Relative Complex Permeability Research Articles

Electromagnetic wave absorption properties of mechanically mixed Nd 2Fe 14B/C microparticles

Nd 2Fe 14B/C microparticles were prepared by a mechanical mixing technique using a weight ratio of 2:1. Paraffin-bonded Nd 2Fe 14B/C composites were fabricated using 40 wt% microparticles, and their electromagnetic wave absorption properties were studied and compared with those of the paraffin-bonded Nd 2Fe 14B composites in the 2–18 GHz frequency range and for 1–5 mm thickness. The Nd 2Fe 14B/C–paraffin composites exhibit dual dielectric resonance in complex relative permittivity ( ɛ r ) and essentially flat response in complex relative permeability ( μ r ) rather than showing an abrupt change in both ɛ r and μ r as in the Nd 2Fe 14B–paraffin composites. The results are ascribed to the increased electrical resistivity in the Nd 2Fe 14B/C-paraffin composites and the protection on the magnetic properties of the Nd 2Fe 14B microparticles at 2–18 GHz by the presence of the C phase. Large reflection loss (RL) exceeding −10 dB and an optimal RL of −13.2 dB are achieved in the Nd 2Fe 14B/C–paraffin composites from 9.6 to 18 GHz at a thickness of 1.4–2.6 mm and at 18 GHz at a thickness of 1.4 mm, respectively.

Evaluation of tailored magnetic composite films for near-field electromagnetic noise suppression

The effects of permeability and permittivity of the magnetic nanorods filled in composite films have been studied in the broadband radio-frequency range from 0.5 to 10 GHz on a microstrip line. The transmission power absorption of the composite film on a microstrip line was simulated using 3D FEM HFSS program. The model of microstrip line was designed based on IEC standard (IEC 62333-2). The permeability of composite film with magnetic nanorods could be controlled by the aspect ratio of nanorods. The ferromagnetic resonance frequency and the relative complex permeability with the change of aspect ratio were calculated by the Landau–Lifshitz–Gilbert equation. Given the bulk magnetization of 5 kG, the power loss frequency region has exhibited the 2.5–7 GHz broadband frequency by mixing of nanorods with various aspect ratios from 2 to 10. The permittivity effects have been evaluated by changing the real part of permittivity with a fixed imaginary part value and vice versa. The power losses were increased with the proportional to the imaginary part of permittivity and did not show any significant change with the increment of the real part of permittivity. The conduction electromagnetic noise in near field can be suppressed by controlling complex permeability with various aspect ratios of the magnetic nanorods in the composite.

Composite Electromagnetic Wave Absorber Made of Both Sendust and Aluminum Particles Dispersed in Polystyrene Resin

To design an electromagnetic wave absorber with good absorption properties at frequencies above 1 GHz, the frequency dependences of the relative complex permeability μr*, the relative complex permittivity εr*, and return loss were investigated for the composite made of both sendust (an alloy of Al 5%, Si 10%, and Fe 85%) and aluminum particles dispersed in polystyrene resin. It was found that the frequency dependence of μr* for this composite can be changed by adjusting the particle size of aluminum and the volume mixture ratio of sendust and aluminum. Therefore, a flexible design of an absorber with good absorption characteristics was proposed based on the ability to control μr*. The composite made of both sendust and aluminum was found to exhibit a return loss of less than −20 dB in the frequency range of not only several GHz but also around 20 GHz if appropriate volume mixture ratio and particle size were selected.

Directed Growth and Microwave Absorption Property of Crossed ZnO Netlike Micro-/Nanostructures

Three-dimensional ZnO micro/nanorod networks were synthesized through the direct evaporation of metal zinc and graphite powders in Ar and O2 at 910 °C without any catalyst. The micro/nanorod networks of as-synthesized ZnO were characterized by using scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The branches within one network show very regular cross orientation. The nanorods follow a growth direction [0001]. Mircrowave absorption properties of the ZnO netlike structures have been investigated in detail. The reflection loss (RL) of the netlike structures and nanotetrapod-shaped ZnO were calculated by using the relative complex permeability and permittivity. And the value of minimum RL for the composite with 50 vol % ZnO netlike structures is −37 dB at 6.2 GHz with a thickness of 4.0 mm. These results provide a wide insight for the netlike structure ZnO as desirable materials for the fabrication of micro/nanoscale functional electromagnetic shield devices.

