An Optical Device for Measuring Bending Strain to 5,000 Micro-Strain and Compatible With Optical Fiber Installations
Everett E. Crisman, John S. Derov, Gregory Barchard, Otto J. Gregory, William B. Euler, IEEE Sensors Journal, 2005, 5, 1321 – 1326
Abstract
An optical strain gage is described which can be adjusted to maximize gage factor for predetermined strain ranges. The gages consist of glass tubes coated on the outer surfaces with an optical absorbing layer followed by a reflecting layer. A mechanical strengthening layer can be included to extend the range of strain response. A source laser beam from an optical fiber is injected into one end of the gage. The light remaining in the beam after traveling through the gage is collected via another optical fiber. The optically active layer is adjusted during manufacture to provide a predetermined gage factor. For a given thickness of the absorber layer, the detected light is proportional to the amount of bending strain. In this study, silicon was chosen for the optically active layer and a HeNe laser was employed as the light source.