Meta-Poro-Elastic Materials with Local Resonant Behavior to Improve Sound Absorption at Low Frequencies

Over the past decade, the noise-related health issues and the increase in customer expectation have brought the acoustic design of the products/environments to the attention. Additionally, the trend in the transportation, machine, and construction industry is to go toward lightweight and compact design in order to respect the ecological and economical requirements. These designs not only have poor acoustic performance but also make the (often) heavy and bulky classical acoustic solutions less attractive. In this view, novel cost-effective acoustic solutions, that retain the lightweight and compact design, are required. Among these novel solutions, locally resonant metamaterials show great potential in high noise and vibration insulation over a specified frequency range. The subwavelength-scale nature of these materials makes their design compact and lightweight. However, their narrow-band effect and rather not trivial physical realization may limit their industrial application. On this note, poro-elastic material as a classical solution is known to be a broad-band sound absorbing material, yet their efficiency lies in the high frequency range. Thus, embedding different types of periodic inclusions in poro-elastic materials, to extend their high sound absorption performance to the low frequency range, has been the focus of many researchers. This brings a new class of novel acoustic solutions, known as meta-porous/meta-poro-elastic materials, to the fore. Previous works on meta-porous/meta-poro-elastic materials mainly focused on increasing the dissipated sound wave energy through viscothermal effects by energy entrapment (between the inclusion and the rigid wall or inside the Helmholtz resonator inclusion). Thus, they mainly achieve sound absorption improvement under the quarter-wavelength limit by exploiting the size of the inclusion, where the assumption to neglect the frame vibration and its contribution to the acoustic response of the system is valid. Nevertheless, few investigations considered the frame as an elastic medium, where its modified vibration pattern due to the inclusion addition resulted in (far from perfect) sound absorption peak. This dissertation aims at exploiting the frame vibration by means of introducing local resonant behavior, similar to the one present in locally resonant metamaterial, in poro-elastic materials. This idea is attractive since the dissipated viscous energy at low frequencies is directly associated with the relative motion of the fluid in the pores and the frame. In this view, the effects in meta-poro-elastic systems that induce/modify the frame vibration are identified. Afterward, the correlation between the dissipated (viscous, thermal, and structural) energy, i.e.~absorption improvement, and the frame vibration is evaluated. With the gained knowledge, the driving parameters that improve sound absorption due to the structural resonant behaviors are identified. These parameters comprise the geometrical parameters of the inclusion and the material properties of the poro-elastic host layer. The aforementioned investigations lead to a qualitative design guideline to tune the meta-poro-elastic system to a specified frequency range with a higher sound absorption performance. After evaluating the meta-poro-elastic systems with local resonant behaviors as a concept, some aspects regarding their physical implementation are addressed. The perturbation in the periodicity of the system is considered to account for the uncertainties in the manufacturing process. It is shown that although the imposed geometrical uncertainties alter the acoustic response of the system, the improved sound absorption due to the local structural behavior is robust against the perturbation in periodicity. Moreover, the performance of the proposed meta-poro-elastic systems under oblique angles of incidence is investigated to not only gain insight into the additional effects induced by the in-plane excitation but also to evaluate the robustness of the improved behavior against the variation in the angles of incidence. In the end, the improved sound absorption behavior of the locally resonant meta-poro-elastic material and the driving design parameters are confirmed experimentally. The normal incidence sound absorption of a proposed meta-poro-elastic design is measured using a Kundt tube and are cross-validated with the corresponding numerical models.

Jaar van publicatie:2021

Toegankelijkheid:Closed