Internal defect detection plays a key role in quality assurance of magnetic tile. In order to solve the issue of internal defect identification of magnetic tile using human auditory,bispectrum was used to analyze the acoustic signal generated in a drop impact test of magnetic tile whose internal defect was known.The analysis indicated that internal defect can affect peak distribution of bispectrum. In accordance with this rule,a method based on three-slice analysis of normalized bispectrum was presented for internal defect detection of magnetic tile. With this method,firstly,the three slices were extracted along the specific directions of normalized bispectrum.Secondly,each slice was divided into several frequency regions and all regions were classified,according to the mapping between peak distribution and internal defect.Thirdly,by comparing and calculating the maximum peak of the dissimilar regions,the threshold value was established to distinguish internal defect.The effectiveness of this method was assessed by a verification test at last.The test result showed that the identification accuracy achieved over 97%, which demonstrated that the bispectrum analysis could be applied to the acoustic inspection for internal defect of magnetic tile.
