Pulsed Magnetic Flux Leakage Measurement Using Magnetic Head and Tunneling Magnetoresistance for Defect Detection

It is of great importance to improve the spatial resolution and sensitivity of magnetic flux leakage (MFL) sensors for small cracks’ characterization on pipelines. To solve these problems, a novel pulsed MFL (PMFL) method, using magnetic head (MH) and a side placement of tunneling magnetoresistance (TMR), is proposed. Two symmetrically inclined magnetic cores with a tiny air gap opening form a small detection region, making PMFL focus in that area. The side placement of the TMR ensures a reduction of noise and lift-off influence. A series of comparative tests with different kinds of artificial and natural cracks have been used to verify the high spatial resolution and sensitivity of the proposed method. The higher signal-to-noise ratio (SNR) and sensitivity of the side placement TMR were verified by 2-D and 3-D magnetic maps corresponding to the natural crack. The SNR and sensitivity of the side placement of TMR are greater than that of the under placement by an average of 41% and 160%, respectively.