Microwave Absorption Studies Research Articles

Microwave absorption studies in X-band of magnetized barium hexaferrite

Abstract To enhance the magnetic and microwave absorbing properties, barium hexaferrite, BaFe12O19, was studied in the x-band (7–13 GHz) frequency range. The BaFe12O19 was prepared as non-magnetized and magnetized samples. The crystal structure, surface morphology, magnetic and microwave absorption of BaFe12O19 were studied with X-ray diffraction (XRD), optical microscope, permagraph and vector network analyzer (VNA), respectively. XRD result showed the formation of M-type hexagonal polycrystalline structure. The hysteresis loop results verified the formation of permanent magnet with high saturation magnetization. The VNA results showed that reflection loss and absorption were − 71.07 dB and 67.96% for magnetized barium hexaferrite, respectively.

Enhanced microwave absorption and mechanical performance of polyvinylidene fluoride thin films embedded with novel activated carbon and manganese ferrite

AbstractThin composite films hold great promise for microwave devices for microwave absorption. This work mainly focuses on the investigation of the microwave absorption and mechanical studies of a composite thin film of activated carbon and manganese ferrite as conductive fillers within a polyvinylidene fluoride (PVDF) matrix. The production of activated carbon was successfully accomplished using a pyrolysis technique. Composite films consisting of polyvinylidene fluoride (PVDF) and activated carbon‐manganese ferrite were fabricated using a solution blending method. The composite films maintained a consistent concentration of activated carbon at 5 wt%. The characterization of the materials was conducted using scanning electron microscopy and X‐ray diffraction. The composite consists of 3 wt% of MnFe2O4 and 5 wt% Activated carbon/PVDF showed exceptional absorption properties and achieved a minimum reflection loss of around −38 dB at a frequency of 8–12 GHz at a thickness of 2 mm. Significantly, the composite film exhibited a greater tensile strength than the PVDF film. The results of our study highlighted the enhanced microwave absorption and economical manufacturing technique for producing composite films. These films exhibit promising microwave‐absorbing properties in stealth applications.Highlights A facile strategy to fabricate thin film PVDF composites was proposed. Novel activated carbon was synthesized to enhance the conductivity. Achieved reflection loss of around −38 dB at a frequency of 8–12 GHz. Synergistic effects of fillers enhanced dielectric and magnetic losses. Exhibited efficient mechanical performance and microwave absorption.

Microwave absorption behaviour of novel rib cage structured piper betel leaves: Effect of drying and sintering processes

This paper focuses on a simple and cost−effective technique to explore the impact of the drying and sintering process on the microwave absorption behavior of piper betel leaves. The microwave absorption behavior of dried leaves and leaves sintered at 800 ℃ for 3 h was examined. X − Ray Diffraction (XRD) study confirms the presence of elemental composites such as sucrose, cellulose, hemicellulose, and lignin in the dried sample, while sintered betel powder exhibited crystalline phases of CaSiO5, SiO2, Mg2P2O7, CaO, KPO3, Na2K(P3O9) K2CO3, and CaCO3. Microstructure study showed a unique rib cage and nanorod strand structure in the dried leaves and a porous structure in the sintered leaves. Spectroscopy analysis confirmed the occurrence of chemical composites in both dried and sintered betel leaves. The optical band gap of the sintered and dried leaves was 2.7 and 2 eV, respectively. Dielectric loss and loss mechanism in the betel leaf were studied using the DAK 3.5 kit. Results of the microwave absorption studies revealed that dried betel leaves with a thickness of 9 mm exhibited a high Reflection Loss (RLmax) of − 22.69 dB at 11.37 GHz. Also, the same thickness has an effective absorption bandwidth (EAB) of 3.69 GHz, 87.8% of the X band frequency. On the other hand, sintered betel leaves with a thickness of 9 mm have a reflection loss (RLmax) of − 48.57 dB at 10.52 GHz, with an effective absorption bandwidth (EAB) of 2.88 GHz, covering 68.5% of the X band frequency.

