Acoustic Metamaterials: ‘The Influence of Boundary Effects on Resonant Acoustic Transmission through a Thin Slit’

Resonant transmission of sound through a single, open-ended slit in an aluminium plate is explored. The experimental results demonstrate a significant reduction in the resonant frequency as the slit is narrowed to below ~1% of the fundamental free-space wavelength. This is in agreement with a little referenced study of Lord Rayleigh [Phil. Mag. 1, 3, (1901)] concerning how viscous and thermal effects at the slit walls significantly reduces the sound velocity within the slit, for slit widths substantially greater than the thickness of the boundary layer. The experimental results are in full accord with Lord Rayleigh’s original theory and with numerical modelling.DST