Abstract:

Significance This study focuses on the development of cellulose-based composite materials for electromagnetic interference (EMI) shielding, addressing the growing demand for lightweight and high-performance shielding materials in the era of 5G and beyond. With the rapid advancement of electronic technologies, including 5G communication, wearable devices, and autonomous driving, electromagnetic pollution has become a significant concern, posing risks to both human health and the functionality of electronic devices. Conventional metal shielding materials are limited by their high density and susceptibility to corrosion, making the development of alternative, sustainable, and multifunctional materials of utmost importance. Cellulose nanofibers (CNFs) offer a promising solution by virtue of their low density, high strength, flexibility, and renewable nature. This review highlights the structural design strategies of CNF-based composites and their impact on EMI shielding performance, providing new insights for the development of next-generation shielding materials.

Progress This paper comprehensively reviews the latest research progress in the structural design of CNF-based composites for EMI shielding. Single-layer, bilayer, and gradient structures of films and porous materials are discussed, along with their impacts on EMI performance. Single-layer structures have been widely studied for their simplicity and ease of fabrication. However, they often face limitations in achieving optimal impedance matching and high absorption efficiency by virtue of their uniform material distribution. In order to overcome these limitations, bilayer designs have been developed, which strategically combine conductive and magnetic layers to improve impedance matching and absorption capabilities. These designs leverage the synergistic effects of different material layers to enhance overall shielding performance. Gradient structures, inspired by natural systems, introduce gradual impedance transitions and multiple reflection/absorption pathways. By varying the composition and arrangement of materials within the structure, these designs can achieve ultra-low reflection coefficients and excellent shielding efficiency across broad frequency ranges. Porous materials, particularly aerogels, have also been extensively explored for their high porosity and lightweight nature. These materials enhance EMI shielding by extending the propagation path of electromagnetic waves through multiple reflections and absorptions within the porous network. Research has shown that optimizing the pore structure and incorporating conductive fillers can significantly improve the shielding effectiveness of aerogels while maintaining their low density. These innovations demonstrate the potential of CNFs-based composites to meet the diverse requirements of modern electronics through structural optimization and material integration.

Conclusion and Prospect The development of CNF-based composite materials for EMI shielding has achieved notable advancements, with various structural designs significantly enhancing shielding performance. However, several challenges remain. Current systems often exhibit high reflection coefficients, leading to potential secondary electromagnetic pollution, which is a critical issue that needs to be addressed. Future research should focus on improving impedance matching and reducing reflection losses to minimize secondary pollution. Additionally, enhancing the mechanical properties and durability of these composites is essential for practical applications. This includes optimizing the structural design to improve the composite's resistance to deformation and degradation over time. The development of low-reflection materials through advanced structural designs, such as asymmetric gradient structures and multi-layered composites with tailored material compositions, will be a key direction for future research. Exploring intelligent responsive structures that can adapt to varying electromagnetic environments will also be crucial. These structures could potential offer dynamic control over shielding properties, making them suitable for a wider range of applications. Furthermore, enhancing the structural integrity and long-term performance of composites under stress, through optimized fabrication processes and the incorporation of reinforcing agents, will be vital for their widespread adoption. Overall, continued innovation in structural design and material composition will be pivotal in advancing cellulose-based electromagnetic shielding materials, paving the way for their integration into emerging technologies, particularly in lightweight and flexible electronic devices.

Key words: cellulose-based composite, cellulose nanofiber, electromagnetic shielding, structure design, shielding mechanism, shielding property