Radiation force fields formed by a standing surface acoustic wave in a viscous liquid layer lying on an elastic half-space

The field of a surface acoustic wave in the system “viscous fluid layer—elastic substrate” is calculated taking into account the shear components in the fluid. On the basis of the dispersion equation, the velocity and attenuation of the surface wave are calculated. It is shown that for low-viscosity liquids the change in velocity is insignificant, but the shear components make the main contribution to the attenuation of the wave. The radiation pressure corresponding to a standing surface wave in a viscous fluid and acting on an element of its volume due to the nonlinearity of the equation of motion is calculated. It is shown that taking viscosity into account changes the spatial distribution of radiation pressure. In the presence of suspended particles in the liquid form, the attenuation of the wave causes an additional tendency to collect these particles in the center of the system. The shear components have significant radiation pressure gradients near the interface. They play a decisive role in the formation of ordered ensembles of particles at the last stage of the self-organization process. [The study was supported by the Russian Foundation for Basic Research under Project No. 20-02-00493-a.]