Equivalent circuit method for static and dynamic analysis of magnetoelectric laminated composites

Magnetoelectric equivalent circuit analytical method is presented for laminate composites of magnetostrictive Terfenol-D （TbxDy1-xFe2） and piezoelectric Pb（Zr1-xTix）O3 （PZT） operated in longitudinal magnetized and transverse polarized （or L-T）, and transverse magnetized and transverse polarized （or T-T） modes. Magnetoelectric （ME） couplings both at low-frequency and resonance-frequency have been studied, and our analysis predicts that （i） the ME voltage coefficients of both L-T and T-T modes increase with increasing the thickness of the piezoelectric phase whereas magnetostrictive phase thickness keeps constant, and then tend to saturation when the thickness ratio of piezoelectric phase to magnetic phases is 〉3; （ii） there are the optimum thickness ratios that maximize magnetoelectric （ME） voltage coefficients for the two modes, which are dependent on elastic compliances ratio of piezoelectric phase and magnetostrictive phase; and （iii） the ME voltage coefficients are dramatically increased by a factor of -Qm, when operated at resonance frequency. A series of TerfenoI-D/PZT laminates were fabricated, and the results were compared with the theoretical ones. Experiments confirmed that equivalent circuit method is a useful tool for optimum designs of ME laminates.     

考虑非等长应变的磁电层合材料低频磁电响应特性

本文提出了一种考虑非等长应变的磁电层合材料低频磁电响应模型.该模型以剪切应力传递应变为基础,采用应力函数法分析了磁致伸缩层、压电层的应力和应变,利用粘接处的应变相等,求出了开路状态下磁电层合材料L-T模式的低频磁电响应特性.该模型能研究磁致伸缩材料的柔顺系数、压磁系数、层合比、压电材料的机电耦合系数、压电系数等参数对磁电电压系数的影响,并与等效电路法、两种考虑退磁场的等效电路法以及实验结果进行了对比研究.针对Terfenol-D/PZT/Terfenol-D的研究结果表明:理论结果与实验结果误差为5.42%,与其他方法相比,本文的结果与实验结果吻合得更好.     

Enhancement of magnetoelectric properties in a surface-mount magnetoelectric device

The fabrication and properties of a novel double layered surface-mount magnetoelectric(ME) device are investigated and reported. This ME device is made up of two opposite polarized piezoelectric PZT slices bonded on the same side of a magnetostrictive material Metglas, forming a novel two PZT in-series device. ME voltage obtained from the two PZT in-series is obviously higher than that of single PZT in a magnetic field with certain value. The ME voltage coefficient(αV) of the surface-mount ME device is significantly enhanced by adjusting the thickness of Metglas: 1) At a frequency of 1 k Hz, αV of this device increases with the layer number of Metglas increased, and the maximum value of αV is about 4.25 times than the minimum; 2) At a frequency of 5 k Hz, the maximum value of αV is 458 mV /Oe, which derives from the ME device with three layers Metglas. This novel design provides an effective way to manufacture miniature and high sensitive ME devices, which makes it possible to apply ME device into integrated circuit(IC).     

Selectivity of Crystal Growth Direction in Layered Double Hydroxides

Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/AI molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions wereinvestigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/AI molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/AI molar ratio decreases. The influence of the aging time, aging temperature, and Mg/AI molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.     

Influences of the shape of magnetic material on the magnetoelectric properties of the PZT/Metglas composite

In this paper, the influences of the shape of magnetic material on the magnetoelectric(ME) properties of PZT/Metglas magnetoelectric(ME) composites have been investigated. The results indicate that, with the decrease of the waist length(L_w) of the dumbbell-shaped Metglas, the magnetic flux density in the center region and ME coefficients(α_(ME)) of the composites increase, while the optimal bias magnetic field Hdc decreases on the contrary. In an AC magnetic field of 1 kHz, the maximum αME(α_(Max)) of the composite with L_w= 20 mm exhibits 1.3 times larger than that of the one with L_w=50 mm, and the optimal Hdc deceases by 15%. At the resonant frequencies of each composites, α_(Max) is enhanced by 1.3 times as L_w decreases from 50 to 20 mm. The simulation made by Comsol Multiphysics and the theoretical analysis based on an equivalent magnetic circuit confirm the experimental results.     

