We present results from our recent efforts on the fabrication and acoustic characterization of 3-D printed porous absorbers. The acoustic properties of porous structures are dependent on their cellular microstructural architecture. Thus, controlling their local and global cellular architecture can allow a significant control over the acoustic properties of porous materials. Our focus here is on two different kinds of porous absorbers—open-celled absorbers with novel surface topologies and functional gradients, and bio-inspired fibrous absorbers. First, we apply stereolithographic printing to fabricate open-celled absorbers with novel surface topologies. The effect of parameters such as porosity, relative density, surface topology, and through-thickness porosity gradients on the sound absorption behavior is elucidated. Second, we explore the possibility of fabricating fibrous absorbers using fused deposition modeling. While 3-D printing allows fabrication of complex geometries, printing thin fibrous parts is significantly more challenging. Here, we compare two different techniques of printing such structures and present the effect of the fibrous architecture on the acoustic properties of the structure. The obtained results show that 3-D printing offers a promising new avenue of designing porous structures with tailored acoustic properties.

Additive manufacturing allows the cost-effective fabrication of cellular porous structures with tailorable geometries. Structures with small pore sizes offer improved acoustical performance; however, they often result in increased structural weights and are difficult to produce using low-cost additive manufacturing methods. Here, we leverage our recent work demonstrating the fabrication of fibrous structures using 3D printing, to develop multifunctional porous structures with enhanced acoustical properties. Our method allows the addition of fibers to a structural host, which helps improve the acoustical performance without a significant weight or flow-reduction penalty. In this presentation, we outline the fabrication method and study the effect of adding fibers to the acoustical performance of porous structures with periodic gyroid unit cells. The effect of fibers on the acoustical impedance and flow resistance is studied using an impedance tube and a flow bench, respectively. We then use an inverse characterization method to analyze the effects of changing fiber and structural parameters on the acoustical performance. Our results show that adding fibers to porous host structures can drastically improve their broadband noise reduction potential.