巨磁电阻读出磁头

用巨磁电阻（GMR）材料构成的磁电子学新器件,已开始在计算机存储领域成功地获得了应用,本文介绍了用于计算机硬件磁盘驱动器的巨磁电阻磁头,描术字它的工作原理、性能特点及研究现状和发展趋势。     

加工工艺对Cu-Co合金GMR性能的影响

利用金相和电子显微镜对熔体快淬及熔体快淬后不同时效条件下Cu-Co合金的微观组织进行的分析表明,熔体快淬过程中在Cu80Co20合金的组织内出现了富Co相,Cu75Co25合金则产生了液相分解。对于含Co10%-30%(质量分数）的熔体快淬Cu-Co合金,时效过程中形成的球状富Co沉淀相不仅出现在晶界两侧,也出现在晶粒内部。时效工艺对熔体快淬Cu-Co合金GMR性能的影响研究表明,时效温度的提高和时效时间的延长,巨磁电阻（GMR）随磁场强度的增加而增加的速率提高,使低磁场下的MR增加。研究发现,当时效温度一定时,在一定的时效时间范围内,出现MR的极小值。时效进行到一定程度时,熔体快淬并人工时效的Cu-Co合金可在1．0T外磁场强度下出现磁化饱和。     

金属颗粒膜巨磁电阻效应的机制和影响因素

由于巨磁电阻效应在磁记录设备和传感器的潜在应用，具有该效应的材料得到了广泛地研究。特别是继金属多层膜之后的金属磁性颗粒膜，由于其制备简单，巨磁电阻效应的机理较为复杂，受到人们的青睐。本文综述了金属磁性颗粒膜中巨磁电阻效应的自旋相关散射机制和影响因素。在此基础上，指出了当前值得注意的研究方向。     

智能大楼布线系统的电磁防护问题

为对雷电流在金属柱体表面的分布进行测量研究, 研制了二维巨磁阻(Giant Magneto Resistive, GMR)表面电流测量系统, 采用该测量系统对金属柱体表面雷电流密度进行了测量研究, 实测结果和CST软件仿真结果一致.结果表明：研制的二维GMR表面电流测量系统可用于测量研究金属柱体表面雷电流的分布.     

Co_xAg_(100-x)颗粒膜的巨磁电阻效应及其物理机制研究

用超高真空电子束蒸发沉积方法制备了ＣｏｘＡｇ１００－ｘ颗粒并研究了其中的巨磁电阻（ＧＭＲ）效应。实验结果表明：１５ｋＯｅ外磁场下，玻璃衬底上制备态Ｃｏ３９Ａｇ６１颗粒膜室温ＧＭＲ效应值高达２０２％，并随氮气中退火温度上升而单调减小；颗粒膜的电阻与其磁化强度直接相关，可用四次多项式偶函数来描述。     

Multimodal Damage Detection in Self‐Sensing Fiber Reinforced Composites

Internal delamination damage is detected in fiber reinforced polymer composite materials containing active functionality. Damage‐triggered magnetization of the delaminated zone is accomplished using a vascular system to deliver fluids that precipitate magnetic particles upon mixing. Multiple modes of detection are used to sense the presence of this magnetic material. Visual detection is accomplished by the high contrast between damaged and undamaged areas provided by the biomimetic “bruise” formed by the magnetic particles. Magnetic scanning is also used to detect the particles, even if obscured by paint or by opaque reinforcement, such as carbon fiber. Additionally, thermal detection is accomplished by inductively heating the magnetic particles and sensing the temperature differential with an infrared camera. The effectiveness of each detection mode is discussed and compared to industry standard C‐scan to assess accuracy. Using the damage area measured with C‐scan as the benchmark, visual detection measures the damage area with 76% accuracy, and magnetic detection measures the damage area with 91% accuracy. Thermal detection accuracy is time‐dependent as expected. All detection modes consistently detect the presence of damage. The multifunctionality of this material can tailor damage detection techniques for the application and provide a parallel system to augment and potentially enhance self‐healing.     

基于GMR单元的电子指南针的研究

无人机、移动设备、车载导航等方面需要用到地磁定向,而指南针在这些应用中起到关键的作用.针对车载导航的姿态控制和导航精度,以广东东莞新科技术开发有限公司的GMR单元为基础,结合其专利技术-磁纠正技术,应用GMR对地磁场的灵敏快速的反应,开发的一款三轴方向传感器-Electronic Compass.测试数据和动态演示表明...     

Low-frequency noise in planar Hall effect bridge sensors

The low-frequency characteristics of planar Hall effect bridge sensors are investigated as function of the sensor bias current and the applied magnetic field. The noise spectra reveal a Johnson-like spectrum at high frequencies, and a 1/f-like excess noise spectrum at lower frequencies, with a knee frequency of around 400 Hz. The 1/f-like excess noise can be described by the phenomenological Hooge equation with a Hooge parameter of γ_H = 0.016. The detectivity is shown to depend on the total length, width and thickness of the bridge branches. The detectivity is improved by the square root of the length increase. Moreover, the detectivity is shown to depend on the amplitude of the applied magnetic field, revealing a magnetic origin to part of the 1/f noise.     

基于ＧＭＲ效应的非铁磁性金属裂纹涡流检测

为了补充常规电涡流检测在低频应用场合的不足,研究了基于巨磁电阻(giant magneto resistance,简称GMR)效应的裂纹涡流检测技术及其系统.分析了该技术的工作原理、理论基础及制约该技术应用的影响因素,设计制作了探头及信号处理电路,进行了探头的标定试验和非铁磁性金属材料微裂纹的检测试验.试验结果检验了该系统对非铁磁性金属材料裂纹的检测性能,验证了理论分析的正确性及该技术用于裂纹检测的可行性.     

An experimental comparison of multi-frequency and chirp excitations for eddy current testing on thin defects

Non-destructive evaluation of materials and structures is still a key issue in some industrial scenarios as the production process and the quality inspection. In the case of metallic materials, economic and implementation reasons push for the use of eddy current testing techniques. In the last years, the effort of the research activity is been focused on the development of eddy current measurement procedures capable of providing as much information as possible about the presence, the location and the geometrical characteristics of defects. To this aim, newer signals characterized by a wide spectral content able to penetrate in the different layers of the material under test are substituting the older sinusoidal excitation. Among these, multi-frequency and chirp represent two optimal candidates within the class of frequency domain-based signals. The former is characterized by the simultaneous presence of many sinusoidal tones, while the latter exhibits a constant envelope and an instantaneous frequency that increases or decreases with time. In literature many interesting papers dealing with both excitation types are reported but an experimental performance comparison on a number of real defects is missing. Moreover the comparisons are usually executed on single measurements collected in presence of a defect in the location corresponding to the highest defect signal. Even if this strategy allows the analysis of the defect signature in time and in frequency domain, from both experimental and practical point of view, this approach is extremely sensitive to noise and it could be also difficult to be applied in on-line or in-situ inspections. In this paper, the proposed comparison aims at highlighting the suitability of each considered excitation method with respect to the extraction of defects geometrical features. It is proposed to combine the various excitation signals with image processing: indeed by developing a proper 2D image procedure from 1D eddy-current data it is possible to improve the defect detection capability when difficult cases are experienced (such as annealed and small cracks) and to extract more accurate information about the defect’s geometric characteristics. After the image processing application, the multi-tone and the chirp approaches are quantitatively compared by using an ad-hoc figure of merit.