Relative Complex Permeability Research Articles

High-frequency permeability of Fe-Co and Co granular composite materials

The relative complex permeability and permittivity spectra of Fe50Co50 (Permendur) and Co granular composite materials containing heat-treated particles have been studied in the microwave frequency range up to 20 GHz. Fe50Co50 granular composite materials have a larger relative permeability value than Co composites at the same particle content owing to the differences in the magnetizations and the magnetic anisotropies between Fe50Co50 and Co particles. Negative permeability dispersions were observed in both composites at frequencies above 6 GHz. The effect of a dc magnetic field on the permeability spectra revealed that the permeability dispersion of Co composites could mainly be attributed to the gyromagnetic spin resonance in the microwave range. From the relative permittivity spectrum, these two metal granular composites have a dielectric property even at high particle contents.

Microstructures induced microwave resonance peak shift of Co/Al2O3 nanocomposites prepared by ball milling

Microstructures play an important role in materials’ functional performances. In this work, the microstructures including interfaces induced microwave resonance peak shift of Co/Al2O3 nanocomposites is studied. Nanosized Co/Al2O3 composites were successfully fabricated via direct ball milling. The hcp and fcc Co phases coexist for a long milling duration and the interface effect is prominent in the nanocomposites. The measured relative complex permittivity of the Co/Al2O3 nanocomposite–paraffin wax mixture indicates that a high electrical resistivity and a dielectric loss exist in the Co/Al2O3 nanocomposites. The dielectric loss mainly arises from the polarization of the metal/insulator interfaces. The imaginary part of the relative complex permeability of the mixture exhibits a broad resonance peak centered at 8.3GHz which originates from the natural resonance of Co. In comparison to the reported value 6.5GHz, the shift of the resonance peak to higher frequency can be attributed to the surface anisotropy induced by prominent interface effects, which was confirmed by NMR. The position of the resonance peak results from the competition between the surface anisotropy and the dipolar coupling interaction of the Co grains. The calculated reflection loss curves show that the reflection loss value of the Co/Al2O3 nanocomposite–paraffin wax mixture can reach −10dB in a broad frequency range. The improved microwave characteristics are closely related to the microstructures, and can be tailored by controlling the content of Co and the thickness of the sample.

Synthesis and Microwave Absorbing Properties of Cu-Doped Nickel Zinc Ferrite/Pb(Zr0.52Ti0.48)O3Nanocomposites

Nanocomposites based on Cu-doped nickel zinc ferrite and lead zirconium titanate exhibited significant microwave absorbing properties in the X-band (8.2–12.4 GHz) region. Coprecipitation and homogeneous precipitation methods were utilized to synthesize Cu-doped nickel zinc ferrite (Cu0.2Ni0.4Zn0.4Fe2O4) and lead zirconium titanate (Pb(Zr0.52Ti0.48)O3) nanoparticles, respectively. To develop nanocomposites, dispersion of these nanoparticles into epoxy resin (LY665) polymeric matrix was carried out by using mechanical stirrer. Phase analyses of the nanoparticles were done by X-ray diffraction (XRD). Moreover, morphological characterization was done by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDS) confirmed the chemical constituents present in the nanocomposites. Complex relative permittivity and complex relative permeability values of the nanocomposites were measured in different microwave frequencies in the X-band (8.2–12.4 GHz) region by employing vector network analyzer (model PNA E8364B), and return loss (dB) values were calculated to identify the microwave absorbing performance of the present nanocomposites. Brilliant microwave absorbing properties have been achieved by the nanocomposites with the minimum return loss of −49.53 dB at 8.44 GHz when sample thickness was 3 mm. For the present nanocomposites, mainly dielectric loss was responsible for loss mechanism.

The Effects of Doping on Crystal Structure, Magnetic and Microwave Properties of SrFe12−2x La x (Mn0.5Zr0.5) x O19 Nanoparticles

M-type hexagonal ferrite powders, SrFe12−2x La x (Mn0.5Zr0.5) x O19 (x=0.0, 0.2, 0.4, 0.6, 0.8), have been synthesized by the coprecipitation method. The X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer and vector network analyzer all were used to characterize the structure of the samples, their magnetic and microwave properties. The value of the saturation magnetization increased up to x=0.2 and then slowly decreased with increasing doping. A decreasing trend was observed in the value of coercivity with increasing substitution degree, and its value reached a minimum of 2420 Oe for x=0.6 and then increased with further increasing x. The relative complex permittivity and permeability of the composite powders were investigated in the X-band frequency range (8.2–12.4 GHz).

