FeGa/BTO/FeGa层状复合结构中的磁电效应

采用区域熔炼法制备了FeGa磁致伸缩材料并测量了其磁致伸缩性能.利用该材料制备了FeGa/BTO/FeGa层状复合结构,并对该样品的磁电性能进行了系统研究.结果表明,该材料在共振频率95kHz下,磁电性能高于低频下性能7～10倍.磁电电压随直流偏磁场的变化发生明显变化,出现5.97×104A/m的优化偏置场,这主要是由FeGa层的压磁系数q随偏磁场的变化所致.3层复合材料的磁电系数与交流驱动场变化呈线性关系.另外,较薄的BTO压电层可以提高压应力,从而获得较高的磁电性能.     

压电-磁致伸缩双层磁电复合材料的机电谐振

基于压电相和磁致伸缩相的本构方程以及弹性体的运动方程,简要推导了一维机电谐振模式下压电-磁致伸缩双层磁电复合材料横向磁电电压系数的表达式。采用相应的材料参数计算分析了Tb_1-x Dy_x Fe_2-y (TDF)-Pb(Zr,Ti)O₃(PZT)双层磁电复合材料的横向磁电电压系数与交流磁场频率的关系,以及复合材料的长度和压电相体积分数对机电谐振频率的影响。计算与分析结果表明,双层磁电复合材料在机电谐振频率处具有明显的磁电 响应特性。当有效机械品质因数为50,在谐振频率55.2 kHz处横向磁电电压系数达到峰值11.2 V·cm^-1·Oe^-1,是低频下峰值(281.9 mV·cm^-1·Oe^-1)的40倍。机电谐振频率随复合材料长度的减小和压电相体积分数的增加而上升。实验结果说明TDF-PZT双层磁电复合材料在机电谐振频率处具有显著增强的磁电效应,实际有效机械品质因数约为48。     

层状复合材料磁电效应的数值分析

压电与压磁(或磁致伸缩)层合板具有大的乘积效应磁电效应。本文采用有限元分析方法对压电/压磁层合板的磁电转换进行了计算,结果表明:外磁场方向对磁电转换效应有很大的影响,在层合板上下两面增加约束可以大大提高层合板的磁电转化效应;感生电压值随压磁/压电板厚比的增加而增加,而整个层合板的电场强度值在板厚比为1时达到最大。     

树脂基稀土-铁系超磁致伸缩复合材料的磁致伸缩及其高频磁性能

以粉末粘结、模压成型方法,研制了0-3型的E-44环氧树脂基稀土-铁系超磁致伸缩复合材料。采用电阻应变片技术与Agilent 4294A型动态阻抗分析仪,研究了超磁致伸缩合金/环氧树脂复合材料的磁致伸缩性能及高频磁性能,并对所制备的磁致伸缩复合材料的磁导率、截止使用频率等随频率和树脂体积分数的变化规律进行了系统研究。结果表明:树脂的添加,不仅可以提高复合材料的截止频率和高频磁性能,使其具有良好的高频响应特性,其截止频率达30 MHz以上;而且通过适当选择树脂的体积分数,复合材料仍能保持良好的磁致伸缩性能,当树脂体积分数分别为20%、30%时,磁致伸缩系数分别达808×10-6、821×10-6,而当复合材料中树脂的体积分数为50%时,其磁致伸缩系数仍高达592×10-6。探讨了树脂/磁致伸缩复合材料的磁电耦合机制。      

磁电复合材料PMN-PT/Terfenol-D/PMN-PT磁电耦合性能的有限元分析

由铁电相和铁磁相组成的磁电复合材料被证明有非常显著的磁电耦合效应,近年来受到越来越多的关注。利用有限元PDE的方法对磁电复合材料PMN-PT/Terfenol-D/PMN-PT的磁电耦合性能进行了分析,主要研究了边界条件、结构尺寸对磁电耦合性能的影响。研究发现,当上下表面y方向固定,其它表面自由时,磁电复合材料长度方向伸缩更加明显,具有更大的磁电耦合系数;铁电相和铁磁相厚度比与磁电耦合系数程非线性关系,当铁电相厚度为1.1mm,铁磁相厚度为1.9mm时,磁电耦合系数具有最大值3.354((V/m)/A/m));当铁电层尺寸保持不变,铁磁层长度超过10mm后,铁磁层长度对磁电耦合系数影响不明显。该理论结果可以用于提高磁电耦合性能同时达到节省材料的目的。     

