Figure 1.

Enlarged view of the velocity dispersion curve of the Lamb complex in 4 mm steel plate"

Figure 2.

Time difference between two receiving Lamb waves"

Figure 3.

Main structure and PZT sensor layout scheme (a)Double steel plate construction (b)Sensor layout"

Table 1.

Double-layer steel plate PZT sensor coordinates (with the center of the steel plate as the coordinate origin)"

Figure 4.

Experimental site of the steel plate"

Figure5.

A typical Lamb wave signal acquired by a PZT sensor (a)Time domain (b)Frequency domain"

Figure 6.

EMD exploded of signal received by sensor S1 of the first layer of steel plate"

Figure 7.

IMF component spectrum of received signal by sensor S1 of the first layer of steel plate"

Figure 8.

3D-Hilbert spectrum of signal received by sensor S1"

Figure 9.

Reconstructed penetration signal"

Figure 10.

Reconstructed signal separation waveform"

Figure 11.

Reconstructed signal S0 modal wave"

Figure 12.

Comparison of the received signal of the double-layer steel plate S1sensor"

Figure 13.

The signal waveform of the first layer of steel plate sensor reconstruction"

Figure 14.

The signal waveform of the second layer of steel plate sensor reconstruction"

Figure 15.

Reconstruction signal location results (a)The first layer (b)The second layer"

Figure 16.

Original signal location results (a)The first layer (b)The second layer"

Table 2.

Localization results of penetration damage of double-layer steel plate(with the center of the steel plate as the coordinate origin)"