共查询到19条相似文献,搜索用时 140 毫秒
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采用Bitter粉纹技术详细观察和研究了微型磁阻元件在磁化和反磁化过程中的磁畴结构,结果表明Barkhausen噪声来源于磁化和反磁化过程中的磁畴活动和畴壁态极性转变。磁阻元件中的曲折状畴的产生、强化和畴壁合并及畴壁态极性转变是不可逆过程,是磁阻元件输出信号噪声的主要根源。实验发现,在磁阻元件和引线的连接处存在着磁畴结构,且这一过程是不可逆的。目前尚未见过报道。这必然也是磁阻元件输出信号噪声的来源之一。 相似文献
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采用Bitter粉纹技术详细观察和研究了微型磁阻元件在磁化和反磁化过程中的磁畴结构,结果表明Barkhausen噪声来源于磁化过程中的磁畴活动和畴壁态极性转变,磁阻元件中的曲折状畴的产生,强化和畴壁合并及畴壁态极性转变是不可逆过程,是磁阻元件输出信号噪声的主要根源。实验发现,在磁阻元件和引线的连接处存在着磁畴结构,且这一过程是不可逆的。目前尚未见过报道,这必然也是磁阻元件输出信号噪声的来源之一。 相似文献
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PMNT单晶电畴结构随组分与结构的变化 总被引:1,自引:0,他引:1
利用多种方法观察了弛豫型铁电单晶PMNT中电畴结构随组分与结构的演变过程与特征.观察发现,在PMN-PT的三方相区内,随PT含量的增加,电畴结构表现出微畴一(亚微畴)-不规则宏畴一规则宏畴转变历程;在三方-四方相变中,非180°电畴发生71°(或109°)宏畴-90°宏畴的转化,同时电畴图像变得更为规则.根据不同组分PMNT电畴的显示特征,提出晶体的最大双折射率可以作为度量其弛豫性强弱的光学参数.观察到了电畴的分布不均匀与多级结构现象,前者与组分或结构的起伏有关,后者与多期式马氏体转变有关.本文还分析了偏光显微镜、DIC、SEM、SEAM等观察方法中电畴的成像特征. 相似文献
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研究了LiNbO3单晶周期极化畴结构的制备工艺, 讨论了外电场的特性对周期极化过程的影响. 在对周期畴制备各工艺步骤进行实验研究的基础上, 提出解决LiNbO3单晶周期畴制备中一直存在的边缘击穿问题, 必须选择合适的周期电极形式并对脉冲波形进行优化. 采用所提出的工艺, LiNbO3周期极化畴的成品率提高到了90%. 为解决周期极化过程中反转畴的侧向扩展, 在对周期极化物理过程进行分析的基础上, 采取了对周期电极宽度进行优化设计和在样品上包覆聚酰亚胺绝缘胶的方法, 有效克服了这一问题, 制备了占空比符合预期的高质量的周期畴结构. 相似文献
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Stefan Riehl Paul Steinmann 《International journal for numerical methods in engineering》2017,109(9):1315-1343
This contribution presents a novel approach to structural shape optimization that relies on an embedding domain discretization technique. The evolving shape design is embedded within a uniform finite element background mesh which is then used for the solution of the physical state problem throughout the course of the optimization. We consider a boundary tracking procedure based on adaptive mesh refinement to separate between interior elements, exterior elements, and elements intersected by the physical domain boundary. A selective domain integration procedure is employed to account for the geometric mismatch between the uniform embedding domain discretization and the evolving structural component. Thereby, we avoid the need to provide a finite element mesh that conforms to the structural component for every design iteration, as it is the case for a standard Lagrangian approach to structural shape optimization. Still, we adopt an explicit shape parametrization that allows for a direct manipulation of boundary vertices for the design evolution process. In order to avoid irregular and impracticable design updates, we consider a geometric regularization technique to render feasible descent directions for the course of the optimization. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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The present study is a fundamental research for precise measurement of fuel amounts in a compressed natural gas (CNG) tank where an analysis of receiving sensitivity was conducted as a result of changes in the contact surface shape in the number of piezoelectric element of the ultrasonic sensor as well as in the internal pressure of the tank. Experiments were conducted as a function of changes in the contact surface shape between the ultrasonic sensor and outside of the aluminum tank and in the number of piezoelectric element as well as in the internal pressure of the tank. According to the experimental results, it could be confirmed that the maximum receiving sensitivity value was increased by about 60 % when the contact surface shape of the transmission and receiving ultrasonic sensors compared with the ultrasonic sensor in the Line-Line shape selected as the reference model was changed to the surface. As a whole, the highest receiving sensitivity values were observed when the transmission sensor of surface shape produced as multiple piezoelectric elements and the receiving sensor of surface shape produced as a single piezoelectric element were used. It could be confirmed that receiving sensitivities were improved at the same voltage value as a result of changes in the contact surface shape of the ultrasonic sensor and in the number of piezoelectric elements. 相似文献
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W. Scholz H. Forster D. Suess T. Schrefl J. Fidler 《Computational Materials Science》2002,25(4):331-546
Domain wall pinning is the coercivity mechanism of permanent magnets used in high temperature applications. In SmCo based magnets domain walls get trapped at the cellular precipitation structure causing a high coercive field. The motion of domain walls and their propagation velocity are important in soft magnets as used in sensor applications. A finite element micromagnetic algorithm was developed to study the motion of domain walls in complex microstructures. The cellular microstructure of SmCo magnets or the cylindrical soft wires can be easily built using tetrahedral finite elements. The pinning of the domain walls has been studied for different material compositions. Attractive and repulsive domain wall pinning are observed and their behaviour for increasing thickness of the precipitation structure is explained. The motion of domains in magnetic nanowires was calculated using adaptive mesh refinement. The wall velocity strongly depends on the domain wall structure. Transverse and vortex walls have been observed and their velocity in wires of different thickness has been studied. 相似文献
