对称磁电层合板磁电转换效应理论研究

磁致伸缩和压电层合材料通过磁致伸缩和压电效应的乘积可以获得大的磁电效应.通过材料的力学本构方程，建立了对称磁电层合板磁电耦合的静态力学模型；采用ANSYS 80多物理场有限元分析软件，对层合结构的磁电转化效应进行了数值计算，并与理论计算值进行了对比.研究结果表明：磁致伸缩/压电的厚度比增加使磁电电压系数增大；所推导的磁电电压系数公式的计算值与等效电路模型推导的公式计算值符合很好；有限元数值计算结果介于两种模型的计算结果之间. 关键词： 磁电效应 层合板 本构方程 有限元分析     

Ni/Pb(Zr,Ti)O3/TbFe2层状复合材料的谐振磁电特性研究

采用化学镀和黏接法制备层状磁电复合材料Ni/PZT/TbFe₂,研究其磁电性能及谐振频率随Ni层厚度的变化情况. 结果表明:Ni/PZT/TbFe₂层状磁电复合材料与其他结构的磁电性能不同,其一阶弯曲谐振峰值和纵向谐振峰值都很大. 随着Ni层厚度的增加,Ni/PZT/TbFe₂层状磁电复合材料的一阶纵向谐振峰值逐渐增大. 结合实验数据和理论计算值得出了材料的一阶弯曲谐振频率fr1和一阶纵向谐振频率f 关键词： 磁电效应 正磁致伸缩 负磁致伸缩 谐振频率     

磁致伸缩/压电叠层复合材料磁-机-电耦合系数分析

分析和推导了磁致伸缩/压电叠层复合材料的机-电耦合系数、磁-机耦合系数及磁-电耦合系数与磁致伸缩层和压电层性能参数及几何参数之间的关系.进一步分析表明,叠层复合材料低频时的磁电电压系数正比于磁-电耦合系数,谐振时的磁电电压系数正比于磁-电耦合系数与机械品质因素的乘积;磁电电压系数还与复合结构的本征阻抗有关,本征阻抗越大磁电电压系数越大.通过性能差异较大的Terfenol-D和FeNi基弹性合金分别与压电材料PZT5-H和PZT8相互组合构成复合材料的比较分析,进一步阐明了磁电复合材料磁-电耦合系数和机械品 关键词： 磁电效应 磁-机-电耦合系数 磁致伸缩材料 压电材料     

铁电/铁磁1-3型结构复合材料磁电性能分析

磁致伸缩和压电复合材料通过机械力作用可获得较大的磁电效应，由Terfenol-D粉末与树脂黏接剂构成压磁相，和压电陶瓷PZT黏结在一起，形成1-3型柱状阵列结构，可获得很大的磁电转换系数.采用有限元方法，对此结构的复合材料进行静态分析.复合材料的介电常数和磁电系数的计算结果和实验数值一致，得到样品中应力、应变和电极化分布情况及其关系，并给出进一步提高磁电转换系数的途径，该种复合方式有望成为一种新型高性能的磁电结构. 关键词： 复合材料 磁电效应 有限元     

偏置磁场对磁致伸缩/弹性/压电层合材料磁电效应的影响

根据磁致伸缩材料的非线性本构关系得到其动态杨氏弹性模量和动态压磁系数,结合等效电路法得到磁致伸缩/弹性/压电层合材料的磁电效应与磁致伸缩材料的动态杨氏弹性模量和动态压磁系数的关系,讨论了偏置磁场对这种层合材料的谐振频率和谐振磁电电压转换系数的影响.理论推导和实验结果均表明,存在最佳偏置磁场使磁致伸缩/弹性/压电层合材料的谐振磁电电压转换系数最大. 关键词： 磁致伸缩/弹性/压电层合材料 磁电效应 偏置磁场 非线性本构关系     

