Proof-of-Concept System
The prototype SHM system we developed incorporates an integrated hardware and
software design to implement a simple star-topology wireless sensor
network. A
wireless SHM system with a star-topology includes multiple wireless sensing
units assembled in a network with one central server coordinating the
activities of the network. The
wireless sensing units are responsible for acquiring sensor measurements,
analyzing data, and transferring data to the central server for permanent
storage or further data interrogation.
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The design of the wireless sensing unit consists of three functional modules: the sensing interface, the computational core, and the wireless communication channel. The sensing interface converts analog sensor signals into a digital format usable by the computational core. The digitized sensor data is then transferred to the computational core through a high-speed Serial Peripheral Interface (SPI) port. Besides a low-power 8-bit Atmel ATmega128 microcontroller, external Static Random Access Memory (SRAM) is integrated with the computational core to accommodate local data storage and analysis. Through a Universal Asynchronous Receiver and Transmitter (UART) interface, the computational core communicates with the MaxStream 9XCite wireless transceiver, which provides a wireless connection between the unit and other wireless devices or between the unit and the central server. The 9XCite operates on the unlicensed 900MHz radio frequency spectrum and can achieve communication ranges of 300m in open space and 90m in an indoor environment.
