Smart Optical Waveguide Sensors for Cumulative Damage Assessment
Otto J. Gregory, William B. Euler, Everett E. Crisman, Hanan Mogawer, and Kimberly A. Thomas, Proceedings SPIE: Smart Structures and Materials 1999: Smart Systems for Bridges, Structures, and Highways, S. C. Liu, editor, SPIE Press, Bellingham, WA, vol. 3671, 1999, 100 – 108
Abstract
A strain gage is being developed, based on optical modulation that is capable of gage factors on the order of 500 for strains in excess of 2000 microstrain. The strain sensing element is a coated, hollow, glass waveguide of dimensions 0.5 mm ID × 1 mm OD × 100 mm long. Since the geometry is compatible with standard telecommunication optical fiber such gages it can be readily incorporated into smart system arrays for damage assessment in structures such as buildings, roads and bridges. Optical fibers bring the excitation light signal to and the response signal from the sensing element. The small diameter glass tubes act as the substrate for a multiple thin film layers which can be optimized to provide the maximum dynamic range for a predetermined strain excursion. The sensor responds to bending strain by attenuating the optical intensity of the excitation signal. The gage elements exhibit little or no hysteresis and are insensitive to temperature. Also, they are environmentally stable and are not affected by factors such as corrosion or electromagnetic fields. The preliminary experimental results will be presented for this type of strain gage system operating to 2000 microstrain. Also, the model for the physical process will be discussed.