Abstract

An optical moire technique for real-time metrological measurements is proposed. Temporal behavior of periodic as well as nonperiodic vibrations can be accurately determined. We demonstrate the method by measuring the mechanical vibration of a driven speaker membrane.

© 1985 Optical Society of America

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References

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  1. See, for example, J. E. Solid, “Holography Applied to Structural Components,” Opt. Eng. 14, 460 (1975):P. Shajenko, “Holographic Testing of Loudspeakers,” J. Acoust. Soc. Am. 53, 1061 (1973).
    [CrossRef]
  2. See, for example, R. Ritter, H.-J. Meyer, “Vibration Analysis of Plates by a Time-Averaged Projection-Moire Method,” Appl. Opt. 19, 1630 (1980);K. G. Harding, J. S. Harris, “Projection Moire Interferometer for Vibration Analysis,” Appl. Opt. 22, 856 (1983).
    [CrossRef] [PubMed]
  3. F. P. Chiang, R. M. Jung, “Vibration Analysis of Plate and Shell by Laser Speckle Interferometry,” Opt. Acta 23, 997 (1976).
    [CrossRef]
  4. A. J. Durelli, V. J. Parks, Moire Analysis of Strain (Prentice-Hall, Englewood Cliffs, N.J., 1970).
  5. J. Der Hovanesian, Y. Y. Hung, “Moire Contour-Sum Contour-Difference, and Vibration Analysis of Arbitrary Objects,” Appl. Opt. 10, 2734 (1972).
    [CrossRef]
  6. A. Livnat, O. Kafri, “Fringe Addition in Moire Analysis,” Appl. Opt. 22, 3013 (1983).
    [CrossRef] [PubMed]
  7. E. Keren, E. BarZiv, I. Glatt, O. Kafri, “Measurements of Temperature Distribution of Flames by Moire Deflectometry,” Appl. Opt. 20, 4263 (1981).
    [CrossRef] [PubMed]

1983

1981

1980

1976

F. P. Chiang, R. M. Jung, “Vibration Analysis of Plate and Shell by Laser Speckle Interferometry,” Opt. Acta 23, 997 (1976).
[CrossRef]

1975

See, for example, J. E. Solid, “Holography Applied to Structural Components,” Opt. Eng. 14, 460 (1975):P. Shajenko, “Holographic Testing of Loudspeakers,” J. Acoust. Soc. Am. 53, 1061 (1973).
[CrossRef]

1972

BarZiv, E.

Chiang, F. P.

F. P. Chiang, R. M. Jung, “Vibration Analysis of Plate and Shell by Laser Speckle Interferometry,” Opt. Acta 23, 997 (1976).
[CrossRef]

Der Hovanesian, J.

Durelli, A. J.

A. J. Durelli, V. J. Parks, Moire Analysis of Strain (Prentice-Hall, Englewood Cliffs, N.J., 1970).

Glatt, I.

Hung, Y. Y.

Jung, R. M.

F. P. Chiang, R. M. Jung, “Vibration Analysis of Plate and Shell by Laser Speckle Interferometry,” Opt. Acta 23, 997 (1976).
[CrossRef]

Kafri, O.

Keren, E.

Livnat, A.

Meyer, H.-J.

Parks, V. J.

A. J. Durelli, V. J. Parks, Moire Analysis of Strain (Prentice-Hall, Englewood Cliffs, N.J., 1970).

Ritter, R.

Solid, J. E.

See, for example, J. E. Solid, “Holography Applied to Structural Components,” Opt. Eng. 14, 460 (1975):P. Shajenko, “Holographic Testing of Loudspeakers,” J. Acoust. Soc. Am. 53, 1061 (1973).
[CrossRef]

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Figures (8)

Fig. 1
Fig. 1

Schematic diagram of the experimental setup. The shadow of a grating is projected on an object. A photograph of this (object) distorted grating is taken by a camera. The processed film is then placed at the back of the camera. A photo-detector monitors the fringe brightness, and an oscilloscope trace is taken of the detector photo-current, which is proportional to the displacement of a point on the vibrating object vs time.

Fig. 2
Fig. 2

Transmitted intensity vs relative phase shift between the two gratings.

Fig. 3
Fig. 3

Applied driving current (upper curve) and membrane motion (lower curve). Note the phase lag between the two sinusoidals (2 msec/div).

Fig. 4
Fig. 4

Membrane amplitude vs frequency.

Fig. 5
Fig. 5

Phase lag between the driving oscillation and the oscillation of the membrane vs frequency.

Fig. 6
Fig. 6

When the membrane displacement is greater than the fringe increment, a new fringe is formed and a folding effect of the signal occurs. Due to this folding effect, the apparent frequency of the signal may appear higher than the vibrational frequency of the membrane.

Fig. 7
Fig. 7

Oscillation amplitude as a fraction of position along the radius of the speaker (at 250-Hz driving frequency).

Fig. 8
Fig. 8

Membrane motion (upper curve) and driving oscillation (music—Beethoven's Fifth Symphony) (lower curve) (2 msec/div).

Equations (1)

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Δ h = p / tan β ,

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