Ultrathin Mechanically Robust Strut-alterable Trussed Waterborne Metamaterial for Broadband Sound Absorption

Waterborne acoustic metamaterials have emerged as promising platforms for manipulating underwater sound propagation within the subwavelength regime. Despite their critical role in underwater stealth applications, conventional designs face dual limitations: inefficient low-frequency broadband absorption and poor mechanical load-bearing capacity due to their inherently soft architectures. The longstanding acoustic-mechanical trade-off underscores an urgent need for co-design strategies that synergistically reconcile these conflicting requirements. Herein, an ultrathin strut-alterable trussed composite waterborne metamaterial is proposed as an acoustic-mechanical coupling design paradigm. By strategically tuning the truss geometry via an artificial neural network (ANN), this design enables precise acoustic impedance matching through tailored local resonances while simultaneously constructing a stress-redistribution framework for mechanical reinforcement. Experimental results demonstrate the outstanding broadband sound absorption performance (average sound absorption coefficient >0.88) spanning 0.8–10 kHz with a subwavelength thickness of ∼λ/33.8 at 1.2 kHz. Remarkably, the waterborne metamaterial structure achieves a maximum bearing stress of 18.48 MPa, representing an order of magnitude enhancement compared to non-trussed counterparts (0.035 MPa) at the same strain. This work opens a new multi-functional design path and provides more possibilities for the applications of underwater vehicles.