Synthesis and Characterization of Zr4+-Y3+ Substituted Ba-Sr Hexaferrite Nanoparticles for Microwave Absorption and Electromagnetic Shielding Applications

Novel compositions of Ba0.5Sr0.5Fe12-1.1xZrxY0.1xO19 (0.0≤x≤0.5) nanoparticles were synthesized using sol-gel citrate precursor method. X-ray diffraction confirmed the formation of magneto-plumbite hexagonal phase with average crystallite size of 55-70 nm. The fourier transformed infrared spectroscopy revealed the presence of metal cations vibrational modes in 460-600 cm−1 range. The Zr-Y contents influenced magnetic behavior and shielding properties with maximum total shielding effectiveness of -31 dB in K band, and -21 dB in X-band, observed for x=0.35. The microwave absorption studies revealed optimum reflection losses with maximum value of -32 dB at 6.4 GHz frequency for x=0.35. The obtained values validate the candidacy of Zr-Y substituted Ba-Sr hexaferrite nanoparticles for uninterrupted airborne surveillance, radar absorption and high frequency shielding applications.

Reflection Loss is a Parameter for Film, not Material

In studies of microwave absorption in the current literature, theories such as reflection loss, impedance matching, the delta function, and the quarter-wavelength model have been inappropriately applied. As shown in this case study, these problems need to be corrected as they are representative of similar work in the literature.

Microwave absorption and bandwidth study of Y2Co17 rare earth soft magnetic alloy with easy-plane anisotropy

The easy-plane anisotropy of the Y2Co17 rare earth soft magnetic alloy has high saturation magnetization and operating frequency, and good impedance matching. Therefore, it is expected to become a kind of high-performance microwave absorbing material. In this paper, Y2Co17 alloy was prepared by a reduction-diffusion method, and its micropowder was prepared as polyurethane (PU) based composite absorbing materials (Y2Co17/PU composites). The microwave properties of composites with different volume fractions were calculated. The composites showed outstanding absorption characteristics in the range of 20–30 vol%, and the minimum reflection loss (RL) was less than −50 dB. When the volume fraction was 25%, the effective absorption bandwidth could cover the X-band at a thickness of 1.5 mm, and the Ku-band at a thickness of 1.08 mm. The absorption mechanism was analyzed by the interface reflection model. The RL absorption peak bandwidth mechanism was discussed by using the amplitude relation and calculating the effective absorption bandwidth at different thicknesses. The effective absorption bandwidth values were in good agreement with the theoretical expectation.

Synthesis and microwave absorption studies on 2D graphitic carbon nitride loaded polyaniline/polyvinyl alcohol nanocomposites

A light weight electromagnetic interference (EMI) shielding and microwave absorbing composite films has been developed by loading varying weight content of graphitic carbon nitride (g-C3N4) nanosheets and polyaniline (PANI) into polyvinyl alcohol (PVA) matrix. The prepared PVA/PANI/g-C3N4 (1%, 3%, 5%) composites has been subjected to FTIR, X-Ray powder diffraction, SEM, Thermal studies, Dielectric studies and electromagnetic shielding effectiveness (EMI SE) analysis. The PVA/PANI/g-C3N4 (1%, 3%, 5%) composites was discovered to have improved electrical conductivity, dielectric loss, and dielectric constant. It is observed from the SEM images that the sheet layers of g-C3N4 are wrapped by the polymer matrix and the morphology to PVA/PANI composite in the g-C3N4 indicates homogeneous blending of PVA/PANI without any phase separation and has porous in it. The PANI/g-C3N4 fractured surfaces present are smooth but irregular in appearance indicating good compatibility between the PVA and PANI matrices. The dielectric properties was found to increase on increasing the concentration of the g-C3N4 nanofiller and reached a maximum of 9.8 × 106 at 1 MHz for 3% g-C3N4 in PVA/PANI. The incorporation of g-C3N4 into PVA/PANI enhanced the conductivity and the 5% g-C3N4 loaded composite film exhibited a conductivity value of 0.043 S/cm at 1 MHz. The PVA/PANI/g-C3N4 (1%, 3%, 5%) composites exhibited potential EMI SE values ranging from 24 to 35 dB at 8.6 GHz and from 42 to 63 dB at 12.4 GHz, for instance the PVA/PANI/g-C3N4 5% composite showed highest value of 63 dB at 12.4 GHz. The PVA/PANI/g-C3N4 5% exhibits the maximum highest reflection loss 8 GHz–12 GHz in which the higher absorption of −36 dB is observed at 10.3 GHz of the X-band region.

