The equation of state of a microinhomogeneous medium and the frequency dependence of its elastic nonlinearity

In the framework of a theological model, a nonlinear dynamic equation of st ate of a microinhomogeneous medium containing nonlinear viscoelastic inclus ions is derived. The frequency dependences of the effective nonlinear param eters are determined for the difference frequency and second harmonic gener ation processes in the case of a quadratic elastic nonlinearity. It is show n that the frequency dependence of the nonlinear elasticity of the medium i s governed by the linear relaxation response of the inclusions at the prima ry excitation frequency, as well as by the relaxation of the inclusions at the nonlinear generation frequencies. (C) 2001 MAIK "Nauka/Interperiodica".