Abstract

A new method of multiplexing the speckle patterns needed in multicomponent digital shearography systems is presented. Frequency-division multiplexing (FDM) of the measurement channels is achieved by recording speckle patterns from objects illuminated by intensity-modulated sources. Each source is modulated at a discrete frequency, which is less than half of the camera frame rate, and a bank of images of the modulated speckle patterns is captured. This allows for pixel-by-pixel Fourier-based extraction of the individual speckle patterns from peaks in the power spectra. The approach is demonstrated with a two-component in-plane shearography instrument.

© 2013 Optical Society of America

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  1. D. Francis, R. P. Tatam, and R. M. Groves, “Shearography technology and applications: a review,” Meas. Sci. Technol. 21, 102001 (2010).
    [CrossRef]
  2. M. Kalms and W. Osten, “Mobile shearography system for the inspection of aircraft and automotive components,” Opt. Eng. 42, 1188–1196 (2003).
    [CrossRef]
  3. U. Paul Kumar, M. P. Kothiyal, and N. Krishna Mohan, “Microscopic TV shearography for characterization of microsystems,” Opt. Lett. 34, 1612–1614 (2009).
    [CrossRef]
  4. W. Steinchen and L. Yang, Digital Shearography (SPIE, 2003).
  5. S. W. James and R. P. Tatam, “3D shearography for surface strain analysis,” Proc. SPIE 3783, 247–256 (1999).
    [CrossRef]
  6. T. O. H. Charrett, D. Francis, and R. P. Tatam, “Quantitative shearography: error reduction by using more than three measurement channels,” Appl. Opt. 50, 134–146 (2011).
    [CrossRef]
  7. D. T. Goto and R. M. Groves, “Error analysis of 3D shearography using finite-element modelling,” Proc. SPIE 7718, 771816 (2010).
    [CrossRef]
  8. D. Francis, S. W. James, and R. P. Tatam, “Surface strain measurement of rotating objects using pulsed laser shearography with coherent fibre-optic imaging bundles,” Meas. Sci. Technol. 19, 105301 (2008).
    [CrossRef]
  9. R. M. Groves, S. W. James, and R. P. Tatam, “Full surface strain measurement using shearography,” Proc. SPIE 4448, 142–152 (2001).
    [CrossRef]
  10. R. M. Groves, S. W. James, and R. P. Tatam, “Polarization-multiplexed and phase-stepped fibre optic shearography using laser wavelength modulation,” Meas. Sci. Technol. 11, 1389–1395 (2000).
    [CrossRef]
  11. R. Kästle, E. Hack, and U. Sennhauser, “Multiwavelength shearography for quantitative measurements of two-dimensional strain distributions,” Appl. Opt. 38, 96–100 (1999).
    [CrossRef]
  12. Y. Y. Hung, “Shearography: a new optical method for strain measurement and nondestructive testing,” Opt. Eng. 21, 213391 (1982).
    [CrossRef]
  13. S. W. James, R. M. Groves, and R. P. Tatam, “Surface strain characterisation using time-division-multiplexed 3D shearography,” Proc. SPIE 4101, 121–129 (2000).
  14. H. A. Aebischer and S. Waldner, “Strain distributions made visible with image-shearing speckle pattern interferometry,” Opt. Lasers Eng. 26, 407–420 (1997).
    [CrossRef]
  15. S. W. James, R. P. Tatam, and R. L. Elder, “Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications,” Rev. Sci. Instrum. 68, 3241–3246 (1997).
    [CrossRef]
  16. K. Creath, “Temporal phase measurement methods,” in Interferogram Analysis: Digital Fringe Measurement Methods, D. W. Robinson and G. T. Reid, eds. (IOP, 1993), pp. 94–140.
  17. Python Software Foundation, “Python,” http://www.python.org .
  18. T. O. H. Charrett, “Python Toolkit,” http://pythontoolkit.sourceforge.net/ .
  19. “SciPy: open source scientific tools for Python” (2001), http://www.scipy.org .
  20. M. Frigo and S. G. Johnson, “Fastest Fourier transform in the west,” http://www.fftw.org .
  21. J. Schwider, R. Burow, K.-E. Elssner, J. Grzanna, R. Spolaczyk, and K. Merkel, “Digital wave-front measuring interferometry: some systematic error sources,” Appl. Opt. 22, 3421–3432 (1983).
    [CrossRef]
  22. A. Aebisher and S. Waldner, “A simple and effective method for filtering speckle-interferometric phase patterns,” Opt. Commun. 162, 205–210 (1999).
  23. M. A. Herráez, M. A. Gdeisat, D. R. Burton, and M. J. Lalor, “Robust, fast, and effective two-dimensional automatic phase unwrapping algorithm based on image decomposition,” Appl. Opt. 41, 7445–7455 (2002).
    [CrossRef]

