Smart autonomous wireless acoustic sensors for aeronautical SHM applications

Ultrasound technologies are of great interest for aeronautical structure inspection. Mainly deployed through Phased Array (PA) ultrasonic transducer, ultrasound inspection is currently used as a complementary tool for the local examination of the structure to determine geometry, damage or composition of invisible flaws like cracks, delamination and corrosion. This approach cannot be easily automated since the access to the area of interest often requires to pass through the complex aeronautical structure. Moreover this approach relies on a high degree of human interaction, as the user often decides the spatial inspection sampling according to his intuition and experience of the structure composition and vulnerability. Structure Health Monitoring, namely SHM, overcomes these limitations by enabling rapid, automated, remote, and real-time monitoring of the structure to reduce operational costs and increase lifetime of structures. This inspection strategy gains its strength from the use of a large amount of individual embedded sensors with embedded intelligence (sensing, signal processing, communicating and storing relevant data in non-volatile memories) organized in dense network, a Neural Network. We present in this paper the developments of a novel autonomous wireless acoustic sensor node, including: a flat flexural acoustic sensor capable of working in transmit and receive, a custom vibrational piezoelectric energy harvesting device (PEH) charging a 0.5 Farad buffer supercapacitance through a commercial rectifying IC, an ARM based cortex M3 microprocessor driving digitization, signal processing, data storage and two ways RF communication. The main objective was to create a versatile hardware platform that can be embedded within the structure to monitor, and capable of hosting different acoustic inspection strategies.