The fourth semester of the WAVES programme is dedicated to the Master Thesis. This thesis is prepared during an internship with a duration between 4 and 6 months. The internship is hosted either in a company or in a research lab in the acoustics and vibrations area, under the supervision of a local tutor and an academic tutor (part of the WAVES Pedagogical Committee).

The internship results in the writing of the Master Thesis which then defended by the end of September.

Internships 2023

Analysis and optimization of perforated panels making use of metamaterial concepts

Gabriela Czuprynska

Universidade de Coimbra, under the supervision of Luis Godinho

Sound-absorbing materials enhance acoustic comfort by controlling reverberation and reducing noise levels. Porous materials like open-cell foams excel at absorbing medium to high frequencies but are less effective at lower frequencies, while resonant structures such as perforated panels offer durability and customization. Such panels normally use simple perforation shapes.
This study focuses on improving sound absorption by exploring panels with varied internal geometries such as tapered, hourglass, inverse-hourglass, perforations with rounded bubble-shaped extensions, and perforations with embedded resonant structures. The influence of rounding the edges and filling the air gap with porous materials is also investigated. An analytical model based on the transfer matrix method and a finite element model are implemented to analyse the systems. The analytical results show good agreement with the FEM results; however, an angle limitation in a tapered perforation case is identified, which can be due to the 1D simplification assumed in the TMM. FE models are used for examining the structures with embedded resonators. Parametric studies are performed to identify the influence of varying geometrical parameters on absorption.
A design method based on optimisation of the geometrical characteristics of a tapered panel is proposed. Three optimal samples with tapered perforations and one with an embedded torus-shaped resonator with arbitrarily chosen dimensions were 3D printed. The samples were experimentally tested using the procedure presented in ISO 10534-2. A good agreement between the predictions and measurement results was found.