Polyvinylidene fluoride/nanocrystalline iron composite materials for EMI shielding and absorption applications (original) (raw)
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In this paper, the composites of polyvinylidene fluoride (PVDF)/nickel (Ni) prepared through simple blending and hot-molding process have been investigated for dielectric, electromagnetic shielding, and radar absorbing properties. In order to study complex permittivity of the composites in 40 Hz–20MHz frequency range, impedance spectroscopy (IS) technique is used. Besides, the complex permittivity and permeability in addition to shielding effectiveness (SE), reflection coefficient (backed by air), and loss factor are calculated using scattering parameters measured in X-band (8.2–12.4 GHz) by waveguide method. Further, in X-band, a theoretical analysis of single layer absorbing structure backed by perfect electrical conductor is then performed. A flanged coaxial holder has also been designed, fabricated, calibrated, and tested for electromagnetic interference SE measurement in the broad frequency range (50 MHz–18 GHz). The IS results indicate large enhancement in dielectric constant as a function of Ni loading in the polymer-metal composite (PMC) phase. This result has been explained using interfacial polarization and percolation theory. The frequency dependent response of ac conductivity has been analyzed by fitting the experimental data to the “Johnscher’s universal dielectric response law” model. The results obtained for SE (in X-band over broad frequency range) and reflection coefficient indicate that PVDF/Ni composites give better electromagnetic interference shielding and radar absorption properties at filler concentration (fcon)fc in the PMC, whereas at fc<fcon, the charge storage mechanism dominates in the insulator regime of the composite phase. Therefore, the range of PMC compositions below and above percolation threshold has been observed to have different variety of applications.
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In our previous work, the lanthanum iron garnet-filled PVDF-polymer nanocomposite has been prepared. The real and imaginary parts of relative permittivity and permeability of mentioned sample were obtained simultaneously using the Nicholson-Ross-Weir (NRW) method based on the measurement of the reflection and transmission coefficients of the materials. In this study, the electric field distribution and attenuation at rectangular waveguide loaded sample were investigated based on the Finite Element Method (FEM). The computations of the reflection and transmission coefficients (S-parameters) were implemented using both the FEM and NRW methods. The results were compared with the measured reflection and transmission coefficients using the rectangular waveguide in conjunction with an Agilent N5230A PNA-L Vector network analyzer (VNA) at X-band frequencies (8 GHz-12 GHz). The results of the relative error indicated that, among the two applied methods, the FEM is more accurate than the NRW method.
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Improvement of microwave-absorbing materials (MAMs) is the most important research area in various applications, such as in communication, radiation medical exposure, electronic warfare, air defense, and different civilian applications. Conducting polymer, polyaniline doped with para toluene sulphonic acid (PANI-PTSA) as well as cobalt ferrite (CoFe 2 O 4) is synthesized by sol-gel method and intensely blends in different ratios. The characterization of the composite materials, CoFe 2 O 4 /PANI-PTSA (CFP1, CFP2, CFP3 and CFP4), was performed by X-ray diffraction (XRD), atomic force microscopy (AFM) and vibrating sample magnetometry (VSM). The microwave-absorbing properties' reflection loss (dB) and important parameters, such as complex relative permittivity (ε r ′-jε r ″) and complex relative permeability (µ r ′-jµ r ″) were measured in different microwave frequencies in the X-band (8.2-12.4 GHz) region. The composite material CFP3 showed a wider absorption frequency range and maximum reflection loss of − 28.4 dB (99.8% power absorption) at 8.1 GHz and − 9.6 dB (> 90% power absorption) at 11.2 GHz, and so the composite can be used as a microwave absorber; however, it can be more suitable for application in daily life for making cell phones above 9 GHz. Also the results showed that the thicker composites like CFP3 (4 mm) exhibit obviously better EMI SE as compared with the thinner ones (0.19, 0.19, 0.3 mm); this may be related to the low transmission of the EM wave from the composites.
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In this work, EMI shielding behaviors in the X-band frequency have been investigated for flexible polyvinylidene fluoride (PVDF) composites containing globular- and tubular-shaped carbonaceous nanostructures embedded with mono-metallic (Ni) and bi-metallic (FeNi, CoNi, MnNi) alloy nanoparticles. Pyrolysis was carried out at two different temperatures (800 °C and 1000 °C) to synthesize carbonaceous materials with two different morphologies. Carbon nanotubes (CNTs) are predominantly seen in the samples synthesized at lower temperature (800 °C), whereas carbon globules (CGs) are observed for the samples synthesized at higher temperature (1000 °C). The PVDF-CNT composites show superior microwave shielding behavior than the PVDF-CG composites, which is attributed to the enhanced absorption of the microwave through Ohmic conduction and interfacial polarization loss. The 1-D structure of CNTs provides the required conduction path for the electrons and forms a network to trap the microwave within them via multiple scattering. The microwave absorption behavior of the composites predominantly results from the metallic nature of the embedded nanoparticles, the graphitic layer encapsulating them and the graphitic walls of the CNTs. We further demonstrate the direct correlation of the EMI shielding behavior of the nanocomposites with the morphology of carbonaceous nanomaterials and the conductivity of the embedded metallic nanoparticles.
Composites Part A: Applied Science and Manufacturing, 2016
Conductive polymer composites (CPCs) that contain a segregated structure have attracted significant attentions because of their promising for fulfilling low filler contents with high electromagnetic interference (EMI) properties. In the present study, segregated poly(vinylidene fluoride) (PVDF)/multi-walled carbon nanotubes (MWCNTs) composites were successfully prepared by mechanical mixing and hot compaction. The PVDF/MWCNTs samples with 7 wt% filler content possess high electrical conductivities and high EMI shielding effectiveness (SE), reaching 0.06 S cm-1 and 30.89 dB (in the X-band frequency region), much higher than lots of reported results for CNT-based composites. And the EMI SE greatly increased across the 2 frequency range as the sample thickness was improved from 0.6 to 3.0 mm. The EMI shielding mechanisms were also investigated and the results demonstrated absorption dominating shielding mechanism in this segregated material. This effective preparation method is simple, low-cost, and environmentally-friendly and has potential industrial applications in the future.
Magnetic and Microwave Absorption Properties of PVB/Fe3O4 and PVB/NiFe2O4 Composites
Electromagnetic and microwave absorbing properties of Polyvinylbutyral (PVB)/Fe3O4 and PVB/NiFe2O4 com- posites were investigated in the 1-14 GHz. PVB/filler particles (Fe3O4 and NiFe2O4) composites were pre- pared with 90/10 mixture ratios via Ultrasonic Probe Sonicator method in solution. The complex permittivity (e0 2je00) and permeability (l0- jl00) of the composites have been measured at different microwave frequen- cies in 1–14 GHz employing vector network analyzer (Keysight N9926A). The reflection loss (RL) of compo- sites was calculated and evaluated using theory of the absorbing wall. It was found that, both composites exhibit the large reflection loss and broadband within the frequency range from 1 to 14 GHz for 3, 5, and 7 mm. However, the RL results show that, when the thickness is 7 mm, the minimum RL was found to be 222.9 dB (99% power absorption) at the frequency of 13.93 GHz. The Fe3O4/PVB and NiFe2O4/PVB compo- sites have potential application for microwave and radar absorptions. POLYM. COMPOS., 00:000–000, 2017. VC 2017 Society of Plastics Engineers