含弱界面的复合材料层合板对水平剪切波的散射

对含有弱界面的复合材料层合板,采用弱连接界面的剪切弹簧模型,借助波函数法研究了水平剪切波入射时层合板对波的散射,得到了解析结果.数值计算结果表明,弱界面处在不同位置时,对以一定角度入射到复合材料层合板的水平剪切波,其反射和透射系数有明显变化;当层合板中弱界面的力学性能参数强弱不同时,以入射角为变量所得到的透射系数和反射系数曲线呈现出明显差异.证明了根据含弱界面复合材料层合板所得到的水平剪切波的散射规律,不仅能够确定反映弱界面力学性质的参数R的大小,而且还能够判明弱界面所在的位置,这将为复合材料层合板中弱界面的超声无损检测提供依据.     

云纹法对钢丝帘线－橡胶复合材料力学性能测定的研究

帘线－橡胶复合材料力学性能的精确测定是轮胎有限元分析成功应用的关键。采用云纹技术直接测量应变来确定这些力学性能较为适宜。本文应用云纹法对不同体积分数的单层钢丝帘线－橡胶复合材料力学性能进行了测量研究，并与哈尔平－蔡等公式的理论计算值作了对比讨论。发现云纹法测得试验结果与帘线一橡胶复合层表面材料的力学性能有关。此外对试样没长不同长宽比也进行了对比，表明试样尺寸在本文中所取的长、宽比范围内对帘线－橡胶复合材料性能影响不大。     

Voltage-controlled Kerr response in Ni/Pb（Zr0.52Ti0.48）O3 heterostructures

Voltage-modified magneto-optical Kerr effect（MOKE） is widely used to describe the converse magnetoelectric（ME） effect in the ferroelectric/ferromagnetic（FE/FM） heterostructures. However, the applied voltage can possibly give rise to electro-optical effect of the FE layer, which would also affect the Kerr signals in the MOKE system. Here, we used an AC voltage to modulate the magnetization in the Ni/Pb（Zr0.52Ti0.48）O3（PZT） heterostructures with different pre-polarization states of the PZT layers to investigate the complexity of the Kerr signals. The results suggested that the voltage control of Kerr signal contained several origins; however, the straininduced ME effect dominated in the ME effect in the heterostructures.     

导电高分子复合材料的有效电导率模型

基于Maxwell理论和平均极化理论,建立了导电高分子复合材料的有效电导率模型。有效电导率描述为各组成成分的体积、形状和颗粒尺寸的函数。利用该模型,讨论了渗流阈值与导电颗粒的大小及轴长比的关系,得到了导电高分子复合材料的有效电导率随导电颗粒轴长比和半径变化的规律。用该模型计算了碳纤维聚脂树脂复合材料的有效电导率,计算结果与实验结果符合较好。     

层状周期压电复合材料的动态有效性质分析

基于细观力学的均匀化理论,对层状周期压电复合材料进行均匀化处理。推导了布洛赫波下层状周期压电复合材料的均匀化本构关系及频散关系,并通过退化验证了理论推导的正确性。以PZT-5H/BaTiO_3复合而成的层状周期复合材料为例进行数值计算,得到了动态有效模量与频率之间的关系。将经典弹性问题的均匀化理论推广到了压电耦合问题,为预测压电复合材料动态力学性能提供了方法。     