Effective microwave magnetic response of two-component metaferrite

The complex effective relative permeability of a two-component ferrite-like metamaterial was studied for the two cases of electromagnetic wave propagation with respect to direction of dc magnetic bias field, namely, parallel and transverse. The metamaterial of interest is the host dielectric with periodically embedded ferric cylindrical or spherical inclusions. The inclusions are saturated with the biasing magnetic field and the magnetic losses are taken into account. The analysis was performed utilizing the Microwave Effective Medium Theory for two-component artificial composite materials with saturated losslessferricinclusions (1). Computations revealed thatlowvalues ofrefractiveindexaswellasnegativevalues ofpermeability can be achieved.

Relation Between High-Frequency Properties and Direction of Anisotropy Magnetic Field in Magnetic Thin Film for RF Inductor Applications

A relation between high-frequency properties, and angle θ of the easy axis in soft magnetic film and ac applied field was investigated in order to fabricate the film for RF spiral inductor without a localized EMI (Electro-Magnetic Interference). This relationship was measured using a soft CoFeSiO/SiO2 granular multilayer magnetic thin film and simulated by using LLG (Landau-Lifshitz-Gilbert) micromagnetic simulator. The measured and calculated frequency dependence of the film's complex relative permeability, μr' and μr'', compared well with 10% mean error. The real part of complex relative permeability μr' was dependent on approximately sin2θ . The ferromagnetic resonance (FMR) frequency, fr, and the FMR half-width, Δfr were not dependent on the angle, θ . They were estimated to be 2.54 GHz and 0.3 GHz, respectively. These results are significant for the design of various magnetic thin film spiral inductors in RF integrated circuits without localized EMI.

Effect of Annealing on the Magnetostatic and Microwave Electromagnetic Properties of Glass-Coated Fe-Rich Microwires

Glass-coated FeCuNbVSiB microwires was annealed in the temperature range of 380 °C to 600 °C. The microstructures and magnetostatic properties of the glass-coated microwires were characterized by X–ray diffraction (XRD), Vibrating Sample Magnetometer (VSM) respectively. Relative complex permeability and complex permittivity was measured by transmission/reflection (T/R) coaxial line method in the frequency range of 2-18 GHz for as-casted and annealed Fe-rich microwires samples. The measured results show that the coercive field of the Fe-rich microwires decrease to 1.54 Oe at 470 °C, and then increase rapidly with the increasing of the annealing temperature. The coercive field and saturation field of the microwire samples increased abruptly with the outgrowth of the Fe-B hard magnetic phase in the Fe-rich microwire samples. The imaginary part of permeability and the natural ferromagnetic resonance frequency decrease for the thermal treatment below 470 °C, and then increase with the annealing temperature up to 530 °C. The change of magnetostatic and microwave electromagnetic properties of the microwires samples with the annealing process come from the change of the anisotropy caused by the internal stress.

Design and Fabrication of the EM Wave Absorber with Excellent Characteristics for ETC System

In this paper, the EM wave absorber for ETC system was designed and fabricated. We fabricated several samples in different composition ratios of flaked 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 according to composition ratio. The optimized mixing ratio of flaked sendust and CPE was found as 60 : 40 wt.% by experiments and simulation. Then the EM wave absorber was fabricated and tested using the simulated data. As a result, the developed EM wave absorber has the thickness of 2.75 mm and absorption ability was 22.5 dB in the case of normal incidence at 5.8 GHz. Therefore, it was confirmed that the newly developed absorber can be used for ETC system.

