Complex permittivity, complex permeability and microwave absorption properties of ferrite–polymer composites (original) (raw)
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Fabrication and characterisation of selected microwave absorbing ferrite-polymer composites
2012
Although absorbing materials are a useful part of modern-day defence systems, very little published knowledge exists on the fabrication of such materials especially microwave absorbing materials. The present research attempts to fabricate absorbing material compositions suitable for microwave absorption from 8 to 18 GHz. Various compositions of composite ferrites were prepared using mechanical alloying and sintering. The starting metal oxide raw materials were weighed according to the targeted proportion and milled for 10 hours using a SPEX8000D mill to get nanosized particles. The resulting mixture was poured into a PVA solution as a binder and stirred while drying it using an ultraviolet lamp until the powder contained ~1 wt% PVA. It was then pressed into pellet/toroid-shaped samples and sintered at temperature 900 °C for 10 hours. Then, a composite of ferrite powder with polymer paint as matrix was prepared. The composite paint produced was applied on the surface of a metal sheet of specified surface dimensions. Physical characteristics of the as-prepared filler samples were studied using X-ray diffraction (XRD), scanning transmission electron microscopy 65 5.3.1 Microstructural properties 65 5.3.2 Complex Permeability Component μ" and μ" 72 5.4 Composition materials in X-band (8-12 GHz) and Kuband (12-18 GHz) frequency range 77 5.4.1 The effect on reflection loss and absorption of ferrite in polymer matrix composites with metal back 5.4.1.1 The influence of physical thickness 5.4.1.2 The influence of materials with different composition 77 78 84 5.4.2 Microwave absorption characteristics of the prepared polymer matrix composites on metal plate
Microwave Absorption Characteristics of some Ferrite-Filled Polymer Composites
Advanced Materials Research, 2014
Prior to their use for microwave absorption, different compositions of NixZn1-xFe2O4 (x = 0.5, 0.6, 0.7 and 0.8) were prepared via mechanical alloying and sintering. X-ray diffractometry (XRD) was used to investigate the crystalline phase formation. Scanning transmission electron microscopy (STEM) and field emission electron microscopy (FeSEM) were used to investigate the particle size and surface morphology respectively. The complex-permeability components, μʹ and μʺ, were also measured using an Agilent 4291B material analyzer from 1 MHz to 1 GHz. From the XRD results it is shown that at 900oC the full phase of nickel zinc ferrite was formed. The μʺ values suggest that the ferrite sample can absorb well microwave energy for frequencies 1 MHz to 1 GHz and higher. This is proved by microwave absorption measurements carried out up to 12 GHz.Keywords: NiZn-ferrite, microwave absorption, magnetic materials
Journal of Applied Physics, 2007
The electromagnetic (EM) and microwave absorption properties of (Co2+-Si4+) substituted barium hexaferrite compositions BaCox2+Fey+2Six+y4+Fe12-2x-2y+3O19 (x=0.9 and y=0.0, 0.05, and 0.2) and its polymer composites prepared from hexaferrite, polyaniline, and carbon powders dispersed in polyurethane matrix have been investigated at the microwave frequency range of the X band (8.2-12.4 GHz). The hexaferrite compositions were synthesized by solid-state reaction technique, whereas polyaniline, by chemical route. The permeabilities of a ferrite are drastically reduced at higher gigahertz frequencies. The permittivities, however, can be enhanced by appropriate choice of composition and processing temperature. In the present ferrite composition, silicon content is taken in excess so as to convert some of the Fe3+ ions to Fe2+ ions. This conversion has been shown to enhance EM and absorption properties. Mössbauer spectroscopy on the samples establishes that addition of excess Si4+ converts some of the Fe3+ to Fe2+. The sintered ferrites have shown resonance phenomena, but the composites do not. The EM parameters ɛ', V'', μ', and μ'' were measured using a vector network analyzer (Agilent, model PNA E8364B). These measured EM parameters were used to determine the absorption spectra at different sample thicknesses based on a model of a single layered plane wave absorber backed by a perfect conductor. The sintered ferrite composition (x=0.9 and y=0.05) showed the best absorption properties [a minimum reflection loss of -17.7 to -14.3 dB over the whole frequency range of the X band (8.2-12.4) for a sample thickness of just 0.8 mm], and it is used in the composite absorbers in powder form along with other constituents. The optimized composite absorber has shown dielectric constant V'~11.5, dielectric loss V''~2.3, and a minimum reflection loss of -29 dB at 10.97 GHz with the -20 dB bandwidth over the frequency range of 9.7-12.2 GHz for a sample thickness of 2.0 mm. The magnetic parameters μ' and μ'' for the composite remained nearly 1 and 0, respectively, throughout the measured frequency range. Both sintered ferrite and composite absorbers can fruitfully be utilized for suppression of electromagnetic interference and reduction of radar signatures (stealth technology).
