## 1 Introduction
### Active Thermography Method  
Active thermography involves the utilization of an external energy source to generate a thermal contrast within the examined specimen [12]. The investigation of thermal imaging techniques for potential application in the analysis of large-scale objects, such as complex concrete structures, is conducted in many research centers around the world. One potential approach involves the utilization of passive thermography, which is a technique that relies solely on natural sunlight, as opposed to active thermography, which utilizes an external heat source. It is important to take into account the fact that the implementation of this methodology requires extended periods of observation, with the outcomes dependent on factors such as diurnal variations and meteorological conditions [13]. Many techniques involve the utilization of active thermography, wherein conventional heat sources, such as halogen lamps, flash lamps, infrared radiators, and hot air [12; 13; 14; 15; 16; 17; 18; 19; 20], are employed. In this case, the results are no longer dependent on the external condition, but again, the main problem is the extended duration required for heating, which can be attributed to the substantial size of the structure under examination. In this case, it is important to bear in mind that the transfer of heat within the material takes place via conduction, wherein heat is transmitted from the heated surface to the interior of the object. The inherent specificity of these forms of excitation results in a substantial increase in inspection time. One potential approach to address this issue involves the utilization of vibrothermography techniques [21; 22; 23] (including classical, burst, and self-heating vibrothermography), which use dissipation processes and mechanical energy for defect detection. The excitation in this instance takes the shape of an acoustic wave, which passes through the tested structure and dissipates in damaged areas and defects. Although this is very effective, the acoustic methods typically involve the necessity of establishing direct contact between the exciter and the test object, which is a requirement that may present challenges in certain applications. Moreover, these methods are most appropriate for the identification of deeply located defects, such as cracks. The present study suggests the utilization of microwave irradiation as a heating method. Microwave heating has been widely employed in the literature for various purposes related to concrete structures, including expediting the curing process, decontaminating cement, and facilitating the drilling or melting of concrete [24; 25; 26; 27]. In this proposal, microwaves are suggested as a potential energy source for infrared thermography [28; 29; 30; 31; 32; 33; 34]. The primary benefit of utilizing microwave heating lies in its volumetric nature. The rapidity of this technique is attributed to the heating of a specific volume of the specimen at a given time. Conversely, with regard to this alternative energy source, the heating ratio is contingent not solely upon the thermal characteristics of the substance but also upon certain electrical properties, especially the dielectric constant [24; 35]. An interesting phenomenon is observed when microwaves interact with conductive materials, such as CFRP. The heating effect is constrained by a lower penetration depth value. Following the application of heat, a thermography imaging device is utilized to visually examine the surface of the specimen under inspection. Non-uniform heating of a sample can be attributed to the presence of inner material flaws, such as delamination and lack of adhesive. These flaws result in the manifestation of hotter or cooler regions visible in the temperature distribution on the sample's surface [36; 37; 38; 39; 40].