Star Type Wireless Sensor Network for Future Distributed Structural Health Monitoring Applications

Abstract

A star type wireless sensor network based on nine-axis micro-electromechanical inertial motion sensors with the potential to include up to 254 sensor nodes is presented, and an investigation into the mechanical and structural effects of bell ringing on bell towers is presented as a possible application. This low-power and low-cost system facilitates the continual monitoring of mechanical forces exerted by swinging bells on their support and thus helps avoid structural degradation and damage. Each sensor measures bell rotation, and a novel method utilising only the instantaneous rotational angle is implemented to calculate the force caused by bell ringing. In addition, a commonly used, however, previously experimentally unconfirmed assumption that allows great simplification of force calculations was also proven to be valid by correlating predicted theoretical values with measurement data. Forces produced by ringing a 1425 kg bell in Durham Cathedral were characterised and found to agree with literature. The sensor network will form the basis of a toolkit that provides a scalable turnkey method to determine the exact mechanisms that cause excessive vibration in mechanical and architectural structures, and has the potential to find further applications in low-frequency distributed structural health monitoring.