Fe3O4-PDMS纳米复合材料磁电阻特性及变化模型的研究

主要研究了复合材料磁电阻特性,提出了复合材料的制备方法,并测量了材料形貌、磁化特性、磁电阻随磁场的变化特性。结果表明,复合材料在环境磁场中能够产生磁电阻效应,其磁电阻特性受材料中分散的纳米颗粒的磁化特性所影响,并且复合材料磁电阻随着材料中纳米颗粒的分散浓度的增大而增大。根据磁场环境下复合材料中纳米颗粒之间沿磁场方向的相互作用以及聚合物材料的粘弹性,重点分析了该复合材料的磁电阻变化机理并提出了复合材料的磁电阻变化模型。随后,利用纳米颗粒的磁化数据以及PDMS的动力学参数进行了复合材料磁电阻变化特性的数值仿真,并将仿真数据与实测数据进行对比,对比结果显示该模型能够准确描述复合材料的磁电阻变化特性。     

Terfenol-D颗粒取向对树脂基磁致伸缩复合材料性能的影响

已有的研究表明,在树脂基磁致伸缩复合材料固化过程中,施加一定的磁场使Terfenol-D颗粒沿磁场方向取向排列可以形成伪1-3型复合结构,其静态磁致伸缩性能较颗粒随机取向的0～3型复合材料有一定程度的提高。本文旨在研究颗粒取向对磁致伸缩复合材料其它性能的影响。以Terfenol—D颗粒体积含量为50％的0-3型和1-3型环氧基磁致伸缩复合材料为研究对象,通过实验和计算对比两种材料的动静态磁致伸缩性能、增量磁导率、弹性模量、磁机械耦合系数。结果表明．颗粒取向不仅可以提高树脂基磁致伸缩复合材料的静态磁致伸缩性能和动态磁致伸缩性能,还能略微提高其弹性模量,但会适度降低其磁机械耦合系数。     

超声作用下树脂基磁致伸缩复合材料的制备及其性能

树脂基磁致伸缩复合材料是由Terfenol-D颗粒分散在树脂基体内形成的一类复合材料,颗粒的分散均匀性以及颗粒与基体界面的粘结紧密性是影响其性能的两个重要因素.由于颗粒与基体润湿性差,机械搅拌制备的磁致伸缩复合材料,普遍存在分散不均,孔隙率高等缺点.高强度超声在液态树脂中传播时,会产生空化、声流等非线性声学效应,对促进颗粒分散和改善固液界面具有一定的作用.以环氧树脂为基体,分别采用机械搅拌法和高能超声法制备了Terfenol-D颗粒体积含量为50%的树脂基磁致伸缩复合材料.对两种材料进行了SEM分析及力学和磁致伸缩性能测试.实验结果表明,较之机械搅拌法,超声分散法制得的磁致伸缩复合材料具有颗粒分散均匀,孔隙率低,颗粒与基体的界面结合性好,弹性模量高,磁致伸缩应变大等优点.     

