An Impact-Echo Experimental Approach for Detecting Concrete Structural Faults

Figure 4

Parts of the spectrogram. (a) 3-spectrogram of metal bellows; (b) 4-spectrogram of metal bellows; (c) 7-spectrogram of metal bellows; (d) 9-spectrogram of metal bellows.

(a)

(b)

(c)

(d)