“…These waves appear in a multitude of through-thickness deformation (wave) modes and propagate in in-plane direction. In a mathematical sense, the measurement P (x R , x S , ω) can be written as the convolution of AE source signal S i (x S , ω) with wave propagation transfer function W i (x R , x S , ω) and sensor transfer function D i (x R , ω), and the addition of noise P N (x R , ω) [33,34]. When propagating in the form of guided waves, each component can be dependent on the wave mode i = [1..n] for n modes, the source location x S , sensor location x R and frequency ω.…”