Patent ID: 8440974

Claim:
A method of performing acoustic thermography on a structure, the method comprising: applying a sound input signal to the structure; sensing an input energy corresponding to the sound input signal applied to the structure, and the sensing an input energy comprising producing an input energy signal corresponding to the sensed input energy; detecting a thermal release from the structure produced as a result of the sound input signal and producing an output signal effective to indicate a defect in the structure; verifying an input power of the sound input signal to the structure based on a comparison of the input energy signal to a reference signal; and performing a filtering of the output signal including identifying the output signal for inclusion in an analysis based on a comparison of the input energy signal to the reference signal; wherein the step of comparing the input energy signal to the reference signal includes: a) applying a Fourier transform to the input energy signal to provide a test Fourier transform spectrum of the vibration output, and the reference signal comprises a predetermined reference Fourier transform spectrum for comparison to the test Fourier transform spectrum of the vibration output; b) determining whether a criteria is met comprising identifying a correspondence of peak locations between the test and reference Fourier transform spectra, indicating a predetermined level of correspondence of harmonic response frequencies between the input energy signal and the reference signal; and c) determining whether at least one other criteria is met, the at least one other criteria characterizing an input energy of the test Fourier transform relative to the reference Fourier transform at the harmonic response frequencies.