Structured wave-transparent metamaterials for simultaneous broadband electromagnetic and acoustic absorption

Controlling electromagnetic radiation and acoustic noise is increasingly important for environmental mitigation and stealth-relevant engineering systems; however, integrating broadband absorption for both wave types within a compact, manufacturable architecture remains challenging. This work presents a heterogeneous metamaterial architecture in which a structured wave-transparent layer plays a central role in enabling simultaneous electromagnetic and acoustic absorption. The wave-transparent layer is geometrically engineered to form single- and double-neck acoustic resonators while simultaneously enhancing low-frequency microwave absorption, whereas a lossy multilayer pyramidal base provides graded impedance matching and multi-scale acoustic cavities. This dual-material design effectively decouples the absorption mechanisms for sound and electromagnetic waves, offering high flexibility in functional design. Experiments demonstrate broadband electromagnetic absorption with reflectivity below −10 dB from 2.8 to 40 GHz and below −15 dB over 91% of this band, alongside an average acoustic absorption coefficient of 0.84 across 500–3000 Hz. This strategy provides an innovative solution for pollution control and stealth applications by enabling simultaneous absorption of sound and electromagnetic waves, paving the way for integrated environmental management and advanced stealth technologies.