Microwave absorption enhancement of rectangular activated carbon fibers screen composites

Zang, Yongju; Xia, Shaoxu; Li, Liwei; Ren, Guizhi; Chen, Qiping; Quan, Haiyu; Wu, Qilin

doi:10.1016/j.compositesb.2015.03.059

Cited by 46 publications

(8 citation statements)

References 34 publications

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“…Otherwise, multi-reflections and backscattering occur in a porous matrix, between the air/matrix [9,44]; these losses are negligible compared to the measured losses of our composites. Multi-reflections occur also between the matrix and the fibers [35] and the attenuation of the waves (by trapping) in fiber agglomerates is expected [45]. In our composites, the shape and the dimensions of the agglomerates are random, but we can suggest that the crossed long CFs, will trap and absorb (by multi-reflections) the EM waves of long wavelengths (low frequencies) as schematized in Figure S8a; while small EM wavelengths (at high frequencies) will be able to pass through these agglomerates (Figure S8b).…”

Section: Effect Of Carbon Fiber Lengths On Dielectric Properties Of Cf-loaded Compositesmentioning

confidence: 99%

Long Carbon Fibers for Microwave Absorption: Effect of Fiber Length on Absorption Frequency Band

et al. 2020

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This work presents lightweight epoxy foams loaded with very low weight percentages (≤0.5 wt.%) of carbon fibers (CFs) with different lengths (3 mm, 6 mm, and 12 mm) as broadband microwave absorbing materials for anechoic chamber application. The effect of CF length on microwave absorption, especially on the absorption frequency band, is investigated for frequencies between 1 and 15 GHz. For the elaboration of composites, three different methods—spatula, shear mixing, and ultrasounds—are used for the dispersion of CFs. The observation of these CFs, after the dispersion step, shows a high fiber breakage rate when shear mixing is used, unlike when spatula or ultrasounds methods are used. On the other hand, the characterization of the elaborated composites highlights a correlation between the mixing methods, hence the fiber brakeage, and the measured reflection coefficient (reflection loss) of the composites. As a result, the minimum value of the reflection coefficient is shifted toward the high frequencies when the fiber breakage is observed, suggesting that short CFs absorb at high frequencies while long CFs absorb at low frequencies. Dielectric properties, extracted from the measurement in free space, of composites elaborated with different fiber lengths (3 mm, 6 mm, and 12 mm) confirm that short CFs (3 mm) show maximum losses at high frequencies (around 15 GHz) while long CFs (12 mm) show maximum dielectric losses at low frequencies (below 4 GHz). However, no significant variation is observed on the real part of the relative permittivity, as a function of fiber length, for these porous composites loaded with very low CF rates. A hybrid composite, with a mix of different CF lengths, is prepared and characterized. The simulation of the absorption performance of a pyramidal absorber, based on this hybrid composite, is compared to the one of pyramidal absorber based on composites loaded with a single length of carbon fibers. The pyramidal absorber-based hybrid composite predicts the best absorption performance, especially at the low frequency band. The simulated reflection coefficient of this absorber is less than −12 dB in all the studied frequency range, and less than −40 dB for frequencies higher than 3 GHz. This result confirms the interest of using a mix of carbon fiber lengths to achieve a broadband microwave absorber.

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Section: Effect Of Carbon Fiber Lengths On Dielectric Properties Of Cf-loaded Compositesmentioning

confidence: 99%

Long Carbon Fibers for Microwave Absorption: Effect of Fiber Length on Absorption Frequency Band

et al. 2020

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“…Composites and nanocomposites are basic examples of CNT-based structures [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. In order to achieve electromagnetic wave absorption, special coatings called radar absorption materials (RAM) including multi-walled carbon nanotubes (MWCNT) are mostly used in the defense industry [ 21 , 22 ].…”

Section: Introductionmentioning

confidence: 99%

Behaviors of Electromagnetic Wave Propagation in Double-Walled Carbon Nanotubes

Basmaci

2021

Materials

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In this study, behaviors of electromagnetic wave propagation in a double-walled carbon nanotube (DWCNT) are investigated theoretically. For this purpose, the effects of carbon nanotube’s inner and outer tubes’ material property parameters (μ, ε) on electromagnetic wave propagation are discussed. The effects of interaction between the carbon nanotube’s inner and outer tubes on the electromagnetic wave propagation are defined. Nonlocal effects of the DWCNT on electromagnetic wave propagation are examined. Besides, the electromagnetic wave propagation frequencies are specifically investigated, taking the DWCNT’s nonlocal effects and material property parameters (ε, µ) into account. When the wavenumber, k, is greater than 1.8 × 1010, the frequencies of the fundamental mode and the second mode converge to 3.554 × 108 Hz. Additionally, the electromagnetic wave propagation frequencies decrease with the increase of the DWCNT’s nonlocal parameter (ν) and decrease with material parameter (D).

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“…Carbonyl iron powders (CIPs) are a kind of traditional magnetic loss SE filler with good temperature stability and high magnetic conductivity [7]. However, due to their small size, large specific surface areas, and low dielectric constants, CIPs did not show obvious advantages in EMI shielding materials.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Shielding Performance of Layered Carbon Fiber Composites Filled with Carbonyl Iron and Carbon Nanotubes in the Koch Curve Fractal Method

et al. 2020

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Layered carbon fiber composites (CFC) with enhanced shielding effectiveness (SE) were prepared with mixed fillers of carbon nanotubes (CNTs) and carbonyl iron powders (CIPs) in the form of a Koch curve fractal. In the layered composite structure, glass fiber (GF) cloth was used in the wave–transmissive layer (WTL), and the carbon fiber (CF) cloth was used in the supporting layer (SL). Between WTL and SL, CNTs and CIPs were distributed in epoxy resin in the form of a Koch curve fractal to act as an absorbing layer (AL), and copper foil was used as a reflective layer (RL) and bonded at the bottom of the whole composites. The layered structure design and excellent interlayer interface integration obviously improved the SE performance of the CFC. The SE of different samples was investigated, and the results show that, with the increase in the number (n) of Koch curve fractals, the SE of the samples enhanced in the low frequency scope (1–5 GHz). The sample with n = 2 has the highest SE value of 73.8 dB at 2.3 GHz. The shielding performance of the fractal sample filled by CNTs and CIPs simultaneously has a comprehensive improvement in the whole scope of 1–18 GHz, especially for the sample with n = 2. The cumulative bandwidth value of the SE exceeding 55 dB is about 14.3 GHz, accounting for 85% of the whole frequency scope, indicating the composite fabricated in this paper is an electromagnetic shielding material with great prospect.

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Microwave absorption enhancement of rectangular activated carbon fibers screen composites

Cited by 46 publications

References 34 publications

Long Carbon Fibers for Microwave Absorption: Effect of Fiber Length on Absorption Frequency Band

Long Carbon Fibers for Microwave Absorption: Effect of Fiber Length on Absorption Frequency Band

Behaviors of Electromagnetic Wave Propagation in Double-Walled Carbon Nanotubes

Enhanced Shielding Performance of Layered Carbon Fiber Composites Filled with Carbonyl Iron and Carbon Nanotubes in the Koch Curve Fractal Method

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