A Defect Visualization Method Based on ACFM Signals Obtained by a Uniaxial TMR Sensor

This article presents a visualization method for defects using the alternating current field measurement (ACFM) technique. Only a single-axis tunneling magneto-resistive (TMR) sensor is used to collect the
${B}_{x}$
signal, which can determine the length and width, and indicate the depth of the defect simultaneously. A simulation is conducted to explore the changing rule of the
${B}_{x}$
signal with the dimensions of the defect. The simulated
${B}_{x}$
signals are processed by taking partial differentials with respect to the
${x}$
- and
${y}$
-axes. It is found that the distances between peaks and troughs of partial differentials in both directions (
${l}_{x}$
and
${l}_{y}{)}$
can represent the defect length and width, respectively. A magnetic imaging algorithm is proposed to calculate the morphology of the defects based on simulation results. An aluminum work-piece with two types of defects is tested to validate the proposed imaging method using an elaborate ACFM detection system. Experimental results show that the defects can be characterized visually and accurately.