Broadband multi-unit composite metamaterial for simultaneous sound wave and electromagnetic wave absorption

We propose a broadband multi-unit composite metamaterial consisting of nine sub-units capable of simultaneously achieving broadband noise reduction and electromagnetic wave absorption. A theoretical model was established to calculate the sound absorption coefficient and the teaching–learning-based algorithm was used to optimize the geometric dimensions. The optimized average sound absorption coefficients were 0.836, 0.907, 0.957, and 0.97 within the frequency ranges of 1–500 Hz, 1–1000 Hz, 1–3000 Hz, and 1–20000 Hz, respectively. Complex plane analysis indicated that the broadband multi-unit composite metamaterial exhibits quasi-perfect sound absorption. In addition, the change of the metal patch comprises double-C open circular rings, and the bottom plate is composed of dielectric substrates and metal substrates could affect the electromagnetic wave absorption effects under TE and TM modes and explain the reason for the excitation of Fano resonance absorption peaks under the TE mode. Next, the optimized double-C open circular rings result in the broadband multi-unit composite metamaterial exhibiting an absorption coefficient exceeding 0.5 between 12 and 30 GHz. The advantage of this design were verified through acoustic impedance tube and bow-shaped reflectance system. These results provide a reference for the development of multifunctional stealth technologies.