Complex higher order spectra vs. it's magnitude for nondestructive testing of nonlinearity in structures

This technical brief compares experimentally the use of complex higher order spectra (HOS) and HOS magnitude for nondestructive testing (NDT) of nonlinearity level of the structure. Normally, the nonlinearity level of the structure is changed due to structure damage. The HOS of order is the complex valued function and proportional to the multiplication of Fourier transforms of signal components. The study demonstrates that the use of complex HOS is more efficient for nonlinearity NDT due to the following two reasons: (i) complex HOS contains both amplitude and phase information of HOS whereas the magnitude of HOS contains only amplitude information; and (ii) usage of HOS components allows constructing optimal decision-making rule.