Multi-material 3-d printing of customizable membrane-type acoustic metamaterials

Kurzfassung

Achieving sound attenuation through lightweight structures challenges the conventional mass–frequency law due to advancements in acoustic metamaterials. Among these, membrane-type acoustic materials have attracted significant interest owing to their simple construction and ultra-thin design. The sound manipulation performance of membrane-type unit cells is realized through the incorporation of an attached mass—specifically by adjusting its magnitude and distribution on the membrane, as well as by modifying the membrane’s pre-stress. Altering one or both parameters enables shifting of the frequencies at which maximum and minimum sound transmission occur. However, the widespread application of membrane-type acoustic metamaterials is limited by uncertainties arising from their fabrication processes. This limitation primarily stems from the high sensitivity of the structure’s vibro-acoustic response to the positioning of the attached mass and to the magnitude of the membrane pre-stress. These issues can be addressed through the implementation of a consistent manufacturing process and a controlled method for applying membrane pre-stress. Utilizing the broad material selection offered by the fused deposition modeling (FDM) method, membranes can be fabricated from flexible materials, while the attached masses and frame components can be produced from relatively rigid materials—all within a single-step multi-material 3D printing process. In this study, as a first step, various unit cell designs are analyzed using finite element analysis to demonstrate configurability through modifications in the geometry of the attached mass—while maintaining its magnitude constant—and through systematic variations in membrane pre-stress. Subsequently, the metamaterial unit cell samples are fabricated using multi-material 3D printing. Sound transmission loss measurements are performed on the fabricated unit cells using an impedance tube, and the results are compared with numerical simulations. The resulting effects on the vibrational characteristic to the acoustic performance i.e. resonance and anti-resonance modal behaviors to the sound attenuation performance, of the unit cells are then analyzed and presented. Furthermore, impedance-tube-scale multi-celled arrays are designed such that each unit cell contains the same attached mass, while the membranes are subjected to different pre-stress magnitudes. The metamaterial arrays are then fabricated and analyzed using the same approaches. This configuration is used to explore sound manipulation performance through pre-stress adjustment, targeting multi-tonal noise attenuation. Finally, the effectiveness achieved through modifications in mass geometry and membrane pre-stress is discussed for both single unit cells and multi-celled arrays.