Study of Reflection Loss In Ku Band By CNM Decorated With Metal Nano Particles

Abstract: The study of microwave absorption and thus reflection loss in Ku band has received much attention recent years. 12 – 18 GHz microwave frequency band mainly used for tracking of military objects through radar i.e stealth technology of aircraft anti radar detection and wireless, satellite communication applications. Carbon nanomaterials (80-90 nm) decorated with metal nanomaterials (40-50 nm) were synthesized from plant-based precursors using Taguchi optimization methodology. The samples under study showed reflection loss to the extent of -37.11 dB at 14.31 GHz and -34.78 dB at 17.76 GHz whereas, -5 dB RL was observed throughout the Ku band frequency range and importantly in most cases the samples showed -10 dB loss for 1 GHz bandwidth in the 14-15 GHz and 17-18 GHz frequency range. Thus, the synthesized materials could be a good microwave absorbing candidate for particularly 14-15 GHz and 17-18 GHz microwave frequency range bandwidth.

Taguchi Optimization Methodology Directed Synthesis of CNMs from Plant Fibres Decorated with Metal Nano Particles for Study of Microwave Absorption in S and C Bands

Carbon nano materials (CNM) in the form of Graphene oxide and Reduced Graphene oxide decorated with metal nano particles were prepared from cotton as precursor – a green sustainable method. Various parameters were used for synthesis of carbon materials. Taguchi Optimization methodology – a statistical method, was used to arrive at the optimized parameters for synthesis to reduce the number of experimentations thus accentuating the green technology. Microwave is used in various techniques like communication, cell phones & satellite, military weapons viz. stealth technology, RADAR etc. The synthesized CNMs were assessed for their Microwave Absorption (MA) properties for their possible use as RADAR absorbing materials. 96 to 99% MA was observed in 2-8 GHz frequency range with reflection loss up to -25dB. These studies were carried out in the materials having thickness of 2-5 mm. Deviation in MA as well as in reflection losses were also observed when the decorating metal was changed due to the difference in the size of the metal atoms and corresponding shielding effects.

The Low-Field Microwave Absorption in EMR Spectra for Ni50-xCoxMn35.5In14.5 Ribbons.

This paper contains a detailed study of low-field microwave absorption, which is observed in EMR spectra registered for a series of () Heusler alloys polycrystalline in situ and annealed at 1173 K ribbons. The LFMA spectra for all ribbons were performed at X-band (∼9.5 GHz), at temperatures below Curie temperature. Additionally, for annealed ribbons, the LFMA signal dependencies of the external magnetic field modulation amplitude, modulation frequency, microwave power and microwave magnetic field phase were registered. These results confirm the resonant character of LFMA. To determine the basic EMR parameters, such as linewidth and resonance field, the experimental data were fitted by the Dyson function. The LFMA signal is satisfactorily matched by the two lines, and the variability of the component lines with temperature is remarkable.

Preparation and electromagnetic microwave absorption performances of sulfurated and oxidized polyacrylonitrile carbon fibers

Polyacrylonitrile carbon fibers (PAN CFs) were sulfurated at high temperatures and then oxidized with an H2O2 solution. Thermal and chemical analysis showed high thermal stability and the sulfur content up to 4 mmol g−1. From the microwave absorption studies, the voltage standing wave ratio and the attenuation through one adsorbent layer decrease almost linearly with increasing frequency. The reflection coefficient equals 0.79 ± 0.017 and 0.473 ± 0.02 at 10 and 30 GHz. "Transparency windows" with a bandwidth of about 300 MHz are observed at 30 and 36 GHz. The 1000 times attenuation of the signal power is found at 30 GHz.

