where S1(t) S4(t) are sensors outputs, L(t) is the AE source signal,
n1(t) n4(t) are un-wanted signals and ambient noises, o is attenuation
factor caused by the acoustic path differences and D1 D3 are
time differences. In this study, the geometrical coordinates of S1
position is considered as (0, 0) and others are chosen following
S1. The position of AE source is O(x, y). The sensor-source distances
can be obtained by: