The paper presents semi-anlytical method of the calculation of SAR (Specific Absorption Rate) coefficient and such approach enables investigating of the internal structure of the coefficient. It is possible to trace the influence of electromagnetic parameters, such as frequency and polarisation on the value of SAR. The biological model is an isotropic lossy dielectric spheroid. The excitation is a uniform plane wave. The correctness of this approach has been verified by an experiment made on spheroidal phantom.