The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Mar. 10, 1992
Filed:
May. 25, 1990
John Tyson, II, Wayne, PA (US);
John W Newman, Berwyn, PA (US);
Laser Technology, Inc., Norristown, PA (US);
Abstract
Two laterally-displaced images of a test object interfere with each other to form a shearogram. Two shearograms, taken while the object is unstressed and stressed, respectively, are compared electronically to yield a composite interference pattern. According to the invention, each shearogram is formed by the interference of pairs of distinct rays of coherent light, reflected from different points on the object. The first ray of each pair is reflected from the object, strikes a mirror spaced from the object, and is reflected from the mirror. At the same time, the second ray of each pair is reflected from the object and strikes a beam splitter positioned beside the mirror. The beam splitter directs a portion of the second ray in the same direction as the reflected first ray, and a portion of the first ray passes through the beam splitter without being reflected. Since the two rays have the same polarization angle, and are mutually parallel, the rays interfere. A detector is positioned to receive light from the beam splitter. The detector observes the interference between pairs of rays over the entire field of view, and the result is an interference pattern, i.e. a shearogram, formed from the optical interference of the two laterally-displaced images of the object. The amount of shearing can be controlled by varying the angle of the mirror. Subsequent computer processing can be used to compare the shearograms electronically. Such processing can include the averaging of several shearograms, taken sequentially, with different phase shifts induced by linearly moving the mirror.