Bioinspired Hierarchical Lattice Trifunctional Metamaterials with Excellent Mechanical, Electromagnetic, and Acoustic Properties

Multifunctional metamaterials that manage stress, electromagnetic wave (EMW), and sound are essential for lightweight protection and stealth. However, compact integration of these functions remains challenging due to inherent design incompatibilities and functional trade-offs. Inspired by the unique optical and acoustic stealth mechanisms of lepidopteran insect, we propose a multifunctional hierarchical lattice (MHL). Through the coupling of photonic crystals and perforated resonant structures in a multi-scale hierarchical design, the MHL achieves stress regulation while simultaneously promoting enhanced wave manipulation via multiple electromagnetic reflections and dual-porosity acoustic resonance. This design effectively circumvents the conventional incompatibility between mechanical functionality and wave-manipulation performance, while demonstrating significant array-level design potential within an on-demand framework based on Kolmogorov–Arnold networks. Hence, the MHL simultaneously enhances mechanical (~21.9-fold enhancement in in-plane specific energy absorption), electromagnetic (EMW absorption bandwidth covering ~93.5% across 2–40 GHz), and acoustic performance (average sound absorption coefficient of ~0.9 over 600–900 Hz), while the total thickness of 24 mm is 36.9% of that of traditional functional stacking designs. This work establishes a general design paradigm for multifunctional metamaterials, offering new routes toward lightweight, mechanically robust structures for noise control and EM shielding in high-end engineering systems.