| Abstract |
The development of road, railways and ariport infrastructures, as well as industries around urban areas worldwide is linked to noise pollution issues. Thus, the negative effects of noise are the source of and ever-increasing concern among public administrations and several industrial sectors (construction and automotive, among others), not only because of the annoyance potential (affecting customer satisfaction and competitive advantage), but especially due to the related impact on human health (sleep disturbance, increased stress levels, etc.). While there are a number of sound sources contributing to this problem, the more concerning ones are on the low-frequency region of the frequency spectrum (i.e., below 500 Hz). The so-called environmental noise originates from the most common sources (e.g., traffic noise, speech communication) and it is the most difficult (and expensive) to deal with. In this context, the Multiresonant Layered Acoustic Metamaterial (MLAM) concept has been recently conceived as a novel technology capable to effectively attenuate sound at low-frequency ranges without requiring impractical amounts of mass (which is the foundation of existing solutions). In particular, the composite nature of such material and the specific combination of layers give it two unique features that distiguish it from any other technology currently present in the market: (1) it exploits the local resonance effects characteristic of conventional acoustic metamaterials, but through an unprecedented coupled mechanism that allows to extend the attenuation bandwidth towards a broad range in the frequency region of interest; and (2) it achieves these properties employing standard materials in a layer-based configuration that makes it easy to manufacture with well-established fabrication processes (increasing its potential towards an eventual low-cost/mass-production setting). Thus, the ever-increasing market need for a lightweight, thin and inexpensive solution to address the low-frequency sound insulation problem could be fulfilled thanks to the exceptional soundproofing capabilities provided by the MLAM techology. The introduction of a MLAM-based panel-like product in the market has the potential to revolutionize the construction sector (allowing to meet prospect, more stringent standards for sound insulation in housing and/or office buildings on urban areas with an affordable solution), and the transport sector (where lightweight, thin solutions are key). |
