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

1. Introduction 4.4 mg/cm³, although with an EAB of only 7 GHz. Despite
these advancements, considerable room remains for
With the rapid advancement of electronic information optimizing designs to achieve broader bandwidths, lighter
technology and the widespread proliferation of electronic weight, and thinner structures.
devices, electromagnetic radiation has emerged as a
significant source of environmental pollution. Such Among numerous biological templates, the sunflower
radiation poses substantial risks in critical areas, exhibits a particularly promising structural geometry for
including personal health care, military stealth, wireless bio-inspired engineering applications. Sunflower petals
communication, and environmental safety. To mitigate have inspired novel solar collectors integrating pulsating
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these harmful effects, substantial research efforts have been heat pipes into flat-plate designs. Besides, sunflower
directed toward developing effective microwave-absorbing stem pith is identified as an ultra-lightweight porous
materials. These materials typically include dielectric loss structure exhibiting exceptional mechanical properties
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materials (e.g., MXene and silicon nitride ), magnetic and energy absorption capabilities. In addition, the spiral
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loss materials (e.g., ferrites and metallic powders ), and arrangement of sunflower heads has informed the design
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conductive loss materials (e.g., carbon black, graphene, of efficient deployable structures utilizing flat-folded
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and carbon nanotubes ). isogonal spiral patterns. 27
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Traditional absorbing coatings exhibit strong adhesion Motivated by these unique characteristics, this study
to object surfaces; however, their intrinsic absorption proposes a novel sunflower-inspired microwave-absorbing
properties are insufficient to achieve broadband metastructure, fabricated from a carbon black-carbonyl
electromagnetic wave absorption. 12-14 Consequently, it iron powder/polylactic acid (CB-CIP/PLA) composite
remains a significant challenge to develop absorbers via fused deposition modeling (FDM). By mimicking the
simultaneously characterized by a broad bandwidth, sunflower disk’s spiral pattern, the proposed metastructure
lightweight, thin profile, and high structural strength. aims to achieve enhanced broadband microwave
Achieving these attributes is essential for effectively absorption performance, reduced structural thickness,
reducing the reflection and scattering of electromagnetic and a simplified fabrication process. Experimental
waves across a broad frequency range. analyses and electromagnetic simulations confirmed
excellent microwave absorption under wide-angle and
To address these challenges, biomimetic approaches
have become increasingly attractive by leveraging varying polarization conditions. The insights gained
from this research are expected to significantly advance
structural and functional inspirations from nature. Many the development and practical application of broadband
organisms have evolved intricate surface microstructures microwave absorption materials, particularly in military
capable of manipulating electromagnetic waves, stealth technology and wireless communication systems.
offering potential solutions for advanced absorber
designs. Examples include algae, bamboos, moth 2. Methodology
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eyes, honeycombs, butterfly wings (e.g., Pachliopta
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aristolochiae), and corals. Through detailed examination 2.1. Design of sunflower-inspired metastructure and
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of these natural structures, researchers have successfully electromagnetic simulation
translated biological principles into effective microwave- The sunflower is characterized by a unique spiral
absorbing metastructures. For example, inspired by the arrangement of seeds in its flower head. The sunflower
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gyroidal microstructures on butterfly wings, An et al. head exhibits two distinct sets of constant-velocity spirals,
designed a bionic metastructure, achieving ultra-wide one rotating clockwise and the other counterclockwise,
absorption bandwidth and exhibiting stable microwave interwoven with each other (Figure 1A). This arrangement
absorption even at an incident angle of 60°, despite the positions sunflower seeds at intersections of spirals, enabling
total thickness reaching 15 mm. Similarly, Chen et al. dense packing with minimal spacing. Consequently, the
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fabricated a moth-eye-inspired microwave absorber using sunflower head achieves stable and smooth growth from
conductive graphite powder, resulting in an effective bracts to a large floral disk.
absorption bandwidth (EAB) of 13 GHz across the C, X,
and Ku bands. However, this design required a relatively While sunflowers do not directly influence microwave
thick structure of 20 mm. Plant-inspired designs have absorption, their distinctive seed arrangement can inspire
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also been explored. For example, Chen et al. developed effective absorber designs. This seed pattern resembles a
a layered aerogel based on liquid metal MXene, drawing constant-velocity spiral (Figure 1B), which can be modeled
inspiration from plant structures. This design achieved a in polar coordinates as follows:
maximum reflection loss (RL) of −73.2 dB at a density of R = k × θ i (I)
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Volume 4 Issue 3 (2025) 2 doi: 10.36922/MSAM025220048