The Research on Steel Plate Defects Inspection by Magneto-acoustic Testing with Induction

随着工业化的发展，钢材被应用在了各种各样的领域，比如：天然气管道、轮船、汽车等等。然而，随着时间的推移，钢材在使用过程中会出现腐蚀、裂纹等缺陷，这些缺陷严重影响了使用的安全，所以必须在事故发生之前对其进行检测以评估其安全性。本文在对比多种无损检测方法及研究感应式磁声成像的基础上提出了感应式磁声检测的新方法。该方法是在静态磁场下，通过脉冲电流激励被测钢板表面，进而在钢板内部发生电－磁－声的相互转化，最后提取钢板表面的磁声信号。该方法与被测材料无接触，无耦合，可在恶劣环境下进行工作，非常适合钢板的在线检测。 本文首先分析了基于磁致伸缩机理下的感应式磁声检测技术的基本原理，并且推导出了磁声信号的波...With the development of industrialization, steel is used in a variety of areas, such as: natural gas pipelines, ships, cars, etc. However, with the time gone, the steel will appear corrosion, cracks and other defects, which seriously affect the use. Before the accident ,we test the steel to assess it’s safety. This paper proposed a new detection method－Magneto-acoustic Testing with Induction which...学位：工学硕士院系专业：物理与机电工程学院_机械电子工程学号：1992012115271

Overmodulation strategy for flux trajectory tracking PWM and analysis of its characteristics

结合磁链轨迹跟踪的PWM生成原理,讨论了一种过调制实现策略。根据实际磁链对期望磁链的跟踪特性,分析建立了相位和径向两类误差模型;结合两类误差模型,定义评价指标:跟踪能力,并由此确定了过调制Ⅰ区和过调制Ⅱ区的分界点;从理论上证明了实现过调制极限状态六阶梯波调制的可行性,并给出其实现条件。开展了仿真验证和样机试验,结果表明新策略能有效提高直流母线电压的利用率,保持从线性调制、过调制Ⅰ区、过调制Ⅱ区直至六阶梯模式的平滑过渡,并明显抑制调制过程中的输出电压总谐波畸变率(THd)。A overmodulation strategy was studied based on the flux trajectory tracking PWM.First,phase error and radial error were analyzed based on the flux trajectory model.Then,combining two types of error model,a new evaluation for tracking capability was defined,and the demarcation point of overmodulation was determined.Then,the feasibility of six-step operation was proved theoretically,and the achievement conditions of six-step operation was given.Finally,the overmodulation strategy was theoretically analyzed,simulated and experimented.The results show that the new strategy effectually enhance the utilization rate of DC bus voltage and keep smooth transition form linear modulation,overmodulation to six-step operation,and markedly reduce the total harmonic distortion( THD) of the output voltage.国家自然科学基金(51177141); 福建省自然科学基金(2010J01310); 中央高校基本科研业务项目(2010121041); 航空基金(2012ZD68003

Mechanism and experimental research on skin depth in AC magnetic flux leakage testing

随着管道、储罐的推广使用,管道、储罐腐蚀泄漏事故频发。漏磁检测方法是当前最频繁使用的管道无损检测技术。探讨了交流漏磁检测中趋肤深效应的机理。首先,对交流漏磁检测的涡流效应进行实验和分析;然后,根据麦克斯韦方程组推导出模型的三维交流漏磁场分布,分析了不同频率下钢板的磁力线分布情况,从而得出交流漏磁检测中趋肤深度的规律。最后,制造一系列人工缺陷并开展实际漏磁检测实验,以验证三维仿真结果的有效性,对进一步研究该方法的机理提供了理论和实验依据。With the wide use of pipelines and tanks,corrosion leakage accidents happen frequently.The magnetic flux leakage( MFL) testing method is currently the most commonly used nondestructive pipeline inspection technique.In this paper,the mechanism of the skin effect in AC MFL inspection is discussed.Firstly,the eddy current effects in AC MFL detection were tested and analyzed.Then,according to the Maxwell equations,the 3-D MFL field distributions were deduced,and the distributions of the magnetic induction lines under different frequencies in steel plate were analyzed,thus the law of the skin depth in AC MFL inspection was acquired.Finally,a set of artificial defects were made and the actual MFL test experiments were performed to verify the effectiveness of the 3-D simulation results,which provides a theoretical and experiment basis for further studying the mechanism of the method.国家自然科学基金(51177141); 福建省自然科学基金(2010J01310); 中央高校基本科研业务项目(0620ZK1007)资

高量子效率前照式GaN基p-i-n结构紫外探测器

研究了Al0.1-Ga0.9N／GaN异质结p-i-n结构可见盲紫外探测器的制备与性能,P区采用Al组分含量为0．1的AlGaN外延材料形成窗口层，使340-365nm波段的紫外光可以直接透过P区到达i区并被吸收，有效提高了这个波段的响应率与量子效率,并且研究了不同P区AlGaN外延层厚度对探测器性能的影响，制备了两种不同P区厚度（0．1μm和0．15μm）的器件，测试结果表明，P区的厚度对200-340nm波段光吸收的量子效率影响较大，而i区的晶体质量的提高可以有效提高340-365nm波段光吸收的量子效率,并且当P区AlGaN厚度为0．15μm时，器件的峰值响应率达到0．214A／W，在考虑表面反射时外量子效率高达85．6％，接近理论极限，并且在零偏压时暗电流密度为3．16nA／cm^2,表明器件具有非常高的信噪比

背照式GaN／AlGaN p-i-n紫外探测器的制备与性能

文章研究了p-GaN／i—GaN／n-Al0.3Ga0.7N异质结背照式p-i—n可见盲紫外探测器的制备与性能。器件的响应区域为310～365nm，最大响应率为0．046A/W，对应的内量子效率为19％，优值因子R0A达到1．77×10^8Ω·cm^2，相应的在363nm处的探测率D^＊=2．6×10^12cmHz^1/2W^-1

空间用紫外探测及AlGaN探测器的研究进展

文中介绍了与空间应用有关的紫外探测。首先，介绍了美、欧等西方国家在空间天文以及行星、卫星探测等方面多年来的紫外应用情况，包括卫星探测器上搭载的紫外有效载荷；然后，评述了目前在空间使用的紫外探测器状况，以及在未来的空间应用中极具发展潜力的AlGaN紫外探测器；最后，对AlGaN紫外焦平面探测器国内外近年来的研究进展进行了阐述