Studies of Frequency-domain Feature Extraction and Defect Characterization in Pulsed Eddy Current Testing

脉冲涡流检测是近年来发展迅速的一种比较先进的无损检测技术。由于脉 冲激励频谱分量丰富，因此相比于传统的涡流检测技术，其可以同时检测到被 测部件中不同深度的缺陷，获得更多的缺陷信息，在航空航天、核能电力、石 油化工等领域有着广阔的应用前景。本文研究脉冲涡流检测的信号特征提取和 缺陷表征方法，以提高脉冲涡流检测技术对缺陷的分类识别能力，从而推动脉 冲涡流检测技术的进步。 目前对脉冲涡流检测缺陷识别的研究主要集中在时域上，对脉冲涡流丰富 的频域信息的应用较少。脉冲激励信号可以被看作是一组多频不等幅正弦合成 信号，由于趋肤效应的存在，高频成分仅受到上表面缺陷的影响，而低频成分 会同时...Pulsed eddy current testing (PECT) is a nondestructive testing technique that develops fast in the recent years. The pulsed excitation comprises a broad band of frequencies and the response signal provides more information about defect than that of traditional eddy current testing. Therefore, PECT will play an important role in the maintenance of aircrafts, nuclear power plants, oil and gas tr...学位：工学硕士院系专业：物理与机电工程学院_航空宇航制造工程学号：3202011115271

Structure design and preparation of porous SiGe/Si heterostructure material microcavity

提出了采用多孔SIgE/SI异质多层结构来获得布拉格反射镜方法.首先采用传输矩阵方法设计了多孔SIgE/SI异质材料微腔结构,并通过超高真空化学气相沉积与电化学阳极腐蚀相结合的方法实验制备了两种结构的微腔,同时对微腔进行光学性质表征,并详细讨论了实验结果.We propose a method for preparing the Bragg reflectors by porous SiGe/Si heterogeneous multilayer structure.Two kinds of structure of porous SiGe/Si microcavity are prepared through a method by combining ultra-high vacuum chemical vapor deposition and electrochemical anode,based on the numerical simulations of transfer matrix method.The optical properties of the microcavity are characterized,and the experimental results are discussed in detail.福建省省教育厅基金项目(JB11128);闽江学院科技启动项目(KQ1004

Study of Si-Based Multilayer Ge Quantum Dots Near-Infrared Photodetector

采用超高真空化学气相沉积(uHV/CVd)技术在SI衬底上外延生长了PIn结构多层gE量子点探测器材料。PIn探测器结构由n型SI衬底,多层gE量子点吸收区,和原位掺杂P型SI盖层构成,电极分别制作于n-SI和P-SI上,以获得好的欧姆接触。制备的SI基gE量子点光电探测器具有较低的暗电流密度(-1 V偏压下为7.35x10-6A/CM2),与SI相比,探测波长延伸到1.31μM波段。The structure of multilayer Ge quantum dots( QDs) was eptaxial grown on Si substrate by ultra-high vacuum chemical vapor deposition( UHV / CVD) technique for detector fabrication.The intrinsic multilayer Ge QDs were acted as an absorption region,while the N-Si substrate and the in situ capped P-Si layer were chosen for the formation of ohmic contact.The fabricated photodetector has a low dark current density( 7.35 × 10- 6A / cm2at- 1 V),and the wavelength limit is extended to 1.31 μm compared with Si photodetector.国家重大科学研究计划(2012CB933503

Research of the Multi-Object in Eddy Current Testing Simulation

传统涡流仿真模型仅包含单一求解区域,将所有物体囊括在内。随着近代工业科技的飞速发展,被检物体日趋复杂,从而使得传统涡流仿真模型的计算效率降低。将单一求解区域划分为数个子区域,可以有效克服网格模型复杂的问题。简要介绍分解区域在电磁及涡流检测中的应用。Tradition eddy current testing models have only one solution domain,including all objects.With the high speed develop of Industrial Sciences and Technology,the detected objects become complex,so the convention models are inefficiency.Decomposing the whole domain into some sub-domain is a way to overcome the problem of complex meshes.In this article,author will introduce the domain decomposition method using in electromagnetic problems and application in eddy current testing

