The disclosure relates to a method for calculating electromagnetic radiation emitted by a computer system. The method models the characteristic radiation from a central processing unit as a modulated Gaussian pulse. The method solves Maxwell's equation using finite differences in the time domain. After solving Maxwell's equation the method determines if the radiation emitted by the heat sink is capacitively coupled to the radiation emitted by the remaining components of the computer system. The method also determines whether radiation emitted by the heat sink is inductively coupled to the radiation emitted by the remaining components of the computer system. Finally, the method uses a fast Fourier transform to translate time domain data to the frequency domain. The method also teaches using a computer system, with instructions coded on a computer readable medium to make the calculations described.