Ni0.48Cu0.12Zn0.4Fe2O4+ paraformaldehyde nanocomposites as microwave absorbent dominant materials

A series of nanocomposite materials were developed to study microwave absorption properties in 8.2–12.4 GHz (X-band) and 12.4–18 GHz (Ku-band) regions. Nanocomposites of ferrite and polymer constituents with ordered combination (x) wt% Ni0.48Cu0.12Zn0.4Fe2O4 + (1-x) wt% paraformaldehyde, (x = 1, 0.9, 0.7, 0.5, 0.3, 0.1, 0) were prepared by mechanical alloying method. Microwave digestion system was used to prepare nanopowders of Ni0.48Cu0.12Zn0.4Fe2O4 by microwave hydrothermal method. Microwave absorption studies revealed that synergistic combination of ferrite and paraformaldehyde phases in the synthesized composites enhanced the ability to absorb electromagnetic waves screening maximum of 99.7% power of incident electromagnetic waves in X and Ku band frequency regions. The results proved that maximum reflection coefficient of 0.925 and minimum absorption coefficient of 0.072 at 12 GHz were achieved and maximum shielding effectiveness of 26.7 dB was obtained with significant contribution from absorption. The studies proved that maximum synergistic effects were achieved for 50% polymer phase of the sample wherein balanced combination of dielectric and magnetic losses gives rise to minimum reflection loss. The results confirmed that the prepared absorbent dominant materials are found to be potential candidates for designing microwave filters in radar, stealth and satellite applications.

Synthesis and microwave absorption characteristics of BaFe12O19/BaTiO3/MWCNT/polypyrrole quaternary composite

In this research, microwave absorption properties of the barium hexaferrite (BaM)/ barium titanate (BT)/ multi-wall carbon nanotubes (MWCNTs) / polypyrrole (PPy) quaternary composite were investigated. The barium hexaferrite and barium titanate powders were fabricated through co-precipitation and hydrothermal methods, respectively. Polypyrrole was synthesized through in-situ polymerization in the presence of either one of MWCNTs, BT and BaM phases or all of them. Microstructural, magnetic and microwave absorption properties of the prepared composites were investigated. The XRD and FTIR results revealed a successful preparation of the composites. The obtained composites were mixed with polyurethane resin in a mass ratio of 1:4 for microwave absorption studies. The microwave absorption properties of the samples were investigated by the network analyzer. The amounts of minimum reflection loss (RL) obtained for BT/BaM/CNT@PPy, BT@PPy/BaM/CNT and BT/BaM@PPy/CNT samples with the thickness of 3.5 mm were − 3.7, − 5, and − 5.68 dB, respectively while for the sample in which all three components of BaM, BT, and MWCNT were coated by polypyrrole, RL obtained about − 6.88 dB at 9 GHz. The results indicated that the in-situ synthesis of polypyrrole in the presence of all composite components led to a conductive network with the improved dielectric and magnetic properties as well as a better impedance matching conditions providing a higher absorption performance.

Microwave absorption study of low-density composites of barium hexaferrite and carbon black in X-band

