  In several merging clusters of galaxies so-called cluster radio relics have
been observed. These are extended radio sources which do not seem to be
associated with any radio galaxy. Two competing physical mechanisms to
accelerate the radio emitting electrons have been proposed: (i) diffusive shock
acceleration and (ii) adiabatic compression of fossil radio plasma by merger
shock waves. Here the second scenario is investigated. We present detailed
3-dimensional magneto-hydrodynamical simulations of the passage of a radio
plasma cocoon through a shock wave. Taking into account synchrotron, inverse
Compton and adiabatic energy losses and gains we evolved the relativistic
electron population to produce synthetic radio maps in Stokes I-, Q-, and
U-polarisation. In the synthetic radio maps the electric polarisation vectors
are mostly perpendicular to the filamentary radio structures.
