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Item type:Publication, Access status: without files , Aircraft side wall with improved low-frequency sound insulation using a lining panel with Helmholtz resonators(International Institute of Acoustics and Vibration (IIAV), 2019); ; ; The continuous development of aircraft engines aims to reduce fuel consumption by increasing the bypass ratio. However, an increased bypass ratio changes the sound emission of the engine, such that the sound spectrum inside the cabin can be dominated by low frequency tones with high sound pressure levels, penetrating more efficiently the current cabin wall than sound of higher frequencies. Thus, the comfort level of the passengers could be adversely affected. This contribution presents a new side wall panel design that is capable to significantly increase the transmission loss of low frequency tones. The rear side of the lining is fully covered by a resonator system of a cantilever integrated into a Helmholtz resonator. With this approach, the lining with resonators can be tuned with respect to two resonance frequencies to improve the sound transmission loss of the cabin wall. A transfer matrix for the Helmholtz resonator panel is derived and the transmission loss of the proposed side wall design is determined. The analytically calculated transmission loss is compared to numerical and experimental results obtained under diffuse field conditionsPublicationtype: Conference Paper145 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Perforated membrane-type acoustic metamaterialsThis letter introduces a modified design of membrane-type acoustic metamaterials (MAMs) with a ring mass and a perforation so that an airflow through the membrane is enabled. Simplified analytical investigations of the perforated MAM (PMAM) indicate that the perforation introduces a second anti-resonance, where the effective surface mass density of the PMAM is much higher than the static value. The theoretical results are validated using impedance tube measurements, indicating good agreement between the theoretical predictions and the measured data. The anti-resonances yield high low-frequency sound transmission loss values with peak values over 25 dB higher than the corresponding mass-law.Publicationtype: Journal Article72 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A membrane-type acoustic metamaterial with adjustable acoustic properties(2016-07-07); ; ; The proposed design distinguishes itself from other realizations by a stacked arrangement of two MAMs which is inflated using pressurized air. The static pressurization leads to large nonlinear deformations and, consequently, geometrical stiffening of the MAMs which is exploited to adjust the eigenmodes and sound transmission loss of the structure. A theoretical analysis of the proposed inflatable MAM design using numerical and analytical models is performed in order to identify two important mechanisms, namely the shifting of the eigenfrequencies and modal residuals due to the pressurization, responsible for the transmission loss adjustment. Analytical formulas are provided for predicting the eigenmode shifting and normal incidence sound transmission loss of inflated single and double MAMs using the concept of effective mass. The investigations are concluded with results from a test sample measurement inside an impedance tube, which confirm the theoretical predictions.Publicationtype: Journal Article113