共查询到18条相似文献,搜索用时 218 毫秒
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同面阵列电极电容成像技术应用于工件缺陷无损检测时,因电极布置在同一平面内,若采用常规的单一介质作为空场或满场时,往往导致测量精度不高等问题。提出了一种空场/满场的相对设定方法,同时采用空气和被测材料两种介质作为空场和满场设定条件,通过分别改变两种介质的空间位置和大小,实现空场/满场可调节且不唯一;阐述了同面阵列电容传感器的工作原理,并以隔热材料和环氧树脂作为测量物场,通过有限元仿真获取了灵敏度矩阵。针对空场和满场的设定方法进行了电容成像实验研究,结果表明该方法可改善成像效果,能够反映出被测物体中缺陷的平面位置信息,验证了该方法的有效性。 相似文献
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随着MEMS技术的发展,对微纳尺寸器件的需求日益凸显,微能源的研究变得尤为重要,而微型超级电容器则是其中一种基于电化学电容实现储能的微型能量存储器件.设计了一种基于氧化钌功能薄膜的三维微柱阵列电极,并进行了相关的扫描电镜(SEM)、循环伏安(CV)和交流阻抗谱(EIS)测试.测试表明在2 mm×2 mm的硅片上,直径为50μm、高为100μm的三维微柱阵列电极的比电容为2.43 F/cm2,具有良好的电化学性能.与同容量的二维平面电极相比,基于三维结构的微型超级电容器具有明显的小尺寸优势. 相似文献
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针对粗晶材料超声检测信噪比低的问题,提出了一种水平分置线性双阵列超声成像方法。将两个线阵超声换能器沿直线水平分置在待检区域表面两侧,用收发分离的信号采集模式,一侧激发,另一侧记录各通道数据,进行聚焦成像。相比单阵列和同位置双线阵检测,文中的方法有效地减少了背向散射信号对缺陷信号的干扰,提高了成像信噪比。在粗晶铜质试块上的成像实验结果表明,当缺陷距离阵列较近时,文中的方法优于单阵列和同位置双线阵方法,成像信噪比提高约5~10 dB;当缺陷距离阵列较远时,单阵列模式和同位置双线阵检测方法失效,但文中的方法依然可以识别缺陷。文中的研究为粗晶材料的超声检测提供了一种可行的方案。 相似文献
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提出了一种基于传感器线阵的多重信号分类(Multiple Signal Classification,MUSIC)损伤成像方法用于航空复合材料的损伤监测。该方法采用MUSIC阵列信号处理方法,通过对传感器阵列信号进行协方差特征值分解,在结构上进行方向扫描并构建监测区域的空间谱,从而实现对结构损伤的成像,具有一维传感器阵列易于布置的优点。所提出的方法在变厚度航空复合材料油箱结构上进行了验证,结果表明,该方法能够准确实现航空复合材料结构上的损伤成像,定位误差小于2cm。 相似文献
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Air-coupled Lamb wave tomography 总被引:1,自引:0,他引:1
Wright W Hutchins D Jansen D Schindel D 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1997,44(1):53-59
An entirely air-coupled inspection system using a pair of micromachined silicon capacitance transducers has been used to image defects in thin plates of different materials (0.7 mm to 2.22 mm thick) using air-coupled Lamb wave tomography. A filtered back projection algorithm was used in a form of difference tomography to reconstruct images of defects up to 10 mm diameter machined in aluminium and perspex (Plexiglas) plates, as well as in samples of carbon fiber reinforced polymer (CFRP). The technique was able to resolve non-central defects as well as multiple flaws within the scan area. This flexible tomographic system was able to produce images of the change in a variety of different acoustic variables from only one set of experimental data, with success dependent on the size, shape, and location of the defect in the scan area. 相似文献
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针对目前工业生产线上的VVT(variable valve timing,可变气门正时)发动机转子存在尺寸误差和外观缺陷等问题,大多数工厂采用人工方式来测量尺寸和检测缺陷,但人工测量和检测的精度易受外部环境和主观意识的影响,从而产生过检和漏检。为此,设计了一种基于机器视觉的VVT发动机转子缺陷检测系统。首先,针对VVT发动机转子凸台外边缘磕碰点对外径测量的干扰,提出一种基于梯度特征和位置序列的磕碰点检测算法,先通过分析轮廓点的距离-位置序列、梯度-位置序列曲线来筛选并去除凸台外边缘的磕碰点,再采用最小二乘法对筛选后的轮廓点进行圆弧拟合以实现外径测量。然后,针对VVT发动机转子端面上的划痕、划伤等缺陷,提出一种基于改进HOG(histogram of oriented gradient,方向梯度直方图)特征的SVM(support vector machines,支持向量机)分类算法,先采用连通域分析方法得到待检测的目标区域,再提取目标区域的改进HOG特征,并利用SVM进行分类,以实现端面缺陷的检测。实验结果表明,所设计的缺陷检测系统在测量VVT发动机转子外径时的绝对精度可达到0.01 mm,且能够准确地筛选出凸台外边缘的磕碰点;因改进的HOG特征优于传统的HOG特征,所设计的缺陷检测系统在检测转子端面缺陷时具有较低的过检率和漏检率。综上可知,基于机器视觉的VVT发动机转子缺陷检测系统可实现外径的精确测量和外观缺陷的有效检测,基本满足工业检测要求,具有较高的实用价值。 相似文献
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MXene是一种新型二维过渡金属碳/氮化物, 具有优异电化学性能的赝电容型超级电容器电极材料。本研究尝试用同步氨化/碳化制备MXene平面多孔电极。以滤纸为多孔平面模板, 通过浸渍-烘干的手段把MXene固定在滤纸的纤维上, 然后在氨气的气氛中热处理, 得到了MXene/C平面多孔复合电极。分析结果表明: MXene纳米片均匀包覆在由滤纸碳化形成的碳纤维上。当浸渍5次时, 在2 mV/s的扫速下测试, 制备出的复合电极的面积比电容达到403 mF/cm 2。在电流密度为10 mA/cm 2下进行恒流充放电循环测试2500次后, 比电容仍然与初始电容几乎相同, 表现出良好的倍率性能和循环稳定性。在不使用高分子粘合剂和金属集流体的情况下, 同步氨化/碳化法制备出的MXene/C平面多孔复合电极表现出优良的电化学性能。 相似文献
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J. PEÑA‐MACIAS M. C. PÉREZ R. MARTÍNEZ‐OÑA Y. GÓMEZ‐ULLATE F. MONTERO DE ESPINOSA G. KAWIECKI 《Fatigue & Fracture of Engineering Materials & Structures》2008,31(12):1019-1030
