If you put a piece of filter paper over a speaker, the wind it creates suddenly gets 20 times stronger.
Sound waves usually move air very weakly, but adding a thin, porous layer amplifies this 'acoustic wind' dramatically. This discovery could allow us to levitate heavier objects or cool electronics using nothing but silent sound waves.
Order-of-magnitude enhancement of airborne acoustic streaming using porous materials
SSRN · 6546325
Thin layers of porous materials are shown to produce an unexpected order-of-magnitude amplification of bulk-driven acoustic streaming generated by a high-powered airborne transducer, increasing the streaming velocity from 0.12 m/s to 2.5 m/s. Particle image velocimetry (PIV) measurements were used to characterise the streaming field produced by a Langevin horn operating at 27 kHz with a range of thin porous layers (various filter papersand a woven Kevlar fabric) placed in front of the source. We