Investigation of a Magnetic Tunnel Junction Based Sensor for the Detection of Defects in Reinforced Concrete at High Lift-Off.

Muhamad Arif Ihsan Mohd Noor Sam,Mikihiko Oogane,Zhenhu Jin,Yasuo Ando

doi:10.3390/s19214718

Muhamad Arif Ihsan Mohd Noor Sam, Mikihiko Oogane + Show 2 more

Open Access

https://doi.org/10.3390/s19214718

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Abstract

Magnetic flux leakage (MFL) testing is a method of non-destructive testing (NDT), whereby the material is magnetized, and when a defect is present, the magnetic flux lines break out of the material. The magnitude of the leaked magnetic flux decreases as the lift-off (distance from the material) increases. Therefore, for detection at high lift-off, a sensitive magnetic sensor is required. To increase the output sensitivity, this paper proposes the application of magnetic tunnel junction (MTJ) sensors in a bridge circuit for the NDT of reinforced concrete at high lift-off. MTJ sensors were connected to a full-bridge circuit, where one side of the arm has two MTJ sensors connected in series, and the other contains a resistor and a variable resistor. Their responses towards a bias magnetic field were measured, and, based on the results, the sensor circuit sensitivity was 0.135 mV/mT. Finally, a reinforced concrete specimen with a 1 cm gap in the center was detected. The sensor module (with an amplifier and low pass filter circuits) could determine the gap even at 50 cm, suggesting that MTJ sensors have the potential to detect defects at high lift-off values and have a promising future in the field of NDT.

Highlights

Non-destructive testing (NDT) is the evaluation of a specimen without causing damage
This setup ensured that each measurement started at 0 V, so the output voltage change corresponding to the leaked magnetic flux could be clearly seen
The system showed a good linear response, and, based on the measurement of a real concrete specimen, the system was able to identify the presence of the crack even at high lift-off values

Summary

Introduction

Non-destructive testing (NDT) is the evaluation of a specimen without causing damage. One of the applied areas of NDT is in the testing of reinforced concrete, which is one of the most popular materials in the world and is used in many structures, such as buildings and bridges. It increases the structural integrity of structures, it is still susceptible to corrosion and breaks when exposed to harsh environments or an excessive amount of force [1,2]. Both of these methods are time-consuming or need expensive equipment to determine corrosion in the depth of the reinforced concrete

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