Jongwoo Jun

Scan Type Magnetic Camera Images with a High Spatial Resolution for NDT Obtained By Using a Linearly Integrated Hall Sensors Array

Magnetic flux leakage testing (MFLT), which measures the distribution of a magnetic field on the magnetized specimen by using a magnetic sensor such as the Hall sensor, is an effective nondestructive testing (NDT) method for detecting surface crack on magnetized ferromagnetic materials. A scan type magnetic camera, based on the principle of MFLT, uses inclined Hall sensors array on the printed circuit board (PCB) to detect small cracks in high speed. However, the waveforms appear in the direction perpendicular to the scan, because the sensors are bonded at different gradients and heights on a PCB in spite of careful soldering. In this paper, the linearly integrated Hall sensors (LIHS) on a wafer are proposed to minimize these waves and to improve the probability of crack detection. The specimen took from a billet is used to determine the effectiveness of the LIHS in the multiple cracks detection.

Quantitative Nondestructive Evaluation of the Crack on the Austenite Stainless Steel Using the Induced Eddy Current and the Hall Sensor Array

Nondestructive evaluation (NDE) has been effective in the prediction and evaluation of cracks on the surface of structures. Austenite stainless steel such as SUS304 and SUS316 is a paramagnetic metal with delta -ferrite structure. Small amount of partial magnetization is generated in the austenite stainless steel due to the final heat treatment and the mechanical working. The MOI (magneto-optical/eddy current imaging) was developed to inspect fatigue cracks and corrosions. But the surface cracks on the partially magnetized paramagnetic metals, such as austenite stainless steel, are difficult to inspect because the magnetic domains were saturated by external magnetization of the delta -ferrite. In this paper, the magnetic camera with the 64 arrayed Hall sensors by matrix (sensor matrix) was developed to confirm the real time inspection and quantitative nondestructive evaluation (QNDE). As the result, QNDE algorithm was proposed by using single sensor scanning, and the algorithm was introduced in QNDE by sensor matrix. Also, the cracks were inspected in the real time by sensor matrix, which were arrayed with 3.5 mm spatial resolution in square.

Nondestructive Testing of Train Wheels Using Vertical Magnetization and Differential-Type Hall-Sensor Array

This study proposes a differential-type Hall-sensor array and vertical magnetizers used to improve the detection ability of crack in express-train wheels. In addition, exclusive parallel signal-conditioning circuits, analog-to-digital converting circuits, and interface were developed to reduce measurement time. The permanent magnet applies a vertical magnetic field on the wheel, while the differential-type linearly integrated Hall-sensor array measures the distribution of the magnetic field around a crack. The proposed method was verified by experiments.

Eddy current imager based on bobbin-type hall sensor arrays for nondestructive evaluation in small-bore piping system

A bobbin coil with bobbin-type solid-state Hall sensor arrays was proposed for eddy current testing. A 32×32 matrix of InSb Hall sensors was set on a cylinder 15 mm in diameter and 25 mm long. The distorted alternating magnetic fields around inner diameter (ID) and outer-diameter stress corrosion cracks (ODSCCs)were imaged at 1 fps. The effectiveness of the proposed techniquewas verified with a standard copper alloy specimen with hole-type circumferential ID-and ODSCCs.