

Small Battery-Free Wireless Sensor Networks for Structural Health Monitoring
Abstract
Battery-free wireless sensors developed at the University of Maine under a cooperative agreement with NASA enable a myriad of structural health monitoring (SHM) applications. Embedding these sensors in structures without the need for changing batteries, their rugged design to withstand harsh environments, and coded communication with multiple access features makes this new technology a desirable candidate for a variety of aerospace and civil infrastructure monitoring applications. This paper presents sensor characteristics, communication schemes, and multi tier networking strategies developed to deliver a reliable wireless sensor system for SHM. A large scale inflatable lunar habitat structure built by NASA and instrumented by UMaine is used as test-bed for technology demonstration. Various aspects of this system have been studied and results are published in conferences and journals as presented in the references section. These aspects are summarized in this paper and include: distributed sensing and coding, throughput optimization, channel estimation error analysis, signal detection in presence of interference, two-tiered networking, turbo coding and decoding in distributed sensor networks, cooperative relaying methods, and impact localization. Testing the developed battery free sensors in lab environment with multi-path and interference effects resulted in 16 ft operation range with under 20 mW power. This range can be even extended further if a second tier with battery-operated sensors is added to the network. Noting that several passive sensors and only a few active sensors is required to build this multi-tier architecture, the cost savings in power combined with coding gain is significant compared to conventional sensor networks.