Two-microphone method for in-situ sound absorption measurements of metamaterials

Abstract: The study conducted this past month focused on analyzing the acoustic absorption properties of a 3D-printed metamaterial sample, which is composed of a structure featuring space-coiling labyrinthine elementary cells of various sizes. The majority of the effort was dedicated to experimental data collection, where the two-microphone method was utilized to derive the sound absorption coefficient from the complex-valued transfer function between the sound pressure measured at the two microphone positions. Once the experimental results were collected, the influence of time window parameters (specifically, the Adrienne window), the angle of incidence, and the method's repeatability were investigated. The results were then compared with an analytical model that leverages the Stinson approximation and the Johnson-Champoux-Allard (JCA) model to simulate the panel's ideal absorption spectrum. Finally, a numerical approach was also explored. In this approach, a panel composed of individual rectangles, each assigned an impedance derived from the analytical method, was created to minimize simulation time. This was done to subsequently attempt to implement the phenomenon of diffraction in a way that closely approximates reality. All collected data will later be used to find valid simulations to feed into a neural network previously trained for porous materials. The ultimate goal is for the network to 'presumably' predict the sound absorption coefficient of a metamaterial as if its size were infinite.