磁致伸缩/压电层叠复合材料磁电效应分析

采用有限元分析软件COMSOL5.0建立了三维悬臂梁模型,分析了磁致伸缩/压电/磁致伸缩叠层复合材料的磁电系数α_(ME),并就几何参数对复合结构磁电系数的影响进行了优化分析.首先,利用稳态求解器研究了磁电层状复合结构内部的应力、应变、位移以及电势分布情况,利用瞬态求解分析了磁电复合结构各变量动态分布规律;其次,应用小信号频域分析研究了该结构的谐振频率以及在不同偏置磁场对输出电压的影响,结果表明,随着直流偏置磁场的增加,输出电压逐渐减小.改变复合材料不同层的厚度,分析了磁电层与压电层厚度比t_m/t_p对磁电系数的影响,结果表明,随着厚度比增加,α_(ME)逐渐增大,其增加速率逐渐减小;最后,分析了磁电系数α_(ME)随复合结构面积、长宽比的变化情况.分析表明,α_(ME)随磁电复合结构面积的增加逐渐增加,其增加速率逐渐减小;当磁电复合结构面积恒定时,其磁电系数随长宽比L/W增加表现出先增加后减小的趋势,存在最优值.     

引入界面耦合系数的长片型磁电层状复合材料的等效电路模型

针对长片型磁电层状复合材料,提出了一种适用于准静态和动态磁场激励的引入界面耦合系数的等效电路模型,旨在为基于长片型磁电层状复合材料的传感器、换能器等器件的设计、制作和应用提供理论指导.考虑到磁电层状复合材料实际工作过程中磁致伸缩层和压电层的应变并不相同,首先利用运动方程分别对磁致伸缩层和压电层进行建模,提出了一个从物理上反映相间应变传递的界面耦合系数表达式,然后利用一个变比恰为界面耦合系数的理想变压器将两层材料的等效电路耦合,构成改进的磁电层状复合材料的等效电路模型,得到包含界面耦合系数的磁电电压系数和最佳层合比的表达式.对12个具有不同尺寸和负载条件的样品进行实验,制作过程中承受500g砝码负载的样品的界面耦合系数为0.15,最佳层合比为0.57;承受100g砝码负载的样品的界面耦合系数为0.10,最佳层合比为0.50.磁电电压系数和最佳层合比的实验值与各自包含界面耦合系数的理论值基本符合,证明了改进的等效电路模型的合理性和正确性.     

双层纳米磁电薄膜模型及分析

以层状磁电复合材料弹性力学模型为基础,建立了自由状态下双层纳米磁电薄膜的弹性力学模型,并以此为基础简单介绍了推导其磁电电压系数表达式的方法.计算了CoFe₂Ｏ₄/Pb（Zr_0．52Ti_0．48）Ｏ₃双层纳米复合薄膜的磁电电压系数理论值,分析结果表明基片对薄膜存在强烈的夹持效应,而且基片对压电与磁致伸缩两相材料间最佳体积比有一定的影响. 关键词： 磁电理论 磁电薄膜 铁电材料 磁致伸缩     

磁场作用下PMN-PT/CFO的磁电效应研究

在弹性力学模型下,推导非理想耦合状态的磁电(ME)电压系数公式.利用CFO随磁场变化的磁致伸缩特性,得到PMN-PT与CFO复合材料的磁电电压系数随磁场以及各参量的变化关系公式.研究了磁电电压系数在磁场下随磁场强度、压电相体积分数v、界面耦合系数k以及PMN-PT介电常数之间的变化关系.研究结果发现:磁电电压系数随PMN-PT体积分数和磁场强度的增大,表现为先增大,后逐渐减小至零;磁电电压系数强烈地依赖于界面耦合系数,耦合系数减小会极大降低复合材料的磁电效应;同时,磁电效应具有一定的频率特性,随着频率的逐渐增大而增大,直至达到稳定.     

