RESUMO
An approximate method for calculating the radiation from a moving charge in the presence of a dielectric object is developed. The method is composed of two steps. The first step is calculation of the field in the medium without considering the external boundaries of the object, and the second step is an approximate (ray-optical) calculation of the wave propagation outside the object. As a test problem, we consider the case of a charge crossing a dielectric plate. Computations of the field are performed using exact and approximate methods. It is shown that the results agree well. Additionally, we apply the method under consideration to the case of a cone-shaped object with a vacuum channel. The radiation energy spectral density as a function of the location of the observation point and the problem's parameters is given. In particular, the convergent radiation effect is described.