Complex permittivity, permeability and wide band microwave absorbing property of La 3+ substituted U-type hexaferrite

Polycrystalline samples of U-type hexaferrite series: (Ba 1−3 x La 2 x ) 4Co 2Fe 36O 60 with 0.10≤ x≤0.20 in step of 0.05, are prepared by conventional solid state reaction route. Partial substitution of Ba 2+ ions with La 3+ ions enhances the electron hopping and reduces the magnetic interaction in the samples over the entire X-band frequencies; leading to wide band microwave absorption in all sample. Relative complex permittivity ( ε r = ε′− jε″) and permeability ( μ r = μ′− jμ″) of the prepared samples were measured using Vector Network Analyzer (VNA, Agilent PNA-L N5230A) for X-band (8.2–12.4 GHz) frequency range. The maximum absorption of 99.8% was obtained for x=0.10 sample for thickness t m =1.8 mm and all sample showed absorption ≥96%. The reflection loss ( R L ) calculated using the measured parameter (ε r = ε′− jε″ and μ r = μ′− jμ″) shows good agreement when compared with the return loss measured directly using VNA for sample x=0.20. The material can be expected to find relevance in suppression of electromagnetic interference (EMI) shielding and reduction of radar signatures.

Preparation and electromagnetic properties of multiwalled carbon nanotubes/Ni composites by γ-irradiation technique

Multiwalled carbon nanotubes (MWCNTs) were coated with Ni nanoparticles prepared from reduction of Ni 2+ by a γ-irradiation technique, producing MWCNTs/Ni composite. It was determined that surface modification of MWCNTs and generation of hydrophilic environment by γ-irradiation was crucial to the dispersion of metal nanoparticles on MWCNTs. The prepared MWCNTs/Ni composite was demonstrated to be a ferromagnetic material, and the relative complex permeability and permittivity were studied. It was calculated that after coating with Ni nanoparticles, the reflection loss properties of MWCNTs were greatly improved in the frequency range between 3.8 GHz and 18 GHz, with a maximum absorption of −7.2 dB at 6.4 GHz. Furthermore, the microwave absorbing properties could be modulated simply by manipulating the thickness of the prepared MWCNTs/Ni composite for application in different frequency bands.

Microwave Penetration Depth in Materials with Non-zero Magnetic Susceptibility

A simplified equation for determining the transverse electromagnetic mode (TEM) power penetration depth of microwaves in materials having both magnetic and dielectric response was derived. The penetration depths for a magnetite concentrate were calculated using this “full-response” equation, and a significant difference is shown compared with the penetration depth obtained using only the dielectric response (i.e., assuming no imaginary part of complex relative permeability). The temperature dependence of the power penetration depth, up to 1000°C, was determined using measured values of the real and imaginary parts of complex relative permittivity, εr′, εr″ and permeability, μr′, μr″. The accurate determination of penetration depths can help in optimizing the dimensions of a load in a microwave furnace, producing more uniform heating under microwave irradiation and avoiding thermal runaway.

Preparation and evaluation of composite electromagnetic wave absorbers made of aluminum fine particles dispersed in polystyrene medium

AbstractWe developed composite electromagnetic wave absorbers consisting of dispersed aluminum fine particles in a polystyrene medium and evaluated their properties in order to realize single‐layer electromagnetic wave absorbers with good absorption in the gigahertz region. Polystyrene particles with two diameters (approximately 200 μm and 1 μm) and fine aluminum particles were mixed by mechanical milling. The mixture was heated above the melting point of polystyrene and then cooled naturally in air. The frequency characteristics of the complex relative permeability and the complex relative permittivity were calculated from the values of the scattering parameters of a coaxial line loaded with a sample of a toroidal‐core shape. Both the diamagnetism and the magnetic loss increased in proportion to the volume mixing ratios of aluminum particles up to approximately 34 vol for samples made of polystyrene particles with approximately 200 μm or 1μm diameter. The diamagnetism was almost frequency‐independent and the magnetic loss decreased with increasing frequency for all samples. These results were in agreement with qualitative theoretical prediction. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 93(1): 30– 40, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10169

Effect of Sendust Particle Size on Absorption Characteristics of Composite Electromagnetic Wave Absorber

The effects of the particle size of sendust, which is an alloy of Al 5%, Si 10%, and Fe 85%, on the absorption characteristics of composite electromagnetic wave absorbers made of polystyrene resin and sendust were investigated in the frequency range from 1 to 40 GHz. The size of sendust particles was varied between approximately 5 and 20 m. A metal-backed single-layer absorber made of 20 m sendust particles absorbed more than 99% of electromagnetic wave power at frequencies above 20 GHz. Meanwhile, a composite made of 5 m particles exhibited a return loss of less than −20 dB in the frequency range of not only several GHz but also above 30 GHz. In addition, the relative complex permeability r* was shown to be controlled by adjusting the particle size of sendust, and an electromagnetic wave absorber with a flexible design was proposed.

