磁性纳米复合材料的可调控宽带微波吸收机制研究

Recently, much attention has been paid to magnetic nanocompistes as microwave absorbers due to their high resistivity, low density, adjustable electromagnetic parameters and special interactions between magnetic nanoparticles and microwaves. At present, from the fundmental research and application point of view, adjusting and broadening the microwave absorption band are the main problems for such nanocomposites as microwave absorbers. The location and bandwidth of absorption band of magnetic nanocomposties is closely related to the resonance frequency and complex permeability, both of which, based on the ferromagnetic theory, can be changed by changing the composition and shape of the magnetic particles. So the absorption band can be adjusted indirectly by changing the composition and shape of the magnetic particles. Compared to the methods mentioned above, however, this project will take another different ways to adjust the absorption band. For the adjustment of the resonance frequency, the effective anisotropy of magnetic nanoparticles is changed by changing their surface anisotropy through the change of the particle size. For the change of the values of the complex permeability, a new magnetic loss will be introduced in GHz frequency band by changing the particle size. Based on the above results, this project is focused on the study of the magnetic nanocomposite absorbers with controllable and broadband microwave absorption band. From the fundamental research point of view, this project provides a novel way to adjust the absorption band. And in terms of the military and civil application, this project will facilitate the development of the broadband microwave absorbers.

磁性纳米复合材料，由于磁性纳米颗粒对微波的特殊吸收作用及具有高的电阻率、低的密度、电磁参数灵活可调等优点，近年来成为吸波材料领域研究的热点。目前，如何有效的调控和扩展吸收频带是这类材料在实际应用和研究中需要解决的重要问题。吸收频带的位置和带宽与共振频率和磁导率相关。根据铁磁性理论，改变磁性颗粒的成分和形状可改变其共振频率和磁导率，从而可对吸收频带进行调控和扩展。与传统理论不同，本项目将从"磁性纳米颗粒的尺寸变化将引起其表面各向异性和共振机制的改变"入手，通过改变颗粒尺寸，改变表面各向异性和有效各向异性，调控共振频率；通过研究颗粒尺寸变化引起的共振机制变化对磁谱的影响，调控磁导率。在此基础上研究磁性纳米复合材料的可调控宽带微波吸收机制，并最终获得频带可调的宽带吸波材料。宽带吸波材料的研发在基础研究，国防和民用技术方面都具有重要意义。本项目的实施将为其设计开发提供新的思路、理论指导和科学依据。

微波吸收材料在国防和民用领域中具有重要应用。目前，吸收频带的调控和扩展是微波吸收材料研发中的重点。在本项目中，我们研究了铁磁性金属/氧化物纳米复合材料中磁性金属纳米颗粒的尺寸对其吸收频带的位置和带宽的影响。研究结果表明通过改变复合材料中磁性金属纳米颗粒的尺寸可实现此类纳米复合材料的可调控宽带微波吸收。主要研究结果如下：（1）在铁磁性金属/氧化物纳米复合材料中，当磁性金属纳米颗粒的尺寸小于交换共振发生的理论临界尺寸时，可在自然共振的基础上引入交换共振，从而使磁性纳米复合材料的磁损耗共振峰在微波段得到有效拓展。（2）铁磁性金属纳米颗粒的尺寸对磁性纳米复合材料磁导率和共振频率的影响规律为随颗粒尺寸增加，磁导率数值增加，自然共振频率和交换共振频率向低频移动。（3）磁性纳米复合材料的阻抗匹配机制为几何效应匹配，因此随颗粒尺寸的增加，共振频率的降低和磁导率数值的增加将使其微波吸收频带向低频移动。（4）得益于磁损耗共振峰的拓展，当磁性纳米复合材料的磁导率数值随颗粒尺寸的增加而增大时，其磁导率虚部可在宽的频率范围内保持较高的数值。反射损耗曲线计算表明这不仅降低了磁性纳米复合材料作为微波吸收剂使用时的厚度，而且也使其电磁参数在宽的频率范围内接近阻抗匹配条件，因此有效地扩展了磁性纳米复合材料的吸收带宽，使其表现出优异的宽带微波吸收性能。在本项目中“通过改变磁性纳米颗粒的尺寸调控共振频率和磁导率”是一种新颖的调控方式，扩充了现有的以改变颗粒的形状和成分为主的调控手段。“通过改变磁性纳米颗粒的尺寸调控吸收频带的位置和带宽”也为磁性宽带微波吸收材料的设计开发提供了一种新的思路，理论依据和科学指导。