A method for seeking the optimum probing frequency in vibro-acoustic modulation testing

Vibro-acoustic modulation is a non-destructive testing technique used in nonlinear acoustic methods for defects detection. However, the optimum probing frequency is still a problem in many cases. In this study, a swept-signal was used as probing excitation, the modulation intensity distribution in a wide probing frequency range was measured with metal beam structures. The results indicate that when the probing frequency was higher than a critical value, the modulation intensity cannot be easily predicted with existing modulation model. Finite element analysis indicated that it may be caused by the high modal density and strong coupling between closely spaced modes in high probing frequency range. A new method was proposed to predict the modulation intensity distribution, which is also based on the previous model, while it only needs the high frequency structure response curves. The results demonstrated that this method was effective in the applied probing frequency range, and the efficiency of Vibro-acoustic modulation can be further improved.