Fannin P C, Bunoiu O M, Malaescu I, Marin C N, Ursu D
Department of Electronic and Electrical Engineering, Trinity College, Dublin 2, Ireland.
Faculty of Physics, West University of Timisoara, V. Parvan Ave., no. 4, 300223, Timisoara, Romania.
Eur Phys J E Soft Matter. 2021 Jun 22;44(6):83. doi: 10.1140/epje/s10189-021-00087-w.
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, [Formula: see text], and relative dielectric permittivity, [Formula: see text], 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, [Formula: see text](f, H), the phase constant [Formula: see text](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, [Formula: see text](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.
本文报道了在0.1 - 6 GHz频率范围和0 - 90.7 kA/m静磁场强度（H）下，一种基于煤油的含磁铁矿颗粒的铁磁流体在磁场梯度中过滤后的微波传播参数对频率（f）和静磁场（H）的依赖性。在所研究的范围内，该样品呈现出铁磁共振现象和麦克斯韦 - 瓦格纳介电弛豫。与研究微波在不同介质中传播的常规方法不同，本文定义了一种沉积在全反射支撑体上、厚度为w的材料的总反射系数Rw(f, H)，它同时考虑了材料内部波的衰减以及空气 - 材料界面处的反射。基于所测量的相对磁导率[公式：见原文]和相对介电常数[公式：见原文]，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，这组铁磁流体参数还包括电磁波的衰减常数[公式：见原文](f, H)、相位常数[公式：见原文](f, H)、折射率的实部n'(f, H)和虚部n"(f, H)、空气 - 材料界面处的反射系数R(f, H)以及材料中的四分之一波长[公式：见原文](f, H)。基于对铁磁流体的理论考量和特性，给出了传播参数的简化实用公式，并提出了结果的可能应用（如电磁吸收器、移相器、微波透镜和振动传感器）。理论与实验结果之间的这种联系为铁磁流体微波应用的初步设计提供了一个示例，进而也为任何由分散在介电基质中的磁性纳米颗粒组成的材料提供了示例。
