[COST] – Excessive noise has long been known to cause serious health issues, including hearing loss, increase of stress, and even heart disease. But, what if we told you that there are innovative solutions offering hope for a quieter and healthier world? One of the most promising of these solutions is acoustic metamaterials with their wide range of applications. From insulating aircraft engines to soundproofing homes, the possibilities of metamaterials are endless. Thanks to the efforts of researchers like Dr Theo Cavalieri, a young scientist from the Designs for Noise Reducing Materials and Structures (DENORMS) COST Action, we’re learning more about the potential of this revolutionary technology.
At the recent COST Academy networking event ‘Sustainability of COST Actions’, Dr Theo Cavalieri shared his insights and experience about metamaterials with a new generation of COST Actions leaders. Join us as we explore the world of metamaterials and discover the exciting future of noise control.
Metamaterials and their applications
Metamaterials are artificially created structures that possess exceptional physical properties not found in natural materials such as wood, rock, or sand. Now, imagine an assembly made of sand, wood, and rocks in a specific order and shape, then tuning its size and arrangement – that’s one way we might create a metamaterial with extraordinary effective properties.
Another way is to manufacture structured materials using a 3D printer. Regardless of how it is created, a metamaterial can be used to reduce or mitigate the intensity and behaviour of certain phenomena. For example, if it is not possible to control the source of a phenomenon, such as electromagnetic waves, vibrations or sound waves, the environment can be adapted by using a metamaterial that can absorb, reflect, or manipulate these waves.
Metamaterials have a wide range of applications and can be used to address noise problems in different ways. For example, they can be used in anti-seismic structures by drilling periodic holes in the ground to prevent targeted waves from propagating in certain directions. They can also be used in acoustic barriers, where light- and air-porous rigid wooden rods placed periodically act as a metamaterial, to replace concrete walls along railways and highways.
Metamaterials can help with noise reduction in the construction industry, which is imposing stricter acoustic standards, and buildings constructed with conventional materials such as glass, metal, and concrete sometimes fail to meet the modern requirements. These types of buildings reflect sound waves like mirrors, causing the sound to bounce back multiple times without being absorbed. To mitigate this issue, metamaterials can be a useful solution as they can be made very thin and lightweight, achieving noise reduction without sacrificing space.
Again, metamaterials could be used as vibration dampers in machinery to absorb vibrations, resulting in less noise and longer-lasting machines. Or in offices, restaurants, or even in orchestra pits to provide a more diffused sound to the musicians and to the audience.
Theo Cavalieri cautions, however, that despite their vast potential, metamaterials are not a single-stop solution to everything. His PhD research focused on using metamaterials to reduce noise in aircraft engines, and he found a paradox: as engines become quieter, noise standards and regulations would allow for more engines to fly. More engines equals more planes. But are more planes part of a sustainable vision of the future?
Furthermore, metamaterials still present a costly proposition, and their integration often requires withstanding temperature variations, UV exposure, rain, and other environmental factors. All these constraints need to be taken into account when exploring the potential applications of metamaterials.
Contribution of the DENORMS COST Action
According to Theo Cavalieri, the community of acoustic treatments and metamaterials has been strengthened thanks to the DENORMS Action. DENORMS allowed industrial experts to get in direct contact with scientists in the field. Despite the proliferation of non-disclosure- and consortium agreements making the cooperation between industry and researchers in the field of physical acoustics challenging, DENORMS created a trustful environment allowing participants to collaborate on shared acoustic challenges. By providing a common objective for both research and industrial actors, DENORMS also enabled cooperation between competitors and strengthened the community of acoustic treatments and metamaterials. In addition, working together within the EU has additional benefits, such as the diversity of norms and customs that accelerates certain processes.
DENORMS has already had a lasting impact, with several industrial actors such as Trèves, Safran, BASF, Phononic Vibes, Metacoustic, SNCF, and Saint-Gobain Ecophon developing large-scale research programs focused on acoustic materials. This collaboration has also resulted in new opportunities, such as the creation of the postdoc position that Theo currently occupies, which emerged from informal interactions during DENORMS events.
The DENORMS network is still alive, and on several different levels. For example, the participants of the DENORMS Action have often been asked to collaborate in organising training schools and workshops. In addition, the creation of SAM (Symposium on Acoustic Metamaterials) has allowed the different participants of DENORMS to regularly meet and maintain contacts, especially with regards to younger researchers from YRAM (Young Researchers in Acoustic Metamaterials).
During its final event, held in Coimbra, Portugal, DENORMS organised ‘Acoustics and Beyond’, a scientific exhibition in the Science Museum of the University of Coimbra. This free exhibition was available for several months, and has since been improved and shown at several international events, such as Le Mans Sonore in 2022. More recently, an international research project, METAVISION, gathered research groups and industrial groups, some of whom were previously involved in DENORMS.
Dr Théo Cavalieri: “Today’s trend is oriented towards slim, efficient, and multi-functional materials, but it requires additional efforts for them to reach the market, as meta-materials are often not as cheap and integrable as conventional treatments.” In conclusion, the potential of metamaterials is vast, and the DENORMS Action has paved the way for cooperation and innovation in the field of acoustic treatments and metamaterials. By continuing to collaborate, we can build a quieter and healthier future for all.