Ac hopping conduction at extreme disorder takes place on the percolating   cluster
  Simulations of the random barrier model show that ac currents at extreme disorder are carried almost entirely by the percolating cluster slightly above threshold; thus contradicting traditional theories contributions from isolated low-activation-energy clusters are negligible. The effective medium approximation in conjunction with the Alexander-Orbach conjecture leads to an excellent analytical fit to the universal ac conductivity with no nontrivial fitting parameters. 
Thomas B. Schr{\o}der and Jeppe C. Dyre