Page 138 - MSAM-4-3

Materials Science in Additive Manufacturing Sunflower-inspired microwave-absorbing metastructure

Figure 3. Fabrication of CB-CIP/PLA composite filaments and 3D printing process of the sunflower-inspired metastructure sample for microwave
absorption testing
Abbreviations: CB-CIP/PLA: Carbon black-carbonyl iron powder/polylactic acid; FDM: Fused deposition modeling

homogenized using a dual-motion high-energy mixer Table 1. Processing parameters in fused deposition modeling
(Zhengzhou Gold Co-Powder Technology Co. Ltd., 3D printing
China) with cylinder and blade speeds set at 28 rpm and Parameter Value
17 rpm, respectively, for 1 h. The uniformly mixed material
was then fed into a micro twin-screw extruder (Wuhan Printing speed (mm/s) 40
Ruiming Experimental Instrument Manufacturing Co. Layer height (mm) 0.2
Ltd., China) to produce filaments with a diameter of 1.75 Nozzle temperature (°C) 210
± 0.10 mm. The composite filaments were subsequently Bed temperature (°C) 50
used to fabricate the designed metastructure through an Filling density (%) 100
FDM 3D printer (DDKUNT3040, Creative 3D Technology
Co., Ltd., China) using the processing parameters as listed 3. Results and discussion
in Table 1. The printed metastructure sample (180 mm
× 180 mm), composed of an array of 10 × 10 units, was 3.1. Morphology and electromagnetic properties of
finally prepared for microwave absorption testing. CB-CIP/PLA composite filaments

2.3. Characterization and measurement Figure 5A demonstrates the SEM image of the CB-CIP/PLA
composite. The CB and CIP particles are largely uniformly
The microstructure of the fabricated composite was dispersed within the PLA matrix, facilitated by high-
characterized using scanning electron microscopy temperature extrusion and frictional shear during twin-screw
(SEM). Electromagnetic parameters were measured processing. However, due to the high specific surface area
in the frequency range of 2 – 18 GHz using a vector and surface energy of CB, agglomeration is observed. These
network analyzer (Keysight, USA) and adopting a CB agglomerates contribute to the formation of conductive
coaxial transmission line method. Test specimens used networks, thereby enhancing the electrical conductivity
for parameter measurements had an outer diameter of and dielectric constant of the composite. Similarly, CIP
7.00 mm, an inner diameter of 3.04 mm, and a thickness particles, characterized by high surface activity, also show
of 2.00 mm. signs of localized agglomeration during the melting or

The microwave absorption performance of the printed molding process (as highlighted in Figure 5A). These CIP
metastructure was evaluated via a modified bow-shaped agglomerates increase local eddy current losses and suppress
28
measurement method (Figure 4). Unlike the conventional natural resonance behavior. Note that the CB and CIP
bow-shaped method, where horn antennas and the sample contents influence the microwave absorption performance
are placed horizontally, this modified approach positions of the filaments, with the combination of 20 wt.% CB and
the horn antennas horizontally and the test sample 30 wt.% CIP yielding the optimal absorption properties.
28
vertically. Incident electromagnetic waves, transmitted The electromagnetic parameters of the composite were
from one horn antenna, are partially reflected off the characterized in the frequency range of 2 – 18 GHz. As
sample surface. The reflected waves are either captured shown in Figure 5B, the real and imaginary parts of the
by the receiving antenna or absorbed by corner foam complex permittivity remain relatively stable across the
absorbers. This configuration enables precise measurement measured frequency range. In contrast, both the real and
and analysis of microwave absorption performance across imaginary components of the complex permeability exhibit
different incident angles and polarization states. a decreasing trend with increasing frequency.

Volume 4 Issue 3 (2025) 4 doi: 10.36922/MSAM025220048