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运用XRD、TEM、EDS等实验手段,研究了Si离子掺杂对PMS-PZT材料的相结构、微观结构以及电畴形貌的影响.XRD测试结果表明,所有材料都显示钙钛矿结构,四方度(c/a)随着掺杂量的增加而增大.TEM研究结果表明,随着Si离子掺杂量的增加,电畴的形貌由鱼刺型过渡到微米级的带状畴,最后转变为波浪状的电畴.EDS表明在材料的晶界处含有纳米级的SiO2和PbSiO3,并且发现单斜晶系的孪晶ZrO2在晶界附近析出.本文对孪晶ZrO2的析出及其析出量随着硅离子含量增加而增加的原因作了解释,最后对材料压电性能的降低进行了探讨. 相似文献
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Doo Kie Kim Chung‐Bang Yun 《International journal for numerical methods in engineering》2003,58(12):1837-1855
This paper presents a time domain method for soil–structure interaction analysis under seismic excitations. It is based on the finite element formulation incorporating analytical frequency‐dependent infinite elements for the far‐field soil region. Equivalent earthquake input forces are calculated based on the free‐field responses along the interface between the near‐ and far‐field soil regions using the fixed exterior boundary method in the frequency domain. Then, the input forces are transformed into the time domain by using inverse Fourier transform. The dynamic stiffness matrices of the far‐field soil region formulated using the analytical frequency‐dependent infinite elements in the frequency domain can be easily transformed into the corresponding matrices in the time domain. Hence, the response can be analytically computed in the time domain. A recursive procedure is proposed to compute the interaction forces along the interface and the responses of the soil–structure system in the time domain. Earthquake response analyses have been carried out on a multi‐layered half‐space and a tunnel embedded in a layered half‐space, and results are compared with those obtained by the conventional method in the frequency domain. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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试论现代化妆品的包装设计 总被引:3,自引:2,他引:1
从包装设计的各个要素入手,阐述了与化妆品直接接触的内包装设计.指出随着材料的丰富、造型结构的创新、装潢设计的精美,化妆品的包装设计已经发展到一个凸现个性的时代.实践证明只有将材料、造型结构、装潢设计合理运用的化妆品,这样的包装设计才是最符合消费者需求的包装. 相似文献
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John C. Bruch George Zyvoloski 《International journal for numerical methods in engineering》1974,8(3):481-494
A finite element weighted residual process has been used to solve transient linear and non-linear two-dimensional heat conduction problems. Rectangular prisms in a space-time domain were used as the finite elements. The weighting function was equal to the shape function defining the dependent variable approximation. The results are compared in tables with analytical, as well as other numerical data. The finite element method compared favourably with these results. It was found to be stable, convergent to the exact solution, easily programmed, and computationally fast. Finally, the method does not require constant parameters over the entire solution domain. 相似文献
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An optical-fiber sensor is reported which is capable of detecting ethanol in water. A single optical-fiber sensor was incorporated into a 1-km length of 62.5-/spl mu/m core diameter polymer-clad silica optical fiber. In order to maximize sensitivity, a U-bend configuration was used for the sensor where the cladding was removed and the core exposed directly to the fluid under test. The sensor was interrogated using optical time domain reflectrometry, as it is intended to extend this work to multiple sensors on a single fiber. In this investigation, the sensor was exposed to air, water, and alcohol. The signal processing technique has been designed to optimize the neural network adopted in the existing sensor system. In this investigation, a discrete Fourier transform, using a fast Fourier transform algorithm, is chosen and its application leads to an improvement in efficiency of the neural network i.e., minimizing the computing resources. Using the Stuttgart neural network simulator, a feed-forward three-layer neural network was constructed with the number of input nodes corresponding to the number of points required to represent the sensor frequency domain response. 相似文献
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Fatigue life prediction under wide band random loading 总被引:3,自引:0,他引:3
G. PETRUCCI B. ZUCCARELLO 《Fatigue & Fracture of Engineering Materials & Structures》2004,27(12):1183-1195
In this paper, a method for the high‐cycle fatigue life prediction of components subjected to gaussian, stationary, wide band random loading is presented. It allows the user to evaluate the fatigue life of components subjected to uniaxial stress states directly from the stress power spectral density (PSD), avoiding onerous simulations in time domain. The proposed method can be applied to random stress processes having PSD of any shape, and the fatigue life predictions obtained are more accurate than that provided by most of the frequency domain techniques proposed in literature. 相似文献