A slim subwavelength absorber based on coupled microslits

Designing a perfect low frequency acoustic absorber with subwavelength thickness is always a challenge. Various designs including micro-perforated panels, acoustic metamaterials and metasurfaces have attracted significant interests in recent years. The present paper reports a slim subwavelength absorber based on a regular array of coupled microslits to achieve low frequency absorption. The absorption mechanism by the coupled microslits is investigated using acoustic impedance together with the reflection coefficient in the complex frequency plane. The geometry of the coupled microslits is optimized using a differential evolution algorithm to enhance the absorption in the frequency band from 300 Hz to 800 Hz under different condition. The ratio of the absorber thickness to wavelength at the lowest absorption peak is less than 3.4%, which confirms its operation in deep subwavelength regime. Finally, wide band absorption using coupled microslits is demonstrated by the experiment and simulation.