Viscoelastic effects in a spherical Gravitational Wave antenna
  Internal friction effects are responsible for line widening of the resonance frequencies in spherical gravitational wave detectors, and result in exponentially damped oscillations of its eigenmodes with a decay time which is proportional to the quality factor of the mode and to its inverse frequency. We study the solutions to the equations of motion for a viscoelastic spherical GW detector based on various different assumptions about the material's constituent equations. Quality factor dependence on mode frequency is determined in each case, and a discussion of its applicability to actual detectors is made. 
J.A. Lobo and J.A. Ortega