Microwave Absorption Properties Of Composites Research Articles

Electrically conductive epoxy/polyaniline composite fabrication and characterization for electronic applications

This study reports on the electrical conductivity, dielectric, and electromagnetic interferenc (EMI) shielding properties of conductive epoxy/PAni blend containing various concentrations. Polyaniline (PAni) was synthesized using oxidative chemical polymerization technique and then dispersed into epoxy resin using a sonication bath. Infrared spectra confirm the curing of composites. Increasing the aspect ratio of PAni in epoxy increased the electrical conductivity and improves the microwave absorption properties of composites in the microwave range (0.1 GHz–20 GHz). Electrical conductivity was measured by using the four-probe method, and the maximum conductivity of the composite was achieved 3.51 × 10−13 Scm−1 with 30 wt% of PAni. The maximum porosity of the composite with 30 wt% of PAni was 15.5%. EMI shielding was measured by a vector network analyzer (VNA) in the microwave region (0.1 GHz–20 GHz), which gives the maximum value of 63 dB. IR shielding was measured by IR spectroscopy and less than 0.5% transmission was observed in NIR (700 nm–2500 nm) region. The average particle size of PAni is found to be 113 nm. These composites were used as a potential candidate for conductive coatings, EMI shielding purposes, and electronic applications.

Research on the microwave absorbing properties of ferrite/acetylene carbon black composites with different structures

This experimental study was aimed to investigate the microwave absorbing properties of composites with different structures prepared by filling nitrile rubber (NBR) with ferrite and acetylene carbon black (CB). The results show that the input impedance of the ferrite-filled composite was smaller than that of the CB-filled composites. The ferrite filled composite also matched the free space better than the CB filled composite. The two-layer and four-layer composites performed significantly better than the single-layer structure composites in absorbing microwaves. The maximum absorption attenuation of the four-layer NBR/CB composites reached 11.38dB.

Enhanced Dielectric Loss and Magnetic Loss Properties of Copper Oxide-Nanowire-Covered Carbon Fiber Composites by Porous Nickel Film

The porous nickel film with agglomerate nanoparticles and 1.5~2.0 μm in thickness was used to enhance microwave absorption and ferromagnetic properties of nanowire-like copper oxide-covered carbon fiber composites. Firstly, the porous nickel film/carbon fiber composites were prepared by plating route, when the current intensity was 120 mA for 30 min (sample S1) and 40 min (sample S2), respectively. Then, the copper oxide/porous nickel/carbon fiber (CNCF1 and CNCF2) composites were synthetized by electroless deposition copper and thermal oxidation route (the sample S1 and sample S2), respectively. The microwave absorption properties of composites were investigated over frequency range, 1-18 GHz. The results showed that the strongest reflectivity loss (RL) values of CuO/carbon fiber (CCF) and CNCF1-2 composites were -25.93 dB at 3.59 GHz with a matching thickness layer of 2.4 mm, -27.87 dB at 6.67 GHz with a matching thickness layer of 2.5 mm, and -54.82 dB at 9.23 GHz with a matching thickness layer of 2.192 mm. When the RL values of CCF and CNCF1-2 composites were lower than -10 dB, the absorption frequency range from 8.12 to 9.64 GHz (1.52 GHz in absorption bandwidths, 1.5 mm in thickness), 6.45 to 8.81 GHz (2.36 GHz in absorption bandwidths, 2.4 mm in thickness) and 10.51 to 14.35 GHz (3.84 GHz in absorption bandwidths, 1.8 mm in thickness), respectively. Therefore, the CNCF2 composites showed more excellent microwave absorption properties, and are potential microwave absorption candidates for making a thin thickness, strong absorption and wide-frequency.

Temperature-dependent dielectric and microwave absorption properties of silicon carbide fiber-reinforced oxide matrices composite

Simultaneous improvement of mechanical and microwave absorption properties of the composites at high temperatures still undergoes considerable challenges. We have investigated the high-temperature microwave absorbing properties of the silicon carbide fiber-reinforced oxide matrices (SiCf/mullite–SiO2) composite on the basis of our previous work. Results indicate that the complex permittivity increases from 8.19 − j5.09 to 16.39 − j9.83 at 10 GHz with the temperature rising from 200 to 600 °C. The SiCf/mullite–SiO2 composite has relatively high tanδ values indicating superior microwave attenuation ability. The reflection loss (RL) values of the composite increase with rising thickness. It can be noticed that the RL response curves of different thicknesses are basically consistent at 200 and 400 °C. In addition, the RL value of the composite is less than − 5 dB in the whole X band when the thickness is under 2.9 mm and the temperature is below 400 °C. The hybrid oxide matrices of mullite and SiO2 are beneficial to improve the dielectric properties, especially high-temperature microwave absorption properties of the SiC fiber-reinforced ceramic matrix composite. The superior microwave absorption properties indicate that the SiCf/mullite–SiO2 composite is a promising candidate in aircraft engine nozzle and aerodynamic heating parts of aircrafts at high temperatures.

