Dielectric and Radar-Absorbing Properties of Exfoliated Graphite Dispersed Epoxy Composites

Abstract

Electromagnetic absorbers based on carbonaceous materials, i.e., carbon black, polyaniline, polypyrrole, carbon fiber, etc., are prominently employed to attenuate incident electromagnetic waves. In the current work, exfoliated graphite (EG) was synthesized with swollen expanded volume from graphite flake by using a simple and inexpensive method. After synthesis, a series (8.9, 22.9, 33.3, 41.4 and 44.7 volume percentage) of EG-epoxy composites were prepared using a wet mixing method. EG and the prepared composites were characterized by x-ray diffraction analysis, field-emission scanning electron microscopy, and energy-dispersive x-ray analysis. An Agilent vector network analyzer (model PNA E8364B) was employed to compute the complex permittivity (e r = e¢ À je¢¢) of the prepared composites in the frequency range of 2 GHz to 18 GHz. The dielectric loss of the prepared EG-epoxy composites was quantified in terms of the loss tangent (tand e = e¢¢/e¢). Their radar absorption properties were evaluated in terms of the return loss (RL), which in turn was calculated for varying thicknesses of the prepared composites using the computed complex permittivity data. The measured minimum RL was À26.4 dB for the absorber with thickness of 4.0 mm, and the bandwidth achieved was 5.2 GHz for RL £ À 10 dB in the effective frequency region of 8 GHz to 14 GHz. The matching frequency shifted towards downwards with increasing EG content in the epoxy thermosetting matrix according to both the calculated and measured data. Consequently, the prepared composites exhibited good complex permittivity, dielectric tangent loss, and microwave absorption and could be utilized in the design of electromagnetic interference shielding and absorbers for stealth applications.

Fe3O4–Graphite Composites as a Microwave Absorber with Bimodal Microwave Absorption

“…Due to the stacked structure of graphite sheets, it has specific absorbing properties . The absorbing properties of Fe 3 O 4 /graphite composites formed by loading Fe 3 O 4 on graphite sheets have been greatly improved. , First of all, graphite with low density, high specific surface area, and good electrical conductivity is beneficial to the absorption and attenuation of electromagnetic waves. ,,− Second, Fe 3 O 4 nanoparticles can enhance the magnetic loss of the material so that the composite material has both magnetic loss and electrical loss, which is beneficial to improve the impedance matching characteristics of the material . Finally, the reflection loss of Fe 3 O 4 generally occurs at a lower frequency region, and the reflection loss of graphite is usually located in the high-frequency region .…”

Shielding effectiveness performance of polyaniline-NiFe2O4:Cu composites for sub-8 GHz applications

“…The shielding materials can be divided into two groups: (1) wave-reflection dominating materials and (2) wave-absorption dominating materials. Magnetic materials like spinel ferrites, nonconductor materials like carbon nanotubes, graphite and graphene, and conductive polymers are some of the most common wave absorber materials (Li et al 2006;Rohini 2014;Pratap et al 2020;Peymanfar et al 2020b).…”

Capacitive Properties of Modified and Non Modified Thermally Expanded Graphite Composites With Polyaniline

“…Використання графіту як компонента композиційних матеріалів на основі ПАн дозволяє поєднувати низький коефіцієнт тертя, високу електропровідність, механічну міцність і велику питому поверхню вуглецевих матеріалів [2,3] з фізико-хімічними властивостями та реакційною здатністю ПАн. Поєднання електрохімічних властивостей ПАн з електропровідністю і високорозвиненою поверхнею вуглецевих матеріалів є, зокрема, основою створення високоємнісних електрохімічних конденсаторів [4], сенсорів [5], джерел струму [6], спеціальних покриттів [7] та ін. Крім того, сукупність електропровідних властивостей ПАн і вуглецевих матеріалів може призводити до синергетичного ефекту, який виражається, зокрема, у збільшенні електропровідності композиту порівняно з відповідними вихідними компонентами [8].…”