Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-04-13
1990-07-03
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
73800, 356 355, 356354, G01D 534
Patent
active
049393685
ABSTRACT:
A method and apparatus for measuring strain of an object is provided. The object to be measured is provided with a diffraction grating which is illuminated with radiation including at least two frequencies to produce an interference pattern. At least a portion of the interference pattern corresponding to at least one of the frequencies is detected and analyzed to determine strain. In some embodiments, the frequency of a portion of the diffraction pattern is detected, for example, by a human eye and the detected frequency compared with known frequencies to determine strain. In other embodiments, the relative angular position of portions of the pattern corresponding to different frequencies is detected. Since the relative angular position and intensity is affected by strain but not by certain rigid body rotations, strain measurement free of body rotation error may be made.
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Beck George C.
Massachusetts Institute of Technology
Nelms David C.
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