Structural Health

About

Background Fiber-optic sensors have become an important class of sensors for structural health monitoring in aerospace and automobile applications. Power modulation based sensors are of particular interest for such applications because of their simple construction and sensing principle. These sensors rely on optical intensity losses through curved waveguides. Bending an optical fiber beyond a critical radius results in optical power losses through the curved section due to coupling between guided and radiation modes. The higher order modes in a multimode optical fiber are coupled out of the fiber. This phenomenon in multimode fibers results in a linear relation between displacement and intensity change. The NYU team has taken fiber-optic displacement technology a step further. Traditionally, fiber-optic sensors could measure substantial displacements would not have the sensitivity to accurately measure small displacements as well due to a smoothing over of the small intermediate peaks. The NYU sensor can measure both, however. The sensor is capable of measuring up to 5 mm displacement with resolution of 1 micron. This is presented in a simple design that is compact, cheap, and potentially easy to use. The sensor can be attached to the surface of the specimen or structure. It can also be embedded inside the structure because the sensor thickness is only about 250 microns. The sensor can also be used as a long probe for conducting measurements in a remote area. Applications In addition to the current applications in the aerospace and automotive industries, the affordable, compact nature of the NYU fiber-optic loop-sensor opens up other potential applications. The NYU team is currently looking into using the sensor to monitor aging civil infrastructure, buildings, and to measure extension in biomaterials during tensile testing.