The work outlined in this paper is a part of a wider effort aimed at the development of a built‐in system for real‐time damage detection in aircraft structures. The objective of this study was to show the feasibility of applying low‐frequency phased‐array transducers for damage detection in metallic structures with bonded repairs and, also, in structures made of composite materials. This paper is divided into two main portions: a component dedicated to the monitoring of crack growth under a simulated composite repair and a part describing an introductory study done for composite panels monitoring. The data acquisition system is also described. The results of the study described in this paper indicate that a low‐frequency, built‐in phased‐array system can successfully estimate the length of a crack growing under a bonded repair. Satisfactory results of monitoring simulated defects in composite structures are presented, as well. 相似文献
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纳米NiO/C复合电极电化学电容特性的研究 总被引:1,自引:0,他引:1
为满足高性能电化学电容器发展的需要,采用循环伏安法(CV)和电化学阻抗谱(EIS)研究了纳米NiO/C复合电极在KOH溶液中的电化学电容特性。这种纳米NiO/C复合电极材料是经热解柠檬酸镍凝胶制得的,由大约85%的纳米NiO和15%的纳米C组成,粉体的比表面积为181m^2/g,颗粒粒径〈30nm,微孔直径分布在4~10nm。结果表明,纳米NiO/C复合电极的比电容受KOH浓度和扫描速度的影响,高的电解质浓度和低的扫描速度有助于获得高的比电容。电极的电化学过程研究显示出法拉第反应和双电层特性,因而电极电容由法拉第准电容和双电层电容组成,电极比容量可达116.4F/g。由纳米NiO/C复合电极组成的电容器,其比能量达13.2kJ/kg,比功率达1.6kW/kg,且具有良好的循环稳定性。 相似文献
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Jungmin Kim Minhhuy Le Jinyi Lee Young Ha Hwang 《Journal of Nondestructive Evaluation》2014,33(4):471-480
This study proposes an automated inspection system to inspect far-side corrosion around rivets in the F-5 supersonic aircraft. The system includes a linear integrated Hall sensor array, a C-type exciter, and an automated scanning system. The inspection system was tested on a modified elliptical intake having artificial defects with 10-mm diameter and 0.12–1.11-mm depth. An algorithm was produced to detect the defects. The probability of detection (POD) curve was obtained with hits/misses data using a log–logistics model. Defect with depths of 0.67 and 0.98 mm were detected with 90 % POD and lower 95 % confidence bound. 相似文献
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《Composites Science and Technology》2007,67(7-8):1747-1750
Electrical double-layer capacitors are now developing very fast and people put their eyes on the investigation about materials for electrodes, such as activated carbon with high surface area. One of the main ways to enhance the capacitance of porous carbonaceous materials was to improve the porosity and specific surface area. In this paper, a novel preparation process to increase the capacitance of activated carbon without changing pore structure was discussed and expanded graphite, which was usually used in the polymer material system, was used as the composite template for activated carbons. Expanded graphite with worm-like and symmetrical pores could provide good environment for activated carbon particles to touch with each other and the structure defects at the contacting sites were offset at a certain extent. The adsorption properties of activated carbons had not been changed much more after composite preparation but the capacitance of each composite had been improved greatly because that activated carbon particles were surrounded by plenty of graphite layers with better electrical conductivities. As a result, electrical double-layer capacitors made with composites had higher capacitance comparing with activate carbons themselves and had good performance under larger discharging currents. 相似文献