T. Bravo and C. Maury
26th International Congress on Sound and Vibration
Del 7 al 11 de julio de 2019, Montreal, Canada.
The use of perforated and micro-perforated structures for applications with minimum weight penalties has been traditionally employed with good performance in the middle frequency range. In the search to improve performance at low frequencies, functionally-graded materials composed of layer of perforated panels with varying physical parameters are studied in this work. Several analytical formulations have been implemented and compared with other classical impedance translation methods. A modal matching formulation combined with Fourier-Floquet expansion has been selected in terms of accuracy and computational cost-efficiency to perform parametric studies carried out under normal incidence. Conclusions have been drawn concerning the dependency of the acoustic band gaps on the thicknesses of the fluid/solid layers, on the perforation ratio and on their variation within the structure. An optimization procedure using the simulated annealing algorithm has considered a cost function for absorptivity of the system, which could provide simultaneously high absorption and low transmission. Frequencies have been identified at which one-sided critical coupling condition is achieved and for which the effective characteristic impedance matches that of the surrounding medium. To further enhance performance over a broader frequency range, a membrane has been added at the transmitting face of the partition. A comparison with other classical perforated or micro-perforated devices shows that, with a proper distribution of the parameters, the ultrathin membrane is able to improve the blockage of the transmitted sound without the drawback of increasing the reflection in the frequency range of interest.
Acknowledgments
This work has been funded in Spain by The Ministerio de Economía y Competitividad, project TRA2017-87978-R, AEI/FEDER, UE, “Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad”. It was supported in France by the French National Research Agency (ANR Project VIRTECH) and by the Labex Mechanics and Complexity AAP2 managed by the Excellence Initiative Programme of Aix-Marseille University (A*MIDEX).
