Jacob H. Galbreath

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.

Frequency Agile Wireless Sensor Networks

Our goal was to demonstrate a wireless communications system capable of simultaneous, high speed data communications from a variety of sensors. We have previously reported on the design and application of 2 KHz data logging transceiver nodes, however, only one node may stream data at a time, since all nodes on the network use the same communications frequency. To overcome these limitations, second generation data logging transceivers were developed with software programmable radio frequency (RF) communications. Each node contains on-board memory (2 Mbytes), sensor excitation, instrumentation amplifiers with programmable gains & offsets, multiplexer, 16 bit A/D converter, microcontroller, and frequency agile, bi-directional, frequency shift keyed (FSK) RF serial data link. These systems are capable of continuous data transmission from 26 distinct nodes (902-928 MHz band, 75 kbaud). The system was demonstrated in a compelling structural monitoring application. The National Parks Service requested a means for continual monitoring and recording of sensor data from the Liberty Bell during a move to a new location (Philadelphia, October 2003). Three distinct, frequency agile, wireless sensing nodes were used to detect visible crack shear/opening micromotions, triaxial accelerations, and hairline crack tip strains. The wireless sensors proved to be useful in protecting the Liberty Bell.