Influence of different matrices on the mechanical and microwave absorption properties of SiC fiber-reinforced oxide matrix composites

Fiber-reinforced ceramic matrix composites have excellent mechanical and microwave absorption properties, but still present considerable challenges. We prepared a SiCf/mullite-SiO2 composite (composite A) and a SiCf/Al2O3-SiO2 composite (composite B) by a precursor infiltration and sintering (PIS) process. Compared with the composite B, the composite A was easily densified. The flexural strength of the composite A reached 216MPa, whereas that of the composite B was 159MPa. The imaginary part of permittivity for composites A and B, which was determined by the contents of matrix and porosity, varied in the range of 2.5–3.5 and 3.6–5, respectively. The microwave absorption properties of the composite A were significantly enhanced in the range of 8.2–12.4GHz. The results indicate that an optimal reflection loss of −44dB was reached at 12GHz with a thickness of 2.9mm for the composite A. These SiC fiber-reinforced oxide matrix materials have promising applications in microwave absorption, especially at high temperatures.

Development of Low Density, Heat Resistant and Broadband Microwave Absorbing Materials (MAMs) for Stealth Applications

The development of low density and broadband microwave absorbers are the need of the hour to cater for the needs of all military platforms for stealth technology. The low density and broadband properties can be inculcated in microwave absorbers using dielectric lossy materials (e.g. carbon fibres, carbon nanotubes, carbon black, fullerene, graphite, graphene and silicon carbide fibre). Therefore, we designed low density and heat resistant microwave absorbing materials (MAMs) using a novel approach of ceramic fibre board manufacturing technology. The microwave absorbing composites were prepared with varying percentage of milled carbon fibres, discontinuous aluminosilicate fibres and silicone resin as the matrix. The physico-mechanical properties of microwave absorbing composites were determined. Reflection loss of microwave absorbing composites was measured in the frequency range 2–18 GHz by unique single horn interferometry technique. The electromagnetic properties were measured in X-band using free space measurement system. Based on these properties the effect of thickness on the microwave absorbing properties in X-band was simulated The effect of weight % variation of milled carbon fibres on the microwave absorbing properties of composites have been studied in the frequency range 2–18 GHz.

Improved microwave absorbing property provided by the filler's alternating lamellar distribution of carbon nanotube/ carbonyl iron/ poly (vinyl chloride) composites

The microwave absorbing properties of composites with filler's uniform and selective distribution were comparatively investigated. The calculated and experimental results demonstrated that, compared with the uniform distribution, filler's selectively alternating lamellar distribution was more effective in decreasing the minimum reflection loss (RL-min) and broadening the effective bandwidth (EB, RL < −10 dB, for 90% microwave absorption). For examples, for the normal blending samples 3#, the multi-layer structure decreased the RL-min from −21.0 to −48.1 dB, broadened the EB from 2.9 to 5.0 GHz. The layer number, filler content and layer arranging sequence also have strong effects on the microwave absorbing properties. The mechanism behind these effects was the competition between two effects (transmission blocking and attenuation enhancement) provided by the multi-layer structure. The matching frequency could be adjusted by changing the layer number rather the sample thickness. This study provided a facile way to construct a filler's selective distribution morphology, and a more effective method to combine different absorbents, which could be applicable in the designing and fabricating of high-efficient structural microwave absorbing materials.

Multi-interfacial Co@CoNx@C(N) nanocapsules with nitrogen substitutions in graphitic shells for improving microwave absorption properties

Integrating multiple components with heterogeneous interfaces has been widely proven effective for optimizing the microwave absorption properties of composites. We herein report on an arc-discharging strategy to synthesize the onion-like Co@CoNx@C(N) nanocomposite with dual core@shell heterogeneous interfaces. The graphitic carbon shells are in-situ functionalized by nitrogen substitutions, resulting in the formation of pyridinic, pyrrolic and graphitic nitrogen substitutions. Such a structural configuration contributes to a significant enhancement in dielectric loss capacity, presenting three main attenuation peaks at the frequencies of 6.6 GHz, 13.5 GHz and 17.1 GHz, respectively. The Co@CoNx@C(N) nanocomposite simultaneously possesses on the synergistic effect of heterogeneous interfaces and the atomic-scale substitutions in a nanoscale system and thus has important implications in designing novel microwave absorption materials.

