Noise pollution is a serious and pervasive problem. Barrier materials are vital for noise abatement. Typically, barriers are either, i) dense materials that resist sound wave transmission or, ii) assemblies of lighter decoupled structures filled with porous absorbing materials that reduce sound transmission. The latter is preferred especially in building and engineering industries, since minimising weight is a critical issue and filling materials such as fiberglass have become widely employed, for instance in double-leaf walls. However, many engineering industries demand high-performance, customised solutions for attenuating a target noise spectrum employing the minimum amount of material barrier, e.g. sound insulation in aerospace or automotive industries, public transportation or musical and leisure facilities with strict noise standards. The range of up-to-date applications to reduce wave transmission is still not able to serve this large and growing market need because they remain severely limited by the fact that the internal structure of the material is not exploited to its full potential. Currently, best practice solutions depend on and yet are hampered by the use of material layers that result in too heavy and bulky products for highly specialised applications.
The highly innovative solution that METACOUSTIC offers to the market for the first time is a breakthrough service that allows to provide bespoke soundproofing solutions that meet and exceed the specific soundproofing requirements of customers, with a particular focus on being able to identify and supress the exact and unique noise spectrum signature that needs to be attenuated. The proposed Multiresonant Layered Acoustic Metamaterial (MLAM) solution exploits locally resonant properties of artificially designed microstructures together with the coupled resonances mechanisms. The locally resonant acoustic metamaterial is able to cancel or attenuate incident sound waves with frequencies close to its natural frequencies, which emerge from its internal structure or topology. The coupled resonances concept hinge on providing enhanced sound attenuation capabilities in terms of a double-peak sound transmission loss response by means of a layered configuration suitable for large scale manufacturing.
The MLAM solution consists of different resonance layers required to produce different attenuation peaks to establish a target operating frequency range for noise attenuation. By generating these different peaks, the overall attenuation band in the selected range can be tuned and widened, in contrast to existing concepts based on a single resonance. The resulting attenuation peaks are not dispersed, but instead produce a continuous attenuation band thanks to the inclusion of a connecting layer between the resonant layers, without resorting to the viscous properties of the materials, which avoids problems related to complex material behaviour caused by viscoelastic effects. Each layer is a thin laminate of constant thickness and a single material phase, with or without holes, which facilitates mass manufacturing (large-scale production) with the technologies available today: lamination, die-cutting, etc. This laminate concept is essential to avoid problems related to the manufacture of composite material concepts based on complex inclusions embedded in a matrix. In order to validate the MLAM concept experimentally, a set of 3D-printed prototypes were tested. The results showed an attenuation intensity of almost 20 dB above the homogeneous solution over a range of 100 Hz.
MLAM can be produced in panel form for ease of transport and application in a specific setting. Typically, noise abatement from building construction and transportation (trains, airplanes, etc.) are scenarios where the product can be exploited. The overall market research developed during the project makes the research team conclude that a) there is a market in the construction and the transportation business; b) that weight and costs are critical factors; c) that it seems that we can be in line with the needs of the industry for weight and cost; and d) that our product will be of interest to a range of industrial companies specialized in the design and manufacturing of panels made out of different advanced materials.
In view of the considerations above, the METACOUSTIC project has led to the creation of a spin-off company of CIMNE (METAMATERIALS SOLUTIONS), with participation of CIMNE and the MLAM inventors as shareholders. The company, whose constitution will take place in the next weeks, aims at the licensing, exploitation and commercialization of the MLAM invention, as well as future inventions in the field of metamaterials.