A novel two‐port probe for complex permittivity and permeability measurement of liquid and powder type materials

AbstractIn this article, we propose a new method to measure the complex relative permittivity (εr = ε − jε) and permeability (μr = μ − jμ) of liquid‐ or powder‐type materials using a two‐port probe which is constructed from coaxial transmission lines. The two‐port probe is a simple structure that can be easily fabricated with low cost in comparison with conventional probes which are the type of the cavity and waveguide. And we have adopted the Cole–Cole equation and air‐filled coaxial cable for calibrating the proposed probe. To verify the performance of the proposed probe, we measured the properties of materials in the form of liquids and powders and compared the results with those measured by the air‐filled coaxial cable, which shows good agreement. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2977–2979, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24793

Composite electromagnetic wave absorber made of soft magnetic material and polystyrene resin and control of permeability and permittivity

The frequency dependences of the relative complex permeability μ r * , the relative complex permittivity ε r * and the absorption characteristics for composite electromagnetic wave absorbers made of polystyrene resin and sendust particles or permalloy particles were investigated in the frequency range from 1 to 40 GHz. The size of sendust particles was varied between approximately 5 and 20 μm and the particle size dependence of μ r * was observed. The value of μ r * was shown to be controlled by adjusting the particle size of sendust, and an electromagnetic wave absorber with a flexible design was proposed. A metal-backed single-layer absorber made of sendust particles or permalloy particles absorbed more than 99% of electromagnetic wave power at frequencies above 20 GHz. In addition, a composite made of 5 μm particles exhibited a return loss of less than −20 dB in the frequency range of not only several GHz but also above 30 GHz.

Broadband RF Noise Suppression by Magnetic Nanowire-Filled Composite Films

The characteristics of the electromagnetic noise suppression have evaluated using magnetic nanowire-filled composite film on a microstrip line in the broadband radio-frequency range from 0.5 to 20 GHz. The ferromagnetic resonance frequency and the relative complex permeability with the change of aspect ratio were calculated by Kittel's and Landau-Lifshitz-Gilbert equations. The FMR frequency is gradually increased with the increment of aspect ratio (up to 50) of magnetic nanowire. When the magnetic nanowires were mixed with various aspect ratio in composite, the FMR frequency exhibited the broadband frequency regions with 10-28 GHz, 5-14 GHz, 2.5-7 GHz, and 1-2.7 GHz for the change of magnetizations (4piMs: 20, 10, 5, and 2 kG), respectively. Using the calculated FMR frequency profile, the power losses were obtained in broadband frequency region. The transmission power absorption of the composite film on microstrip line was simulated using a 3-D FEM HFSS simulation program. The microstrip line model was composed of Cu conductor line and grounded dielectric substrates, which was designed by IEC standard (IEC 62333-2). The conduction electromagnetic noise was suppressed by the various aspect ratios of the magnetic nanowire-filled composite films in broadband frequency region.

2.4 GHz 무선LAN 전자파 환경대책용 전파흡수체 개발

본 논문에서는 실내 무선LAN 환경에서 발생하는 다중반사에 의한 통신속도 저하 및 데이터 손실과 같은 문제점을 해결하기 위한 전파흡수체를 설계하였다. 먼저 자성손실 재료인 Sendust와 지지재인 CPE(Chlorinated Polyethylene)조성비별 전파흡수체 샘플을 제작하였고, 각 샘플의 재료정수를 이용하여 시뮬레이션 한 결과, 최적의 조성비가 Sendust : CPE = 80 : 20 wt.% 임을 확인하였다. 그리고 시뮬레이션 결과를 토대로 전파흡수체를 실제작하였다. 제작된 전파흡수체의 측정 결과 시뮬레이션 결과와 잘 일치하였으며, 제작된 전파흡수체는 두께 3.2 5mm 조성비 Sendust : CPE = 80 20 wt.%이며, 중심주파수 2.4 GHz에서 19 dB의 전파흡수 특성을 보였다. In this paper, the EM wave absorber was designed and fabricated for improvement of Wireless LAN environment at 2.4 GHz. We fabricated several samples in different composition ratios of Sendust and CPE(Chlorinated Polyethylene). Absorption abilities were simulated in accordance with different thicknesses of the prepared absorbers and changed complex relative permittivity and permeability due to composition ratio. The mixing ratio of Sendust and CPE was searched as 80: 20 wt.% by experiments and simulation Then the EM wave absorber was fabricated and tested using the simulated data. As a result, the EM wave absorber was fabricated based on simulated data. Simulated and measured results agreed well. As a result, the developed EM wave absorber with thickness of 3.25 mm has absorption ability of 19 dB at 2.4 GHz.

