Abstract

The paper reports on the frequency (f) and static magnetic field (H) dependencies of the microwave propagation parameters, in the ranges 0.1–6 GHz and 0–90.7 kA/m, of a kerosene-based ferrofluid with magnetite particles, filtered in magnetic field gradient. In the investigated range, the sample exhibits ferromagnetic resonance phenomenon and Maxwell–Wagner dielectric relaxation. Unlike the usual way of studying the propagation of microwaves through different media, in this paper we have defined an overall reflection coefficient, Rw(f, H), of a material with thickness, w, deposited on a total reflective support, which takes into account both the attenuation of wave within the material and the reflection at the air–material interface. Based on the measured relative magnetic permeability, \(\mu _{r}\), and relative dielectric permittivity, \(\varepsilon _{r}\), a comprehensive and meaningful set of microwave propagation parameters are determined. Apart from Rw(f, H), this set of parameters of ferrofluid includes the attenuation constant of the electromagnetic wave, \(\alpha \)(f, H), the phase constant \(\beta \)(f, H), the real, n’(f, H), and imaginary, n”(f, H), components of the refractive index, the reflection coefficient at the interface air–material, R(f, H), and the quarter wavelength in material, \(\lambda _{\textit{1/4}}\)(f, H). Based on the theoretical considerations and characteristics of ferrofluid, simplified and practical formulas of the propagation parameters are given and also possible applications of the results are suggested (such as electromagnetic absorber, phase shifter, microwave lenses and vibration sensor). This connection between theory and experimental results offers an example for the preliminary design of microwave applications of ferrofluids and, by extension, for any material consisting of magnetic nanoparticles dispersed in a dielectric matrix.

Graphic abstract

中文翻译：

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磁流体中微波传播参数的磁调谐

摘要

该论文报告了微波传播参数的频率 ( f ) 和静磁场 ( H ) 相关性，范围为 0.1-6 GHz 和 0-90.7 kA/m，基于煤油的磁铁矿颗粒铁磁流体，过滤后磁场梯度。在研究范围内，样品表现出铁磁共振现象和麦克斯韦-瓦格纳介电弛豫。与研究微波通过不同介质传播的常用方法不同，在本文中，我们定义了厚度为w的材料的总反射系数Rw(f, H)，沉积在全反射支撑上，它考虑了材料内的波衰减和空气-材料界面处的反射。基于测得的相对磁导率\(\mu _{r}\)和相对介电常数\(\varepsilon _{r}\)，确定了一组全面且有意义的微波传播参数。除了Rw(f, H) 之外，这组铁磁流体的参数还包括电磁波的衰减常数\(\alpha \) (f, H)，相位常数\(\beta \) (f, H)，实数n'(f, H)和虚数n”(f, H)，折射率的分量，空气-材料界面处的反射系数R(f, H)和材料中的四分之一波长\(\lambda _{\textit{1/4}}\) (f, H）。基于铁磁流体的理论考虑和特性，给出了传播参数的简化和实用公式，并建议了结果的可能应用（如电磁吸波器、移相器、微波透镜和振动传感器）。理论和实验结果之间的这种联系为铁磁流体的微波应用的初步设计提供了一个例子，进而为由分散在介电基质中的磁性纳米粒子组成的任何材料提供了一个例子。

图形摘要