Fiber Bragg Grating Sensors for Acoustic Emission and Transmission Detection Applied to Robotic NDE in Structural Health Monitoring

Distributed acoustic emission sensors are used in structural health monitoring (SHM) for the detection of impacts and/or strain, in real time. Secondary damage may result from the initial impact or strain. This damage may include surface pitting, erosion, or cracking. This type of damage may not be detectable by the SHM system, specifically in passive fiber optic based sensing systems. The integration of non-destructive evaluation (NDE) by robots into SHM enables the detection and monitoring of a wider variety of damage. Communicating via acoustic transmissions represents a wireless communications method for use by NDE inspection robots to communicate with an integrated SHM system that does not require any additional hardware, as piezoelectric transducers are commonly used in the NDE of materials. In this paper, we demonstrate the detection of both acoustic emissions and transmissions with a fiber Bragg grating (FBG) sensor. The acoustic communications channel comprises of a piezoelectric transmitter, an aluminum panel as the transmission medium, and a FBG receiver. Phase Shift Keying was used to encode the acoustic transmissions. Results for the frequency and transient response of the channel are presented.