T. Bravo and C. Maury
24th Internationa Congress on Acoustics
Del 24 al 28 de octubre de 2022, Gyeongju, Corea del Sur.
Micro-perforated resonance absorbers have proved to be efficient wall acoustic treatments in the mid-frequency range with applications in building acoustics and in severe environments such as duct flows and turbo-engines. In order to broaden their half-bandwidth absorption while keeping high acoustical performance, a strategy is to decrease the holes diameter while increasing the perforation ratio, thereby achieving impedance matching over the whole bandwidth. In practice, this is difficult to achieve with standard micro-perforated panels due to manufacturing constraints. The current study examines the absorption properties of micro-capillary plates (MCP) characterized by a dense distribution of micro-holes with diameter between 1 and 60 microns and with a typical open area ratio greater than 60%. Impedance modelling and Kundt tube measurements show that MCPs have almost zero reactance and constant resistance that can be tailored to achieve a target absorption value over a broad frequency band. Unbacked MCPs provide wideband absorption greater than 0.85 at low frequencies whereas the half-bandwidth of MCPs backed by a shallow cavity may span more than 3 octaves with an absorption staying above 0.8. The influence of the acoustical load behind unbacked MCPs is examined as it greatly affects their acoustical performance.
