SBIR Phase I: Optical Fiber Sensor for Relative Humidity

This Small Business Innovation Research Phase I project proposes to develop a discrete multi-point embeddable optical fiber sensor to monitor relative humidity inside concrete structures. Relative humidity is a major factor that affects a number of processes related to the deterioration of civil structures. Humidity alone does not degrade concrete, however it does promote the action of agents that are ultimately responsible for accelerated corrosion, e.g., carbon dioxide and chloride ions. The proposed sensor can be embedded inside a structure to provide real-time data and can be custom designed to achieve a spatial resolution of up to 3 mm over the entire fiber length. This device uses a fluorescent cladding fiber that has a spectroscopic response dependent on relative humidity and can be manufactured to sense multiple simultaneous parameters such as chloride ions and pH. Currently, humidity measurements are achieved today with single point sensors in a semi-destructive fashion. Unlike existing devices, the proposed sensor can provide data at several points along the fiber length in a non-destructive fashion. It has been estimated that the cost of repairing and replacing concrete bridges in the United States is more than $20 billion and increases at an annual rate of $500 million. Once demonstrated, it will have applications in atmospheric sciences and in the monitoring of soil humidity to optimize the irrigation of cultures.