Applied Physics A
The electromagnetic ͑EM͒ and microwave absorption properties of ͑Co 2+-Si 4+ ͒ substituted barium hexaferrite compositions BaCo x 2+ Fe y +2 Si x+y 4+ Fe 12−2x−2y +3 O 19 ͑x = 0.9 and y = 0.0, 0.05, and 0.2͒ and its polymer composites prepared from hexaferrite, polyaniline, and carbon powders dispersed in polyurethane matrix have been investigated at the microwave frequency range of the X band ͑8.2-12.4 GHz͒. The hexaferrite compositions were synthesized by solid-state reaction technique, whereas polyaniline, by chemical route. The permeabilities of a ferrite are drastically reduced at higher gigahertz frequencies. The permittivities, however, can be enhanced by appropriate choice of composition and processing temperature. In the present ferrite composition, silicon content is taken in excess so as to convert some of the Fe 3+ ions to Fe 2+ ions. This conversion has been shown to enhance EM and absorption properties. Mössbauer spectroscopy on the samples establishes that addition of excess Si 4+ converts some of the Fe 3+ to Fe 2+. The sintered ferrites have shown resonance phenomena, but the composites do not. The EM parameters Ј, Љ, Ј, and Љ were measured using a vector network analyzer ͑Agilent, model PNA E8364B͒. These measured EM parameters were used to determine the absorption spectra at different sample thicknesses based on a model of a single layered plane wave absorber backed by a perfect conductor. The sintered ferrite composition ͑x = 0.9 and y = 0.05͒ showed the best absorption properties ͓a minimum reflection loss of −17.7 to − 14.3 dB over the whole frequency range of the X band ͑8.2-12.4͒ for a sample thickness of just 0.8 mm͔, and it is used in the composite absorbers in powder form along with other constituents. The optimized composite absorber has shown dielectric constant Ј ϳ 11.5, dielectric loss Љ ϳ 2.3, and a minimum reflection loss of −29 dB at 10.97 GHz with the −20 dB bandwidth over the frequency range of 9.7-12.2 GHz for a sample thickness of 2.0 mm. The magnetic parameters Ј and Љ for the composite remained nearly 1 and 0, respectively, throughout the measured frequency range. Both sintered ferrite and composite absorbers can fruitfully be utilized for suppression of electromagnetic interference and reduction of radar signatures ͑stealth technology͒.
Synthesis of Polymer Blend Ferrite Composite for Microwave Absorption at X-Band Frequency
Open Journal of Metal
The microwave absorption properties of polymer composite PANI/PVA/NiFe 2 O 3 are investigated. The polymer composites of PANI/PVA and NiFe 2 O 3 are prepared in two steps. NiFe 2 O 3 is synthesized by modified sol gel method and PANI by chemical polymerization method. Microwave absorption parameters of polymer composite are measured at X-band. The microwave absorption is found to be −28 dB (99%) at 10.2 GHz. Different characterization techniques such as SEM-EDX, FTIR and XRD are done. The SEM result shows flakes like structure for PANI/PVA and crystalline structure for NiFe 2 O 3. FTIR of the composite reveals the interaction between the PANI/PVA and NiFe 2 O 3 .
Microwave Absorbing Properties of NiZnCu Ferrite and Polychloropren Composites
Journal of Aerospace Technology and Management
Radar-absorbing materials (RAMs) have been used in military applications for several decades to reduce radar detection of vessels and aircrafts. In the present work, the performance of Ni0.35Zn0.35Cu0.3Fe2O4 ferrite as a RAM is investigated. The ferrite was firstly synthesized by combustion reaction and then calcinated at 1200 °C for 1 h. Composites were prepared with 80:20, 70:30 and 60:40 concentrations in weight of ferrite:polychloroprene. The X-ray diffraction (XRD) analysis showed a single phase ferrite formation and the scanning electron microscopy (SEM) analysis of the composites showed a good dispersion of the ferrite in the polychloroprene matrix. The electromagnetic (EM) characterization of the composites revealed that the EM attenuation is mainly attributed to magnetic losses observed in the material. The 80:20 composite achieved the best performance and presented a reflectivity of -26.7 dB at 10.2 GHz.
