Innovative origami-based solutions for enhanced quarter-wavelength resonators

Sound absorption at low to moderate frequencies using quarter-wavelength resonators requires significant resonator's length (for instance 28 cm for 300 Hz), a condition very often uncompatible with a practical use of this kind of resonators for sound absorption applications. To deal with this drawback, we investigate in this study innovative ways to design more compact and confined quarter-wavelength resonators by shifting their resonance frequency while keeping constant their length. This exploratory process led to a hybrid solution: a paper-folded (origami) spiral is inserted in the resonator and acts as an equivalent porous medium whose inner characteristics enhance the absorption properties of the resonator. Especially, by modifying the resonator's tortuosity, origami-spirals make possible to artificially extend the resonator's length, thus obtaining with shorter geometries the absorption properties of longer resonators. (c) 2018 Elsevier Ltd. All rights reserved.