Vibroacoustic properties of thin micro-perforated panel absorbers

Abstract

This paper presents theoretical and experimental results on the influence of panel vibrations on the sound absorption properties of thin micro-perforated panel absorbers (MPPA). Measurements show that the absorption performance of thin MPPAs generates extra absorption peaks or dips that cannot be understood assuming a rigid MPPA. A theoretical model is established that accounts for structural-acoustic interaction between the micro-perforated panel and the backing cavity, assuming uniform conservative boundary conditions for the panel and separable coordinates for the cavity cross-section. This model is verified experimentally against impedance tube measurements and laser vibrometric scans of the cavity-backed panel response. It is shown analytically and experimentally that the air-frame relative velocity is a key factor that alters the input acoustic impedance of thin MPPAs. Coupled mode analysis reveals that the two first resonances of an elastic MPPA are either panel-cavity, hole-cavity, or panel-controlled resonances, depending on whether the effective air mass of the perforations is greater or lower than the first panel modal mass. A critical value of the perforation ratio is found through which the MPPA resonances experience a frequency "jump" and that determines two absorption mechanisms operating out of the transitional region.

Acoustic Metamaterials: A Potential for Cabin Noise Control in Automobiles and Armored Vehicles

“…In this paper, the key design parameter is the influence of open-area ratio on the acoustical performance of a MPP, where an optimum sound absorption is achieved at specified open-area ratio. This is aligned with the findings of other recent works [Bravo et al, 2012[Bravo et al, , 2013Zhao et al, 2015]. However, the difficulty in realizing MPP with much smaller orifices (< 0.3 mm in diameter) is a concern due to limitations of current manufacturing techniques; including additive manufacturing methods.…”

Enhancing sound absorption and transmission through flexible multi-layer micro-perforated structures

“…3 When considering absorbers made up of thin MPPs, extra absorption peaks or dips are observed due to the MPPs flexural or membrane-type effects. 11,12 Suitable choices of the MPP and air layer constituent parameters such as perforation ratio, diameter, holes interspacing, and thickness can bring these extra peaks closer together and so widen the absorption bandwidth. 13 Bravo et al 12 have shown that the magnitude and phase of the air-frame relative velocity over the MPP of a single layer absorber determines the beneficial or detrimental effect of these resonances.…”

Study on inhomogeneous perforation thick micro-perforated panel sound absorbers

“…The discrepancy of the Maa model results and the measurement ones are around 4% up to 14 % at half absorption frequency range. Some peaks are also present that are related with the panel resonances [19,20]. Those peaks are not considered in the Maa model so they are missing from the predicted results.…”