Enhancing the Sound Absorption of Small-Scale 3-D Printed Acoustic Metamaterials Based on Helmholtz Resonators

Abstract

Acoustic metamaterials have recently become of interest for their ability to attenuate sound by breaking the massdensity law. In this paper, acoustic metamaterials based on Helmholtz resonators and capable of attenuating sound up to 30 dB are fabricated for sound absorption applications in the smallscale. The proposed metamaterials are subwavelength at a factor of / with respect to the lateral dimension of the units. The directional response due to the position of the acoustic source on the sound attenuation provided by the metamaterial is investigated by controlling the location of a loudspeaker with a robot arm. To enhance and broaden the absorption bands, structural modifications are added such that overtones are tuned to selected frequencies, and membranes are included at the base of the resonators. This design is made possible by innovative 3D printing techniques based on stereolithography and on the use of specific UV-curable resins. These results show that these designs could be used for sound control in small-scale electroacoustic devices and sensors.

Fabrication and Characterization of 3D Printed Thin Plates for Acoustic Metamaterials Applications

“…An Asiga Pico Plus 27 (Sidney, Australia) with a pixel image resolution of 27 by 27 μm, and a minimum build layer thickness of 1 μm was used to 3D print the samples. A circular shape was selected for the plate, since the analytical model of circular membranes and thin plates is well known and also due to previous research based on cylindrical Helmholtz resonators [4] that could be integrated with thin plates in future work. A hollow cylinder 1 mm in height and with 1 mm thick walls was also designed to support the plate.…”

“…While the resin described above was used to print the thin plate, the support material was made of PEGDA 250, 0.1% Sudan I and 1% Irgacure 819. The exposure time to light contributes to determining the thickness of the membrane [18] and different exposure times between 0.5 second and 9 seconds where tried for different materials as reported in [4]. Since the Asiga 3D printer software does not allow to change the exposure time to light or other parameters while the print has started, the chosen exposure time of 5 seconds was of a duration that allowed to print both the materials of the support and the materials of the membrane.…”

“…With commercial resins, even when the build layer thickness was set to 10 μm or less, the plates resulted to be 1 mm thick. As shown in Figure 3, when adding SI to the resin to reduce the amount of light, it was instead possible to finely control the resolution and to obtain a thickness down to 35 μm [1], [4]. In this case, the fabricated plate had a thickness of 70 μm, which was measured using a digital micrometer.…”

“…ecent advances in additive manufacturing techniques have now made it possible to fabricate thin membranes and plates that are essential for the study of several acoustic applicationsfor example, microphones and loudspeaker prototyping and acoustic metamaterials [1]- [4]. In laboratories, these membranes are usually obtained through a procedure where a piece of material is cut and glued on a rigid frame or support.…”

“…For example, in this paper the goal is to fabricate thin plates that could be included in small-scale devices, such as headphones and smart speakers, and at the same time having a low resonance frequency. Therefore, a polymer that had a low Young's modulus with respect to other materials used in previous work [4] was selected. The 3D printing technique here developed made it possible to fabricate layers 70 μm thick.…”