Characterizing the properties of ultrasonics propagating on the surface of materials with defect by Laser-ultrasonics method

A laser ultrasonics method is used to characterize the propagation properties of surface wave traveling on the surface of materials with sub-surface defect in 2D.Linear and nonlinear propagation properties of ultrasonics caused by the defects have been detected in experiment. A theoretical model is proposed and used to study the linear and nonlinear properties of ultrasonics caused by the defect.The numerical results indicate that the nonlinear ultrasonic wave will be excited when a finite amplitude ultrasonics propagates on the surface of materials with sub-surface defect.The theoretical analysis confirms that the nonlinear wave is caused by the "clapping"of the interface of defect instead of the mode conversions of ultrasonics.     

Analysis of ultrasonic guided waves propagating in long bones and cortical thickness based on time-frequency methods

The ultrasonic signals in long bones contain multiple guided modes which are mutual superposed.The velocities of guided waves in long bones are very sensitive to cortical thickness (CTh).In this paper,Hilbert-Huang transform(HHT) was proposed to analyze multi-mode guided waves,which can decompose superposed waves into many independent modes.Then the group velocity of each mode was obtained at corresponding frequency,which was compared with the results of short time Fourier transform(STFT).The CTh was also obtained by comparing with the theoretical calculation.The results showed that the experimental determined thickness was in agreement with the actual CTh,indicating that measuring the velocity of the guided mode can be used to estimate the CTh.The HHT is an effective method to identify multimode guided waves.     

PrefaceJin CHENG Jijun LIU Masahiro YAMAMOTO

Inverse problems and ill-posed problems are motivated by many applications in science and engineering, and have become an important area of applied mathematics. The mathematical analysis and numerical algorithms on this subject have broad impacts on the rapid development of engineering areas, including nondestructive tests, medical imaging, remote sensing, geophysics and so on. The main difficulties in studying the inverse problems for partial differential equations are their nonlinearity and ill-posedness. Since the 1980s, there have been many new mathematical results on the theory of inverse problems and the regularization of ill-posed problems.     

无损贮存及涨罐饱和相热力学模型研究

在低温液体无损贮存及涨罐研究方面,经常采用一种假设容器内气、液相均为饱和相的热力学模型.这种模型比较符合实际,并能够大大简化容器内的热力学状态,是一种比较常用的热力学模型.文中利用一个5m3低温贮罐进行的液氮无损贮存及涨罐试验,对该热力学模型进行了对比研究,讨论了饱和相热力学模型误差产生的原因,对于无损贮存和涨罐研究具...     

同步加速器无损检验艺术品和化石

 梵高曾向他的兄弟抱怨自己的向日葵油画很快就褪色了，而现在看起来他的向日葵不是褪色了，而是由黄色变成棕色了。这种变化是由于染料中的六价铬缓慢还原为三价铬，使绿色化合物转变为棕色化合物造成的。这是意大利佩鲁贾大学(University of Perugia)的莫尼科(Letizia Monico)与比利时安特卫普大学(University of Antwerp)的同行在法国格勒诺布尔(Grenoble)利用欧洲同步辐射装置(European Synchrotron Radiation Facility，ESRF)的密集X 射线通过实验进行无损光谱学检测得出的结论。
这里的X 射线同样被法国国家自然历史博物馆( National Museum of Natural History ) 的何赛(Alexandra Houssaye)用于制作9500 万年前有足蛇化石的3D 影像。目前全世界仅发现3 件有足蛇化石，它们表明蛇最初像蜥蜴一样是有腿的，后来才渐渐失去。何赛研究的这件蛇化石看起来只有一条腿，其实还有一条腿埋在岩石之中，借助欧洲同步辐射装置后才看清了化石的细节。     

第15届固态传感器、传动器与微系统国际会议(Ⅱ)

本届会议的专题报告按日程安排分述如下:(1)T Wacharalindu:以液态半导体为基础的微功率源--采用反射能量转换;(2)C M Waits,MMc Carthy,R Ghodea:供小规模动力系统中输送燃料用的、微电动机械系统的涡轮泵;(3)I D Block、P c Mcthals、M Ganoch:增强荧光与无标记成像联用仪;(4)L H Loo、Y D Lau:应用微结构的流体动力学偶联方法进行微型悬臂的质量因子的调谐;(5)K Imagawa,H Horilauchi,K Ikoda:应用心脏肌肉细胞的药物模拟方法的自给加热与流体泵送凝胶;(6)N Suhkl:供模拟在任何硅取向的表面组织与几何形态用的连续分格自动化技术.     

平面式一阶梯度计的设计和制备及其在无损检测上的应用

我们在10×10mm2的SrTiO3双晶基片上,设计并制备了YBCO双晶结dc-SQUID一阶平面式梯度计.其基线长度为5.5mm,该梯度计能够在无屏蔽环境下稳定的工作.在77K下,200Hz时,其磁通噪声为1×10-4Φ0/Hz,能够分辨的最小磁场梯度为94pT/m.我们将该器件作为磁传感器,可以利用涡流检测的原理对非磁金属进行无损检测.实验结果表明,可以很清楚地分辨出10mm以下的缺陷.同时,我们还研究了激励线圈的尺寸与空间分辨率的关系,结果表明若激励线圈足够大,则对于梯度计和缺陷而言感受到的是均匀磁场的激励,因此涡流的分布只与缺陷的形状有关,而空间分辨率取决于梯度计的基线长度和磁场分布.     

光纤白光干涉法与膜厚纳米测量新技术研究

运用薄膜光学干涉原理、光纤技术和干涉光谱分析技术,用光纤反射式干涉光谱仪(Reflectromic Interference Spectroscopy)直接测试宽带入射光在单晶硅表面超薄SiO₂膜层前后界面反射形成的干涉光谱曲线,并用专业软件对被测光谱信号数据处理后,可直接用公式准确计算出SiO₂氧化膜的厚度和光学折射率通过对单晶硅片表面超薄SiO₂氧化膜的实测,并与成熟的椭圆偏振仪测试结果相比,测试误差≤2nm但该方法测试简单、快速,精度高,不需要制定仪器曲线和数表,可对薄膜任意位置的厚度在线测试经过对不同厚度聚苯乙烯薄膜的厚度测试表明,该方法适合0.5～20μm薄膜厚度的精确在线测量,测量误差小于7nm.