## 4 Conclusions  
In the presented study, the feasibility of MIRT for monitoring reinforced concrete structures strengthened with CFRP was examined. For this purpose, a numerical model (with continuous and modulated excitation), corresponding to the laboratory setup in the same manner, was developed to accurately analyze the examined phenomenon and to apply scenarios that were not executed experimentally. The compliance of the results from both approaches (numerical and experimental) in the case of modulated excitation allowed for validating the numerical model for detecting a defect in a CFRP reinforcement. The defect area, which was represented by the absence of an adhesive (or the presence of the air), had a higher surface temperature than the temperature of the area without a defect. Both approaches yielded similar results, which emphasized the non-uniformity of the microwave beam. This phenomenon must be taken into account, as it can potentially lead to the misinterpretation of thermograms when attempting to identify defects. In addition to validating the numerical model via experimental testing, the broader context of the study was provided by the numerical model itself. This included determining the influence of the defect's position on its detectability and evaluating the efficiency of the modulated excitation method in comparison with continuous excitation. This study demonstrated the superiority of MIRT over alternative active thermography techniques, particularly in terms of its ability to ensure efficient and fast inspection, even for large structures. Furthermore, the non-contact nature of this method is of utmost significance in numerous instances of field research. Our previous research on the MIRT method demonstrated its versatility, making it applicable to various materials, particularly those with low conductivity (but not only these materials, as it can be employed to analyze surface defects in metals). The method's broad range of applications stems from its ability to detect both inner and shallow defects through volumetric heating. Active thermography is a technique that enables the detection of various types of defects, such as cracks, delamination, corrosion, voids, lack of adhesive, and inclusions. This method is particularly effective, as it exhibits sensitivity to any structural alterations present in the objects being tested. The present study offers potential perspectives in terms of applying the MIRT method to investigate the durability of composites under various conditions, such as different types of defects or varying environmental conditions. Additionally, the research encompassed the advancement of the detection technique utilizing various excitation systems, such as alternative microwave generators and antennas. This was done to accommodate diverse types of defects and commonly employed composite materials. Our research team intends to proceed with the subsequent phases of the research outlined in this study. These phases include the analysis of specific structures to identify additional types of defects, such as moisture or material deterioration caused by reinforcement corrosion. Furthermore, we plan to explore the application of microwave systems with alternative configurations, specifically investigating the influence of electromagnetic wave frequency and frequency modulation on the outcomes obtained. Additionally, we aim to employ machine learning techniques, particularly artificial neural networks, to automate the assessment of identified defects. Conceptualization, S.A.K. and B.S. ; methodology, S.A.K. and B.S. ; formal analysis, S.A.K. and B.S. ; investigation, S.A.K., C.L.R. and B.S. ; data curation, S.A.K. and B.S. ; writing--original draft preparation, S.A.K. and B.S. ; writing--review and editing, S.A.K. and B.S. ; visualization, S.A.K. and B.S. ; supervision, D.D. and F.B. ; funding acquisition, D.D. and F.B. All authors have read and agreed to the published version of the manuscript.