An investigation of multi-parameter fiber optic sensors with an application for strain and temperature differentiation using a novel controlled gauge length dual two-mode fiber-optic sensor.

摘要

Optical fibers, while commonly associated with communication functions, are finding increasing usefulness as sensors. In particular as large area structural sensors, they can be configured to measure strains caused by events such as structural vibrations, crack growths, pressurization and material yielding. This can lead to the creation of a nervous system within a structure, which if coupled with processing and actuation capabilities can result in the formation of a "smart structure." One disadvantage that fiber optic sensors do exhibit is a sensitivity to temperature effects which can mask or be confused with strain changes. A fiber optic sensor to eventually be practical must also have a controlled sensing region, have the capability to be multiplexed, not require a separate reference fiber, require only a single, relatively inexpensive laser/light source, have a large dynamic range and have an inherently robust, potentially inexpensive to manufacture design. Although various techniques had been developed to address some of these requirements, there was still a need for a sensor which could meet all of these requirements while having a large but well defined sensing section.; This treatise explores the basis for multi-parameter sensing in optical fibers, and describes past efforts in this area. The research outlined in this dissertation resulted in the creation of a novel fiber optic sensor system with a controlled sensing region which can measure and separate the effects of axial strain and temperature changes, as well as meet the other previously stated requirements. This sensor was formulated through the creation of two sensors or two sensing channels within a single optical fiber such that each sensor exhibits a different response to strain and temperature. The resulting sensor outputs were then processed to extract the strain (elongation) and/or temperature changes experienced by the sensor system. Insensitive lead-in and lead-out fibers were used to create a large, but well defined sensing section. Testing of the sensor system under various strain and/or temperature conditions revealed the successful operation of this sensor system.