过冷大水滴粒径分布的欧拉-拉格朗日混合抽样算法及对冰型影响

过冷大水滴（supercooled large droplet,SLD）云雾环境不同于常规粒径范围的过冷水滴,具有更大的粒径范围和复杂的水滴粒径分布形式,使得结冰的冰型异常复杂,从而给飞行器的飞行安全带来了前所未有的挑战。现有结冰数值模拟方法仅能模拟单一粒径的水滴,无法准确模拟真实SLD云雾环境“双峰分布”的粒径分布特性和相应的冰型。为了准确高效模拟SLD这种粒径分布特性,本文提出了一种基于Rosin-Rammler 分布函数进行欧拉-拉格朗日混合抽样的水滴轨迹模拟算法。通过该方法收集水滴,再利用结冰模型与水膜模型计算表面溢流传热和冰高,从而实现了准确高效的SLD粒径分布的结冰数值模拟,并通过2.5维算例研究了SLD粒径分布对机翼结冰的冰型特征以及冰型空间随机性的影响。结果表明SLD的粒径分布对冰型有较大的影响,冰型特征和冰型随机性与MVD和粒径分布方差紧密关联。     

SiC颗粒特性对无压熔渗SiCp/Al复合材料热物理性能的影响

采用粉末注射成形-无压熔渗相结合技术制备出了电子封装用高体积分数SiCp/Al复合材料. 重点研究了SiC粒径、体积分数以及粒径大小等颗粒特性对所制备复合材料热物理性能的影响规律. 研究结果表明,SiCp/Al复合材料的热导率随SiC粒径的增大和体积分数的增加而增加;SiC粒径的大小对复合材料的热膨胀系数(CTE)没有显著的影响,而其体积分数对CTE的影响较大. CTE随着SiC颗粒体积分数的增加而减小,CTE实验值与基于Turner模型的预测值比较接近. 通过对不同粒径的SiC粉末进行级配,可以实现体积分数在53%～68%、CTE(20～100℃)在7.8×10-6～5.4×10-6K-1、热导率在140～190W·m·K-1范围内变化.     

微孔结构对多孔材料细观力学特性的影响

在三维孔隙材料如泡沫材料中，胞孔的形状及大小并非完全均匀，因此借助二维均匀化方法来讨论胞孔形状及大小对多孔材料性能的影响。在线弹性范围内，根据均匀化理论，基于虚位移原理，结合有限元方法推导出二维周期性结构的均匀化的有限元格式。取具有不同孔洞形状的正方形胞元作为周期性结构的代表胞元，将三维孔隙材料简化为截面上具有规则孔洞的二维结构，来计算不同微孔形状及大小下的等效弹性常数；比较分析了微孔结构对多孔材料等效弹性常数的影响。计算结果分析表明，多孔材料的等效弹性参数不仅取决于微孔结构的数量，而且对微孔结构的形状也有一定程度的敏感，同时对基体材料的泊松比的变化敏感与否也与微孔结构有关。     

复合型压电俘能器的力电特性研究

研究了由金属及压电陶瓷构成的复合型压电俘能器的动力学及力电转换特性。基于薄板小挠度理论,对复合型压电俘能器进行振动分析,确定了在周期性均布载荷作用下该结构所产生电压、功率与其几何参数之间的关系。同时结合实验,研究了不同负载电阻情况下压电俘能器的输出功率并讨论了能量转换效率问题,并分析了压电俘能器的几何参数、不同金属材料对力电转换特性的影响。     

中空银纳米球的制备及其性能研究

新型的金属纳米粒子因为独特的由表面等离子体共振诱导(SPR)的光学性质和很多的潜在应用而受到社会广泛的关注。在具有SPR效应的贵金属纳米粒子中,中空纳米结构有一个很高的散射系数,其共振频率通过改变中空核的尺寸和壳的厚度可以很容易地被控制。本论文中拟采用电化学方法结合电偶置换法在高定向热解石墨(HOPG)及金膜表面制备不同尺寸具有中空结构的银纳米阵列,研究了中空银纳米阵列的局域表面等离子效应(L-SPR),为其在SPR定性和定量研究中的应用提供理论指导。     

Magnetoelectric and converse magnetoelectric res ponses in TbxDy1-xFe2-y alloy ＆ Pb（Mg1/3Nb2/3）（1-x）TixO3 crystal laminated composites

