###### Abstract
Spectral analysis of impedance or frequency derivative related quantities, such as extrema of the real or imaginary parts of the variable, suggested that the top layer's thickness could be determined using characteristic features taken from high-frequency signals, and the lower layer's thickness could be determined later using characteristic features taken from lower frequency signals [11; 12]. [PERSON] et al. also proposed a hybrid serial/parallel multi-frequency measurement method for measuring the impedance/inductance of eddy current sensors. They proposed a combination of parallel multi-frequency measurement which has a higher measurement speed but a lower signal-to-noise ratio, and the serial multi-frequency (sweeping frequency), which has a lower measurement speed but a higher signal-to-noise ratio. The proposed method allows for the flexible combination of these two features to deliver the desired speed and SNR according to the requirements of a specific application [13; 14; 15; 16; 17]. [PERSON] et al. conducted measurements utilizing SFECT on a plate specimen of austenitic steel AISI 316L with artificial electro-discharge machined notches probed by two eddy current probes. The study was conducted over a wide frequency range, with the probes comprising transmitting and receiving coils set in a fixed place. The effect of the defect length on the response signals was assessed to study the method's resolution. Results showed that the resolution between the response signals of defects of various lengths allows for the detection of defects, however, the resolution between the response signals is only possible up to a certain defect length, which is related to inspection probe dimensions [12]. Further study of crack geometry influence on transmission frequency characteristics experimentally studied by [PERSON] et al. was focused on various lengths and depths of artificial notches. The presented results clearly show that the frequency transfer functions depend on the defect's dimensions [18; 19]. This paper deals with SFECT numerical and experimental inspection of various flaws differing in geometry. Two AISI316L plates are inspected using a transmitter-receiver eddy-current probe in three different configurations. The plates contain electro-discharge machined surface flaws of the cuboid shape. At the first plate, only the length dimension of notches is varied, whereas the second plate contains flaws with different depths, keeping other dimensions the same. The flaws are numerically modelled and experimentally inspected. During the inspection of each flaw, the probe is fixed over the center of that flaw and the frequency of the exciting signal is changed in a wide range while response signals are sensed. The frequency range is selected to cover the range from low to high frequencies. The response signals for each particular flaw are further processed in order to investigate the differences between the signals for flaws obtained numerically and experimentally. The presented results report positive findings and the paper thus brings a new perspective on the possibilities of non-destructive evaluation of flaws from SFECT signals. This paper is organized as follows, as shown in Figure 1. The numerical model of the studied plates and sensors, as well as the simulation results, are briefly described in Section 2-line 1 progress in Figure 1. Section 3 describes the experimental setup and experiments-line 2 progress in Figure 1. Section 4 contains the experimental data and comments. Section 5 brings conclusions with a summary of the findings.