Evaluation of composite electromagnetic wave absorber made of isolated Ni‐Zn ferrite or permalloy

AbstractIt has been found that if a composite material consists of a magnetic material isolated in a dielectric medium, the relative complex permeability of the composite material does not obey Lichtenecker's law, which is well known to explain the relative complex permeability and permittivity of composite materials. This characteristic leads to the absorption of electromagnetic wave power at frequencies above 1 GHz. We proposed an isolation model to simulate the frequency dependence of the relative complex permeability and developed a composite electromagnetic wave absorber made of ferrite–SiO2 or a permalloy–polystyrene system in which magnetic materials are isolated. The mechanical milling method was employed to isolate the magnetic material in the dielectric medium. Ni‐Zn ferrite particles could be isolated in the SiO2 medium and the measured values of the relative complex permeability were close to those calculated from the isolation model. Consequently, this absorber could absorb electromagnetic wave power in the frequency range from 1 to 3 GHz. Permalloy particles were also isolated in a polystyrene resin medium. The absorber made of permalloy and polystyrene resin exhibited good absorption characteristics in the frequency range between 3 and 8 GHz. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(5): 14–22, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10045

Synthesis and Microwave Absorption of the Silica-coated Fe Nanocomposites

采用非平衡物理气相蒸发法在氢气-氩气混合气氛下制备了氧化硅包覆铁“壳/核”型纳米复合粒子.通过X射线衍射（XRD）、透射电子显微镜（TEM）和能谱分析（EDS）等方法表征了纳米复合粒子的相组分、结构以及颗粒形貌.结果表明,制备的氧化硅包覆铁纳米复合粒子的尺寸在50nm左右,在铁纳米粒子的表面还出现了非晶态的氧化硅纳米棒,长度为150-200nm.利用电磁参数模拟微波吸收特性得出,涂层厚度为1.79mm时,在15.4GHz频率处达到最小反射损耗值为-14.5dB,反射损耗在8-18GHz的频段低于-10dB,且损耗机制为自然共振.

Complex Permittivity and Permeability of SiO2 and Fe3O4 Powders in Microwave Frequency Range between 0.2 and 13.5 GHz

The real and imaginary parts of relative complex permittivity (e′ and e″) and relative complex permeability (μ′ and μ″) were measured for powder and bulk SiO2 and Fe3O4 in the frequency range of 200 MHz–13.5 GHz. The e′ and e″ values of SiO2 powder samples are in good agreement with the previous data. The e′ values of powder SiO2 and Fe3O4 samples with the relative density below 1 are smaller than the values estimated using the linear relation between e′ and the relative density, and larger than those estimated using the Lichtenecker's logarithm mixed law. The μ″ values of powder Fe3O4 samples show the peaks in the frequency range of 706 MHz to 3.21 GHz. The frequency at the peak of the μ″ vs. frequency curve decreases with an increase in the particle size of Fe3O4 sample. All the powder samples with an identical relative density have almost the same μ″ values around 2 to 3 GHz irrespective of the particle size. Above ca. 3 GHz, the μ″ values of all samples become smaller as the measurement frequencies become higher. These results suggest that 2.45 GHz, the frequency of the most commercially prevailing microwave generators, may be the most suitable one for microwave heating of iron ores.

