Composite inspection

1. A method of detecting inconsistencies in a composite structure, the method comprising:

directing a pulsed laser beam towards the composite structure comprised of a number of composite materials, wherein wide-band ultrasonic signals are formed in the composite structure when radiation of the pulsed laser beam is absorbed by a surface of the composite structure;

detecting the wide-band ultrasonic signals over a duration of time to form data, wherein the data comprises an ultrasonic A-scan spectrum;

processing the data to identify a structure signal in a frequency domain of the ultrasonic A-scan spectrum, wherein processing the data comprises:

applying a moving time-window in a time domain to an ultrasonic A-scan to form time-windowed signals, wherein the moving time-window has a Gaussian shape sized to contain between two and five plies of the number of composite materials; and

determining at least one of a mean frequency or a maximum frequency of a Fourier spectrum taken for each of the time-windowed signals, including determining a maximum frequency of a windowed signal of an ultrasonic A-scan using the equation S n =Σ k=1 p α k *S n-k , where S n is an A-scan signal at sample point n, p is a quantity of coefficients, α k is a k th Fourier coefficient, and S n-k is the A-scan signal at prior sample point n-k; and

determining whether the inconsistencies are present in the number of composite materials by comparing the structure signal of the ultrasonic A-scan spectrum to a structure signal of a composite structure standard.

2. The method of claim 1 , wherein determining whether the inconsistencies are present in the number of composite materials comprises:

determining whether a first width of the structure signal of the ultrasonic A-scan spectrum in the frequency domain differs from a second width of the structure signal of the composite structure standard in the frequency domain.

3. The method of claim 2 , wherein determining whether the inconsistencies are present in the number of composite materials further comprises:

determining a wrinkle is present in the number of composite materials if the first width differs from the second width.

4. The method of claim 1 , wherein determining whether the inconsistencies are present in the number of composite materials comprises:

determining whether the structure signal of the ultrasonic A-scan spectrum is shifted in the frequency domain relative to the structure signal of the composite structure standard.

5. The method of claim 4 , wherein determining whether the inconsistencies are present in the number of composite materials further comprises:

determining compaction of the number of composite materials is undesirable if the structure signal of the ultrasonic A-scan spectrum is shifted in the frequency domain relative to the structure signal of the composite structure standard.

6. The method of claim 1 , wherein the wide-band ultrasonic signals are detected using a point detector.

7. A method comprising:

directing a pulsed laser beam towards a composite structure comprised of a plurality of layers, wherein wide-band ultrasonic signals are formed in the composite structure when radiation from the pulsed laser beam is absorbed by a surface of the composite structure;

detecting the wide-band ultrasonic signals over a duration of time to form data, wherein the data comprises a plurality of ultrasonic A-scans for at least a portion of the composite structure;

applying a moving time-window in a time domain to each of the plurality of ultrasonic A-scans, wherein the moving time-window has a Gaussian shape sized to contain between two and five plies of the number of composite materials;

determining a frequency measurement within the moving time-window for each of the plurality of ultrasonic A-scans, including determining a maximum frequency of a windowed signal of an ultrasonic A-scan using the equation S n =Σ k=1 p α k *S n-k , where S n is an A-scan signal at sample point n, p is a quantity of coefficients, α k is a k th Fourier coefficient, and S n-k is the A-scan signal at prior sample point n-k;

determining a structure signal in a frequency domain of an ultrasonic A-scan spectrum for each of the plurality of ultrasonic A-scans using the frequency measurement; and

comparing the structure signal of each ultrasonic A-scan spectrum of the plurality of ultrasonic A-scans to a structure signal for a composite structure standard to form a plurality of comparisons.

8. The method of claim 7 , wherein the frequency measurement is selected from a mean frequency or a maximum frequency.

9. The method of claim 7 further comprising: analyzing the plurality of comparisons to determine if at least one of an undesirable compaction or a number of wrinkles is present in the composite structure.

10. The method of claim 7 , wherein comparing the structure signal of each ultrasonic A-scan spectrum of the plurality of ultrasonic A-scans to the structure signal of the composite structure standard comprises: comparing a respective width of each structure signal of each respective ultrasonic A-scan spectrum of the plurality of ultrasonic A-scans to a width of the structure signal of the composite structure standard.

11. The method of claim 7 , wherein comparing the structure signal of each ultrasonic A-scan spectrum of the plurality of ultrasonic A-scans to the structure signal of the composite structure standard comprises: comparing a respective location of each structure signal of each respective ultrasonic A-scan spectrum of the plurality of ultrasonic A-scans in the frequency domain to a location of the structure signal of the composite structure standard in the frequency domain.