## 6 Summary, Conclusions, and Outlook  
The possibility of identifying the dimension, depth and orientation of planar heat sources buried below the surface from IR thermography surface temperature data in time domain has been analyzed. These heat sources are representative for defects that produce heat under any type of excitation, such as cracks excited with ultrasounds or metallic inclusions in electrical insulators excited inductively. A sensitivity analysis has been conducted showing that two perpendicular surface temperature profiles measured at the end of the burst together with the temperature history at one position of the surface gather the spatial and temporal information needed to retrieve the lateral dimensions, inclination, depth, and flux of tilted squared heat sources, univocally. The sensitivity study also shows that optimum results are obtained when the thermal diffusion length associated to the duration of the burst coincides with the maximum depth at which heat is emitted: for shorter bursts the sensitivity to the height might be too low and longer bursts harm the decorrelation between parameters. A sensible rule of thumb could be to use the shortest burst able to sense the target layer under inspection. The fittings of synthetic data with added noise show that the quality of the results worsens as the SNR is reduced and the inclination of the heat source approaches the vertical. Fittings of experimental data confirm that the height of the heat source is the most challenging parameter, especially when the heat source makes an angle higher than 45\({}^{\circ}\) with the surface. The width and depth can be retrieved within 5 to 10% and the angle within 9\({}^{\circ}\) from the true value. This first study proves that it is possible to characterize rectangular tilted heat sources from surface temperature data obtained by infrared thermography. However, there is still room to improve the experimental results in several aspects. The first question refers to the protection of the infrared camera against the effect of the electromagnetic field. This effect may eventually harm the electronic system of the camera but also induces noise in the data during the excitation period. In addition to the protection of the camera itself and the associated noise reduction, an improved shielding would also allow to reduce the distance between the camera and the sample/coil system, thus improving the spatial resolution in the experiments, which is highly desirable for heat sources with dimensions similar to the ones handled in this work. Another aspect to pay attention to is the quality of the samples, in terms of eventual lack of adherence between the Cu slab and the resin, which can lead, among others, to unwanted thermal resistances and distorted temperature distributions. Finally, regarding future perspectives and with the aim of characterizing tilted planar defects that produce heat in thermographic nondestructive testing techniques, the next step is the characterization of planar, tilted heat sources of arbitrary shape. The conclusions drawn from this study suggest that some additional information both spatial and temporal, might be necessary to characterize defects of any shape. Nevertheless, these first quantitative results open the possibility of characterizing tilted flaws in any thermographic modality with internal thermal excitation of defects. Conceptualization, A.M. and A.S.; methodology, L.F. and P.V. ; software, L.F.; validation, P.V., U.G. and A.S.; formal analysis, A.M. and L.F.; investigation, A.M. and L.F.; resources, I.S.d.O. and P.V. ; data curation, P.V. ; writing--original draft preparation, A.M.; writing--review and editing, P.V., L.F., I.S.d.O., A.S. and U.G. ; visualization, A.M. and L.F.; supervision, U.G. and A.S.; project administration, U.G. ; funding acquisition, A.S., A.M. and I.S.d.O. All authors have read and agreed to the published version of the manuscript.