Analysis on The Ageing Mechanism of GaN-based Blue and Green LED by Electrical Stresses

对IngAn/gAn多量子阱蓝光和绿光lEd进行了室温20,40,60 MA加速电流下的电应力老化研究,发现蓝光与绿光样品经过60 MA电流老化424 H后,其电学性能表现出一定的共性与差异性:在小测量电流下,绿光样品的光衰减幅度较蓝光样品大~9%;而在较大测量电流(20 MA)下,两者的光衰减幅度基本相同(18%)。同时,蓝绿光样品的正向电学性能随老化时间的变化幅度基本一致,反映出它们具有相似的退化机制,绿光样品老化后增多的缺陷大部分体现为简单的漏电行为,而并非贡献于非辐射复合中心。在此基础上对gAn基外延结构进行了优化,优化后的lEd长期老化的光衰减幅度较参考样品降低了3%。The behavior of the related reliability of InGaN-based blue and green LED chips were investigated with 20,40,60 mA constant current stress up to 424 h at room temperature.Under 60mA constant current stress,the green LED chip showed more prominent optical power degradation at low measuring current levels than high measuring current levels.While,the blue LED chip showed the consistent optical power decrease at different measuring current levels.It should be pointed out that,at high measured current levels( 20 mA),blue and green LED chips expressed similar optical degradation( 18%) after the aging tests.Meanwhile,the aging stress does not significant affect the forward-bias electrical characteristics of blue and green LED chips,which indicated the similar degradation process in some aging tests.It is believed that the induced defects in blue LED by electrical stress mainly contribute to the nonradiative recombination centers,while in green LED chip the defects contribute to the localized leakage paths rather than the nonradiative recombination centers.Based on the mechanism analysis of blue and green LED,the design of GaN based epitaxial structure was optimized,and the thickness of quantum barrier was reduced to weaken the internal electrical field in the active layer to improve the reliability of LED.国家自然科学基金(61176050、61176092); 华侨大学科研基金(12BS226)资助项

Comparison of Two Axisymmetrical Finite Element Models for Pulsed Eddy Current Simulation

脉冲涡流检测技术是近年来发展迅速的一种新型涡流检测技术。由于其激励信号频谱宽广,不同频率分量的涡流能够渗透到不同深度,使其检测信号包含更丰富的深度方向的缺陷信息,在航空维修等工业领域有着重要的意义。对脉冲涡流检测的仿真可以指导脉冲涡流检测技术的研究。本文利用二维轴对称模型,介绍了脉冲涡流有限元仿真的两种方法—傅里叶变换法和时间步进法,并详细比较了这两种方法的优缺点。Pulsed eddy current testing(PECT) is one of the new techniques of eddy current testing.Thanks to the large amount of frequency components,the response signal contains rich information about defect and material properties along the depth direction.Therefore the PECT plays a significant role in the maintenance of aircrafts,nuclear power plants and so on.This paper introduces the two main methods used in the finite element modeling of PECT.Comparison of the methods is given.航空科学基金项目资助(批准号:2009ZD68004

Resonant Cavity-enhanced Si Photodetectors with Distributed Bragg Reflector

采用电子束蒸发和键合技术,制作了具有高反射率的、表面为薄层单晶Si的分布Bragg反射器。用标准光刻工艺在单晶Si薄层上制作出窄带谐振腔增强型(RCE)金属-半导体-金属(MSM)光电探测器,响应峰值波长分别在836、900、965和1 030 nm处,其中在900 nm处峰值半高宽为18 nm。该器件具有波长选择特性,可有效抑制相邻频道间的串扰,而且容易制成集成面阵。Si distributed Bragg reflector with crystal Si thin film on the reflector was fabricated by electron beam evaporation and bonding techniques.Narrow band Si resonant-cavity-enhanced(RCE) metal-semiconductor-metal(MSM) photodetectors were fabricated by standard photolithography with responsivity peaks at 836 nm,900 nm,965 nm and 1 030 nm respectively.The full-width-at-half-maximum was about 18 nm at 900 nm.The wavelength selectivity of the device could eliminate crosstalk between channels,and the integrated array could be easily realized.福建省青年科技人才创新资助项目(2004J021

