Passive distributed vibration absorbers for low frequency noise control

It is well known that standard poroelastic materials and viscoelastic damping materials are ineffective at reducing low frequency sound and vibration. This paper overviews two new treatments developed at Virginia Tech which attempt to address this problem. Heterogeneous blankets consist of poroelastic material with embedded multiple small masses. The masses combine with the natural elasticity of the poroelastic material matrix to create multiple embedded vibration absorbers with a range of natural frequencies in the low frequency region. The embedded masses are found to significantly increase the low frequency transmission loss and absorption of the poroelastic material. The second treatment, distributed vibration absorbers, spread mass and spring elements over a large area while still maintaining a viable reactive damping effect at low frequencies. DVAs are found to provide global reduction of low frequency vibration of structures in a compact, lightweight configuration. The paper will summarize the concepts, development and testing of both devices. Applications of the new treatments to realistic structures will be considered.