VEHSHI - Vibration Energy Harvesting for Structural Health Instrumentation

Critical infrastructures are the mainstay of our nation’s security, health and economic well-being. Bridges interconnecting street networks are bottle necks of the built infrastructure. Disruption due to poorly maintained infrastructure, specifically progressing fatigue damage from initiation to conditions which are ultimately unsafe for operation, is leading to closure or even collapse of bridges. In 2013, The American Society of Civil Engineers graded the infrastructure of the United States at D+, citing poor physical conditions of bridge structures. Currently, in the United States alone, 149,000 bridges have been deemed either functionally deficient or obsolete. Such a sorry state of affairs can be directly attributed to a lack of appropriate infrastructure maintenance, operational procedures, and life-time assessment methods. The US, but also most countries worldwide experience insufficient resilience and safety of bridge infrastructure. The reason for this development is multi-fold. (a) Primary damage source are trucks and their occurrence on streets in the US as well as in other countries worldwide is expected to increase since trucks are most convenient and efficient transportation service from the perspective of logistics. (b) The money invested into bridge maintenance is not sufficient. Recent investigations in Europe have shown that about 1% of the current value of the bridge has to be reinvested annually in maintenance to fight aging and fatigue damage and keep a constant bridge condition. However, currently the reinvested maintenance amounts to only about a quarter of the required maintenance. (c) No continuous monitoring of bridge condition in place, with instead bridge inspections happening in 2-year intervals. (d) The criticality of cracks in structural steel: When a macro crack generates in the structural material, the load-carrying capacity of the respective structural member decreases to zero and instantaneous repair is required. This patent pending technology, i.e. the Vibrational Energy Harvesting for Structure Health Instrumentation (VEHSHI), converts mechanical energy from traffic induced bridge vibrations to electrical energy to power structure health monitoring systems and data transmission. The novelties of the proposed technology compared to other approaches are (1) the architecture of the energy harvesting/structure health monitoring circuit to enable efficient energy harvesting, structure health monitoring, large data transmission and evaluation in real time. The harvested energy loads a 1.0F double layer super capacitor bank until ample power levels are reached and discharges a certain voltage number at once, (2) The VEHSHI prototype harvests bridge vibrations by utilizing an inertial magnetic mass that plunges through a copper coil while floating on a cushion of repulsive magnetic force, allowing to maximize the energy output, (3) the large power output of the energy harvester compared to other energy harvesting approaches, such as piezoelectric materials. The energy harvester prototype tested in this study produces approximately 16 mW of power, and (4) the robustness of the VEHSHI prototype which ages minimally requiring zero maintenance and providing a life time which lasts beyond the bridge infrastructure design life.

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