Table 2 - Smartphone-based detected magnetic field intensities for various damage states Damage State Intact Damage State 1 Damage State 2 Damage State 3 Damage State 4 Damage State 5 Damage State 6 Damage State 7 Damage State 8 Damage State 9 Cracks (mm) None 1 crack (14×3) 2 cracks (14×3) 3 cracks (14×3) 1 crack (34×3) 2 cracks (34×3) 3 cracks (34×3) 1 crack (54×3) 2 cracks (54×3) 3 cracks (54×3) Distance (mm) 200 350 500 200 350 500 200 350 500 200 350 500 200 350 500 200 350 500 200 350 500 200 350 500 200 350 500 200 350 500 Magnetic Field (μT) 286 88 42 287 89.5 43.5 288 91 45 289 92.5 47 288 91.5 46 291 93 48 292 95 50 291.5 92 47.5 293 95 51 296 98 55 Damage State 2 Damage State 3 Damage State 4 Damage State 5 Table 3 - Steel plate magnetic properties used in the numerical simulations Name Type Simple Value Relative Permeability Nonlinear B-H Curve Bulk Conductivity Magnetic Coercivity Vector Magnitude X component Y component Z component Composition 54 Vector Mag Unit Vector Unit Vector Unit Vector - 1 Solid Units - 2000000 Siemens/m - - A/m - - - - IEEE Instrumentation & Measurement Magazine Damage State 9 3 cracks (54×3) 200 350 500 285.1 86.5 41.7 June 2021 Damage State 8 2 cracks (54×3) 200 350 500 285.3 86.6 41.7 Damage State 7 1 crack (54×3) Damage State 6 2 cracks (14×3) 3 cracks (14×3) 1 crack (34×3) 2 cracks (34×3) 3 cracks (34×3) 200 350 500 200 350 500 200 350 500 200 350 500 200 350 500 200 350 500 283.9 86.1 41.5 283.7 86 41.4 285.3 86.5 41.7 283.6 86 41.4 283.7 86.1 41.5 286.9 86.1 41. Table 5 - Detected magnetic field intensities for various damage states in the numerical study Damage State Intact Damage State 1 Cracks (mm) Uncracked 1 crack (14×3) Distance (mm) 200 350 500 200 350 500 Magnetic Field (μT) 284.1 86.1 41.5 283.8 86. 1 41.5 Table 4 - Neodynium magnet magnetic properties used in the numerical simulations Name Type Relative Permeability Simple Bulk Conductivity Simple Magnetic Coercivity Vector Magnitude X component Y component Z component Composition Value 1.0997785406 625000 - Vector Mag -1060000 Unit Vector Unit Vector Unit Vector - -1 Solid Units - Siemens/m - A/m - - - -