Analysis and design of structures with electromagnetic radiation absorption properties for electromagnetic compatibility applications
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Date
2025-08-27
Authors
Σωτηρόπουλος, Απόστολος
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Abstract
The exponential growth of electronic and communication technologies in recent decades has brought increased challenges in maintaining electromagnetic compatibility (EMC) across a wide range of civil, industrial, and defense applications. As systems become more compact and interconnected, the threat posed by electromagnetic interference (EMI) becomes more pronounced, necessitating the development of advanced materials and structures that can effectively absorb or shield electromagnetic (EM) radiation. Addressing this need is central to ensuring the safe and efficient operation of sensitive electronic equipment in environments prone to EM disturbance, such as aerospace platforms, military systems, and high-frequency communication devices.
Among the various solutions explored for EMI mitigation, carbon-based nanocomposite materials—notably carbon nanotubes (CNTs)—have garnered significant attention due to their superior electrical, mechanical, and morphological properties. Since their discovery in 1991 [1], CNTs have been proposed for a range of novel EMC applications, owing to their ability to alter the transmission and scattering characteristics of composite surfaces when organized into arrays. The interaction between carbon nanotubes (CNTs) and electromagnetic waves has been extensively investigated through both theoretical analyses and experimental studies. It is shown that CNTs, when treated as finite dipole elements, can be incorporated into surfaces to create engineered materials capable of EM radiation manipulation. Such arrangements hold potential as effective shielding surfaces, particularly when their geometrical configuration is tuned for specific frequencies.
In this work, initial investigations into CNT-based scatterers demonstrate that the geometry and spacing of CNT elements significantly influence their scattering profiles under plane wave illumination. It is also shown that CNT arrays can produce markedly different scattering patterns compared to traditional perfect electric conductor (PEC) structures, especially at higher frequencies (in the THz range). This behavior was further investigated as a function of frequency, where it was observed that CNT structures maintain a comparable magnitude of scattered fields to PECs only at lower frequencies, while at higher frequencies the scattered fields decrease, which may be beneficial for absorption-focused EMC applications.
Building on these foundational insights, subsequent study turn attention toward multi-layered CNT-based composite structures, particularly in the X-band (8.2–12.4 GHz), where many military and aerospace radar systems operate. In this context, single-walled carbon nanotubes (SWCNTs) dispersed in polymeric matrices like epoxy resin and polyurethane are shown to deliver enhanced electromagnetic interference (EMI) shielding and radiation absorption due to their high electrical permittivity, loss tangent, and impedance-matching capabilities.
Moreover, reflection coefficient (RC) and transmission coefficient (TC) emerge as key parameters for evaluating the suitability of these materials in EMC applications, as they directly quantify the extent of incident power reflected, transmitted, or absorbed. Optimization methodologies, implemented in simulation tools like FEKO, have been used to fine-tune layer thicknesses in these composite structures to achieve minimum RC and maximum absorption, with and without PEC backings.
Further experimental developments included the integration of CNT thin films within glass fiber polymer matrices, where the ultra-thin nature of the CNT layers (e.g., ~70 µm) necessitated embedding within thicker host materials for effective dielectric characterization using waveguide and free-space measurement techniques. These composite samples are tested in WR-90 waveguides and with Vector Network Analyzers (VNAs), with dielectric parameters extracted via the Nicolson–Ross–Weir (NRW) algorithm. Results from both simulation and measurement showed that even with micrometer-scale CNT films, high levels of absorption and shielding effectiveness (SE > 30 dB) could be achieved—underscoring their viability for lightweight, thin, and highly efficient shielding solutions.
These findings are further developed in subsequent studies, where electrically large planar composite structures composed of multi-walled CNT (MWCNT) films were fabricated using polyvinylpyrrolidone (PVP) as a binder and embedded into laminates. Two-layer configurations, one with a mid-plane CNT film and another with dual films near the outer faces, were explored. Measurements in free-space setups, using both spot-focusing lens antennas and rectangular horn antennas, demonstrated that these scalable, lightweight CNT composites can be designed to achieve targeted EMI shielding and absorption, validated against simulation results from Ansys HFSS.
This work highlights the evolution from idealized scattering analysis of CNT arrays to practical, multilayer absorbing and shielding structures optimized for real-world EMC requirements. It underscores the importance of understanding not only the material composition but also the electromagnetic behavior across frequency bands, structural design parameters, and integration within functional systems.
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Keywords
Electromagnetic compatibility, Carbon nanotubes