2011 (1)

2010 (2)

D. T. Goto and R. M. Groves, “Error analysis of 3D shearography using finite-element modelling,” Proc. SPIE 7718, 771816 (2010).
[CrossRef]

D. Francis, R. P. Tatam, and R. M. Groves, “Shearography technology and applications: a review,” Meas. Sci. Technol. 21, 102001 (2010).
[CrossRef]

2009 (1)

2008 (1)

D. Francis, S. W. James, and R. P. Tatam, “Surface strain measurement of rotating objects using pulsed laser shearography with coherent fibre-optic imaging bundles,” Meas. Sci. Technol. 19, 105301 (2008).
[CrossRef]

2003 (1)

M. Kalms and W. Osten, “Mobile shearography system for the inspection of aircraft and automotive components,” Opt. Eng. 42, 1188–1196 (2003).
[CrossRef]

2002 (1)

2001 (1)

R. M. Groves, S. W. James, and R. P. Tatam, “Full surface strain measurement using shearography,” Proc. SPIE 4448, 142–152 (2001).
[CrossRef]

2000 (2)

R. M. Groves, S. W. James, and R. P. Tatam, “Polarization-multiplexed and phase-stepped fibre optic shearography using laser wavelength modulation,” Meas. Sci. Technol. 11, 1389–1395 (2000).
[CrossRef]

S. W. James, R. M. Groves, and R. P. Tatam, “Surface strain characterisation using time-division-multiplexed 3D shearography,” Proc. SPIE 4101, 121–129 (2000).

1999 (3)

S. W. James and R. P. Tatam, “3D shearography for surface strain analysis,” Proc. SPIE 3783, 247–256 (1999).
[CrossRef]

R. Kästle, E. Hack, and U. Sennhauser, “Multiwavelength shearography for quantitative measurements of two-dimensional strain distributions,” Appl. Opt. 38, 96–100 (1999).
[CrossRef]

A. Aebisher and S. Waldner, “A simple and effective method for filtering speckle-interferometric phase patterns,” Opt. Commun. 162, 205–210 (1999).

1997 (2)

H. A. Aebischer and S. Waldner, “Strain distributions made visible with image-shearing speckle pattern interferometry,” Opt. Lasers Eng. 26, 407–420 (1997).
[CrossRef]

S. W. James, R. P. Tatam, and R. L. Elder, “Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications,” Rev. Sci. Instrum. 68, 3241–3246 (1997).
[CrossRef]

1983 (1)

1982 (1)

Y. Y. Hung, “Shearography: a new optical method for strain measurement and nondestructive testing,” Opt. Eng. 21, 213391 (1982).
[CrossRef]

Aebischer, H. A.

H. A. Aebischer and S. Waldner, “Strain distributions made visible with image-shearing speckle pattern interferometry,” Opt. Lasers Eng. 26, 407–420 (1997).
[CrossRef]

Aebisher, A.

A. Aebisher and S. Waldner, “A simple and effective method for filtering speckle-interferometric phase patterns,” Opt. Commun. 162, 205–210 (1999).

Burow, R.

Burton, D. R.

Charrett, T. O. H.

Creath, K.

K. Creath, “Temporal phase measurement methods,” in Interferogram Analysis: Digital Fringe Measurement Methods, D. W. Robinson and G. T. Reid, eds. (IOP, 1993), pp. 94–140.

Elder, R. L.

S. W. James, R. P. Tatam, and R. L. Elder, “Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications,” Rev. Sci. Instrum. 68, 3241–3246 (1997).
[CrossRef]

Elssner, K.-E.

Francis, D.