The low-density composites based on carbon black (CB) nanopowder and barium hexaferrite (BaFe12O19) nanoparticles are synthesized and characterized for microwave absorption properties in X-band (8.2–12.4 GHz). Barium hexaferrite nanoparticles are developed using low-cost autocombustion method that resulted in low-density particles with uniform particle size distribution. Composites are developed by the ball-milling of BaFe12O19 with CB nanopowder in different weight ratios followed by heat-treatment process. The addition of CB in the composite resulted in enhanced electrical properties due to increase in the dipolar polarization between carbon and ferrite. As a result of increasing CB concentration in composite, the dielectric loss tangent increased from 0.31 to 0.366. On the contrary, the magnetic loss tangent decreased from 0.071 to 0.027, which is due to reduction of magneto-crystalline anisotropy of the composite with CB addition. The composite medium containing 80% CB and 20% BaFe12O19 showed excellent microwave absorption properties having minimum reflection loss of −56.266 dB at 11.98 GHz for an effective coating thickness of 1.85 mm. Also, the effective bandwidth of the composite having reflection loss of 90% (−10 dB) reached to 3.53 GHz (84% of X-band) for coating thickness 2.15 mm. The low reflection loss and wide bandwidth microwave absorption of the composite is due to the increased dielectric properties, which resulted in better impedance matching with free space and high electromagnetic (EM) attenuation.

α-MnO2 nanorods-polyaniline (PANI) nanocomposites synthesized by polymer coating and grafting approaches for screening EMI pollution

In this work, α-MnO2 nanorods-polyaniline nanocomposites were synthesized using polymer coating and grafting approaches. The synthesized nanocomposites were characterized by XRD, FESEM, EDAX, TEM, TG-DTA and FT-IR techniques. The Electromagnetic properties of prepared samples were measured using vector network analyzer in the 8–18 GHz (X and Ku-Band) frequency region. The α-MnO2-NH2-PANI nanocomposite synthesized by grafting approach showed better electrical conductivity, excellent dielectric loss with superior microwave absorption ability. In comparison with pure MnO2, the microwave absorption characteristics of α-MnO2-NH2-PANI nanocomposite display considerable improvements, with an effective absorption band at 10.8 GHz and 14.5 GHz under −10 dB and minimum reflection loss (RL) of −30.79 dB at 14.5 GHz. The α-MnO2-NH2-PANI sample also showed considerable shielding effectiveness (SE) i.e. −20.85 dB in the 8–18 GHz frequency region. The observed value of RL and SE surpasses the required value for being utilized at a commercial level. These results are surely helpful to explore the microwave absorption study of different combinations of organic/inorganic nanocomposite materials particularly for shielding and microwave absorption applications.

Dielectric relaxation and FTIR analysis of 2-chlorobenzoic acid with aniline and n-methyl aniline in 1,4-dioxane

Microwave absorption and FTIR studies of hydrogen-bonded complexes of 2-chlorobenzoic acid (2-CBA) with aniline (AN) and n-methyl aniline (NMA) in 1,4-dioxane at a 1:1 mol ratio have been carried out. For a fixed microwave frequency (i.e., 9.43 GHz), various dielectric parameter dielectric constant ε′, loss ε″ and static constants ε0, ε∞ at zero and very high frequency have been determined. Higasi et.al, equation validates the molecular association of title molecules through the relaxation time. On the 1:1 mol ratio, the values of relaxation time are observed maximum due to the complex formation. The FTIR spectra were recorded in the liquid phase, the prominent functional groups of the molecules and their corresponding shifts due to molecular associations are studied and the vibrational modes are determined theoretically by B3LYP/6–311++ at the ground state. It confirms the intermolecular hydrogen bond length and supported the dielectric relaxation analysis.

Microwave absorption properties of polyaniline (PAni) with various amount of carbonaceous material (CM)

This study investigates the microwave absorption properties of polyaniline (PAni) with varying carbonaceous material, CM (Fullerene,C60) contents. PAni nanocomposites were prepared with varying contents of C60 ranging from 5 to 40% through a chemical oxidation method by using carboxylic acid as the dopant. The functional groups of PAni nanocomposites were validated by Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet–visible (UV–Vis) Spectroscopy analyses. The surface morphology of nanocomposites and the presence of titanium dioxide (TiO2) and C60 were confirmed by Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffractometry (XRD), respectively. Microwave absorption studies were carried out using Microwave Vector Network Analyzer (MVNA) from 0.5 to 18.0 GHz. The study showed that PAni nanocomposites with 10% of C60 formed the nanorods/nanotubes with the biggest diameter of 200 nm as compared to other PAni nanocomposites. It was found that PAni nanocomposites with 10% C60 also recorded the highest electrical conductivity and relative permittivity of 1.708 × 10–1 S/cm and 9.97, respectively. The nanocomposite that was formulated with 10% of C60 showed an improvement of interchain and intrachain charge transfer as well as molecular polarization along the PAni backbone. Hence, it eventually reduces the electrical energy dissipated by PAni, and finally enhances the microwave absorption properties with the highest reflection loss (RL) of −61.3 dB at 9 GHz.

