Spectral Multiplexing of Fiber Bragg Grating Sensors for Low-Power Optical Sensor Networks

North Carolina State University, Raleigh NC

Investigators

Abstract

It is important to monitor the structural integrity and performance of large, complex structural systems throughout their service life. In-service monitoring can increase the safety of the structure and reduce downtimes for repairs. The aim of this research is to derive, implement and demonstrate a low-power, optical fiber based, strain sensor network that can be scaled up to a large number of sensors and applied for high-speed testing of large mechanical and aerospace structural systems. The low-power, high data acquisition rate sensor network will be evaluated for two critical applications of composite structures. First, crash-testing of composite automotive structures for accident survivability analysis will better enable the understanding of how these materials behave and absorb energy during a crash. The implementation of the sensor network with a large number of sensors in the automotive structure will permit a detailed analysis of the dynamic failure of the materials during the crash. Second, the sensor network will be applied to lightning strike testing of composite airframe structures. Lightning strikes pose a large problem for carbon composite materials in aircraft structures due to the inherent low conductivity of composite materials, leading to significant material damage as the converted lightning electromagnetic energy propagates through the material. The high-density sensor network will permit a detailed correlation between the lightning strike properties and the resulting material damage. A fundamentally new method for multiplexing fiber Bragg grating sensors based on the measurement of their individual spectral properties will be derived and tested. This multiplexing strategy can be scaled to both a large number of sensors and high-speed data processing, enabling the capability to multiplex a large number of Bragg grating sensors using a single low-bandwidth, low-power, low-cost laser source. An algorithm for sensor data identification and measurement in highly multiplexed fiber Bragg grating sensor networks will be derived based on combined shape profile division multiplexing and wavelength division multiplexing, while incorporating prior knowledge of the sensor network responses for increased accuracy. The outcome of this research would be fiber Bragg grating sensor network multiplexing capabilities with power requirements orders of magnitude less than current systems, enabling future fiber Bragg grating sensor networks on wireless sensing platforms.