T. O. H. Charrett, D. Francis, and R. P. Tatam, “Quantitative shearography: error reduction by using more than three measurement channels,” Appl. Opt. 50, 134–146 (2011).
[CrossRef]

D. Francis, R. P. Tatam, and R. M. Groves, “Shearography technology and applications: a review,” Meas. Sci. Technol. 21, 102001 (2010).
[CrossRef]

D. Francis, S. W. James, and R. P. Tatam, “Surface strain measurement of rotating objects using pulsed laser shearography with coherent fibre-optic imaging bundles,” Meas. Sci. Technol. 19, 105301 (2008).
[CrossRef]

Gdeisat, M. A.

Goto, D. T.

D. T. Goto and R. M. Groves, “Error analysis of 3D shearography using finite-element modelling,” Proc. SPIE 7718, 771816 (2010).
[CrossRef]

Groves, R. M.

D. T. Goto and R. M. Groves, “Error analysis of 3D shearography using finite-element modelling,” Proc. SPIE 7718, 771816 (2010).
[CrossRef]

D. Francis, R. P. Tatam, and R. M. Groves, “Shearography technology and applications: a review,” Meas. Sci. Technol. 21, 102001 (2010).
[CrossRef]

R. M. Groves, S. W. James, and R. P. Tatam, “Full surface strain measurement using shearography,” Proc. SPIE 4448, 142–152 (2001).
[CrossRef]

R. M. Groves, S. W. James, and R. P. Tatam, “Polarization-multiplexed and phase-stepped fibre optic shearography using laser wavelength modulation,” Meas. Sci. Technol. 11, 1389–1395 (2000).
[CrossRef]

S. W. James, R. M. Groves, and R. P. Tatam, “Surface strain characterisation using time-division-multiplexed 3D shearography,” Proc. SPIE 4101, 121–129 (2000).

Grzanna, J.

Hack, E.

Herráez, M. A.

Hung, Y. Y.

Y. Y. Hung, “Shearography: a new optical method for strain measurement and nondestructive testing,” Opt. Eng. 21, 213391 (1982).
[CrossRef]

James, S. W.

D. Francis, S. W. James, and R. P. Tatam, “Surface strain measurement of rotating objects using pulsed laser shearography with coherent fibre-optic imaging bundles,” Meas. Sci. Technol. 19, 105301 (2008).
[CrossRef]

R. M. Groves, S. W. James, and R. P. Tatam, “Full surface strain measurement using shearography,” Proc. SPIE 4448, 142–152 (2001).
[CrossRef]

S. W. James, R. M. Groves, and R. P. Tatam, “Surface strain characterisation using time-division-multiplexed 3D shearography,” Proc. SPIE 4101, 121–129 (2000).

R. M. Groves, S. W. James, and R. P. Tatam, “Polarization-multiplexed and phase-stepped fibre optic shearography using laser wavelength modulation,” Meas. Sci. Technol. 11, 1389–1395 (2000).
[CrossRef]

S. W. James and R. P. Tatam, “3D shearography for surface strain analysis,” Proc. SPIE 3783, 247–256 (1999).
[CrossRef]

S. W. James, R. P. Tatam, and R. L. Elder, “Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications,” Rev. Sci. Instrum. 68, 3241–3246 (1997).
[CrossRef]

Kalms, M.

M. Kalms and W. Osten, “Mobile shearography system for the inspection of aircraft and automotive components,” Opt. Eng. 42, 1188–1196 (2003).
[CrossRef]

Kästle, R.

Kothiyal, M. P.

Krishna Mohan, N.

Lalor, M. J.

Merkel, K.

Osten, W.

M. Kalms and W. Osten, “Mobile shearography system for the inspection of aircraft and automotive components,” Opt. Eng. 42, 1188–1196 (2003).
[CrossRef]

Paul Kumar, U.

Schwider, J.

Sennhauser, U.

Spolaczyk, R.

Steinchen, W.

W. Steinchen and L. Yang, Digital Shearography (SPIE, 2003).

Tatam, R. P.

