T. Bravo and C. Maury
Symposium on the Acoustics of Poro-Elastic Materials, SAPEM 2020+I
E-congress celebrado del 29 de marzo al 2 de abril de 2021.
The study of new absorbers for control of low-frequency noise constitutes a continuous area of research. Micro- perforated panels (MPPs) [1] can be tailored to work optimally at low frequencies, but they are confined in a narrow frequency band as they build on the principle of Helmholtz resonances. To get rid of these limitations, the use of unbacked panels has been considered as an alternative to cavity-backed partitions. Optimization results have shown that reducing the size of the hole diameters down to 10 μm can provide wideband absorption, but at the expense of an increase of the manufacturing cost. This work aims at investigating the acoustic properties of ultra-perforated membranes, denoted micro-capillary plates (MCPs). Although these devices are currently used as image intensifiers or detectors of cosmic rays, they also found potential applications in the field of acoustics to achieve low-frequency anechoic terminations [2]. A MCP is a slab made up of a resistive material with typical thickness between 1 mm and 5 mm, composed of a regular array of slots or micro-channels densely distributed over the whole surface. The micro-channel diameters are between 10 μm and 50 μm and typical perforation ratios vary between 50% and 70%.
In this work, we further investigate the potential of MCPs as wideband acoustic absorbers with respect to other traditional absorbers as well as their optimization. An analytical effective approach will be presented that describes different working flow regimes. It will enable to perform efficient parametric studies that provide the performance prediction of MCPs as a function of their constitutive physical parameters. Results are compared for different MCPs, working in the slip-flow regime, against those corresponding to classical MPPs, operating in the continuum regime. The simulation results obtained for optimised MCP configurations will be validated by measurements of their absorption coefficient in a Kundt tube, showing good agreement with the analytical predictions. Moreover, we will carry out a comparison against published results using a wire-mesh or a textile screen as resistive layers that are able to provide a controlled resistance suited to the particular problem of interest.
