Time-Domain Topological Energy Imaging Method of Concrete Cavity Defect by Lamb Wave

Figure 7

Focusing of the direct and adjoint sound fields at the defect: (a) scattered signals received by all receiving sensors; (b) scattered signal after time reversal; (c) scattered signals reaching the defect; (d) scattered signals reaching the nondefective point.

(a)

(b)

(c)

(d)