Design of Composite Electromagnetic Wave Absorber Made of Fine Aluminum Particles Dispersed in Polystyrene Resin by Controlling Permeability

The ability to control the relative complex permeability ⁄ of composites made of flne aluminum particles dispersed in polystyrene resin was investigated for the purpose of designing electromagnetic wave absorbers with good absorption properties at frequencies above 1GHz. The volume mixture ratio V and particle size of aluminum were varied and the frequency dependences of ⁄, the relative complex permittivity ⁄, and the return loss were measured. Theoretical values of ⁄ for the composites were also calculated using Maxwell's equations. The measured value of 0 , the real part of ⁄ , was found to decrease with increasing frequency in the low frequency range. However, at high frequencies, 0 was almost independent of frequency and decreased proportionately with V: In addition, the measured value of 00 was found to be proportional to V and inversely proportional to the aluminum particle size. These results showed good agreement with the calculated values of 0 and 00 . An electromagnetic wave absorber with a ∞exible design was proposed based on the ability to control 0 and 00 independently by adjusting V and the aluminum particle size.

A study of the magnetic and electromagnetic properties of γ-Fe 2O 3–multiwalled carbon nanotubes (MWCNT) and Fe/Fe 3C–MWCNT composites

A ferromagnetic γ-Fe 2O 3–MWCNT composite was prepared by a reverse microemulsion technique, and was transformed to a Fe/Fe 3C–MWCNT composite by further heat-treatment in H 2 atmosphere at 950 °C. TEM result suggests that MWCNTs are both surface decorated and filled with γ-Fe 2O 3 or Fe/Fe 3C nanoparticles. The saturation magnetization and anisotropy field are particularly strong for Fe/Fe 3C–MWCNT. The reflection loss of Fe/Fe 3C–MWCNT is better than that of γ-Fe 2O 3–MWCNT at all frequencies between 2 and 18 GHz, resulting from enhanced magnetic loss and better matched characteristic impedance, rather than electric loss, as shown by the complex relative permeability μ r = μ ′ r − j μ ″ r and permittivity ε r = ε ′ r − j ε ″ r . The microwave absorbing properties can be modulated simply by manipulating the thickness of the prepared Fe/Fe 3C–MWCNT composite for application in different frequency bands.

Synthesis and electromagnetic characteristics of the flake-shaped barium titanate powder

Abstract The flake-shaped barium titanate (FBT) was prepared by a modified sol–gel method, and their microstructure and electromagnetic (EM) properties (2–18 GHz) were investigated by means of differential thermal analysis (DTA), thermogravimetry analysis (TG), X-ray diffraction (XRD), scanning electronic microscope (SEM) and a network analyser. The reflection loss R of FBT (annealing at different temperatures from 700 to 1200 °C)/paraffin composite samples with thickness of 1 mm and FBT (annealing at 1000 °C)/paraffin composite samples with different thickness from 1 to 5 mm were calculated in 2–18 GHz using the relative complex permittivity and permeability according to the transmit-line theory. It was found that the electromagnetic characteristics and the wave absorption properties of FBT were improved. The maximal reflection loss of FBT (annealing at 1000 °C)/paraffin composite sample reached −29.6 dB at 12 GHz with a matching thickness of 4 mm.

입도에 따른 Flake Sendust 전파 흡수체의 특성 분석

본 논문에서는 연자성 금속 분말인 sendust를 flake화 과정을 통하여 형상과 입도를 변화시켜 전파 흡수체를 제작하고, 그 특성을 분석하였다. 먼저 attrition milling에 의해 입도를 달리한 세 종류의 flake sendust 분말과 지지 재인 CPE(Chlorinated Polyethylene)를 이용하여 전파 흡수체를 제작하고, 이 전파 흡수체로부터 재료 정수를 계산하여 입도에 따른 변화를 조사한 후 전파 흡수능을 측정하여 비교 분석하였다. 그 결과 평균 입도가 <TEX>$140{\mu}m$</TEX>인 flake sendust 분말로 제작된 전파 흡수체가 와전류 손실의 감소(복소비 투자율 증가)와 입자간의 정전 용량의 증가(복소비 유전율 증가)에 기인하여 고주파 대역에서 우수한 전파 흡수능을 보임을 확인하였다. In this paper, we analyzed the characteristics of the EM wave absorber which was fabricated by using flake sendust (soft metal magnetic powder). The flake sendust was made of 3 different granularity by attrition mill. First, we have fabricated 3 kind of EM wave absorbers using the flake sendust and CPE(Chlorinated Polyethylene) and measured the S-parameters of the EM wave absorber. The complex relative permittivity and permeability were calculated from the measured data and the variations according to a change of granularity were researched. As a result, it was confirmed that the EM wave absorber using flake sendust with the <TEX>$140{\mu}m$</TEX> average granularity has outstanding absorption ability in high frequency range(C band) for the reduction of eddy current loss(increase of permeability) and the increase of space charge polarization(increase of permittivity).