Damping and Noise Abatement

Suppression of flexural vibrations in metal plates and bars by application of a thin layer of polymeric material, either spread directly or applied in the form of a tape, has become of great importance both for elimination of noise (especially in vehicles and airplanes) and for improving fatigue characteristics. It was mentioned in Chapter 7 that measurements of resonance frequencies and damping in such compound layered systems can be used for obtaining the viscoelastic properties of the polymeric stratum. Conversely, knowledge of the viscoelastic properties and their dependence on frequency and temperature (and plasticization, incorporation of fillers, etc.) aids in the selection of antidamping materials for specific applications.  

Viscoelastic liquids have also been used to damp vibrations and absorb acoustic energy. Networks with unattached linear molecules may be useful,  

It may be noted that in the acoustic literature the symbol jj is often used not for viscosity but for the loss tangent (equal to the relative response width (Acuy/uto as defined in Chapter 6, Section E). 

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