## 1 Introduction  
Non-destructive testing (NDT) is helpful for manufacturing defect-free products, but it is also used for maintenance and condition inspection of industrial structures and facilities [1]. There are many NDT techniques, each based on different theoretical principles and producing different results concerning the physical properties of an object. The solutions provided through each non-destructive testing technology must be further analyzed to interpret the object's physical properties or structure. However, this interpretation inevitably involves several assumptions [2, 3, 4]. Infrared thermography (IRT), also known as thermal imaging, is a rapidly developing field in science and industry due to the tremendous advances made over the past few decades in microsystem technology in the design of infrared detectors consisting of electronics and computer science [5]. In addition, IRT is an optical measurement technique, evolving rapidly with the development of high spatial resolution and sensitivity detectors and improved computation power. Today, IRT technology is being applied in research and development in various industries [6, 7], including non-destructive testing, detailed structural condition monitoring, predictive maintenance, manufacturing quality assurance,energy cost reduction, metal and composite material evaluation, gas leak detection, and more. Meanwhile, researchers worldwide are working to develop infrared thermography technology to improve the reliability and ability to detect failures such as defects. Every technique has its own limitations, and no technique can be considered good, effective, or perfect. In this context, there is a growing trend to integrate thermography technology into other conventional NDT technologies to compensate for each other's limitations. It will result in better inspection capability and the possibility that more information can be acquired in a single test than a particular technique. Furthermore, it can solve the limitations posed by one NDT technique to obtain the intended information and achieve the required inspection efficiencies. IRT has gained increased recognition in recent years because it has good benefits over its counterparts. The benefits include high-speed contactless functioning, a higher level of safety, and portability with the potential to encompass a large inspection area. IRT is generally divided into two approaches: passive thermography and active thermography. Passive thermography measures thermal variations of a material using an infrared vision device without external thermal sources [8]. Contrary to passive thermography, active thermography requires an external heat source to stimulate the materials under tests. Commonly, halogen lamps, high-power photographic flash, and laser beams are widely used, and other high-power cinematographic lamps and quartz line IR lamps are used [9; 10]. In addition, active thermography is subdivided into lock-in thermography (LIT), pulsed thermography (PT), step-heated thermography (SHT), and vibration thermography (VT) according to external heating methods [11; 12; 13], and PT and LIT are the most utilized. The pulsed thermography (PT) idea was first proposed by [PERSON] et al. [14]. However, other researchers integrated this technique into various NDT applications. The concept of a PT system for defect detection consists of applying a very short time and powerful energy pulse to an object and then recording the temperature rise, decay, or both curves in transient mode. The thermal energy propagates under the surface by thermal diffusion. The presence of subsurface defects interrupts the diffusion rate of the energy pulse. Pulsed thermography is one of the active infrared techniques, which uses an optical device as an external heat source. Among the active thermography techniques described above, it is the easiest to apply and widely used.