Page 12 - ESAM-1-2

Engineering Science in
Additive Manufacturing AM-CFRP structures for EMWA properties

d of CF depend significantly on its type and structural
(VIII) 19
m
r characteristics. High-modulus CFs, with their highly
r
graphitic and ordered crystalline structure, exhibit strong
electrical conductivity, which tends to reflect rather
where t is the thickness of the material, λ is the than absorb microwaves. In contrast, low-modulus
m
wavelength of the material itself, and λ is the free space or polyacrylonitrile (PAN)-based CFs contain more
d
wavelength. |π | and |ε | are the moduli of relative magnetic amorphous regions, reducing conductivity and enhancing
r
r
permeability μ and relative permittivity ɛ , respectively.
r r dielectric loss, making them more effective for absorption.
3. Electromagnetic microwave In addition, the physical form of the fiber plays a role—
characteristics of various fiber-reinforced continuous CFs reflect microwaves along their alignment,
while short-cut or randomly dispersed fibers improve
materials impedance matching and promote internal scattering,
3.1. CF-reinforced composites increasing absorption. To optimize performance, CFs
are modified through oxidation, surface treatments, or
Because of their superior electrical conductivity, low hybridization with magnetic particles like Fe₃O₄, which
weight, and mechanical durability, CF-reinforced combine dielectric and magnetic loss mechanisms for
composites have become very effective EMWA materials. broader absorption bandwidths. 41
Dielectric loss and energy dissipation are improved by the
numerous internal reflections, and scattering of incident The key mechanisms governing microwave absorption
electromagnetic waves is made possible by the high aspect in CF include conductive loss, dielectric loss, and magnetic
ratio and interconnected network of CFs. For example, loss, each playing a critical role depending on the fiber’s
42
Elhassan et al. investigated the efficient synthesis of composition and structure. Conductive loss dominates
38
Fe O /PPy double-carbonized core-shell-like composite in highly graphitic CFs, where free electrons interact with
3
4
for broadband EMA. It achieved exceptional EMWA electromagnetic fields, converting microwave energy into
properties as a wide effective absorption band of 4.64 heat—though excessive conductivity can lead to unwanted
GHz and a minimum RL of −26 dB at 1.6 mm. Moreover, reflection rather than absorption. Dielectric loss, more
randomly distributed CFs tend to produce greater isotropic prominent in disordered or functionalized CFs, arises from
absorption, whereas aligned fibers can create anisotropic dipole polarization and interfacial effects, enhancing energy
43
electromagnetic responses, which may be customized for dissipation. When combined with magnetic materials
39
specific polarization-dependent applications. like iron oxides or ferrites, magnetic loss further improves
absorption by introducing additional energy conversion
Recent studies have concentrated on improving the pathways. Effective microwave absorption ultimately relies
matrix composition and CF concentration for better on balancing these mechanisms while optimizing impedance
broadband absorption and impedance matching. For matching to minimize surface reflection and maximize
20
example, Tang et al. investigated the prominent fiber penetration into the material. While recycled or bio-
40
25
orientation effect and enhanced the electromagnetic based CFs can enhance the sustainability of CF composites
wave anisotropic properties. Copper fibers with slender without compromising electromagnetic performance, their
dimensions form abundant, flexible, multisize equivalent absorption bandwidth and intensity can be further increased
waveguide attenuator structures that promote vector via integration with other lossy materials, such as magnetic
superposition and interference effects, exhibiting RL nanoparticles or conductive polymers.
peaks at 7 GHz and 12 GHz. Additive manufacturing is
frequently used to create these composites’ porous or 3.2. CFs coated with other materials
layered architectures, which further enhance performance Researchers have investigated covering CFs with magnetic
by adding more interfacial polarization sites and or conductive materials, such as metals, metal oxides, or
impedance gradients. High-tech manufacturing methods conductive polymers, to improve the EMWA performance
such as in situ polymerization and magnetic field-assisted of CFs. These coatings improve microwave attenuation
alignment are used to improve CF-reinforced absorbers’ by introducing extra loss mechanisms such as improved
reproducibility.
conductivity, magnetic resonance, and interfacial
For structural applications where both load- polarization. For instance, compared to uncoated CFs,
bearing capacity and stealth functioning are necessary, nickel-coated CFs are effective over a larger frequency
CF-reinforced composites are especially appealing due range because of the conductive nickel layer and its intrinsic
to their mechanical-electromagnetic performance. ferromagnetic characteristics, which cause dielectric and
The electromagnetic microwave absorption properties magnetic losses.

Volume 1 Issue 2 (2025) 6 doi: 10.36922/ESAM025160008