Tb1-xDyxFe2-y-BaTi0.99Mn0.01O3+δ层状复合材料的低频磁电耦合

利用弹性力学模型,推导了低频下磁致伸缩-压电双层复合材料中磁电电压系数的表达式,计算了Tb_1-x Dy_x-Fe_2-y-BaTiO₃层状复合材料中的横向磁电耦合。采用溶胶-凝胶法制备1.0%（摩尔分数）Mn掺杂BaTiO₃（BaTi_0.99Mn_0.01O_3+δ）压电陶瓷片。将Mn掺杂BaTiO₃与Tb_1-xDy_xFe_2-y 胶合制成双层和三层复合材料,研究了复合材料在低频下的横向磁电效应。XRD和DSC分析结果表明,室温下Mn掺杂BaTiO₃保持了其四方钙钛矿结构,降低了BaTiO₃的居里点和相变潜热。在约33 kA/m偏置磁场下,Tb_1-xDy_xFe_2-y-BaTi_0.99Mn_0.01O_3+δ 和Tb_1-xDy_xFe_2-y-BaTi_0.99Mn_0.01O_3+δ-Tb_1-xDy_xFe_2-y 的横向磁电耦合峰值分别为529.4 mV/A和1659.5 mV/A,分别是Tb_1-xDy_xFe_2-y-BaTiO₃和Tb_1-xDy_xFe_2-y-BaTiO₃-Tb_1-xDy_xFe_2-y 的1.48和1.45倍。三层复合材料的横向磁电电压系数约是同类双层的3倍多。     

磁致伸缩复合材料性能的影响因素分析

首先由退磁场效应分析得到有效磁场强度与外磁场强度的关系,继而根据复合材料细观力学中的Eshelby等效夹杂理论和Mori-Tanaka方法导出了颗粒磁场伸缩应变与复合材料磁致伸缩应变的关系,结合Terfenol-D颗粒磁致应变及弹性模量与有效磁场强度的关系,最终预测了环氧基Terfenol-D复合材料磁致应变及有效弹性模量与外磁场强度的关系,并分析了颗粒含量、形状及基体弹模对复合材料饱和磁致伸缩系数及弹性模量的影响.结果表明,磁致伸缩复合材料的饱和磁致伸缩应变随颗粒含量、纵横比增大而增大,随基体弹模增大而减小;有效弹性模量随颗粒含量、颗粒纵横比、基体弹模的增大而增大;颗粒的纵横比越大、含量越大,复合材料的饱和磁场强度越小,磁致伸缩应变随磁场强度的变化越快;复合材料的有效弹性模量亦随磁场强度的增大而增大,其影响程度在颗粒体积含量和颗粒纵横比较大时尤为显著.     

Post-curing effect on magnetoelectric performance of single PZT rod/continuous Terfenol-D fiber/epoxy 1-1-3 composites

A magnetoelectric (ME) composite consisting of a single PZT rod embedded in a matrix of continuous Terfenol-D fiber and epoxy medium has been fabricated and characterized. With an optimized aspect ratio of the composite rods, a large ME effect has been observed. The magnetostrictive effect of the continuous Terfenol-D fiber/epoxy medium can be enhanced by imposing an optimal pre-loading stress on the material and this pre-loading stress can be induced by suitable heat treatment. Experimental results show that the ME effect of the single PZT rod/continuous Terfenol-D fiber/epoxy composites can be enhanced significantly by a post-curing process. A thermal stress-mediated continuous fiber composite model has been used to explain the ME enhancement of the post-cured composites.     

A 64-kHz sandwich transducer fabricated using pseudo 1-3 magnetostrictive composite

A 64-kHz sandwich transducer employing a tube-shaped Terfenol-D/epoxy pseudo 1-3 magnetostrictive composite with 0.61 Terfenol-D volume fraction was developed to alleviate the intrinsic eddy-current losses in magnetostrictive alloy-based transducers. The transducer was designed to operate as a half-wave, longitudinal, mass-spring-mass, linear vibrator. It had a length of 15.7 mm and consisted of a magnetic circuit and a prestress mechanism. The magnetic circuit was composed of the composite tube, a pair of ring-shaped NdFeB permanent magnets, a drive solenoid, and a Ni-based magnetic flux guide. The distributions of the dc magnetic flux lines and magnetic field strength of the transducer were determined using an ANSYS finite-element model. The dynamic performance of the transducer was evaluated by measuring its electrical and vibrational characteristics. The results revealed that the transducer resonates at a frequency of 64.3 kHz with a strain coefficient of 39.2 nm/A, a mechanical quality factor of 39.6, and an effective coupling coefficient of 0.21. Eddy-current losses in the transducer were insignificant in the measured frequency range of 40 Hz-100 kHz. The good transducer performance indicated that Terfenol-D/epoxy pseudo 1-3 composites would be a promising magnetostrictive material for ultrasonic applications.     

