Issue 28

B. Ye et alii, Frattura ed Integrità Strutturale, 28 (2014) 32-41; DOI: 10.3221/IGF-ESIS.28.04 39 Configuration Operation N 50 m 20 ρ 0.1 α 1 β 2 q 0 0.1 C (8×40038.5) −1 t max 500 e 0.01 Table 1 : IACA configuration. Structures Conductivity σ MS/m Permeability μ Thickness t mm Layer 1 18.5 μ 0 1 Layer 2 18.5 μ 0 2 Defect 0 μ 0 Table 2 : Structure parameters. Item Quantity Number of turns N 330 Inside radius r 1 mm 3.0 Outside radius r 2 mm 5.11 Length l mm 20.70 Inductance L 0 mH 1.02 Resistance R 0 Ω 19.84 Frequency f 0 Hz 400 Liftoff l 1 mm 0.0 Table 3 : Coil parameters. In the actual computing process, we find themethod needs a long computing time to find the global optimum, when the estimation of the objective function requires a field analysis bymeans of the FEM. So, we propose a novel methodwith a signal database consisting of impedance signals of different size computed by FEM in advance, applied to the optimization of defect inspection, to reduce the computing time for the whole optimization. The identification results using IACA are shown in Tab. 4. At the same time, the identification results using the least square method are shown in Tab. 5. Group 1 Group2 Group 3 Group 4 True length (mm) 16 17 18 19 TrueHeight (mm) 0.8 1 0.8 1 TrueDepth (mm) 1.2 1.7 1.2 1.7 Estimated length (mm) 16.26 17.16 17.83 18.74 EstimatedHeight (mm) 0.84 1.04 0.77 1.04 EstimatedDepth (mm) 1.22 1.73 1.15 1.66 Length error (%) 1.63 0.94 -0.94 -1.37 Height error (%) 5 4 -3.75 4 Depth error (%) 1.67 1.76 -4.17 -2.35 Table 4 : Identificationof defect using IACA.