# US 10,309,893 B2 · Composite inspection

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- Number: US 10,309,893 B2
- Document ID: US10309893B2
- Status: Granted
- Kind: B2
- Application number: 15/070,357
- Filed: 2016-03-15
- Published: 2017-06-22
- Granted: 2019-06-04
- Earliest claimed: 2015-12-21
- Assignees: The Boeing Company
- Applicants: The Boeing Company
- Inventors: Gary Ernest Georgeson; William P. Motzer; Jill Paisley Bingham; Alan F. Stewart; Steven Kenneth Brady; James C. Kennedy
- Web page: https://patentgrep.com/patent/US10309893B2

## CPC

- G01N 21/1702: {with opto-acoustic detection, e.g. for gases or analysing solids}
- G01N 29/043: {in the interior, e.g. by shear waves}
- G01N 29/0645: {Display representation or displayed parameters, e.g. A-, B- or C-Scan}
- G01N 29/2418: {using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics (photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046)}
- G01N 29/343: {pulse waves, e.g. particular sequence of pulses, bursts}
- G01N 29/348: {with frequency characteristics, e.g. single frequency signals, chirp signals (measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00)}
- G01N 29/4436: {with a reference signal (amplitude comparison G01N29/48)}
- G01N 29/4454: {Signal recognition, e.g. specific values or portions, signal events, signatures}
- G01N 29/46: by spectral analysis, e.g. Fourier analysis {or wavelet analysis (spectral signal processing per se G06F17/14)}
- G01N 2021/1706: {in solids}
- G01N 2291/0231: Composite or layered materials
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

A method of detecting inconsistencies in a composite structure is presented. A pulsed laser beam is directed towards the composite structure comprised of a number of composite materials. 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. The wide-band ultrasonic signals are detected over a duration of time to form data. The data comprises an ultrasonic A-scan spectrum. The data is processed to identify a structure signal in a frequency domain of the ultrasonic A-scan spectrum. The structure signal of the ultrasonic A-scan spectrum is compared to a structure signal of a composite structure standard to determine whether the inconsistencies are present in the number of composite materials.

## Claims

### Claim 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 Sn=Σk=1pαk*Sn-k, where Sn is an A-scan signal at sample point n, p is a quantity of coefficients, αk is a kth Fourier coefficient, and Sn-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.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 2)

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.

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 4)

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.

### Claim 6 (depends on 1)

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

### Claim 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 Sn=Σk=1pαk*Sn-k, where Sn is an A-scan signal at sample point n, p is a quantity of coefficients, αk is a kth Fourier coefficient, and Sn-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.

### Claim 8 (depends on 7)

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

### Claim 9 (depends on 7)

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.

### Claim 10 (depends on 7)

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.

### Claim 11 (depends on 7)

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.