Optimal structural design of acoustic metasurface with sound insulation function and openings for cylindrical waves

The power source of a machine generates noise, so sound insulation measures are taken. However, sound insulation by sealing causes the internal temperature to rise, increasing the risk of damage to the power source. On the other hand, ventilation openings for cooling cause noise leakage to the outside. To solve this trade-off, this study developed a design methodology for acoustic metasurfaces, which are highly functional acoustic devices. To represent a coupled acoustic structural system, a two-phase material model of solid and acoustic phases is used, and topology optimization using the density method is applied. In previous studies, acoustic metasurfaces were mainly designed for plane waves; however, when the noise source is relatively small or at a distance from the shielding material, sound waves need to be treated as cylindrical or spherical waves. In this study, assuming that the sound source is a cylindrical wave, we designed and created a periodic structure that provides both sound insulation and ventilation. This paper outlines this design methodology and its results.