Boundary-layer effects on acoustic transmission through narrow slit cavities
Hibbins, Alastair P.
Sambles, J. Roy
Physical Review Letters
American Physical Society
This is the final version of the article. Available from American Physical Society via the DOI in this record.
We explore the slit-width dependence of the resonant transmission of sound in air through both a slit array formed of aluminum slats and a single open-ended slit cavity in an aluminum plate. Our experimental results accord well with Lord Rayleigh's theory concerning how thin viscous and thermal boundary layers at a slit's walls affect the acoustic wave across the whole slit cavity. By measuring accurately the frequencies of the Fabry-Perot-like cavity resonances, we find a significant 5% reduction in the effective speed of sound through the slits when an individual viscous boundary layer occupies only 5% of the total slit width. Importantly, this effect is true for any airborne slit cavity, with the reduction being achieved despite the slit width being on a far larger scale than an individual boundary layer's thickness. This work demonstrates that the recent prevalent loss-free treatment of narrow slit cavities within acoustic metamaterials is unrealistic.
The authors would like to thank DSTL for their financial support.
Vol. 115, pp. 044302 -
Place of publication