Crack detection methods based on oscillating signals are usually
based on two main factors: the dynamical characteristics of the
structure and the oscillating signal processing methods. In practice,
the change in dynamical characteristics of the structure caused by the
crack is very small and difficult to detect directly from the oscillating
measurement signal. Therefore, in order to detect these minor
changes, modern signal processing methods are given, which is the
method of signal processing in time-frequency domains. These
methods include the Short-time Fourier Transform (STFT), the
Wavelet Transform (WT) v.v. These methods will analyze signals in
two time and frequency domains. When using these methods, the
signals over time will be represented in the frequency domain while
the time information is retained. Therefore, time-frequency methods
will be useful for analyzing small or distorted variations in the
oscillation signal caused by the crack
