Colossal dielectric response and relaxation behavior in novel system of Zr4+ and Nb5+ co-substituted CaCu3Ti4O12 ceramics

In this work, we developed a novel system of isovalent Zr⁴⁺ and donor Nb⁵⁺ co-doped CaCu₃Ti₄O₁₂ (CCTO) ceramics to enhance dielectric response. The influences of Zr⁴⁺ and Nb⁵⁺ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr⁴⁺ and Nb⁵⁺ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu₃Ti_3.8-xZr_xNb_0.2O₁₂ (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr⁴⁺ and Nb⁵⁺ ions than that of single-doped with Zr⁴⁺ or Nb⁵⁺ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~10⁵) at a frequency range of 10²–10⁵ Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr⁴⁺ and Nb⁵⁺ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus.     

FeSiB薄膜的巨磁阻抗和应力阻抗效应研究

软磁材料中存在巨磁阻抗 (giantmagneto impedance ,GMI)效应以及与之相同来源的应力阻抗 (stress impedance ,SI)效应 ,利用这两种效应可以制成具有高灵敏度的微型化的磁场和应力 应变传感器。本文基于传感器的实际应用 ,对图形化的、较大磁致伸缩的FeSiB单层和多层薄膜的巨磁阻抗和应力阻抗效应中频率和退火的影响进行了研究。结果表明 ,对于两种效应 ,经过退火处理的单层和多层膜均可在较低的频率下得到较高的灵敏度 ,而多层膜中的应力阻抗效应将为新型高灵敏传感器的设计和研制开辟一条崭新的途径     

超磁致伸缩作动器的率相关Hammerstein模型与H∞鲁棒跟踪控制

利用Hammerstein模型对超磁致伸缩作动器（Giant magnetostrictive actuators,GMA）的率相关迟滞非线性进行建模,分别以改进的 Prandtl-Ishlinskii（Modified Prandtl-Ishlinskii）模型和外因输入自回归模型（Autoregressive model with exogenous input,ARX）代表Hammerstein模型中的静态非线性部分和线性动态部分,并给出了模型的辨识方法. 此模型能在1～100Hz频率范围内较好地描述GMA的率相关迟滞非线性. 提出了带有逆补偿器和H∞鲁棒控制器的二自由度跟踪控制策略,实时跟踪控制实验结果证明了所提策略的有效性.     

一种新的磁滞非线性前馈补偿算法

针对超磁致伸缩致动器磁滞非线性特征, 建立了描述其非线性行为的Preisach数学模型, 以F函数法求解了该模型的数值模型. 针对当前致动器非线性前馈补偿控制中迭代和执行效率低的缺点, 将磁滞非线性理解为系统干扰, 提出了一种新的非线性前馈补偿算法, 在求解Preisach逆模型过程中,引入稳态误差信号作为参考变量, 以Sigmoid函数变步长算法进行迭代步长自适应动态调整. 计算机仿真和实验研究均表明,与当前的磁滞模型求逆算法相比, 所提出的算法在保证控制精度的同时可以显著提高系统收敛速度, 大大提高了程序的执行效率.     

Magnetoresistance and microstructure evolution upon rapid thermal annealing of giant magnetoresistive Co/Cu/Co/CoNbZr multilayers

The magnetoresistance (MR) variation of Co/Cu/Co/CoNbZr spin valves as a result of rapid thermal annealing has been investigated. MR ratio of 3.8% was obtained in the as-deposited sample and a considerable increase to 6.86% was observed in the 450°C×60 s treated sample. Microstructure studies show that the enhancement of MR ratio is a consequence of the nano-crystallization of amorphous CoNbZr soft layer. The nano-crystallized CoNbZr possess fine and dense microstructure and excellent electrical and soft magnetic properties which leads to the MR enhancement. With increasing annealing temperature or annealing time, interface roughness caused by rapid grain growth decrease the MR ratio rapidly. XRD studies imply that the interfusion of Cu atom into the Co layer is another possible degradation mechanism of Co/Cu/Co/CoNbZr spin valves at annealing temperature beyond 550°C.     

基片对间接耦合式超磁致伸缩薄膜静态磁化性能的影响

间接耦合式超磁致伸缩薄膜是一种新兴的具有优异机械物理性能的功能材料，已成为微型器件材料研究的热点之一。由于是在弹性基片上通过物理沉积方法得到该种薄膜材料，因此基片的物理性能对薄膜材料的磁化性能会产生重要影响。通过对物理性能差异较大的铜、聚酰亚胺两种基片的间接耦合式超磁致伸缩薄膜的磁化曲线、饱和磁化强度等进行实验研究与分析比较，得到不同物理性能基片对超磁致伸缩薄膜特性的影响规律，为进一步制备性能各异的薄膜材料奠定基础。     

An SVM approach with electromagnetic methods to assess metal plate thickness

Eddy current testing (ECT) is a non-destructive technique that can be used in the measurement of conductive material thickness. In this work ECT and a machine learning algorithm (support vector machine – SVM) are used to determine accurately the thickness of metallic plates. The study has been made with ECT measurements on real specimens. At a first stage, a few number of plates is considered and SVM is used for a multi-class classification of the conductive plate thicknesses within a finite number of categories. Several figures of merit were tested to investigate the features that lead to “good” separating hyperplanes. Then, based on a SVM regressor, a reliable estimation of the thickness of a large quantity of plates is tested.Eddy currents are induced by imposing a voltage step in an excitation coil (transient eddy currents – TEC), while a giant magnetoresistance (GMR) is the magnetic sensor that measures the transient magnetic field intensity in the sample vicinity. An experimental validation procedure, including machine training with linear and exponential kernels and classification errors, is presented with sets of samples with thicknesses up to 7.5 mm.     

基于巨磁阻传感器的无损检测系统研究与设计

针对现代工业与安全检测中对非铁磁性工件的表面及近表面缺陷检测需要,基于涡流无损检测原理,采用灵敏度高、体积小、工作频率范围宽(0Hz到MHz)的GMR传感器,结合基于单片机STM32的直接数字频率合成(DDS)信号产生方法及锁相技术研制了一套涡流无损检测系统。实验结果表明该基于 GMR传感器的无损检测系统能够较好的检测出铝板试件表面及表面下2 mm处缺陷的存在,多道扫描结果可清晰判别出缺陷的位置和大小,该系统可以准确完成对导电材料表面及近表面的无损检测。     

A new application of giant reed waste material for ammonium removal

Excess nitrogen is one of the main causes of eutrophication in water bodies. In this study, the undesirable agricultural lignocellulosic material giant reed was used to remove ammonium ions from aqueous solutions. Batch experiments were conducted to investigate the effect of various parameters such as contact time, initial ammonium concentration, adsorbent dosage, pH, particle size, agitation rate and phosphate coexisting during the ammonium adsorption process. The ammonium sorption capacity of fibrous giant reed (FGR) at equilibrium was 12.49?mg?N/g with a maximum removal efficiency of 76% observed within 30?min at pH range of 6.5–9.5. Results revealed that the Freundlich isotherm model fitted better with the sorption process than the Langmuir model, and the adsorption process was well described by pseudo-second-order kinetic model. FT-IR analyses indicated that complexation and ion exchange could be the main mechanisms for the ammonium removal by FGR. Results revealed that FGR has a sorption capacity comparable to that of other natural sorbents with the advantage of greater availability with no cost.