Enhanced microwave absorption property of bowl-like Fe3O4 hollow spheres/reduced graphene oxide composites

A novel kind of Fe3O4 hollow spheres/reduced graphene oxide (r-GO) composites has been synthesized by a facile solvothermal method. The scanning electron microscopy and transmission electron microscopy images show bowl-like Fe3O4 hollow spheres with an average outer diameter of 395 nm and a shell thickness of 100 nm decorating on the both sides of r-GO sheets. The co-existence of both D and G peaks in Raman spectra confirms the presence of r-GO state, and an increased D/G intensity ratio of the composites suggests a substantial increase in disorder degree in the r-GO sheets due to the Fe3O4 hollow spheres anchoring on the surface. Compared to pristine r-GO, pure Fe3O4 nanoparticles, and the reported solid nano-Fe3O4/r-GO, both a wider and stronger absorption have been achieved in the frequency range of 2–18 GHz. In particular, the sample containing 30 wt. % as-synthesized hollow Fe3O4/r-GO with a coating layer thickness of 2.0 mm exhibits a maximum absorption of 24 dB at 12.9 GHz as well as a bandwidth of 4.9 GHz (from frequency of 10.8–15.7 GHz) corresponding to reflection loss at −10 dB. The measured complex relative permittivity and permeability data reveal that the enhanced microwave properties are contributed by a major improved dielectric loss and a minor magnetic loss resulting from the incorporation of hollow Fe3O4 on r-GO.

Multi-resonances behavior of Ni nanobelt/paraffin composites at microwave frequencies

Ni nanobelts are synthesized through a facile hydrothermal method to form magnetic composites for high frequency applications. Four resonance peaks of the relative complex permeability illustrate the multi-resonance behavior in Ni nanobelt/paraffin composites in a frequency range of 2–18GHz. The resonance absorption characteristics are analyzed by fitting the permeability spectrum with the well-known Landau–Lifshitz–Gilbert (LLG) equation and Maxwell–Garnett mixing rule. Unlike previous studies, LLG equation has been deduced on account of the random distribution of Ni nanobelts in paraffin matrix first, and then applied for data fitting and resonance identification. Correspondingly, the first band is attributed to natural resonance, while the other three bands are considered to originate from non-uniform exchange resonance.

Microwave Absorbing Properties of DBSA-doped Polyaniline/BaTiO3-Ni0.5Zn0.5Fe2O4 Nanocomposites

Development of RADAR absorbing materials (RAMs) is the most important research area in camouflage application mainly in Defence. Aniline was polymerized in presence of dodecylbenzene sulphonic acid (DBSA) as a functionalized protonic acid in water medium to form DBSA-doped polyaniline (PANI). Ni0.5Zn0.5Fe2O4 (NZF) nanoparticles were synthesized by co-precipitation method along with Bariun Titanate (BaTiO3) particles to form BaTiO3-Ni0.5Zn0.5Fe2O4 nanoparticles. Both DBSA-doped PANI and BaTiO3-Ni0.5Zn0.5Fe2O4 nanoparticles were thoroughly mixed in different ratios and the mixtures were dispersed in Epoxy Resin (LY556) matrices to produce RAMs. The spectroscopic characterization of the composite materials were examined by using X-ray diffraction (XRD), scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDX), High resolution transmission electron microscopy (HR-TEM). The microwave absorbing properties return loss (dB) and important parameters such as complex relative permittivity (?r´ - j?r´´), complex relative permeability (µr´ - jµr´´) were measured in different microwave frequencies in X-band (8.2-12.4 GHz) region. The composite materials showed that a wider absorption frequency range and showed maximum return loss of -15.78 dB (>97% power absorption) at 10.8 GHz. The mechanism of microwave absorption occurs mainly due to the dielectric loss rather than magnetic loss.

Microwave absorption property of Ni–Co–Fe–P-coated flake graphite prepared by electroless plating

Ni–Co–Fe–P alloy coating was covered on surface of flake graphite by electroless plating process. Morphology, composition, structure, magnetic property and microwave absorbing property of the Ni–Co–Fe–P alloy plating were characterized by scanning electron microscopy (SEM), energy diffraction spectrum (EDS), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), vibrating sample magnetometer (VSM) and vector network analyzer, respectively. The results indicated that uniform Ni–Co–Fe–P alloy plating was deposited on surface of flake graphite by the electroless plating and the coating was composed of 9.75wt% Fe, 7.98wt% Co, 4.13wt% P and 78.14wt% Ni. The Ni–Co–Fe–P alloy plating was stable in the air and the plated flake graphite was magnetic. The complex relative permittivity (ɛ=ɛ′−jɛ″) and permeability (μ=μ′−jμ″) of the samples were measured in the range of 0.1–10GHz. The reflection loss (RL) was calculated using the theory of absorbing wall, and the results showed that the minimum RL of the plated flake graphite with a thickness of 3mm was −12.8dB at 4.6GHz. The plated flake graphite is a kind of ideal microwave absorbing material.