Microwave absorption study of composites based on CQD@BaTiO3 core shell and BaFe12O19 nanoparticles

A novel microwave absorbing composite medium for X-band (8 GHz–12GHz) is developed by mixing of core-shell consisting of carbon quantum dots (CQDs) coated barium titanate (BaTiO3) fibers with barium hexaferrite (BaFe12O19) nanoparticles. CQDs are synthesized from agricultural waste using lemon peel as precursor material while the low density BaTiO3 fibers are synthesized via electro-spinning technique. The increase in diameter of BaTiO3 fibers as an effect of CQD coating has been confirmed using FESEM technique. The XRD and FTIR analysis of CQD coated BaTiO3 fibers are used to confirm the presence of carbon along with barium titanate. Composites based on BaFe12O19 nanoparticles and CQD coated barium titanate (CQD@BaTiO3) fibers were developed by the ball-milling of BaFe12O19 nanoparticles with CQD@BaTiO3 in different weight concentrations. The improved electrical permittivity of the BaFe12O19 and CQD@BaTiO3 composites resulted in the increased reflection loss due to better impedance matching with the free space. The maximum reflection loss of −25.38 dB was achieved for composite containing 85% of BaFe12O19 and 15% of CQD@BaTiO3, for a pellet of thickness 2.75 mm. Also, the maximum −10dB bandwidth (90% absorption) of the composite reaches to 2.7 GHz.

Microwave absorption study of dried banana leaves-based single-layer microwave absorber

AbstractThe ever-increasing use of electronic devices leads to a dangerous upsurge in the emission of microwave radiation; this has drawn appreciable concern in the fabrication of eco-friendly microwave absorber (MA) and it can be a prospective alternative. Present work, in the quest for possible alternatives, explores carbon-rich agricultural residues such as dry banana leaves as a microwave-absorbing material. The variation of microwave absorption efficiency with an increase in the percentage of resin has been already reported. An extensive study on the microwave absorption efficiency of dried banana leaves with sample preparation and reflectivity analysis by hardware measurement, and simulative analysis using CST microwave studio suite for different thicknesses in the frequency range of 1–20 GHz has been also explored in the present work. Single-layer MA thickness variation establishes different microwave absorption performance.

Green synthesis of hierarchically porous carbons with tunable dielectric response for microwave absorption

The optimization of microwave absorption is closely bound up with the of controllable strucuture of absorber materials. Hierarchically porous carbon (HPC) with two level pore structure has thriving as promising candidates for high performance microwave absorption application. However, fabricating HPC with tunable porous structure in a facile and sustainable manner with high yield is still a challenge for vast use in efficient electromagnetic (EM) wave absorption systems. Herein, a series of hierarchical porous carbon materials with different pore structures were synthesized from wheat flour dough through a facile biomass fermentation method. By gradually increasing the fermentation time, the conchoidal cavities gradually evolved to microscale macropore channels, and the number and size of pore increased synchronously. Microwave absorption studies revealed that the formation of macropore channels led to an apparent enhancement of dielectric properties, which can be further increased with the porosity increasing. Consequently, a strong absorption intensity of −52.0 dB at 2.50 mm and a broad microwave absorption bandwidth of 4.6 GHz at only 1.55 mm were achieved. Excellent microwave absorption performance can be ascribed to the improvement in dielectric loss. This approach shed the insights on achieving low-cost, green and industrial-scale production of EM absorber from renewable biomass.