Energy Harvesting for Structural Health Monitoring Systems: State of art and recent developments

A structural system can be defined as complex if its behavior is influenced from nonlinearities, uncertainties or interactions. For such systems, it is consistent to comply with precise levels of safety and serviceability. The correct functioning of complex systems has been in the recent years a concern and a subject of studying in engineering. In particular, in the field of electronic systems engineering, the concepts of dependability and dependable system have been defined since the early days. This dependability framework is extended to complex structural systems, as integration to the broadly accepted structural requirements for the design, construction and maintenance of structures, when considering the optimization of the design process of the system within a performance based approach. Considering the above, the knowledge of the loads and the consequent response of the structural system become important. In the past 30 years, a great research effort has been devoted to establishing effective local and global SHM methods. Structural health monitoring (SHM) technology provides a way to evaluate the safety and durability of a structure during its service life, to ensure its serviceability and sustainability. Analyzing the problem in terms of the expected payoff, the outcome is that, in cases of complex structure and infrastructure systems (long span bridges, high rise buildings etc.) the monitoring process should be planned during the design phase and should be carried out during the entire life cycle to assess the structural health and performance under in-service and accidental conditions. The latter concept has been introduced during the last years in large scale structures and infrastructures in China. Long-term monitoring (of bridges or high rise buildings for example, where long-term designates a period of time from 1 year to decades and desirably the entire life cycle, was pioneered in China and in Japan, and is a quite recent concept, made possible by recent advances in sensing, data acquisition, computing, communication, data, and information management. Modern advances in wireless technology and low-power electronics implemented in SHM, led to a huge research in the area of energy harvesting. The term energy harvesting indicates the process of extracting energy from the environment or from a surrounding system and converting it to useable electrical energy. Due to the remote placement of SHM devices, it is desirable to capture and utilize ambient energy (e.g. sunlight, thermal gradient, wind, vibration, ambient RF energy), where available, in order to provide unlimited energy for the lifespan of the electronic devices (sensors, electronics, etc). As a consequence, devices powered by energy harvesters, can be placed in any inaccessible location, and also can be embedded into the structures, since battery replacement is not a challenge anymore. The feasibility of fabrication of such devices at an industrial level is nowadays realistic.