Wireless acoustic communications for autonomous agents in structural health monitoring sensor networks

Wireless acoustic communications methods have been demonstrated. These include both electro-acoustic and acousto-optic communications. The communications methods are intended for use by autonomous robotic agents in the Non-Destructive Evaluation (NDE) of structures containing a distributed acoustic emission sensor network. The acoustic emission sensors can be based on either piezoelectric or optical fibre sensors. The communications channel comprises of a piezoelectric transducer as the transmitter, an aluminium panel as the transmission medium, and either a second piezoelectric transducer or an optical fibre sensor as the receiver. 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. These types of secondary damage may not be detectable, and hence may not be able to be monitored by the SHM system; specifically in optical fibre based sensing systems. The integration of NDE by robotic agents into a SHM sensor network enables the detection and monitoring of a wider variety of damage. Acoustic communication represents a wireless communication method that does not require any additional hardware, as piezoelectric transducers are commonly used in the NDE of materials. Various modulation methods were investigated for the communications channel. These include Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK). Successful communication was achieved using both the piezoelectric and optical fibre receivers. The optical fibre sensor used was a Fibre Bragg Grating (FBG).