The invention provides a
frequency mixing nonlinear
ultrasonic detection method for structure microcracks based on
bispectrum analysis, and belongs to the detection field of nondestructive examination. The method comprises the steps of firstly, obtaining an amplitude-versus-
frequency curve of an excited probe and an excited receiving probe through frequency sweep experiments, and determining probe excitation frequency or range according to the amplitude-versus-
frequency curve; then, carrying out different lateral excitation
frequency mixing mode experiments, tracking difference frequency and sum frequency signals, and determining an optimal frequency of the excitation signals according to amplitude-versus-
frequency response characteristics of the difference frequency and sum frequency signals; performing
bispectrum analysis on the
time domain signals at the optimal frequency, and determining whether structure microcracks exist in a test piece or not according to whether mixing components appear in the bispectra or not; and scanning the length direction of a test piece and tracking the difference frequency and sum frequency signals by changing time
delay of the excitation signals, and determining the positions of the structure microcracks according to the amplitude-versus-
frequency response characteristics of the difference frequency and sum frequency signals. Influences on experimental results caused by nonlinearity of an experiment apparatus can be prevented by employing two probes to excite the signals; and the positions of the structure microcracks can be identified by making the two signals encountered through controlling the
delay time of the excited signals.