Minhhuy Le

Integration of Hall and Giant Magnetoresistive Sensor Arrays for Real-Time 2-D Visualization of Magnetic Field Vectors

In this study, we combined an array of giant magnetoresistive (GMR) sensors with an array of Hall sensors to measure all three components of magnetic vectors with a high spatial resolution and visualize the magnetic field distribution on a 2-D plane. The sensors were arrayed in a matrix arrangement such that the limitation to the number of sensors could be overcome. To test the device, we generated a magnetic field using a pancake-type magnetizer and a cracked magnetized ferromagnetic specimen and imaged the vectors. We obtained a spatial resolution of 0.78 mm in the z-direction with 1024 Hall sensors and 2.34 mm in the x-direction with 100 GMR sensors. Moreover, the x and z components could be imaged at 6 fps. The proposed device is promising for application in magnetic flux leakage detection.

Bobbin-Type Solid-State Hall Sensor Array With High Spatial Resolution for Cracks Inspection in Small-Bore Piping Systems

Bobbin coil and bobbin-type Hall sensor arrays are proposed as an alternative for crack inspection inside a small-bore piping system. The cracks can be imaged at high speed without using a scanner since the electromagnetic (EM) field is distorted by the cracks. An array of 32 × 32 Hall sensors with 0.78 mm spatial resolution was set in a cylinder with diameter of 15 mm and length of 24.96 mm. A bobbin coil operating at 5 kHz of alternating current was positioned inside of a piping system and the sensor array outside the cylinder. Distorted EM fields around outside diameter stress corrosion cracking was imaged at 1 frame/s.

Magnetic Leakage Testing Using Linearly Integrated Hall and GMR Sensor Arrays to Inspect Inclusions in Cold-Rolled Strips

Inclusions in steel are entrapped foreign materials, which may be metallic or non-metallic; they may be distributed throughout the volume of steel strips during the rolling process and may propagate as narrow cracks in steel strips. In this paper, for inspecting inclusions in steel strips, we propose the use of magnetic flux leakage testing involving a magnetizer and magnetic field sensor arrays, such as linearly integrated Hall sensors (LIHaS) in differential mode and linearly integrated giant magnetoresistance sensors (LIGiS). In the proposed method, images of the distribution of Hall voltage (VH) and giant magnetoresistance voltage (VG) due to the magnetic leakage field around an inclusion are obtained by means of LIHaS and LIGiS, respectively. The magnetic leakage field images are obtained at different magnetization directions relative to the rolling direction by rotating the magnetizer. Different data processing techniques, such as differentiation, noise reduction, and fusion of image data of the inclusion obtained by LIHaS and LIGiS, are applied to enhance the detectability of the inclusion. The effectiveness of the proposed technique was experimentally verified by detecting actual inclusions situated in the rolling direction in a cold-rolled steel strip.

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.

Localization and evaluation of corrosion in a small-bore piping system using a bobbin- type magnetic camera

This paper presents a nondestructive evaluation algorithm for locating, discriminating, and evaluating inner and outer diameter (ID and OD) corrosion on a small-bore pipe by means of a bobbin-type magnetic camera that uses arrayed solid-state Hall effect sensor elements for measuring alternating magnetic fields. The proposed magnetic camera system is used to experimentally measure artificial ID and OD hole-type cracks on a small-bore copper alloy pipe over a low-frequency range (2-8 kHz). The measured amplitude signal is analyzed to determine both the position and type of crack. The volumes of the cracks are estimated with standard deviation of 0.77 mm 3 to be in the range 1.00-9.01 mm 3 .

Non-destructive testing of inclusions in cold-rolled strip steels using hall and giant magnetoresistance sensor arrays

Inclusions in steel are entrapped foreign materials, which may be metallic or non-metallic. The inclusions disrupt the structural homogeneity of the steel and affect its mechanical properties. Moreover, nonmetallic inclusions such as calcium and magnesium can be propagated as narrow cracks in steel strips after the rolling process. In this paper, we propose the use of magnetic flux leakage testing involving the fusion of images obtained by arrays of linearly integrated Hall sensors (LIHaS) and linearly integrated giant magnetoresistance sensors (LIGiS) for inspecting inclusions in steel strips. In the proposed method, the normal (Bz) and tangential (Bx) components of the magnetic leakage field around an inclusion are detected by means of LIHaS and LIGiS,respectively. The images of the magnetic leakage fieldwere obtained at different scanning (magnetization) directions relative to the rolling direction. The Bz and Bx images of the inclusion are then combined by using image fusion technique to enhance the detection of the inclusion. The effectiveness of the proposed image fusion technique was experimentally verified by using LIHaS and LIGiS images of an inclusion in a cold-rolled steel strip.

2-D vector field visualization of corrosion in a small-bore piping system using bobbin-type integrated Hall and GMR sensors arrays

This study proposes a 2-D bobbin-type magnetic field vector camera in nondestructive testing for inspection of corrosions in inner and outer diameter (ID and OD) of a small-bore piping system. 16.1 mm diameter bobbin probe was produced by integrated of 71 Hall sensors (BIHaS) and 71 Giant magnetoresistance sensors (BIGiS) in two circumferential lines at interval of 0.6 mm. The BIHaS and BIGiS could measure radial and axial components of alternating magnetic field. Thus ID and OD corrosions could be imaged in a 2-D magnetic field vector. Two small-bore copper (16.56 mm inner diameter, 1.27 mm thickness) and titanium (17.28 mm inner diameter, 0.86 mm thickness) pipes with ID and OD corrosions were inspected and presented in this paper. The measured signal of each sensor array was displayed in a single contour plot and combined 2-D vector plot in real-time during scan.

Non-destructive evaluation of far-side corrosion around the multi-layered rivet by using the solid-state hall sensor array

Nondestructive testing and evaluation of aircraft are a great importance from the viewpoint of the integrity and flight safety. In aircraft structures, damage is likely to be observed around the rivets that connect the skin to the frames. This paper presents a sensor system which includes a linearly integrated solid-state Hall sensor array (LIHaS). The LIHaS has 64 InSb Hall sensors arrayed in 0.52 mm of interval respect to 33.28 mm length of measurement. The sensor system was tested on two flat layers of Aluminium alloy for inspecting far-side corrosions having 6~14 mm of diameter and 0.1~1.27 mm of depth.

Nondestructive Evaluation of Far-Side Corrosion Around a Rivet in a Multilayer Structure

ABSTRACT This paper presents a sensor system for inspection of far-side defects around rivets in a multilayer structure. The sensor system includes 64 InSb Hall sensors arrayed in 0.52-mm intervals, over a total length of 33.28 mm. The sensor system was tested on two flat specimens, which have two layers of an aluminum alloy, with and without far-side defects around rivets. The sensor system performance was estimated via both the receiver operating characteristic and the probability of detection (POD) curves. Furthermore, a quantitative evaluation of the surface area, depth, and volume of a defect having a POD greater than 90% was carried out.