Energy harvesting wireless sensors and networked timing synchronization for aircraft structural health monitoring

Energy harvesting, combined with wireless sensors, could greatly improve our ability to monitor and maintain critical structures. This paper reports on the development of an integrated structural health monitoring and reporting (SHMR) system for use on Navy aircraft. Our goal was to develop and test a versatile, fully programmable SHMR system, designed to synchronize and record data from a range of wireless and hard wired sensor networks. Wireless sensors included strain gauges, accelerometers, and thermocouples. Hard-wired sensors included gyroscopes, accelerometers, and magnetometers. Data from an embedded Global Positioning System (GPS) provided position, velocity, and precise timing information. These data were collected at multiple sampling rates and time stamped and aggregated within a single scalable database on a base station, termed the wireless sensor data aggregator (WSDA). The WSDA, in addition to providing a central location for collecting wireless (star) and wired network sensor data, also provided a beaconing capability to synchronize each sensor node's embedded precision timekeepers. For flight tests that require a synchronization of sensor data to sub-millisecond accuracies, and with exposure to extreme temperatures, a synchronization beacon should be sent every 5 minutes. Wireless node network synchronization response time, after receipt of a centrally broadcast network command, such as to initiate node sampling, or to synchronize node clocks, was measured at +/- 4 microseconds. Therefore, the system is capable of supporting both burst and periodic sampling modes, with accurate wireless network timing synchronization.