Microwave absorbing performances of multiwalled carbon nanotube composites with negative permeability

Abstract

The permittivity and permeability behaviors of composites made from the multiwalled carbon nanotubes with magnetic impurity Ni and the wax have been studied in 3–18GHz. The unusual permittivity dispersion behaviors have been explained based on the Cole-Cole model and the conductivity contribution model. Permeability is found to have negative imaginary parts within 3–11GHz. The composites are found to show good microwave absorbing performances (reflection loss <−20dB): matching thickness is 1.5mm and absorbing frequency band is 11.6–12.4GHz, and the absorbing performance can be explained by the “geometrical effect.”

Nanostructured composites based on carbon nanotubes and epoxy resin for use as radar absorbing materials

“…With the emergence of new target detection modes, especially multifrequency detection, composites with multiwalled carbon nanotubes embedded into a polymer matrix have been studied for applications in the microwave frequency range, such as antireflections, electromagnetic interference shielding and microwave absorbers 1,2 . Radar Absorbing Materials (RAM) provide energy losses of electromagnetic radiation.…”

“…Theoretical calculations show that CNTs act to like insulators, semiconductors or metals depending on their radii and chiralities. Composites with multiwalled carbon nanotubes (MWNTs) embedded into a polymer host have been use to microwave applications, such as antireflection, electromagnetic interference shielding (EMI) or microwave absorber 1,[47][48][49][50][51][52][53][54] . Thus, the objective of this work was to process nanostructured composite materials based on formulations containing different quantities of multiwalled carbon nanotubes in an epoxy resin matrix, aiming to determine the adequate quantity of CNT for processing X-band microwave absorbing nanostructured composite.…”

Synthesis, characterization and microwave absorption of carbon-coated Cu nanocapsules

“…An optimal RL value of -40.0 dB, corresponding to 99.99 % absorption, is observed at 10.52 GHz for a layer 1.9 mm thickness. It is worth noting that the absorbent with a thickness of 1.1 mm has RL values exceeding -20 dB at high frequencies in broad frequency ranges, which is thinner than the previous reported results [3][4][5][8][9][10][16][17][18][19][20][25][26][27] . As shown in Figure 3b, for all frequencies within the 1-18 GHz range, RL values exceeding -20 dB can be obtained by selecting an appropriate thickness of the absorbent layer between 1.1 and 10.0 mm.…”

Strengthened electromagnetic absorption performance derived from synergistic effect of carbon nanotube hybrid with Co@C beads

“…The maximum μ r ″ value is lower than that of the sample with 60 wt% CNTs/Co@C (0.17), due to the decreased addition amount of CNTs/Co@C. Notably, the μ r ″ values are less than zero in the 8.9-20 GHz range, denoting that the Co/CNTs nanocomposites could be used as a left-hand material. Notably, the μ r ″ values are less than zero in the 8.9-20 GHz range, denoting that the Co/CNTs nanocomposites could be used as a left-hand material [47][48][49]. For a further investigation, the dielectric loss tangent (tanδ E = ε ″ /ε ′ ) and magnetic loss tangent (tanδ M = μ ″ /μ ′ ) were calculated for two samples and are displayed in Fig.…”

“…The transformation of magnetic energy to electric energy indicates that, at high frequency, the EM absorption is mainly ascribed to the dielectric loss in the CNTs/Co@C hybrid. The negative permeability value and totally contrary variation trend of tangent loss have also been observed in other magnetic carbon hybrids such as CNTs/wax composite [49], Fe/Co/Ni nanoparticle-coated carbon nanofibers [50], graphene oxide/ CNT-Fe 3 O 4 composite [10], and porous carbon/Co hybrid [51]. To reveal the EM wave absorption performances of the CNTs/Co@C hybrid, the RL values were calculated according to Eqs.…”