In industrial noise control, architectural acoustics, and military stealth technology, attenuating or absorbing low-frequency acoustic waves using ultralight materials has long posed a severe engineering obstacle. Traditional acoustic media—such as glass wool, polyurethane foams, or dense lead sheets—are either bulky and space-consuming or prohibitively heavy, failing the stringent weight constraints of modern aircraft, high-speed rail, and marine vessels. Aerogels, characterized by extraordinarily low acoustic impedance, offer a paradigm shift in sound wave manipulation and acoustic attenuation.

The propagation of acoustic waves through a medium is governed fundamentally by its mass density and longitudinal wave velocity. Ambient air exhibits an acoustic impedance of approximately 415 Pa·s/m, whereas most solid engineered materials (e.g., metals or structural polymers) possess values exceeding 10⁶ Pa·s/m. This severe impedance mismatch causes incoming sound waves to reflect strongly at solid interfaces, preventing acoustic energy from penetrating deep into the material matrix for viscous dissipation. Because silica aerogels feature porosities exceeding 90% and extremely low densities (down to 3 kg/m³), the longitudinal speed of sound within their framework drops to 100 m/s or lower. Consequently, the acoustic impedance of aerogels falls into the range of 10³ Pa·s/m, functioning as a bridge that minimizes interfacial wave reflection and enables efficient acoustic energy entry.

Once sound waves penetrate the interconnected three-dimensional nanonetwork of an aerogel, energy attenuation proceeds via viscous friction and thermal dissipation within the nanometer-scale pores. The tortuous pore pathways act as an infinite microscopic labyrinth. Acoustic-induced oscillations of trapped gas molecules encounter immense viscous shear against the stationary solid framework, rapidly converting mechanical energy into thermal energy. Concurrently, the immense internal surface area between the nanoscale skeleton and the interstitial gas facilitates rapid thermal exchange, draining energy from periodic pressure waves.

In defense engineering, these acoustic traits render aerogels candidate materials for acoustic stealth architectures. Applied within naval submarine anechoic tiles or engine compartment insulation shrouds, flexible aerogel composites reduce parasitic structural weight while absorbing low-frequency mechanical vibrations and radiated acoustic signatures, thereby mitigating detection by passive and active sonar systems. In commercial sectors, thin aerogel acoustic panels are deployed in aerospace cabins, high-speed railway interiors, and metrology laboratories to achieve broadband sound attenuation within tightly space-constrained envelopes, elevating the boundaries of structural acoustic engineering.