Task 3.2 – Study of passive control by micro-perforated plates
Passive control methods involving micro-perforated plates will be explored in task 3.2 of the TANGO Network. Such plates are used successfully as sound absorbers in room acoustics, but the physical mechanism that causes the absorption is not known. It could be due to the formation of vortices at the sharp edges of the slits, and/or due to the friction between the contacting surfaces at the tips of each slit. On the experimental front, near-field acoustic holography will be used to locate where the acoustic energy is lost. The micro-perforated plate is a two-dimensional periodic system, which will be modelled analytically using the Bloch/Floquet theorem. A single element of this periodic system, i.e. a single orifice with contacting surfaces at the slit tips, will be modelled by finite elements, combined with a describing function approach to capture the nonlinear behaviour by the contacting surfaces. There will be close interaction with task 1.3 of the TANGO Network, which focuses on plates with larger-scale orifices.