Vol. 7, Issue 2, Part B (2025)

Eddy current technology is widely used as a nondestructive detection technique to detect surface cracks or internal defects of metallic materials. In the past, eddy current technology was used only for defect detection of magnetic materials, but in recent years it has been widely used for defect detection of non-magnetic materials. Since stainless steel is widely used in industry, it is very important to detect the internal defects correctly in various types of stainless steel equipment. In this paper, for detecting internal defects located 6 mm below the surface in a 7 mm thick 316 stainless steel plate, an analytical model of a concentric pulsed eddy current sensor and a differential pulsed eddy current sensor is developed and simulated to compare the sensitivity. Concentric and differential sensors were fabricated and those were experimented with notches on 7 mm thick stainless steel specimens. In concentric sensors, the sensor’s detection signal for the defect is too small to detect due to the noise, whereas in differential sensors, much larger signals than noise are detected. The results showed the proposed differential sensor is much superior to the concentric one and is a new type of sensor that can detect defects in the interior of stainless steel material in practice.