## 3 Results  
In order to verify the feasibility of the above method, it has been applied to experimentally obtained Lamb wave signals. The Olympus MX2 flaw detector was used to send the excitation signal and receive mixed Lamb wave signals. The workpiece was a stainless-steel plate with the thickness of 1 mm. The multimodal Lamb waves were excited and received by oblique transducers of 10 mm \(\times\) 10 mm with the central frequency of 2.5 MHz and the incident angle of 26\({}^{\circ}\). A coupling agent was used to facilitate the effective transmission of acoustic energy between the transducers and the steel plate. The data measured by the detector were imported into the computer and processed on the Matlab platform. The whole experiment is shown in Figure 1.  
Figure 1: Experimental schematic. Theoretically, it can be known from the Lamb waves incident angle dispersion curve, as shown in Figure 2, that A\({}_{1}\) and S\({}_{1}\) modes can be excited when the incidence angle is 26\({}^{\circ}\). Although the two modes are very close to each other at a certain frequency domain, there is always no intersection, which will not lead to conversion between modes. Their corresponding center frequencies are 3 MHz and 3.15 MHz, respectively. The multimodal Lamb wave signals at the propagation distance of 1.6 cm and 2.7 cm are recorded and shown in Figure 3.  
According to the above method, the A\({}_{1}\) mode signal at the distance of 1.6 cm is retrieved, as shown in Figure 4. The multimodal Lamb wave signal at the distance of 2.7 cm after compensation using the \(A_{1}\) mode dispersion characteristic is shown in Figure 4a. The separated A\({}_{1}\) mode signal using the proposed method at the distance of 1.6 cm is shown in Figure 4b. Its amplitude spectrum is shown in Figure 4d, and its time-frequency distribution is shown in Figure 4f. The separated A\({}_{1}\) mode signal using the time-frequency blind signal separation method at the distance of 1.6 cm is shown in Figure 4c. Its amplitude spectrum is shown in Figure 4e, and its time-frequency distribution is shown in Figure 4g. Figure 3: Multimodal Lamb wave signals at the propagation distance of (**a**) 1.6 cm and (**b**) 2.7 cm. Figure 2: Lamb waves incident angle dispersion curve. Figure 4: **(a)** The compensated multimodal Lamb wave signal at the distance of 2.7 cm; (**b**) separated A\({}_{1}\) mode time domain waveform using the proposed method; (**c**) separated A\({}_{1}\) mode time domain waveform using the time-frequency blind signal separation method; (**d**) amplitude spectrum of A\({}_{1}\) mode separated using the proposed method; (**e**) amplitude spectrum of A\({}_{1}\) mode separated using the time-frequency blind signal separation method; (**f**) time-frequency distribution of A\({}_{1}\) mode separated using the proposed method; (**g**) time-frequency distribution of A\({}_{1}\) mode separated using the time-frequency blind signal separation method. The S\({}_{1}\) mode signal at the distance of 1.6 cm is also retrieved, as shown in Figure 5. The multimodal Lamb wave signal at the distance of 2.7 cm after compensation using the S\({}_{1}\) mode dispersion characteristic is show in Figure 5a. The separated S\({}_{1}\) mode signal using the proposed method at the distance of 1.6 cm is shown in Figure 5b. Its amplitude spectrum is shown in Figure 5d and its time-frequency distribution is shown in Figure 5f. The separated S\({}_{1}\) mode signal using the time-frequency blind signal separation method at the distance of 1.6 cm is shown in Figure 5c. Its amplitude spectrum is shown in Figure 5e, and its time-frequency distribution is shown in Figure 5g.