Physical basis of methods for measuring viscoelastic properties

The main methods used to measure viscoelastic properties of materials in a wide range of frequencies from $10^{-4}$ to $10^6$ Hz are reviewed. It is demonstrated that the accuracy of many experimental methods can be increased by taking into account the shape factors, which depend on the specimen type. An example of the shape factor for a cylindrical specimen is provided, which was determined numerically on the basis of a two-dimensional deformation model taking into account the specimen geometry and Poisson's ratio. The importance of the precise determination of Poisson's ratio for rubber-like and complex-structured materials is demonstrated. Requirements to such measurements and a setup satisfying these requirements are described. Two methods for measuring viscoelastic properties of living tissues (compliance and disturbance propagation velocity) are considered. Based on the developed method of measuring these parameters for materials with a fixed thickness, methods for standartization of measurements of viscoelastic characteristics of living tissues are proposed.