A comparison of Shannon entropy versus signal energy for acoustic detection of artificially induced defects in Plexiglas

An experimental comparison of scanned images formed from Shannon entropy, total energy, and log energy measurements of acoustic wave propagation in a Plexiglas bar with drill-hole ‘‘defects’’ shows that Shannon entropy, in the instance investigated, is approximately two to three times as sensitive to the presence of small defects than are the two energy measures. This suggests that the Shannon entropy technique may be useful for flaw detection in materials that are too thick or lossy for the conventional use of acoustic energy for flaw detection.