The dark acoustic metamaterials have been proved to be effective in absorbing low frequency sound (100-1000Hz). Thus it is very interesting to investigate whether it is also effective in vibration damping. In this thesis, we experimentally show the acoustic metamaterial structures (the sample) can really help attenuate vibration. We have shown the validity of the sample by pasting it to aluminium plate with fixed boundary condition and with free boundary condition as well as steel plate which is much heavier with free boundary condition. In the first case we measure the velocity response with laser Doppler vibrameter, and in the latter two cases we measure the acceleration response with sensors. Two improvements have been found to be more effective. One is stacking two samples...[ Read more ]

The dark acoustic metamaterials have been proved to be effective in absorbing low frequency sound (100-1000Hz). Thus it is very interesting to investigate whether it is also effective in vibration damping. In this thesis, we experimentally show the acoustic metamaterial structures (the sample) can really help attenuate vibration. We have shown the validity of the sample by pasting it to aluminium plate with fixed boundary condition and with free boundary condition as well as steel plate which is much heavier with free boundary condition. In the first case we measure the velocity response with laser Doppler vibrameter, and in the latter two cases we measure the acceleration response with sensors. Two improvements have been found to be more effective. One is stacking two samples together, the other is adding an aluminium foil to the surface of the sample. 2 stacked samples happen to be more effective than 4 distributed samples, although in both cases 4 samples are comprised. In steel plate, 4 stacked samples are even more effective than rubber layer (4mm thick), moreover the mass ratio of the former is much less than the latter (6.2% vs 14.5%). We also try to find out the mechanism of vibration damping by the sample by eliminating aluminium platelets (only with frame and membrane) and membrane (only with frame). Surprisingly, in most cases the sample is even less effective than frame or frame plus membrane, leaving the mechanism much complicated to understand. In addition, we investigate the damping effect of unit samples, which as a part of the normal sample is thought to play an essential role in damping. We find that unit samples are effective and especially effective when stacking together, with point contact or pasted at the right place. We also find evidence to rule out it is just mass effect. Last, through comsol simulation we get the modes of steel plate with free boundary condition and beam with fixed boundary condition and conclude that the position the sample is pasted is significant.