Dynamics of a spheroidal particle in a leaky dielectric medium in an ac electric field.

We study a system comprising a spheroidal particle with permittivity epsilon 2 and conductivity sigma 2 immersed in a host medium with permittivity epsilon 1 and conductivity sigma 1 in the ac external electric field with a strength Epsilon 0 and frequency omega. We determined conditions when orientation of a spheroidal particle with a finite electric conductivity at t --> infinity coincides with the orientation of the ideal dielectric spheroidal particle, when orientation of a spheroid at t --> infinity is normal to the orientation of the ideal dielectric spheroidal particle, and when orientation of particle is not affected by the external electric field. We found the direct connection between the final orientation of the particle and the existence of two time intervals, T1(omega) and T2(omega), such that during time interval T1 an equilibrium orientation of the particle is the same as the equilibrium orientation of an ideal dielectric particle while during time interval T2 the direction of the stable equilibrium orientation is normal to the equilibrium orientation of an ideal dielectric particle. The values T1 and T2 depend on the frequency of the external field omega and T = T1(omega) + T2(omega), where T=2 pi/omega.