“…The main advantages of this method are: (i) it is a one-step method, (ii) it does not require any a priori information about the number, size, shape or location of the defects, (iii) it has a very small computational cost. Topological derivatives have been successfully used for solving a wide variety of problems related with defect identification in many fields, like in acoustics [6,9,19], electromagnetism [37,42], elasticity [4,25,41], and electrical impedance tomography problems [2,8,11], to mention a few. Related work dealing with thermal problems was published in [7,10], where a two dimensional unsteady thermal propagation problem in an unbounded media was studied.…”