Magnetostrictive vibration sensor for a self- powered structural health monitoring system

Abstract

Previously, we proposed a self-powered vibration-based structural health monitoring system for diagnosing the structural soundness of entire bridges to screen bridges requiring detailed inspection. The core part of the system is the vibration-sensing device that is in the developing phase. This part relies on the Villari effect of magnetostrictive materials. In particular, the vibration-sensing device is a dual-use device that can serve as a vibration sensor and a power generator. This paper describes the design and evaluation results of the device’s performance. Galfenol, a typical magnetostrictive material, was used. Therefore, we first investigate the relationship between the magnetic flux density variation and the compression stress with different bias magnetic fields applied to the Galfenol rod. Moreover, an adequate range of the bias magnetic field was determined to maximize the power-generation performance and sensitivity of vibration. Subsequently, the prototype of the vibration-sensing device was designed and built, and a field test was conducted. The experimental results confirmed that the device works as a vibration sensor with high resolution. The device accurately detected the natural frequency of a bridge, even when subjected to the intermittent load of passing cars. The device generated 30.3 mJ in an hour even though it is a small-sized non-resonant power generator. With such generated energy, diagnosing the structural health at least once every two days can be executed with the developed device.