T. O. H. Charrett, D. Francis, and R. P. Tatam, “Quantitative shearography: error reduction by using more than three measurement channels,” Appl. Opt. 50, 134–146 (2011).
[CrossRef]

D. Francis, R. P. Tatam, and R. M. Groves, “Shearography technology and applications: a review,” Meas. Sci. Technol. 21, 102001 (2010).
[CrossRef]

D. Francis, S. W. James, and R. P. Tatam, “Surface strain measurement of rotating objects using pulsed laser shearography with coherent fibre-optic imaging bundles,” Meas. Sci. Technol. 19, 105301 (2008).
[CrossRef]

R. M. Groves, S. W. James, and R. P. Tatam, “Full surface strain measurement using shearography,” Proc. SPIE 4448, 142–152 (2001).
[CrossRef]

S. W. James, R. M. Groves, and R. P. Tatam, “Surface strain characterisation using time-division-multiplexed 3D shearography,” Proc. SPIE 4101, 121–129 (2000).

R. M. Groves, S. W. James, and R. P. Tatam, “Polarization-multiplexed and phase-stepped fibre optic shearography using laser wavelength modulation,” Meas. Sci. Technol. 11, 1389–1395 (2000).
[CrossRef]

S. W. James and R. P. Tatam, “3D shearography for surface strain analysis,” Proc. SPIE 3783, 247–256 (1999).
[CrossRef]

S. W. James, R. P. Tatam, and R. L. Elder, “Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications,” Rev. Sci. Instrum. 68, 3241–3246 (1997).
[CrossRef]

Waldner, S.

A. Aebisher and S. Waldner, “A simple and effective method for filtering speckle-interferometric phase patterns,” Opt. Commun. 162, 205–210 (1999).

H. A. Aebischer and S. Waldner, “Strain distributions made visible with image-shearing speckle pattern interferometry,” Opt. Lasers Eng. 26, 407–420 (1997).
[CrossRef]

Yang, L.

W. Steinchen and L. Yang, Digital Shearography (SPIE, 2003).

Appl. Opt. (4)

Meas. Sci. Technol. (3)

D. Francis, R. P. Tatam, and R. M. Groves, “Shearography technology and applications: a review,” Meas. Sci. Technol. 21, 102001 (2010).
[CrossRef]

D. Francis, S. W. James, and R. P. Tatam, “Surface strain measurement of rotating objects using pulsed laser shearography with coherent fibre-optic imaging bundles,” Meas. Sci. Technol. 19, 105301 (2008).
[CrossRef]

R. M. Groves, S. W. James, and R. P. Tatam, “Polarization-multiplexed and phase-stepped fibre optic shearography using laser wavelength modulation,” Meas. Sci. Technol. 11, 1389–1395 (2000).
[CrossRef]

Opt. Commun. (1)

A. Aebisher and S. Waldner, “A simple and effective method for filtering speckle-interferometric phase patterns,” Opt. Commun. 162, 205–210 (1999).

Opt. Eng. (2)

Y. Y. Hung, “Shearography: a new optical method for strain measurement and nondestructive testing,” Opt. Eng. 21, 213391 (1982).
[CrossRef]

M. Kalms and W. Osten, “Mobile shearography system for the inspection of aircraft and automotive components,” Opt. Eng. 42, 1188–1196 (2003).
[CrossRef]

Opt. Lasers Eng. (1)

H. A. Aebischer and S. Waldner, “Strain distributions made visible with image-shearing speckle pattern interferometry,” Opt. Lasers Eng. 26, 407–420 (1997).
[CrossRef]

Opt. Lett. (1)

Proc. SPIE (4)

S. W. James and R. P. Tatam, “3D shearography for surface strain analysis,” Proc. SPIE 3783, 247–256 (1999).
[CrossRef]

D. T. Goto and R. M. Groves, “Error analysis of 3D shearography using finite-element modelling,” Proc. SPIE 7718, 771816 (2010).
[CrossRef]

S. W. James, R. M. Groves, and R. P. Tatam, “Surface strain characterisation using time-division-multiplexed 3D shearography,” Proc. SPIE 4101, 121–129 (2000).

R. M. Groves, S. W. James, and R. P. Tatam, “Full surface strain measurement using shearography,” Proc. SPIE 4448, 142–152 (2001).
[CrossRef]

Rev. Sci. Instrum. (1)

S. W. James, R. P. Tatam, and R. L. Elder, “Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications,” Rev. Sci. Instrum. 68, 3241–3246 (1997).
[CrossRef]

Other (6)

K. Creath, “Temporal phase measurement methods,” in Interferogram Analysis: Digital Fringe Measurement Methods, D. W. Robinson and G. T. Reid, eds. (IOP, 1993), pp. 94–140.

