Acoustic black holes: a new approach to vibration damping in light-weight structures

‘Acoustic black holes’ have been introduced and investigated mainly during the last decade. They can absorb almost 100% of the incident wave energy, which makes them attractive for vibration damping and sound absorption. The main principle of the ‘acoustic black hole effect’ is based on a gradual power-law-type decrease in velocity of the incident wave with propagation distance, linear or faster, to almost zero, which should be accompanied by efficient energy absorption using the attached highly absorbing materials. So far, this effect has been investigated mainly for flexural waves in thin plates for which the required gradual reduction in wave velocity with distance can be easily achieved by changing the plate local thickness according to a power law, with the power-law exponent being equal or larger than two. The key advantage of using the acoustic black hole effect for damping structural vibrations is that it requires very small amounts of added damping materials, in comparison with traditional methods, which is especially important for vibration damping in light-weight structures used in aeronautical and automotive applications. The present paper provides a brief review of the theory of acoustic black holes and of the recent experimental work carried out at Loughborough University on damping structural vibrations using the acoustic black hole effect. Experimental investigations have been carried out on a variety of plate-like and beam-like structures containing one- and two-dimensional acoustic black holes. The results of the experimental investigations demonstrate that in all of the above-mentioned cases the efficiency of vibration damping based on the acoustic black hole effect is substantially higher than that achieved by traditional methods.