Deprecated: implode(): Passing glue string after array is deprecated. Swap the parameters in /home/spinnluxnr/www/2018/inc/main.php on line 306
3D printed acoustic metamaterials for small-scale noise control applications
Controlling the propagation of acoustic waves is of great importance to our everyday life, for example to isolate ourselves from industrial or traffic noise and at the same time to be able to enjoy listening to music or to communicate with people around us. Acoustic metamaterials have been studied in the last decade because of their ability to manipulate sound waves in new ways, thanks to their exotic properties such as negative mass density and bulk modulus. By exploiting the resonances in the unit cells that form the structure of the metamaterials it is possible to generate absorption bands where the sound is deeply attenuated. Similar results can be obtained by using phononic crystals, which are materials composed of periodically spaced unit cells, where the wavelength of the frequencies that can be controlled is of the same order of the periodic spacing. However, the properties of acoustic metamaterials are a byproduct of the resonances of their unit cells rather than the distance between them, hence they are subwavelength structures and can enhance acoustic absorption. The objective of the work presented in this poster was to fabricate small-scale acoustic metamaterials that could be included in wearable devices such as headphones or hearing aids and that could attenuate sound in a chosen frequency range. To do so, it was necessary to develop manufacturing techniques to fabricate the unit cells in an accurate and reproducible way. We chose to make use of additive manufacturing technology to fabricate Helmholtz resonators and membranes which are often employed as unit cells at the base of metamaterials. We first 3D printed acoustic metamaterials based on Helmholtz resonators having the shape of soda cans but with a dimension scaled down by a factor of 20 and we were able to obtain absorption bands with a sound transmission loss up to 30 dB. We then modified the dimension of the resonators to “tune” the overtones and achieve multiple absorption bands. Furthermore, we developed a technique to 3D print thin membranes at the base of the resonators to further widen the absorption. These results could contribute to improve the fabrication of metamaterials and hence could lead to applications for noise control such as noise cancelling headphones and smart sensors.