Magnetoelectric coupling of Terfenol-D/P(VDF-TrFe)/Terfenol-D laminates mediated by crystallite size of electroactive polymer

The attention here is focused on the magnetoelectric (ME) coupling in Terfenol-D/P(VDF-TrFE)/Terfenol-D laminated composites. The electroactive P(VDF-TrFE) 75/25mol% copolymer films were prepared using three different annealing conditions: 135°C for 2h , 6h and 140°C for 2h. The results show that the laminate with the copolymer film annealed at 135°C for 2h exhibits the highest ME coupling, while the one with the copolymer film annealed at 140°C for 2h shows the lowest. Microstructure examination demonstrates that the crystallites grow significantly in size with either the annealing time or the temperature although the crystallinity increases slightly. It is suggested that the copolymer film with smaller crystallite size, or higher volume fraction of the amorphous/crystallite interfacial layers, is beneficial to the piezoelectric effect and consequently the ME coupling of the laminated composites.     

用于磁传感器的新结构磁电复合材料

研究了可用于磁场传感器的磁电复合材料, 对传统的磁电复合材料进行了结构创新, 采用条状PZT和 Terfenol-D 的材料体系, 用热固树脂进行粘合, Terfenol-D 沿长度方向磁化且PZT条沿厚度方向极化。与传统的1-3型复合不同的是: 每根PZT的输出极被串联起来。在同样的磁场激励下, 新型复合材料的输出电压为相同体积的同种结构复合材料的2.2倍, 增强了材料对磁场的灵敏度和抗噪声性能。      

An analytical nonlinear model for laminate multiferroic composites reproducing the DC magnetic bias dependent magnetoelectric properties

In this work, we propose an analytical nonlinear model for laminate multiferroic composites in which the magnetic-field-induced strain in magnetostrictive phase is described by a standard square law taking the stress effect into account, whereas the ferroelectric phase retains a linear piezoelectric response. Furthermore, differing from previous models which assume uniform deformation, we take into account the stress attenuation and adopt non-uniform deformation along the layer thickness in both piezoelectric and magnetostrictive phases. Analysis of this model on L-T and L-L modes of sandwiched Terfenol-D/lead zirconate titanate/Terfenol-D composites can well reproduce the observed dc magnetic field (H(dc)) dependent magnetoelectric coefficients, which reach their maximum with the H(dc) all at about 500 Oe. The model also suggests that stress attenuation along the layer thickness in practical composites should be taken into account. Furthermore, the model also indicates that a high volume fraction of magnetostrictive phase is required to get giant magnetoelectric coupling, coinciding with existing models.     

Longitudinal and transverse magnetoelectric voltage coefficients of magnetostrictive/piezoelectric laminate composite: theory

This paper presents a novel, long-type of magnetostrictive and piezoelectric laminate composite design in which the layers are, respectively, magnetized/poled along their length axes, and a theory for modeling its behavior. Using piezoelectric and magnetostrictive constitutive equations, and an equation of motion, a magneto-elasto-electric bieffect equivalent circuit is developed. The circuit is used to predict the longitudinal and transverse magnetoelectric (ME) voltage coefficients of our Terfenol-D/Pb(Zr/sub 1-x/Ti/sub x/)O/sub 3/ laminate design. It is found that the longitudinal ME voltage coefficient is significantly higher (/spl sim/5x) than the transverse one, and that our new laminate design has significantly higher ME voltage coefficients under small applied direct current (DC) magnetic bias fields than designs reported previously by other groups. Experimental values were found to be coincidental with predicted ones.     

Colossal magnetodielectric effect caused by magnetoelectric effect under low magnetic field

The colossal magnetodielectric effect is reported in Pb(Zr,Ti)O₃/Terfenol-D laminate composite under low magnetic field. When the composite is placed in an external a.c. magnetic field, magnetoelectric effect is produced, as a result, the dielectric properties of the Pb(Zr,Ti)O₃ is changed, i.e. magnetodielectric effect. Both the amplitude and resonance frequency change with the external magnetic field. The colossal magnetodielectric coefficient of 5 × 10⁴% at low magnetic field of 20 Oe is achieved near the electromechanical resonance frequency.     