Measured results of magnetoelectric （ME） and converse magnetoelectric （CME） effects of TbxDy1-xFe2-y/ Pb（Mg1/3Nb2/3）（1-x）TixO3/TbxDy1-xFe2-y （TD/PMNT/TD） and PMNT/TD/PMNT laminated composites are presented. ME effect was determined by measuring laminate voltage output under a Helmholtz-generated AC field biased by a DC field （0-1 kOe） （1Oe = 79.58 A/m）. The CME effect was measured by recording the voltage induced in a solenoid encompassing the ME sample while exposed to a DC bias field and PMNT layer driven by a 10 V AC source. The ME and CME responses in the two laminated structure are linear. The highest values of ME coefficients in TD/PMNT/TD and PMNT/TD/PMNT composites are 384 mV/Oe and 158 mV/Oe, respectively, while the highest values of CME coefficients in the two composites are 118 mG/V and 162 mG/V （1 G=10^-4 T）, respectively.     

含He纳米钛膜的XRD研究

本文采用直流磁控溅射方法,在He／Ar混合气氛中,通过分别改变He／Ar流量比和沉积偏压制备不同He含量的钛膜.利用XRD(X-ray diffraction)对含He钛膜的微观结构和晶粒尺寸进行了研究.结果表明,在其它实验参数不变的情况下,当He／Ar流量比从1.0增加到25时,钛膜的平均晶粒尺寸从19.02 nm减小到8.63 nm.随着膜中He含量的增加,衍射峰宽化,晶粒细化,He的掺入有抑制纳米晶粒长大的趋势.而当沉积偏压从24 V增加到151 V时,其平均晶粒尺寸基本不变.He引入引起了（002     

含He纳米钛膜的XRD研究

本文采用直流磁控溅射方法,在He／Ar混合气氛中,通过分别改变He／Ar流量比和沉积偏压制备不同He含量的钛膜。利用XRD(X-ray diffraction)对含He钛膜的微观结构和晶粒尺寸进行了研究。结果表明,在其它实验参数不变的情况下,当He／Ar流量比从1.0增加到25时,钛膜的平均晶粒尺寸从19.02nm减小到8.63nm。随着膜中He含量的增加,衍射峰宽化,晶粒细化,He的掺入有抑制纳米晶粒长大的趋势。而当沉积偏压从24V增加到151V时,其平均晶粒尺寸基本不变。He引入引起了（002）晶面衍射峰向小角度移动,晶格参数c增加,而a不变。     

Effect of microparticle properties on erosion in solid-steam mixtures

Based on a custom-built experimental apparatus, irregular microparticles of different sizes and microparticles of the same size but of different shape were added to wet steam, and erosion experiments were performed on polished medium carbon steel specimens. After the experiments, the eroded surfaces were analyzed by scanning electron microscopy and the degree of damage was evaluated by area loss. The results indicated that microparticle size significantly affects the degree of erosion damage. With an increase in size, variations in the method of damage mainly cause different degrees of damage on an eroded surface. Microparticle shape hardly affects the number of craters. Compared with spherical microparticles, irregular microparticles cause indentations more easily and result in more severe abrasion on the material’s surface.     

LiCoO2电极中锂离子的扩散性能

为使锂离子电池在较高的充、放电倍率下满足动力型电源的需要,对LiCoO2中锂离子的扩散性能进行了理论推导及试验测定。以球状电极模型对LiCoO2电极进行了处理,在简化的假设条件下,推导出LiCoO2电极的扩散电流表达式,并可求得锂离子在LiCoO2电极中的固相扩散系数DLi 。研究结果表明:I对t-1/2在10～150s表现出很好的线性关系,与理论分析结果相符合;不同晶粒大小的LiCoO2样品扩散系数有很大差别,相差1个数量级以上;锂离子扩散动力学特征是由LiCoO2的晶粒尺寸决定的,与其粒径分布、比表面积及表面形貌等参数基本无关。