薄膜磁电复合材料磁-力-电耦合的非线性动力学行为研究

Magnetoelectric (ME) composite thin film is a new type of magnetic sensitive functional composites, which can achieve the energy transformation between magnetic energy and electric energy. It has a promising application in smart structures and miniature devices. The ME effect of ME composite thin film is a multi-field coupling problem, which involves magnetic field, electric field and mechanical field. However, there is only a few researches focus on this kind of ME composites, and dynamic problems are still not solved well so far. Based on thermodynamics, many factors are taken into account in this project, such as the nonlinear characteristics of materials, surface effect and the multi-field couplings, then the expression of total free energy of ME composite thin film will be obtained. On that basis, by solving the dynamic equations, associating with the electrical and mechanical boundary conditions, and a multi-field coupled nonlinear dynamic model for the ME composite thin film will be built. Besides, the corresponding numerical simulation program is designed in this work. Then the distribution characteristics of the stress field, the magnetic field and the electric field will be studied at static and resonant conditions. And the influences of the nonlinear characteristics of materials, surface effect and geometric parameters on the ME effect of ME composite thin film will be analyzed quantitatively. Finally, some special ME structures will be fabricated to achieve a higher ME coefficient and a wider bandwidth, thus ME devices can be operated well in a wider frequency range.

薄膜磁电复合材料是一类新型磁敏感功能复合材料，能够实现磁能和电能之间的相互转换，在微型智能结构与器件中有广泛应用前景。薄膜磁电复合材料的磁电效应是一个涉及了磁场、电场以及弹性场的多场耦合问题，其非线性动力学问题的研究尚不完善。基于此，本项目拟从热力学角度出发，通过考虑组分材料的非线性特性、表面效应、多场耦合等因素，建立薄膜磁电复合材料的自由能范式。在此基础上，结合动力学方程以及力学、电学边界条件，建立薄膜磁电复合材料磁-力-电耦合的非线性动力学模型。并设计与之相对应的数值仿真程序，研究静态及谐振情况下薄膜磁电复合材料的应力场、极化电场、磁场分布特性，定量揭示材料非线性特性、表面效应、几何参数等因素对薄膜磁电复合材料磁电效应的影响规律。对薄膜磁电复合材料进行一些结构设计，使其具有较高的磁电系数，较宽的谐振域，从而实现磁电器件在更宽的响应频率范围内工作。

在充分考虑了组分材料的非线性特性，采用能够反映铁电、铁磁材料微观畴变特性的非线性本构方程，结合相应的力学、电学边界条件，建立了薄膜磁电复合材料的非线性正、逆磁电效应的理论模型，分析预测了薄膜磁电复合材料在不同温度、不同预压力、不同磁场等复杂环境下的磁电性能。同时考虑到偏磁场对层状磁电复合材料磁电效应的影响，理论分析了高磁导率材料的加入对其磁电性能的影响，通过对其磁场、电场、应力场的详细分析，揭示功能梯度磁电复合材料自偏磁电产生的主要原因。考虑到铁电材料中极化强度会随时间和位置的变化，将极化强度作为铁电材料的序参数，建立了铁电材料的自由能范式，并基于相场理论，详细分析了外加电场频率变化时，铁电材料的内部电畴变化过程，同时也分析了极化强度随时间的变化规律，建立了外电场作用下铁电材料的微观畴变与宏观电学参量之间的关系。以上理论研究为包含磁电复合材料的相关智能器件在复杂环境下的多物理场分析，提供一种可靠、方便、快捷的理论计算模型。在理论分析的基础上，考虑到界面性能对磁电系数有很大的影响，设计并制备了两类新型功能磁电结构，类X型和类A型磁电结构，通过测试发现，该类新型磁电结构的磁电系数高于传统层状磁电结构，而且在一个较宽的频率域中都保持较高的磁电转化系数，该类磁电结构在宽频磁电器件中具有潜在的应用价值。