Effect of Particle Shape on Absorption Characteristics of Composite Electromagnetic Wave Absorber Made of Sendust Particles Dispersed in Polystyren Resin

The frequency dependences of the relative complex permeability μr* the relative complex permittivity εr* and the return loss for the composite made of sendust flakes or spherical sendust particles dispersed in polystyrene resin were investigated in the frequency range from 1 to 40 GHz. The values of εr* increased when sendust flakes were dispersed in polystyrene resin and the frequency dependence of μr* was different in the particles shape of sendust. Therefore, absorption characteristics depended on the particle shape of sendust and the absorption of electromagnetic waves with a wide bandwidth in the frequency range from 10 and 20 GHz could be achieved using spherical sendust particle with a low volume mixture ratio.

Permeability spectra of yttrium iron garnet and its granular composite materials under dc magnetic field

Relative complex permeability spectra (μr=μr′-iμr′′) and the dc magnetic field effect on them for a yttrium iron garnet (YIG) and its granular composite materials have been studied to evaluate the negative permeability characteristics. In the sintered YIG, two distinct peaks corresponding to the domain wall and the gyromagnetic spin resonance were observed in the imaginary part μr′′ under zero magnetic field; the real part of complex permeability μr′ shows a small negative value in a certain frequency range. The Lorentz type magnetic resonance with the negative permeability dispersion was observed under dc magnetic field. Permeability spectra were evaluated by the numerical fitting of actual measurement data to a resonance formula using six parameters (resonance frequencies, static susceptibilities, and damping factors of the domain wall motion and the gyromagnetic spin rotation). The dc magnetic field suppresses the domain wall contribution and the spin component becomes dominant. In the YIG granular composite material, the permeability dispersion frequency shifts to higher frequency region due to demagnetizing field; the spin component becomes dominant. Negative permeability spectra were also observed in the high content YIG composites under the dc field. The negative permeability spectra of YIG composite materials can also be applied to the left-handed material as well as the sintered YIG.

Composite Electromagnetic Wave Absorber Made of Ni-Zn Ferrite Particles Dispersed and Isolated in an SiO<sub>2</sub> Medium

In order to design a ferrite absorber that can be used at frequencies of several GHz, the frequency dependences of the relative complex permeability μr*, the relative complex permittivity εr*, and return loss were investigated for a composite made of Ni-Zn ferrite and SiO2. When ferrite particles were dispersed and isolated in an SiO2 medium, the frequency dependence of μr* was different from that for a composite made of SiO2 particles dispersed and isolated in the ferrite medium. Moreover, when ferrite particles were isolated and a suitable mixture ratio of ferrite and SiO2 was selected, the return loss was less than −20 dB at frequencies of several GHz. The dispersion states of ferrite and SiO2 particles are thus important factors to design an absorber, and improvement in the absorption characteristics of the ferrite tile which is used as a practical absorber could be achieved using a composite made of Ni-Zn ferrite particles dispersed and isolated in an SiO2 medium.

Reaction kinetic, magnetic and microwave absorption studies of SrFe12O19/CoFe2O4 ferrite nanocrystals

Mixture of cobalt ferrite and strontium hexaferrite nanocrystals i.e. SrFe12O19/CoFe2O4 exhibiting super paramagnetic nature were synthesized by modified flux method. The resulting precursors were heat treated (HT) at 900 and 1200°C for 4 h in nitrogen atmosphere. During heat treatment, transformation proceeds as instantaneous rate of nucleation and three dimensional growth with activation energy of 135.835 kJ/mole. The hysteresis loops showed a hike in saturation magnetization from 1.045 to 84.362 emu/g with an increase in HT temperature. The ‘as synthesized’ particles have size in the range of 10–20 nm with spherical shape. Further, these spherical shape particles tend to change their morphology to hexagonal plates with increase in HT temperatures. The relative complex permittivity and permeability of the composite powder are investigated. The minimum reflection loss of the composite powder reaches to −27.6 dB at 10.8 GHz which suits its application in RADAR absorbing materials.

