A Synchronized Wireless Sensor Network for Experimental Modal Analysis in Structural Health Monitoring

Structural health monitoring aims to provide an accurate diagnosis of the condition of civil infrastructures during their life span using data acquired by sensors. Wireless sensor networks represent a suitable monitoring technology to collect reliable information about the structure's condition, replacing visual inspections, and reducing installation and maintenance time and costs. This article introduces a time synchronized and configurable wireless sensor network for structural health monitoring enabling a highly accurate identification of the modal properties of the monitored structure. The wireless sensor nodes forming the network are equipped with a 3-axis digital accelerometer and a temperature and humidity sensor. The implemented Medium Access Control layer time synchronization protocol (μ-Sync) ensures a highly accurate synchronicity among the samples collected by the nodes, the absolute error being constantly below 10 μs, also when high sampling frequency (up to 1 kHz) and extended sampling periods (up to 10 minutes) are applied. The experimental results obtained on a wooden model bridge, compared with those derived from acceleration signals acquired by high-quality wired sensors, show that the so synchronized wireless sensor nodes allow a precise identification of the natural frequencies of vibration of the monitored structure (1% maximum relative difference).