Equivalent Circuit-based Design of Flexible Multilayer Metamaterials for Ultra-wideband Microwave Absorption

Microwave absorbing metamaterials have emerged as critical components in advanced stealth technology and civil electromagnetic interference suppression systems. These applications demand metamaterials capable of broadband absorption under thin thickness, presenting significant design challenges. While multilayer metamaterials (MMs) offer a promising approach to address the thin-thickness-broadband absorption challenge, their design methodology remains inherently complex. This study presents a novel optimization framework for achieving effective design of ultrathin broadband MMs. The metamaterial design optimization employs a two-stage approach. First, thickness and material sequence are rapidly optimized through numerical computation replacing simulation that eliminate the need for time-intensive full-wave simulations. Subsequently, patterned resistive films (PRFs) are integrated into the structure, with final design parameters refined using genetic algorithms coupled with full-wave simulation. To support this framework, a comprehensive composite material library was constructed featuring materials with exceptional microwave absorption performance. This library was developed by precisely controlling the mixing ratios of multi-walled carbon nanotubes (MWCNTs) - renowned for their superior dielectric loss properties - and carbonyl iron powder (CIP), which exhibits outstanding magnetic loss characteristics. Leveraging the computational efficiency of numerical optimization, multilayer lossy material configurations with 3, 4, 5, and 6 layers were systematically designed by selecting optimal materials from the composite library to maximize absorption bandwidth. The optimized multilayer structures were then enhanced through PRFs integration, with parameters further refined using genetic algorithms. Results demonstrate that the four-layer metamaterial (4-MMs) configuration achieves exceptional broadband absorption performance (≤ −10 dB) across the entire 2-18 GHz spectrum while maintaining a thickness of only 5.15 mm. Experimental validation through fabricated 4-MMs showed excellent agreement with simulation predictions, confirming the effectiveness and reliability of the proposed design framework. This breakthrough framework establishes a new paradigm for developing ultrathin, broadband MMs with high-efficiency design.