铁电/铁磁三相颗粒复合材料的磁电性能计算

采用格林函数方法给出了三相复合材料的磁电系数的解析式，对稀土-铁合金/压电陶瓷/高分子（Terfenol-D/PZT/PVDF）三相颗粒复合材料的磁电系数进行了计算.计算结果给出了复合材料的磁电性能与材料显微结构的关系，包括三相颗粒复合材料的磁电性能随组分、颗粒的长径比、PZT颗粒的电极化方向以及外磁场的变化趋势，可为实验设计提供参考和指导.通过合理设计，三相磁电复合材料的性能可以达到数百mV/A.作为一种新的磁电复合材料，三相颗粒复合材料有望成为一种新型高性能易制备的磁电材料. 关键词： 磁电效应 复合材料 格林函数     

Electric‐field tuning of magnetoelectric properties in Metglas/piezofiber composites

The tunability of magnetoelectric (ME) properties by applied dc electric field (E) was systematically investigated for a laminate composite consisting of Metglas, Pb(Zr_x Ti_1–x)O₃ fiber, and interdigitated electrodes. The ME coefficients and equivalent magnetic noise were found to be dependent on E. This dependence is attributed to variations in the magnetic properties. The dielectric properties and noise charge density were relatively invariant to E. A 1.3× improvement in the ME coefficient was obtained at the Villari point under E = 300 V/mm relative to E = 0 V/mm. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measurements of the maximum α-particle energy at forward angles in the reaction22Ne+197Au

The energy spectrum of α-particles has been measured for the system²²Ne+¹⁹⁷Au atE _1ab=178 MeV. The reaction products emitted at 0° relative to the beam direction are analysed using a magnetic spectrometer and detected by means of a semiconductorΔE?E telescope. The measured α-particle spectrum strongly differs from the one expected from evaporation. The experimentally measured maximum α-particle energy almost amounts to the maximum possible value calculated from the reaction energy balance. The obtained results are discussed from the point of view of the mechanism of formation of high-energy α-particles.     

Wide-band magnetoelectric characterization of a ferrite-piezoelectric multilayer using a pulsed magnetic field

The use of a pulsed magnetic field for studies on frequency characteristics of the magnetoelectric (ME) effect in multilayer composite structures is described. The method is based on the excitation of a ferrite-lead zirconate titanate multilayer with short magnetic field pulses, followed by the measurement and Fourier analysis of the ME response signal. It is shown that the ME voltage coefficient α_E generally decreases as the frequency increases from 1 kHz to 1 MHz except (i) at some discrete frequencies where the coefficient increases by an order of magnitude due to electromechanical resonance in the structure and (ii) a local maximum at 2-4 kHz in α_E vs. frequency due to relaxation processes caused by the conductivity of individual layers.     

Influence of the stress on magnetoelectric effect in magnetostrictive-PZT bilayers

In this letter, we investigate the influence of the stress on magnetoelectric (ME) effect in a magnetostrictive-PZT bilayer. ME voltage coefficient α*_E = δE / δH, where δE is the induced electric field for an applied alternating current (ac) magnetic field δH, is obtained by solving the stress-related piezoelectric constitutive equation and the conventional magnetostrictive equation with appropriate boundary condition. Based on the free-energy density function of the PZT film in stress state, we get the stress-related piezoelectric charge coefficient ^p d*₃₁ and dielectric permittivity ^pε*₃₃. After taking the cobalt ferrite (CFO) as magnetostrictive phase, it is found that α*_E increases with decreasing 2-d compressive stress for CFO-PZT, which not only is qualitatively consistent with previous experimental measurements, but also provides a possible route to improve the ME effect.      

Direct and inverse magnetoelectric effect in layered composites in electromechanical resonance range: A review

A model is presented for the increase in magnetoelectric (ME) coupling in magnetostrictive-piezoelectric bilayers in the electromechanical resonance region. The ME voltage coefficients α_E have been estimated for transverse field orientations corresponding to minimum demagnetizing fields and maximum α_E. We solved the equation of medium motion taking into account the magnetostatic and elastostatic equations, constitutive equations, Hooke's law, and boundary conditions. The resonance enhancement of ME voltage coefficient for the bilayer is obtained at antiresonance frequency. To obtain the inverse ME effect, a pick up coil wound around the sample is used to measure the ME voltage due to the change in the magnetic induction in magnetostrictive phase. The measured static magnetic field dependence of ME voltage has been attributed to the variation in the piezomagnetic coefficient for magnetic layer. The frequency dependence of the ME voltage shows a resonance character due to the longitudinal acoustic modes in piezoelectric layer. The model is applied to specific cases of cobalt ferrite–lead zirconate titanate and nickel–lead zirconate titanate bilayers. Theoretical ME voltage coefficients versus frequency profiles are in agreement with data.     

