Fig. 7From: Non-destructive inspection on anchorage defect of hollow grouted rock bolt using wavelet transform analysisWaveform diagram of low-frequency analysis for samples 4#, 5#, and 6#. (a) Original signal of sample 4#, 5#, and 6#. (b) Low-frequency decomposition by 5 scale of 4#, 5#, and 6#Back to article page