Design of magnetostrictive/piezoelectric laminate composite for coil-less magnetic force control

We propose a magnetic force control device consisting of laminate composites of magnetostrictive material and piezoelectric material. The magnetic force control is based on energy conversion in the composite, such that the variation of magnetization of the magnetostrictive material induced by the piezoelectric material is converted to the variation of magnetic force by magnetic circuits. Because of the capacitive property of the piezoelectric material, the device requires little current in order to maintain control of a constant force. The laminate composite can be fabricated easily and in small sizes. In this paper, we report the magnetic force control properties of a composite of Terfenol-D and piezoelectric material plates (PZTs) and discuss the design of the laminate composite. Our theoretical magnetic force formulation derived by an equivalent magnetic analysis and finite-element analysis of strain distribution in the Terfenol-D, and measurements with various thicknesses of PZT demonstrated that there are appropriate thicknesses to provide large variation of the magnetic force and energy conversion efficiency. Stacking the composites was found effective for increasing the effective area of the Terfenol-D.     

A theoretical study of nonlinear magnetoelectric effect in magnetostrictive–piezoelectric trilayer

A novel nonlinear theoretical model is established for magnetoelectric (ME) effect in trilayer of magnetostrictive and piezoelectric phases, in which the nonlinear magnetic–mechanical coupling behavior for the magnetostrictive phase is firstly taken into account. In this theoretical model, the interface coupling parameter k is used for characterizing actual bonding conditions at the interface. The coupled magnetic–mechanical–electric effect involving linear and nonlinear coupling interactions in the ME laminated composites is numerically simulated using this nonlinear model. The numerical results predict giant ME effect for Terfenol-D based ME laminated composites. The quantitative dependences of the giant ME effect on the applied magnetic field, the piezoelectric property of piezoelectric phase, the volume fraction of magnetostrictive phase and the interface coupling parameter k are discussed in details. All of these dependences indicate that the nonlinear theoretical model established in this article can accurately capture nonlinear magnetic–mechanical–electric coupling behavior for Terfenol-D based ME laminated composites. The giant ME effect predicted for the Terfenol-D/PMN-PT/Terfenol-D composites is in excellent agreement with recent experimental data available. It confirms the validity and reliability of the obtained nonlinear theoretical model, and demonstrates the significance and necessity of considering the nonlinear magnetic–mechanical coupling behavior of Terfenol-D.     

Resonant Magnetoelectric Effect with Strongly Nonlinear Magneto-Elastic Coupling in Magnetoelectric Laminate Composites

Considering the complex strongly nonlinear coupling characteristic of the magnetostrictive strain and magnetization under the excitation of the bias magnetic field and the pre-stress in the giant magnetostrictive material, this paper adopts the nonlinear magnetostrictive constitutive model and the equivalent circuit method to establish a strongly nonlinear resonant magnetoelectric (ME) effect theoretical model for the ME laminate composites compounding by the giant magnetostrictive material and the piezoelectric material. For the L-T mode magnetostrictive/piezoelectric/magnetostrictive (MPM) ME laminate, the predicted results coincide well with the experiment results of the resonant frequency and the resonant ME field coefficient varying with the external magnetic field when the pre-stress degenerates to zero in our model. The agreement indicates the proposed theoretical model validity. On the basis, we use the theoretical model to forecast the varying characteristic of the resonant ME field coefficient and the resonant frequency effect under the influence of the different bias magnetic field and the pre-stress in ME laminate composites. And we also predict that the resonant ME coefficient and the resonant frequency appear "reversal" with the pre-stress increasing. After that, the influence of the different volume ratio on the ME effect and resonant frequency is analyzed. Particularly, a resonant frequency value not influenced by the volume ratio with increasing bias magnetic or pre-stress occurs. This research can provide theory basis for improving the resonant ME conversion performance and for controlling the resonant frequency under the excitation of the bias conditions (i.e. the bias magnetic field and the pre-stress) for the ME devices (i.e. sensor, transducer, microwave device and so on).