Key Takeaways & Executive Findings
- •• • Achieved EMI shielding effectiveness of 79.23 dB with a reflection coefficient of 0.03 at 4.40 mm thickness, enabling absorption-dominated shielding (SE_R < 3.01 dB) critical for reducing secondary electromagnetic pollution in sensitive electronic environments. • • Maintained effective absorption-dominated shielding at a reduced thickness of 1.40 mm, demonstrating the feasibility of thin, lightweight stealth materials for portable and wearable applications. • • Demonstrated high durability with stable EMI shielding performance under ultrasonic, compression, and bending tests, ensuring reliability in dynamic operational conditions such as flexible electronics and protective gear. • • Integrated flame-retardant thermoplastic polyurethane (TPU) and melamine foam (MF) substrates, providing self-extinguishing properties essential for fire safety in military and aerospace applications.
Abstract
The escalating demand for lightweight, multifunctional stealth materials in modern protective applications necessitates integrated solutions against electromagnetic interference (EMI), infrared (IR) detection, and incendiary threats. This study presents an innovative melamine foam (MF)-based composite featuring an asymmetric dual-nano conductive network, achieving absorption-dominated EMI shielding, IR stealth, and flame retardancy. Inspired by the Salisbury screen, the composite employs MF as an interlayer and flame-retardant thermoplastic polyurethane (TPU) nanofiber membrane as a substrate. The architecture comprises a carbon nanotubes (CNTs)-modified impedance matching nanofiber layer as the top absorber and a silver nanoparticles (AgNPs)-modified nanofiber layer as the highly conductive reflective bottom. Precise control of CNTs content and interlayer thickness enables tunable electromagnetic wave (EMW) absorption, yielding a low reflection coefficient of 0.03 and a high EMI shielding effectiveness of 79.23 dB at a total thickness of 4.40 mm. Even at 1.40 mm, effective absorption-dominated shielding is maintained. The performance remains stable under ultrasonic, compression, and bending tests, demonstrating high durability. The mechanism underlying absorption-dominated EMI shielding at reduced thickness, relying on destructive interference of EMWs enabled by the asymmetric dual-nano conductive network, is thoroughly elucidated. Additionally, the composite exhibits superior IR stealth and self-extinguishing properties. This work offers a feasible strategy for designing high-performance stealth materials with strong potential for personnel and communication equipment protection.
1. Introduction
Modern warfare and advanced detection technologies have transformed combat into an information-centric arena where electromagnetic leakage, infrared signatures, and incendiary threats compromise equipment and personnel. Traditional EMI shielding materials, predominantly reflective, generate secondary electromagnetic pollution, failing to meet the stringent requirements of stealth and environmental compatibility. The green shielding index (g_s) and the criterion of SE_R below 3.01 dB (R < 50%) have emerged as benchmarks for eco-friendly absorptive shielding, yet achieving such performance at reduced thickness remains a bottleneck.
This study addresses the bottleneck by engineering an asymmetric dual-nano conductive network within a melamine foam composite, inspired by the Salisbury screen. The strategic placement of a CNTs-modified impedance matching layer and an AgNPs-modified reflective layer enables destructive interference of electromagnetic waves, achieving high absorption with minimal reflection. This design not only enhances EMI shielding effectiveness but also integrates infrared stealth and flame retardancy, offering a multifunctional solution for next-generation protective materials.
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Jinling Liu, Jiayu Lu, Baoqing Yang, Dongyan Huang, Zhangqi Han, Yan Zhang, Bibo Wang, Dongming Qi, Wei Wang (2026). Multifunctional Melamine Foam Composites Featuring Asymmetric Conductive Networks for Highly Absorptive EMI Shielding and Infrared Stealth. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3873-7
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Frequently Asked Questions
What is the maximum EMI shielding effectiveness achieved and at what thickness? How does the reflection coefficient compare to conventional absorptive shielding materials?
The composite achieves an EMI shielding effectiveness of 79.23 dB at a total thickness of 4.40 mm, with a reflection coefficient as low as 0.03. This corresponds to a reflection shielding effectiveness (SE_R) well below 3.01 dB, meeting the criterion for absorption-dominated shielding. Such low reflection minimizes secondary electromagnetic pollution, a significant advantage over conventional reflective materials.
How does the composite maintain absorption-dominated shielding at reduced thickness (1.40 mm)? What is the underlying mechanism?
At 1.40 mm, the composite still exhibits effective absorption-dominated shielding due to destructive interference of electromagnetic waves, enabled by the asymmetric dual-nano conductive network. The precise control of CNTs content and interlayer thickness allows tuning of the impedance matching and reflection, ensuring that the absorption contribution remains dominant even at thinner profiles.
What are the durability characteristics under mechanical stress and environmental conditions?
The EMI shielding performance remains stable under ultrasonic, compression, and bending tests, indicating high mechanical robustness and adhesion of the conductive layers. This durability is critical for applications in flexible electronics, wearable devices, and protective equipment that undergo repeated deformation and harsh handling.
How does the composite achieve flame retardancy, and what is the significance for practical applications?
The composite incorporates flame-retardant thermoplastic polyurethane (TPU) and melamine foam (MF), which are inherently flame-retardant. The material exhibits self-extinguishing properties, preventing fire propagation. This is essential for military, aerospace, and electronic applications where fire safety is paramount.
What is the potential for scalability and cost-effectiveness of this fabrication approach?
The fabrication involves electrospinning of TPU nanofibers and subsequent modification with CNTs and AgNPs, which are scalable processes. The use of commercially available melamine foam and TPU, along with solution-based coating methods, suggests potential for cost-effective production. However, the precise control of CNTs content and layer thickness may require optimization for large-scale manufacturing.
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