Flexible Probe With Array Tunneling Magnetoresistance Sensors for Curved Structure Inspection

The 3-D curved structures are widely used in industries due to their advantages of flowing geometry, high structural strength, and excellent aerodynamic performance. Damages may occur in curved structures during manufacture or use, which may endanger the equipment’s operation safety. Efficient tools for inspection of buried defects in curved structures are still lacking. This article proposes a flexible nondestructive testing probe with tunneling magnetoresistance (TMR) sensors for inspecting buried defects in curved structures for the first time. The probe contains 16 TMR sensors and the distance between each 2 adjacent sensors is 2 mm. The TMR sensors are fetched from a customized wafer and screened to guarantee the consistency. In this probe, the TMR sensors are wire bonded on a flexible printed circuit board and then protected by polyurethane pouring sealant. The probe can be bent to fit an irregular surface with minimum bending radius 5.5 mm. The selection of the excitation frequency and the proposed probe performance for buried defects’ inspection are studied using a 3-D finite-element numerical model. Experimental results demonstrate that defects buried 3 mm below the top surface of cylindrical samples can be accurately detected. A chromatic confocal distance sensor is employed to sketch the curved surface of an irregular shaped sample. The electromagnetic image and optical image of this sample with curved surface are plotted in a fused image, which presents comprehensive information of the sample about both the structural pattern and the buried defects’ indications.