## 1 Introduction
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Reference** & **Method Used** & **Target Material** & **Sensor Used** & **Calculation Method** & **Performance Metric** & **Limitations** \\ \hline
[15] & Capacitive & & Coplanar & Serial intensity & Contrast & Local detection \\  & Imaging & CFRP & capacitive & & comparative & of defect, \\  & & & sensor & & Defect \\
[16] & & & & & Intensity & Qualitative & detection on \\  & & & & analysis & Evaluation & surface or thin \\  & & & & & & layers \\  & & & & & Reduced \\
[17] & Pulsed active & Buried & FLIR T 650 SC & & & detectability of \\  & thermography & anti-personnel & thermal & & & binarized \\  & & & & camera & & images due to \\  & & & & & low resolution \\  & & & & Feature & & Low accuracy \\
[18] & Feature & Fabric defects & - & extraction, & Accuracy, & of surface \\  & extraction & & & Machine & Precision & & defects \\  & & & & learning & & compared to \\
[19] & Ultrasonic & CFRP & Phased array & Phased array & Quantitative & & requires a lot of \\  & Testing & & transducer & (PA) & Evaluation & data to improve \\  & & & & & accuracy & \\
[20] & Inductive & & & Image & Precision, & Reduced \\  & Thermography & Steel & IR camera & segmentation & Recall & detectability \\  & & & & & & due to noise \\  & & ASTM E399-05 & & & High sensitivity & \\  & & compact & SC3000 IR & Heat capacity & and & Inspection of \\  & & tension & Camera & by frictional & accuracy & localized \\  & & specimen & & heating & inspection for & surface cracks \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of representative classifications in NDT techniques. techniques are used, and noise can be minimized in the binarized image compared to the study in [20]. Active IRT technology can be broadly classified into three types: optical, electromagnetic, and mechanical. The optical method uses a halogen lamp or a flash lamp as an external heat source to perform inspection [2]. It has the advantage of having a periodic heat source in the form of a sine wave or providing instantaneous pulse energy to the object to be inspected and being able to inspect a wide area. However, it has a limitation in that noise is generated in the 2D thermal image due to non-uniform heat source excitation [22]. The mechanical method measures the frictional heat of the microcracks in an object to be inspected with an infrared camera through ultrasonic excitation [21; 23]. When the probe is in direct contact with an object to transmit ultrasound, there is a risk that microcracks may grow or break. Since heat must be generated by friction, it can be applied only to crack-type defects. In addition, general infrared cameras have a low resolution, which makes quantitative analysis difficult, so a high-performance camera is required. The electromagnetic method is a technique of inducing an electric current in an object to be inspected after forming a magnetic field around it by flowing an electric current through a coil [24]. This technique enables uniform heat source excitation and the inspection of various types of defects. However, this is only possible for magnetic materials, and in the case of the static mode, the inspection object and coil are measured together by the infrared camera, which may affect the detectability [25; 26]. Therefore, in this paper, in order to overcome the limitations of the electromagnetic method, a moving mode in which the relative motion of the specimen and the infrared camera occurs was utilized, and a process for acquiring sequence images was performed. In this paper, the detection of subsurface defects in the STS304 specimen was performed using the electromagnetic induction thermography technique. Induction thermography, also called eddy current thermography (ECT), is a technique of inducing electromagnetic waves to inspect objects using an excitation coil. Due to the inherent problems previously described for the other techniques and in order to overcome the limitations of the electromagnetic method, a new method was devised.