## 3 Numerical Modeling Results  
In this section, the results of the numerical modeling for all the previously introduced scenarios will be presented. First, we will present the raw numerical results to assess their quality, and subsequently, we will compare them with the data from the experiments. Figure 8 illustrates the numerical result of subjecting the sample to microwave heating, specifically focusing on the case with a central defect and defects that imitate the effects of ageing (CADS). The presented thermogram was acquired after a simulation period of 100 s, which is equal to the heating period used in the experiments as well. It is evident  
Figure 6: The MIRT test with CFRP specimen: (**a**) photo of the inside of the protection enclosure; (**b**) schema of the experimental set-up (top view). Figure 7: Utilized sample: (**a**) initial state; (**b**) the same sample after 10 years of natural ageing process. that when the sample is positioned at a certain angle to the antenna, a higher temperature is observed at the surface closer to the antenna. The overall temperature increase comes to around 4 \({}^{\circ}\)C, which enables the initial identification of all the defects. Further results depicted in Figures 9 and 10 provide a more comprehensive examination of the numerical modeling outcomes. To enhance the presentation of the data, it was determined that only a part of the sample, specifically the composite reinforcement, would be displayed. First, Figure 9 illustrates a comparison of the results obtained for two samples without the defects-simulating ageing process: NDS and CDS. As can be seen, in this case, the proposed method has a high efficacy as the location of the defect may be identified even after 10 s of heating. Nevertheless, it is important to acknowledge that during short heating, the difference in temperature between the background and the defects is small (approximately 0.3 \({}^{\circ}\)C for the given 10 s heating duration). While it is theoretically feasible to detect this with a highly sensitive thermal imaging camera, it could be exceedingly challenging to identify the defect under real measurement conditions. As the duration of heating increases, the difference between the background and the defect obviously grows. After 50 s, it reaches roughly 1.5 \({}^{\circ}\)C, and after 100 s, it increases to around 2.1 \({}^{\circ}\)C. Figure 8 clearly demonstrates the significant imbalance in sample heating that is associated with the aforementioned angle at which the sample is positioned relative to the antenna. Furthermore, a distinct symmetrical temperature pattern can be observed on the surface being tested, which corresponds directly to the radiating characteristics of the antenna. Nevertheless, it is evident that these aspects do not completely eliminate the defect visibility. Nevertheless, they have an impact on the overall image and can potentially hinder the identification of a flaw. The most interesting feature of this research is the analysis of several elements related to the occurrence of flaws in the sample associated with the process of aging. Our objective was to determine the degree to which the method of active microwave thermography could be used to identify these flaws, as well as to assess the influence these flaws have on the ability to detect other defects in the sample. Figure 10 presents a comparison of temperature distributions for ADS and CADS samples. Evidently, defects associated with the aging process are observable in the periphery of the composite layer. Defects that encompass both the epoxy layer and a portion of the composite layer heat up more compared to defects solely present in the epoxy layer. The provided information indicates that the proposed method enables the detection and quantification of the extent of aging changes. It is evident that the presence of aging changes does not significantly affect the detection of a defect located in the center. The defect remains clearly visible, just like in the previous case shown in the figure.