Electromagnetic Wave Absorption Performances of Metal Alloy/Spinel Ferrite/Polymer Composites
IEEE Transactions on Magnetics, 2012
High-frequency electromagnetic wave (EM-wave) absorbing characteristics of metal alloy/spinel ferrite/polymer composite materials with various metal alloy particle contents were evaluated from measurements of complex permeability by the coaxial reflection method in the frequency interval from 1 MHz to 3 GHz. We varied the volume content of metal alloy in composites from 0 to 60 vol% at fixed 40 vol% content of polymer matrix. The increasing metal alloy content in composites resulted in a smaller matching thickness and larger matching frequency than that of spinel ferrite/polymer composite. The return loss calculations showed that prepared composites are good EM-wave absorbers in the quasi-microwave band (100 MHz-3 GHz) and thus suitable for electromagnetic interference noise suppression in electronic communication systems.
Complex permittivity, permeability, and X-band microwave absorption of CaCoTi ferrite composites
Journal of Applied Physics, 2000
The effect of Co2+Ti4+ substitution on complex permeability, permittivity, and microwave absorption has been studied for [Ca(CoTi)xFe12-2xO19]96.0[La2O3]4.0 ferrite-epoxy composites, wherein x varies from 0 to 1.0 in steps of 0.2, in the frequency range from 8.0 to 12.4 GHz. The ferrites with x>0 exhibit significant dispersion in complex permittivity (ɛ'-jɛ'') with the maximum value of ɛ'' observed for x equal to 0.2. The dispersion in complex permeability (μ'-jμ'') is not significant. The variations of reflection loss and percentage absorption have been studied as a function of frequency, Co2+Ti4+ content, and thickness of the absorber. A maximum reflection loss of 31.0 dB is obtained for composites with x equal to 0.2 and absorber thickness of 2.5 mm. The experimental values of the matching frequency and the matching thickness agree well with the theoretical values obtained from an impedance-matching solution map.
Microwave absorption studies of BaCoTi ferrite composites
A ferrit e series of the compos iti on BaFeI2_2,CoxTixOI9. wherein x varies from 0.0 to 0.9 in steps of 0.2. has been prcpared by the standard ceramic technique. The microwave absorption studies of ferrite-polymer composites with different till-factors have been made in the freq uency range from 8.6-12.4 GHz. A maximum return loss of 14.7 dB has been obtained for compos ites with x equ al 0.3 and absorber thickness of 4.0 mm at 9.2 GH z. The dependence of matching frequency on composition is appa rent for this thickness. The maximum values of dc resistivity and th e Curie tem perature have been found to be 234.8 kQ and 469°C respectively. These values correspond to the same composition for which the return loss is the maximum. A dependence of return loss on complex dielectric constant and permeability has been investigated in the X-band. The magnetic dielectrics, such as M-type hexaferrites, are known to be effective microwave absorbers due to their lossy interaction with the electric and magnetic fields of microwaves, which transforms the microwave energy to thermal energyl.5. The complex permeability and permittivity affect the reflection and atten uation characteristics of these materials. The composites of such ferrites with suitable polymers are quite useful as they can be easily shaped and converted into a paste or a paint that can be applied on the objects of interest. The absorption characteristics of ferrite-po lymer composites depend on the composition of ferrite, nature of polymer, fill factor and thickness of composite layer and can be tailor-made by altering these parameters. Barium hexaferrite has been extensively used for producing permanent magnets and microwave devices 6. The substitution of C0 2 +Ti 4 + ions for Fe 3 + ions in Ba-ferrite is expected to change the anisotropy constant and modify the properties so as to make them effective microwave absorbers. In the present work, we report the microwave absorpt ion characteristics of substituted BaCoTi hexaferrites obtained fro m the observed variations of permeability and permittivity as a function of C0 2 +Ti 4 +-content at different frequencies. It helps to determine the optimum amount of C0 2 +Ti 4 + ions in Ba-ferrite, which yields a minimum reflection loss over a wide freq uency range.
Microwave-Absorbing Ferrite-Dielectric Composites
Journal of the American Ceramic Society, 1976
Two-phase composites of spinel ferrites and lithium aluminosilicates were prepared and investigated as microwave-absorbing materials. The magnetic and dielectric loss parameters which determine the heating characteristics were examined. Low-thermal-expansion composites were developed which were effective absorbers of microwave radiation. Some compositions investigated exhibited a temperature maximum limited by the Curie temperature of the ferrite in the composite.