“…Thus, flexible eddy current sensors were proposed because its shape changes with the surface of the specimen to minimize the lift-off distance [ 7 ]. Up until now, many different coil structures of the flexible eddy current sensors have been designed such as a circular spiral structure [ 8 ], meandering winding magnetometer structure [ 9 , 10 ], trapezoidal structure [ 11 ], double rectangle structure [ 12 , 13 ], rosette structure [ 14 , 15 ], dual driver structure [ 16 ], gradient winding coil structure [ 17 ], mesh-winding structure [ 18 ], new rosette-like structure [ 19 ], same direction line structure [ 20 ] and so on.…”