度. 由此,获得了乙炔分子在12290.12、12311.82和12350.61 cm^-1附近高泛频谱带更准确的振转参数