Low frequency absorption by 3D printed materials having highly tortuous labyrinthine slits in impermeable or microporous skeletons

Zieliński, Tomasz G.; Opiela, Kamil C.; Dauchez, Nicolas; Boutin, Thomas; Galland, Marie-Annick and Attenborough, Keith (2023). Low frequency absorption by 3D printed materials having highly tortuous labyrinthine slits in impermeable or microporous skeletons. In: 10th Convention of the European Acoustics Association, EAA 2023, 11-15 Sep 2023, Torino.

Abstract

The low frequency peaks in the absorption spectra of layers of conventional porous materials correspond to quarter wavelength resonances and the peak frequencies are determined essentially by layer thickness. If the layer cannot be made thicker, the frequency of the peak can be lowered by increasing the tortuosity of the material. Modern additive manufacturing technologies enable exploration of pore network designs that have high tortuosity. This paper reports analytical models for pore structures consisting of geometrically complex labyrinthine networks of narrow slits resembling Greek meander patterns. These networks offer extremely high tortuosity in a non-porous solid skeleton. However, additional enhancement of the low frequency performance results from exploiting the dual porosity pressure diffusion effect by making the skeleton microporous with a significantly lower permeability than the tortuous network of slits. Analytical predictions are in good agreement with measurements made on two samples with the same tortuous slit pattern, but one has an impermeable skeleton 3D printed from a photopolymer resin and the other has a microporous skeleton 3D printed from a gypsum powder.

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