Specific features of the thermal electromotive force in Bi quantum wires in transverse magnetic and electric fields

The thermal electromotive force (emf) in Bi quantum wires has been calculated in the model of potential in the form of a paraboloid of revolution in a uniform magnetic field H, which is normal to the axis of the studied nanostructure, and in a direct-current (dc) electric field E ‖ H. It has been shown that, with an increase in E, the thermal emf α _xx is described by a nonmonotonic function at different values of H. A physical interpretation of this behavior of α _xx as a function of E is proposed with account for the interaction between carriers and the rough surface of the nanowire.     

Dispersion characteristics for low-frequency magnetoelectric coefficients in bulk ferrite-piezoelectric composites

Ferrite-piezoelectric composites are magnetoelectric (ME) due to the interaction between magnetic and electrical subsystems through mechanical forces. A theory for the low-frequency Maxwell-Wagner relaxation in ME coefficients is discussed for bulk composites of nickel or cobalt ferrite and lead zirconate titanate (PZT). ME coefficients versus frequency spectra show two types of relaxation, over 0.1-100 μHz and 1-1000 Hz. The relaxation frequencies and the magnitude of the ME coefficients are dependent on the electrical and composite parameters and volume fraction for the two phases. The ME coefficient α_E is in the range 10⁻¹-10⁴ mV/cm Oe, higher in cobalt ferrite-PZT than for nickel ferrite-PZT, and is strongly dependent on PZT volume fraction v. Estimates of α_E and relaxation frequencies versus v provided here are useful for engineering composites with maximum ME effects for specific frequency bands.     

Multiparameter study of 1H, 3H and 4He in fast neutron induced fission of 235U

The emission probabilities per fission of α-particles, tritons and protons have been measured in fast neutron induced fission of ²³⁵U. The measurements were carried out at neutron energies of 120, 180, 230 and 550 keV. AΔE-E semiconductor detector telescope was used to identify different light charged particles and the fission fragments were detected with an ionization chamber. The three-parameter data corresponding to the pulse heights from the ΔE-E detectors and the ion-chamber were recorded event by event on magnetic tape and were analyzed off-line by computer. No significant variation in the most probable energy ($\text{E}$) and the standard deviation (σ_E) of the energy spectra of different light charged particles with incident neutron energy was observed, although $\text{E}{}_{\mathrm{\alpha }}$ was seen to have a slightly higher value beyond E_n = 230 keV. The yield of α-particles in fission induced by neutrons of E_n ～ 200 keV was found to be higher by about 20 % than that in thermal neutron induced fission. The yields of tritons and protons were found to increase significantly with neutron energy.     

Single- and double-electron charge transfer in collisions of α-particles with hydrogen molecules. II

Dependences of single-electron charge transfer cross sections on the molecule orientation are studied in collisions between α-particles and H₂ molecules in the ground state at collision energies E _c from 1 to 23 keV/u. Probabilities of single-electron capture were calculated in the independent electron approximation in the context of the close coupling equation method under the assumption that the hydrogen molecule consists of two independent hydrogen pseudoatoms. The total and partial single-electron capture cross sections averaged over all orientations of the molecule well agree with available experimental data at E _c > 5 keV/u.     

平面阻塞效应测量Ep=1565keV时27Al(p,α)24Mg共振反应寿命

采用(111)面阻塞效应测量了E_p=1565keV共振时²⁷Al(p,α)²⁴Mg核反应寿命。用解析方法分析实验数据。测到的核寿命τ=17.9_-4.0^+4.4as,与<110>轴阻塞效应测量结果和文献给出的结果在误差范围内一致。测量了E_p=1183.4keV时(111)面的α粒子的阻塞分布,并与理论计算作了比较。 关键词：