Optical strain sensor using median density grating foil: Rivaling the electric strain gauge

Abstract

In this article, a novel compact optical diffraction strain sensor using medium density grating foil is presented. The grating, generally with a frequency of 300–500 lines/mm attached on the surface of a specimen, is illuminated by a focused laser beam. The centroids of diffracted beam spots from the grating are automatically determined with two position-sensitive detector sensors connected to a personal computer. The shift of second-order diffracted beam spots due to the specimen deformation is then detected. The influences of noise sources and system geometry on system performances, such as sensitivity, spatial resolution, strain range, and measurement linearity are discussed. Strain sensitivity of 1.3 microstrain can be achieved. The spatial resolution for strain measurement of 0.4 mm is attainable. The system can be used for continuous measurement and for both static and dynamic tests.