This work proposes a new approach to deal with the problematic caused by the pellet's porosity in THz-TDS measurements of oxide powders. We assume a ternary system (PE matrix + oxide powder + air) and use an algorithm based on a sequential two-step implementation of Effective Medium Models to account individually for each of the phases. The results show up that the capacity that this method has to combine multiple models and adapt to the physical characteristics of each phase is a major advantage compared with previous methods.