Microwave absorbing properties of composites containing ultra-low loading of optimized microwires

A set of composite absorbers with ultra-low loading of down to 0.017 wt.% short-cut microwires were prepared and investigated in terms of their magnetic and microwave properties in the X-band (8–12 GHz). The key parameters that could factor into the performance of the present absorbers have been systematically studied from micro to macro scale, i.e., the magnetic domain structure modulated by different internal stress scenarios, microwire aspect and composite filling ratio, and relative importance of impedance matching and material loss. Longer wires (9 mm) and wires after suitable treatment lead to the enhancement of microwave absorbing property mainly due to the larger magnetic loss resulted from the natural ferromagnetic resonance, which is induced in the domain rotation and reversal process. The internal stress modification by removal of glass and joule annealing has profound effects in formulating the microwave absorption frequency and intensity of microwire composites by tailoring the domain structure and local anisotropy field. It is found that the composites with microwires annealed at 132 mA for 15 min obtain the minimum reflection loss and broadest absorption bandwidth with reference to −10 dB at 1.5 mm thickness, which is −25.7 dB (0.81 GHz) at 11.39 GHz caused by the relative high attenuation constant and best matching condition where Zreal is 1.026 and Zimag is −0.102. This indicates that impedance matching plays a dominant role in tailoring the microwave absorbing property. Remarkably, the unconventional absorption frequency - matching thickness relation based on the quarter-wavelength model offers possibility to address the limitation of thickness for low frequency absorbing application.

Effect of 3D woven fabrics on the microwave absorbing and mechanical properties of gypsum composites using carbon black as an absorbent

In order to improve the S and X band microwave absorbing properties of gypsum based composites with carbon black (CB) as an absorbent, three-dimensional (3D) woven fabric was embedded into the composites and the effects of 3D woven fabric on the dielectric properties, wave absorption, and mechanical properties were investigated. The results show that the microwave absorbing properties of the composites are visibly enhanced after being embedded with the 3D woven fabric. The minimum reflection loss reaches −16 dB and the bandwidth for −10 dB is 1.4 GHz in the S band; and in the X band the minimum reflection loss of −25 dB can be obtained and the bandwidth for −10 dB reaches 2.5 GHz. The introduction of the 3D woven fabrics can decrease the complex permittivity of the composites, resulting in the improvement of impedance matching. Moreover, a new microwave attenuation path is provided by the ‘hollow fibers’ of 3D woven fabric, which can enhance the microwave attenuation capacity. Thus, using 3D woven fabric is an effective way to improve the microwave absorption of an absorber with a dielectric loss absorbent. In addition, the flexural strength of the composites can be evidently enhanced by 3D woven fabrics.

Excellent Microwave Absorption Behaviors of Polyaniline Composites Containing CeO2 Nanorods in the X-Band

Conductive polyaniline/CeO2 nanocomposite powders (PANI/CeO[Formula: see text] were prepared by an in situ polymerization method. The effects of CeO2 content on the microwave absorption properties of composites were investigated. The phase composition, morphological characteristics, electromagnetic parameters and microwave absorption properties of the composites were characterized through X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and vector network analysis. Results show that CeO2 nanorods are coated with PANI to form a well-defined hierarchical structure. CeO2 is well-incorporated into the PANI matrix. CeO2/PANI exhibits excellent microwave absorption properties at 2–18[Formula: see text]GHz. As the CeO2 content increases to 30[Formula: see text]wt.%, an optimal reflection loss (RL) of [Formula: see text]40[Formula: see text]dB (99.99% of electromagnetic wave absorption) is observed at 8.8[Formula: see text]GHz with a thickness of 3.0[Formula: see text]mm. The frequency bandwidth corresponding to 90% of electromagnetic wave absorption crosses the X-band. Therefore, PANI/CeO2 can be used as an advantageous candidate for a new type of microwave absorptive material.