The shape transformation of Si patterned-substrate in thermal decomposition of native oxide during vacuum annealing

利用超高真空化学气相淀积(uHV/CVd)系统,在不同的温度、环境氛围及脱O过程参与等条件下对全息法制备的二维周期图形SI衬底进行退火,通过原子力显微镜(AfM)进行表征与分析,研究真空高温脱O过程对图形衬底表面形态变化的影响。结果表明,真空环境使衬底表面的SI原子可以自由运动,脱O过程增强了SI原子在表面的迁移,温度会影响SI原子的扩散速率,3个因素的共同作用导致图形深度变浅,侧壁坡度变缓。此外,在周期图形台面的边缘,观察到环形有序分布的纳米SI岛。2D-period patterned Si substrate is annealed in ultra-high vacuum chemical vapor deposition(UHV/CVD)under variational conditions including different temperature,environment,thermal decomposition of native silicon oxide.The morphology properties of annealed patterned-substrate are obtained by atomic force microscopy(AFM).The effect of annealing parameters on shape transformation of Si patterned-substrate is studied.The results indicate that the Si atoms can diffuse freely on substrate surface in vacuum and the diffusion is enhanced during thermal decomposition of native oxide.The diffusion velocity is affected by temperature.These effects result in the decrease of the depth of pattern and gradient of side wall.In addition,ordered nanometer Si islands are formed on the mesa of patterned-substrate.国家自然科学基金资助项目(60336010;60676027);国家重点基础研究发展计划“973”资助项目(2007CB613404

横向收集结构锗硅半导体雪崩探测器的设计研究

为了实现高效的微光探测以及满足量子通信的需求,需要研发制备具有高增益、低噪声和高带宽的高性能红外探测器,基于硅衬底材料的锗硅雪崩探测器（Avalanche Photodiode,APD）被认为是有希望实现近红外通信波段高效弱光探测的探测器件。本工作设计研究了一种横向收集结构的锗硅APD,并对其结构参数对电场分布的影响进行了仿真模拟。发现该结构中硅倍增层的掺杂浓度、尺寸等对器件电场分布具有很重要的影响,并且利用能带理论对其进行了解释说明。倍增层掺杂浓度提高后,增强的结效应导致该器件中出现了有趣的双结结构,横向的n+-n-结与纵向的p+-i-p--n-结共同作用于电场分布,并且实现了纵向雪崩与横向载流子收集。在-30 d Bm 1 310 nm光源正入射下,新设计的横向吸收结构APD经过优化带宽可以达到20 GHz;线性响应度0. 7 A/W;由于采用了键合方法,其暗电流可以下降至10-12A。基本满足近红外通信波段弱光探测的高速、低暗电流、探测能力强等要求。国家自然科学基金(No.61534005)项目~

Research and fabrication of silicon based metal-semiconductor-metal photodetector with U-shape trench interdigitated electrodes

为了提高硅MSM结构光电探测器的光电响应度,制备了U型凹槽电极结构的探测器。5 V偏压下,对650 nm波长入射光的绝对光电响应度测试表明,凹槽电极结构的探测器最大光电响应度值为0.486 A/W,比同样尺寸的平版结构光电探测器提高了约6倍。文中也对比了具有抗反射膜和不具有抗反射膜的器件相对响应光谱的差别,并且比较分析了叉指间隙分别为5μm和10μm器件光电响应的不同。The responsivity of silicon based metal-semiconductor-metal(MSM) photodetector(Si-MSM-PD) was improved by placing the planar interdigitated electrodes with U-shape trench interdigitated electrodes.The performance test indicates that the responsivity of Si-MSM-PD with U-shape trench interdigitated electrodes is 0.486 A/W for 650 nm laser at 5 V applied voltage.This responsivity is about 6 times larger than that of Si-MSM-PD with planar interdigitated electrodes whose responsivity is just 0.084 A/W.Besides,the performance of Si-MSM-PDs with different intergitated space of 5 μm and 10 μm was compared.国家自然科学基金资助项目(60576001,60336010,60676027);; 福建省自然科学基金资助项目(A0410008