Python Software Foundation, “Python,” http://www.python.org .

T. O. H. Charrett, “Python Toolkit,” http://pythontoolkit.sourceforge.net/ .

“SciPy: open source scientific tools for Python” (2001), http://www.scipy.org .

M. Frigo and S. G. Johnson, “Fastest Fourier transform in the west,” http://www.fftw.org .

W. Steinchen and L. Yang, Digital Shearography (SPIE, 2003).

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Figures (7)

Fig. 1.
Fig. 1.

(a) Representation of a single-channel shearography system and the imaging optics of the shearographic camera (SC, dotted rectangle) [12]. (b) Three-channel system using multiple illumination directions, i^, around a single SC to vary the sensitivity [13]. (c) Three-channel system using multiple observation directions, o^, formed of multiple cameras around a single laser [7]. (d) Two-channel in-plane system with two lasers arranged at equal angles around the observation axis [4].

Fig. 2.
Fig. 2.

Steps to demultiplex images from an image time series. The example shown is for two-channel demultiplexing.

Fig. 3.
Fig. 3.

(a) and (b) Directly captured images of patterns produced from sources in separate channels across a field of view of approximately 4cm2. (c) and (d) Demultiplexed images of the same patterns that had been multiplexed together by chopping the beams at 1 kHz and 1.5 kHz, respectively, and captured in an image time series of 1024 frames at 11,000 fps. Images in (e) and (f) show the same patterns demultiplexed using the nonlinear method where intensity is the sum of the squares of the windowed power spectrum. Note the nonlinear intensity response produced by that method in the demultiplexed images increases more sharply toward the bright regions. Each image is scaled to the highest intensity in the frame.

Fig. 4.
Fig. 4.

In-plane shearography configuration with beam choppers to facilitate the frequency-division multiplexing of the two channels. Angles ±θ were ±45°, making k1=22.5° and k2=22.5° from the observation vector. Inset: notched-plate test object as viewed by the system; a 40mm2 area was viewed around the fixed end of the notch. Loading involves compressing the two distal ends together, as shown, using a screw.

Fig. 5.
Fig. 5.

Mean power spectrum of an image bank containing two peaks corresponding to the frequencies of the modulation applied to the two channels. The truncated peak at 0 Hz, corresponding to the background light, reached an intensity of 11,500 AU. The shaded regions show the extent of the two window functions used in discriminating channels during demultiplexing. The peaks had different heights due to a difference in intensities between the two illuminating beams.

Fig. 6.
Fig. 6.

In-plane (top) and out-of-plane (bottom) displacement gradient components of a 41 mm by 41 mm area around a compression-loaded notch in a Perspex plate. The left column shows results obtained using TDM, and the right column shows those obtained using FDM. The dashed lines indicate the location of the line plots in Fig. 7.

Fig. 7.
Fig. 7.

Vertical profile taken from the displacement gradient maps shown in Fig. 6, near the apex of the notch. The left plot shows the profiles for the in-plane component, and the right plot is the same for the out-of-plane component.

Tables (2)

Tables Icon

Table 1. Noise Characteristics of an Average Pixel Calculated over 100 Measurements for Single-Frame, Time Averaged, and Demultiplexed Techniquesa

Tables Icon

Table 2. Comparison of Multiplexed Shearography Methodsa

Equations (9)

Equations on this page are rendered with MathJax. Learn more.

Δϕs=2πδsλ[kxus+kyvs+kzws],
us=λ4πδskx(Δϕ1Δϕ2),
ws=λ4πδskz(Δϕ1+Δϕ2),
I(t)=I1(t)+I2(t)++In(t)+C,
IRMS=σIn=|In(t)|2N=|F{In(t)}|2N2,
Ipp=σInσcal,
ϕ=tan1[2(I2+I4)2I3I5I1],
Δϕ1=2πδyλ[kxuy+kzwy],
Δϕ2=2πδyλ[kxuy+kzwy],

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