Affiliation:
1. University of Southampton
Abstract
Low-frequency noise is a growing concern in a world striving for more efficient modes of transportation and more sustainable technologies. A well-known problem in technical acoustics is that many noise protection measures, such as sound barriers, are inefficient at low frequencies because their sound transmission loss is governed by the mass law. The mass law states that doubling the weight of a sound barrier will only increase its sound insulation by 6 dB, which goes against the aim for efficient and lightweight designs in many applications. Acoustic metamaterials offer the opportunity to break through these limitations of the mass law and contribute to a quieter world. Metamaterials consist of a periodic array of unit cells containing resonant scattering elements. The unit cells are typically significantly smaller than the sound wavelength, which can be used to selectively influence the propagation of sound waves within the periodic medium by precisely tuning the unit cells. This makes it possible to create "effective" material properties for sound waves that are not possible with conventional materials (e.g. negative density).This seminar will focus on plate-type acoustic metamaterials (PAM), which have emerged as a potential lightweight and flexible solution for reducing low-frequency noise more strongly than conventional solutions. In principle, PAM can be designed to be as thin and lightweight as a sheet of paper and still block noise at the same level as a concrete wall! There are, however, still a lot of challenges to address in research on PAM for noise control. This seminar will start by summarizing the acoustic properties of PAM and explaining the mechanisms behind their high sound insulation. The presentation will then highlight certain challenges related to PAM (e.g. bandwidth and high-frequency performance) and how these challenges have been addressed in recent research. The seminar will conclude on recently emerging topics aiming to improve the performance of PAM, such as multi-modal designs and actively reconfigurable PAM.