## 4 Results and Discussions  
Ten EDM flaws introduced in two AISI 316L plate specimens were inspected using the SFECT probes according to the explanation provided in the previous section. Figures 10-12 present the obtained results from two different points of view: the data are displayed in the form of magnitude on frequency dependences as well as phase on magnitude dependences, respectively. The goal is to show the differences that are contained on the appropriate sets of signals, based on the different data-processing and displaying methods. The figures show that the resolution between individual signals strongly depends on the type of probe used and inspected flaws. It can be seen that the inspections performed with probes A and B bring unambiguous information about the presence of a flaw in the inspected specimen, and it is easy to visually distinguish this signal from others. Figure 11: Experimental results: specimen No. 1, differential voltage magnitude on frequency dependences (**left**) and phase dependences on differential voltage magnitude (**right**) for individual flaw depths, probe B.  
Figure 10: Experimental results: specimen No. 1, differential voltage magnitude on frequency dependences (**left**) and phase dependences on differential voltage magnitude (**right**) for individual flaw depths, probe A. On the other hand, individual flaws' signals were not sufficiently separated. This deficiency is relatively suppressed in the waveforms obtained with probe C. Basically, the effective frequency interval of the used probes is at the level of tens of kHz. The next three figures (Figures 13-15) present the situation for specimen No. 2, where the length of flaws varies. In this examination, the following conclusions can be stated: when using probes A and B, the signal-to-signal ratio of the signal without defect to the other signals is the most obvious. By using a probe with a ferromagnetic core and a shielding metal cover, the resolution between the individual defect signals was increased. It can be concluded that when using a presented innovative approach using the sweep-frequency eddy-current method (in comparison with the conventional approach), it is possible to extract useful information about the flaw. Following the scanning and signal-processing procedure is necessary. The purpose of using separate sensing and appropriate processing is that such an innovative approach can increase the resolution of the method without the need to further increase the sensitivity of the individual components of the measuring apparatus. Figure 12: Experimental results: specimen No. 1, differential voltage magnitude on frequency dependences (**left**) and phase dependences on differential voltage magnitude (**right**) for individual flaw depths, probe C.  
Figure 13: Experimental results: specimen No. 2, differential voltage magnitude on frequency dependences (**left**) and phase dependences on differential voltage magnitude (**right**) for individual flaw depths, probe A. For the comparison and determination of the degree of correlation between the results of the numerical simulations and performed experiments, the following procedure was used: values of the induced voltage of the Rx coil were acquired and processed from the simulations and measurements. In the simulations, the values of the induced voltage for individual frequencies were obtained from the overall results of each simulation. During measurements, the data processing was more complex. The gained eddy-current signal was in the form of the real and imaginary part of the induced voltage and these are the averaged values from the whole samples. MATLAB software was used to connect these parts to become magnitude and phase values. The induced voltage values \(\mathbf{V}_{\text{Rx}}\) were mathematically adjusted. The results of the induced voltage \(\mathbf{V}_{\text{Rx}}\) in the air were subtracted from the other results for the obtained signal to accurately depict the material's response to the excitation signal. The response to the Tx coil was thus eliminated.