Synthesis, Characterization and Properties of PANI/(La-Nd Doped BaFe&lt;sub&gt;12&lt;/sub&gt;O&lt;sub&gt;19&lt;/sub&gt;) Composites

La-Nd co-doped barium hexaferrites, Ba0.7(LamNdn)0.3Fe12O19 (D-BaM), were successfully prepared by sol-gel method. PANI / D-BaM composites were synthesized by in-situ polymerization in solution. The structure, morphology and properties of samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), four-probe conductivity tester and vector network analyzer. The XRD patterns showed that the crystal structure of all the samples exist as M-type phases. The SEM images revealed that the particles presented a hexagonal platelet-like morphology. The magnetic properties could be improved by substitutions of La and Nd ions. The saturation magnetization (Ms) and coercive force (Hc) increased with the change of La / Nd ratio to the maximum at La / Nd = 3:1. The doped particles have also been embedded in conductive PANI to prepare electromagnetic materials, and the conductivity kept on the order of 10-2. The microwave absorbing properties of composites at 30 MHz-6 GHz improved obviously, the peak value of reflection loss could reach-7.5 dB.

Electroless plating preparation and electromagnetic properties of Co-coated carbonyl iron particles/polyimide composite

To solve the serious electromagnetic interference problems at elevated temperature, one thin microwave-absorbing sheet employing Co-coated carbonyl iron particles and polyimide was prepared. The Co-coated carbonyl iron particles were successfully prepared using an electroless plating method. The microstructure, composition, phase and static magnetic properties of Co-coated carbonyl iron particles were characterized by combination of scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The electromagnetic parameters of Co-coated carbonyl iron particles/polyimide composite were measured in the frequency range of 2–18GHz, and the electromagnetic loss mechanism of the material-obtained was discussed. The microwave absorption properties of composites before and after heat treatment at 300°C for 100h were characterized in 2–18GHz frequency range. It was established that composites based on Co-coated carbonyl iron demonstrate thermomagnetic stability, indicating that Co coating reduces the oxidation of carbonyl iron. Thus, Co-coated carbonyl iron particles/polyimide composites are useful in the design of microwave absorbers operating at temperatures up to 300°C.

Temperature dependent electrical conductivity and microwave absorption properties of composites based on multi-wall carbon nanotubes and phthalocyanine polymer

Phthalocyanine (Pc) polymer composites containing multi-walled carbon nanotubes (MWCNTs) were successfully prepared via thermal annealing and their microwave absorption properties were tuned by changing the annealing temperatures from 300 to 500 °C. The effects of the introduction of MWCNTs into Pc polymer matrices and elevated annealing temperature on the electrical conductivity and the permittivity of the composites have been investigated. The results indicated that the synergistic effect of electrical conductivity and the permittivity endowed the composites with excellent microwave absorbing properties. Particularly, the reflection loss peak achieved a minimum value of −59.50 dB at 11.84 GHz when the sample with a thickness of 2.36 mm was annealed at 450 °C. The tuning of electromagnetic parameters of polymer composites by changing annealing temperature provided a simple and effective technical direction for the design of microwave attenuation materials.

Fabrication and microwave absorbing properties of (Z-type barium ferrite/silica)@polypyrrole composites

The organic–inorganic hybrid materials with many potential applications have been studied widely. Moreover, the fabrication of Z-type barium ferrite/silica (Z-BCF/SiO2) is still challenging owing to the intricate structure and preparation process. Here, the double core–shell (Z-type barium ferrite/silica)@Polypyrrole composites ((Z-BCF/SiO2)@PPy) have been successfully fabricated by in-situ chemical synthesis method. The structure, morphology and electromagnetic performances of the composites were characterized by TG, IR, XRD, SEM, TEM and VSM. The results indicated that the Z-BCF/SiO2 particles were efficiently coated by PPy, and the (Z-BCF/SiO2)@PPy composites have the more superior electrical conductivity than Z-BCF/SiO2 composites, but their saturation magnetization declines to some extent. It is related to the content of relevant component. More meaningfully, the PPy coating improved the microwave absorbing properties of composites in the 2–18GHz frequency range. A minimum reflection loss (RLmin) value of −19.65dB is obtained for the (Z-BCF/SiO2)@PPy composites with 66.67wt% PPy with thickness of merely 2mm, and its absorption bandwidth below −8dB reaches 5.56GHz. Furthermore, the favorable absorption can be extended to the range of 18–26GHz. Therefore, the novel ternary composites with excellent microwave absorbing properties may have potential applications in electromagnetic shielding field.

