Microwave Absorption Properties Of Carbon Research Articles

Influence of pyrolysis temperature on the low-frequency microwave absorption properties of carbon encapsulated nickel/nickel oxide composites

Influence of pyrolysis temperature on the low-frequency microwave absorption properties of carbon encapsulated nickel/nickel oxide composites

Preparation and microwave absorption properties of carbon nanotubes/iron oxide/polypyrrole/carbon composites

Carbon nanotubes/iron oxide/polypyrrole/carbon composites were prepared by in situ polymerization. The weight percentage of the iron oxide nanoparticles was only 8.8 %. The microwave absorption performance of the carbon nanotubes/iron oxide/polypyrrole/carbon composites was researched and the corresponding filler loading of paraffin in the tested samples was 80 wt%. The reflection loss appeared at 13.92 GHz, which was -53.07 dB, the corresponding effective absorption bandwidth was 6.4 GHz, and the matching thickness was 2.2 mm. The synthetic composite materials have both magnetic loss and dielectric loss. The combination between different materials and the improved impedance matching can enhance the electromagnetic wave performance. At the same time, the composite materials have multiple interface and multilayer core-shell structure, which was beneficial to absorbing electromagnetic waves.

Electromagnetic microwave absorption properties of carbon nanocoils/tissue

An economic electromagnetic wave absorber with carbon nanocoils (CNCs)/tissue and paraffin has been successfully synthesized and exhibits excellent microwave absorption property. The CNCs/tissue composite was obtained by growing spring-like CNCs on the tissue substrate with Fe2(SO4)3/SnCl2 catalyst in a chemical vapor deposition method. It is found that the absorbers containing 10wt% and 20wt% CNCs/tissue show strong microwave absorption in a frequency range of 2–18GHz. For the composite with 10wt% CNCs/tissue, the maximum reflection loss (RL) of −46.36dB at 14.72GHz and the bandwidths of 7.44 and 5.68GHz respectively corresponding to RL below −10 and −20dB can be obtained. In addition, the composite with 20wt% CNCs/tissue can also gain broad bandwidth corresponding to reflection loss below −10dB, which is as high as 7.52GHz. It is revealed that the composite with 10wt% CNCs/tissue owns suitable real part of permittivity, which helps to obtain better impedance match and lower reflection coefficient to enhance the absorption of electromagnetic wave.

Enhanced Microwave Absorption Properties of Carbon Black/Silicone Rubber Coating by Frequency-Selective Surface

A square frequency-selective surface (FSS) design has been employed to improve the microwave absorption properties of carbon black/silicone rubber (CBSR) composite coating. The FSS is placed on the surface of the CBSR coating. The effects of FSS design parameters on the microwave absorption properties of the CBSR coating have been investigated, including the size and period of the FSS design, and the thickness and permittivity of the coating. Simulation results indicate that the absorption peak for the CBSR coating alone is related to its thickness and electromagnetic parameters, while the combination of the CBSR coating with a FSS can exhibit a new absorption peak in the reflection curve; the frequency of the new absorption peak is determined by the resonance of the square FSS design and tightly depends on the size of the squares, with larger squares in the FSS design leading to a lower frequency of the new absorption peak. The enhancement of the absorption performance depends on achievement of a new absorption peak using a suitable␣size and period of the FSS design. In addition, the FSS design has a stable␣frequency response for both transverse electromagnetic (TE) and transverse magnetic (TM) polarizations as the incident angle varies from 0° to 40°. The optimized results indicate that the bandwidth with reflection loss below −5 dB can encompass the whole frequency range from 8 GHz to 18 GHz for thickness of the CBSR coating of only 1.8 mm. The simulation results are confirmed by experiments.

Effect of Carbon Black on Dielectric and Microwave Absorption Properties of Carbon Black/Cordierite Plasma-Sprayed Coatings

Carbon black (CB)/cordierite composite coatings with different CB contents were fabricated by a multi-function micro-plasma spraying system developed by the Second Artillery Engineering College. Scanning electron microscopy was employed to investigate the microstructure of the spray-dried powders and as-sprayed coatings. The complex permittivities of the coatings and powders with different CB contents were investigated at the frequency of 8.2-12.4 GHz. The results show that both real and imaginary part of the permittivity increase with increasing CB content, which can be ascribed to the increase of the number of micro-capacitors and the polarization centers. Reflection loss of the as-sprayed coatings with different CB contents and thicknesses was calculated according to the transmission line theory. The coating with 4.54% CB content and 3.0 mm thickness shows optical microwave absorption with a minimum reflection loss of −23.90 dB at 10.13 GHz and reflection loss less than −9 dB over the whole investigated frequency.

Low temperature charge transport and microwave absorption of carbon coated iron nanoparticles–polymer composite films

In this paper, the low temperature electrical conductivity and microwave absorption properties of carbon coated iron nanoparticles–polyvinyl chloride composite films are investigated for different filler fractions. The filler particles are prepared by the pyrolysis of ferrocene at 980°C and embedded in polyvinyl chloride matrix. The high resolution transmission electron micrographs of the filler material have shown a 5nm thin layer graphitic carbon covering over iron particles. The room temperature electrical conductivity of the composite film changes by 10 orders of magnitude with the increase of filler concentration. A percolation threshold of 2.2 and an electromagnetic interference shielding efficiency (EMI SE) of ∼18.6dB in 26.5–40GHz range are observed for 50wt% loading. The charge transport follows three dimensional variable range hopping conduction.

Electromagnetic characteristic and microwave absorption properties of carbon nanotubes/epoxy composites in the frequency range from 2 to 6 GHz

The preparation and characterization of carbon nanotubes (CNTs)/epoxy composites were studied for microwave absorption, which frequency is from 2 to 6 GHz. The absorbing coating with a loading of 15 wt % CNTs/epoxy resin, which thickness is 3 mm, exhibited an absorbing peak of 10.5 dB at 3.85GHz. After being treated by HNO3–H2SO4 acid at the temperature of 100 °C, the real and imaginary part values of permittivity of CNTs have a larger increase in quantity, and the absorbing peak position moves to lower frequency of 3.35 GHz showing an increasing the dielectric loss in lower microwave frequency. Two-layer coating with CNTs/epoxy resin and graphite/epoxy resin composites have been also investigated in order to widen the frequencies range of CNTs microwave sorbent in the low microwave frequency application. The results indicated that two-layer coating (15 wt % loading CNTs/epoxy resin and 9 wt % loading graphite/epoxy resin) can obtain 2.4 GHz broad frequencies band for absorption of 5.0 dB. The absorbing peak intensity and position can be adjusted by changing the thickness of each layer coating in the case of fixed total thickness. The two-layer coating of 15 wt % loading CNTs/epoxy resin (dtop=2 mm) and 9 wt % loading graphite/epoxy resin (dbottom=1 mm) has a strong absorbing peak at 5.52 GHz and achieves an absorbing value of 20.79 dB.

Complex permittivity and microwave absorption properties of carbon nanotubes/polymer composite: A numerical study

Based on an equivalent resistance–capacitance (RC) network, we investigate theoretically the complex permittivity and microwave absorption properties of carbon nanotubes (CNTs)/polymer composite in the frequency range of 50 MHz–3 GHz using the logarithmic mixing rule. Both the real and imaginary parts of the permittivities of CNTs and polymer are considered in detail. The simulated results show that the real and imaginary permittivities of the composite increase explicitly with increasing volume fraction of CNTs, and the latter is more sensitive. The calculated complex permittivity spectra of the composite are in good agreement with the available experimental data. In addition, a good linear relationship between microwave absorbance and frequency is found.