Strategies for practical metamaterial plates with improved sound transmission loss
At LMSSC, Paris, November 22th 2018, 1 p.m.
Bart Van Damme
Researcher, Laboratory Acoustics / Noise Control, the Swiss Federal Laboratories for Materials Science and Technology (Empa), Dübendorf, Switzerland
Elastic and acoustic metamaterials have strong potential to alter the dynamic properties of plane structures. The basic idea is well understood: local changes of the bending wave impedance interact with the out-of-plane motion. Such changes can be achieved mechanically, by adding masses, resonators, or varying the thickness, or by interaction with an electromagnetic network.
Introducing metamaterials in real-world applications is challenging, mainly for economic and practical reasons. Metastructures typically have intricate geometries and are therefore expensive to produce and not suitable as separating walls. The laboratory for Acoustics/Noise Control at Empa aims to be a trendsetter in developing metamaterial panels with improved sound transmission loss.
The presentation will focus on two examples. The first is a plane phononic crystal with a periodic stiffness pattern, demonstrating band gaps for flexural waves. The forbidden frequencies originate from Bragg scattering at middle high frequencies, and might be used to cancel out the coincidence effect. The second example is a decoupling element for double-leaf walls, based on rotary resonance effects. Both approaches can be produced and tested on a larger scale than most prototypes.