Microwave Absorbing Properties of Nickel-coated Graphene

Abstract: Graphene sheets were prepared by using chemical reduction of a colloidal suspension of graphene oxide sheets in water. After hydrophilic treatment and chemical plating, a layer of nickel particles was uniformly coated on the surfaces of the graphene sheets. The morphologies of the pure graphene (GF) and Ni-coated graphene (NGF), nickel element content on the graphene surface and magnetic properties of the NGF were examined by SEM, EDX and VSM, respectively. The complex relative permittivity and permeability of the NGF absorber were measured by using a microwave network analyzer in the frequency range of 2−18 GHz. The reflection loss curves of the GF and NGF were calculated using computer simulation technique. It is found that in the frequency range of 2−18 GHz, with the increase of the matching thickness, the maximum absorbing peaks of the GF and NGF shift to lower frequency region, so GF and NGF are dielectric loss microwave absorption materials. When the matching thickness is 1 mm, the maximum ab-sorption peak of the GF is −6.5dB at about 7GHz. When the matching thickness is 1.5 mm, the maximum absorption peak of the NGF is −16.5dB at 9.25 GHz and the frequency region in which the maximum reflection loss is more than −10.0 dB is 9.5−14.6 GHz.

Morphology-controlled synthesis and novel microwave electromagnetic properties of hollow urchin-like chain Fe-doped MnO 2 under 10 T high magnetic field

Fe-doped MnO 2 with a hollow sea urchin-like ball chain shape was first synthesized under a high magnetic field of 10 T. The formation mechanism was investigated and discussed in detail. The synthesized samples were characterized by XRD, SEM, TEM, EMPA, and vector network analysis. By doping MnO 2 with Fe, the relative complex permittivity of MnO 2 and its corresponding loss tangent clearly decreases, but its relative complex permeability and its corresponding loss tangent markedly increases. Moreover, the theoretically calculated values of reflection loss show that with increasing the Fe content, the as-prepared Fe-doped MnO 2 exhibits good microwave absorption capability.

Microwave Absorption Characteristics of Conventionally Heated Nonstoichiometric Ferrous Oxide

The temperature dependence of the microwave absorption of conventionally heated nonstoichiometric ferrous oxide (Fe0.925O) was characterized via the cavity perturbation technique between 294 K and 1373 K (21 °C and 1100 °C). The complex relative permittivity and permeability of the heated Fe0.925O sample slightly change with temperature from 294 K to 473 K (21 °C to 200 °C). The dramatic variations of permittivity and permeability of the sample from 473 K to 823 K (200 °C to 550 °C) are partially attributed to the formation of magnetite (Fe3O4) and metal iron (Fe) from the thermal decomposition of Fe0.925O, as confirmed by the high-temperature X-ray diffraction (HT-XRD). At higher temperatures up to 1373 K (1100 °C), it is found that Fe0.925O regenerates and remains as a stable phase with high permittivity. Since the permittivity dominates the microwave absorption of Fe0.925O above 823 K (550 °C), resulting in shallow microwave penetration depth (~0.11 and ~0.015 m at 915 and 2450 MHz, respectively), the regenerated nonstoichiometric ferrous oxide exhibits useful microwave absorption capability in the temperature range of 823 K to1373 K (550 °C to 1100 °C).

Structural and microwave absorption properties of Ni (1− x) Co ( x) Fe 2O 4 (0.0 ≤ x ≤ 0.5) nanoferrites synthesized via co-precipitation route

Ni–Co nanoferrites show excellent magneto-dielectric properties and these materials can be used to miniaturize the size of the high frequency devices which is the order of the day. Nanocrystalline Ni–Co ferrites having general formula Ni 1− x Co x Fe 2O 4 ( x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were prepared by co-precipitation method. The structural morphology of the prepared samples was carried out using scanning electron microscopy. The results showed the spherical shaped nanoparticles varying in the range of 16–40 nm. The complex relative permittivity ( ɛ r ) and complex relative permeability ( μ r ) were measured using vector network analyzer for all the samples in the frequency range of 1 MHz to 3 GHz. The variation of complex relative permittivity ( ɛ r ) as a function of frequency is explained in accordance with Maxwell–Wagner model and Koop's phenomenological theory. The effect of frequency and cobalt concentration on permeability are reported. The reflectivity ( R) of nanoferrites is also calculated. The value of minimum reflection loss (RL) is about −18 dB at 2.45 GHz with a thickness of 2.1 ± 0.1 mm. The results indicate that Ni 1− x Co x Fe 2O 4 nanoparticles have excellent microwave absorbing properties and have a great potential for military use.