Microwave absorption properties of carbon black and tetrapod-like ZnO whiskers composites

CB/T-ZnO/EP composites were prepared using carbon black (CB) and tetrapod-like ZnO whiskers (T-ZnO) as absorbents and epoxy resin (EP) as binder. The electromagnetic parameters and microwave absorption properties of the composites were measured in the frequency range of 2–18GHz. The influences of absorbents concentration and composites thickness on microwave absorption properties were studied. Results show that the minimum reflection loss for CB/T-ZnO/EP composites is −19.31dB at 10.4GHz and the bandwidth corresponding to reflection loss blow −5dB is 9.68GHz, when the content of CB and T-ZnO whiskers are 7wt% and 13wt%, respectively, and the composites thickness is 3mm. The mechanisms of microwave absorption performance for CB/T-ZnO/EP composites were briefly discussed. It is supposed that CB/T-ZnO/EP composites have the potential to be applied as microwave absorber with high microwave-absorption and light weight.

Effect of inclusions' distribution on microwave absorbing properties of composites

Effect of inclusions' spatial distributions on the permeability and permittivity of composites is studied using the generalized Maxwell-Garnett equations. The result indicates that inclusions' orientation distribution can increase the longitudinal electromagnetic parameters. For inclusions' random and orientation distribution, single and three-layer absorbers are designed and optimized using genetic algorithm. The result shows that under a given absorbing requirement, absorber with inclusions' orientation distribution is lighter and thinner than absorber with inclusions' random distribution.

Dielectric and magnetic response of Sr–Zn ferrite composite

Sr–Zn ferrite composites were synthesized by chemical coprecipitation with different sintering process. The composites were characterized by XRD, XPS, IR, VSM, and N2-adsorption. The results revealed that the composites were composed of S-type ZnFe2O4 and M-type SrFe12O19. Zn2+ ions inserted and occupied the 12k or 2a sites for Fe3+ ions in M-type SrFe12O19. The Zn2+ ions were therefore not on the external surface of the composites. The microwave absorption properties at a frequency range of 0–18 GHz were estimated using the electromagnetic parameters obtained through the agency of microwave vector network analyzer. The microwave absorbing properties of composites were excellently superior to that of the pure SrFe12O19 or ZnFe2O4 due mainly to the exchange coupling between the hard- and soft-magnetic phases. The synthesis process was found to facilitate mass production for various composite materials, especially the two phases or multiphase composite materials.

Microwave Absorption Properties of BaFe12O19-TiO2 Composite Coated with Conducting Polymer

This study investigates microwave absorption properties of Ba-hexaferrite (BaFe12O19) and titanium dioxide (TiO2) particles coated with conducting polymer (PANI) and BaFe12O19-TiO2 mixture in the frequency range of 8–18 GHz. Samples having different magnetic to dielectric mass ratios and various thicknesses from 1.5 to 4 mm have been prepared to investigate effect of magnetic and dielectric fillers together with influence of conducting polymer layer on microwave absorption properties of BaFe12O19-TiO2 composite. Structural, magnetic, and microwave absorption properties of composites have been investigated using X-ray diffraction, scanning electron microscopy and near field microwave measurements using vector network analyzer. Microwave measurements revealed that composites with PANI coating have much higher absorption values which are independent of an absorber thickness. Among PANI coated absorbers, sample having magnetic to dielectric mass ratio of 2 showed better microwave properties in 8–18 GHz range.

Influence of the morphology of polyaniline on the microwave absorption properties of epoxy polyaniline composites

Abstract This study reports on the electrical conductivity and dielectric properties of conductive epoxy composites containing polyaniline (PANI) with various morphologies. Globular, fibrillar, and flake-like PANIs, with more or less high aspect ratios (ratio of length to diameter or thickness), were synthesized and dispersed into an epoxy resin. It was found that increasing the aspect ratio of PANI reduces the electrical percolation threshold of the composites (from 3.9 to 1.3 vol.%), and enhances their electrical conductivity up to σ > 10 −3 S/cm. Moreover, it was found that flake-like PANI, with increased aspect ratio, improves the microwave absorption properties of the composites in a microwave range: 2.4–8.8 GHz. The imaginary permittivity (e′′) was doubled for composites containing flake-like PANI, compared to globular and fibrillar PANI. These higher values of dielectric losses have been attributed to the highly polarizable structure of flake-like PANI, which contributes to more important polarization mechanisms.