In every phase of aircraft operation, lightweight structures are subject to unavoidable vibrations, whose mechanical energy remains unused. In the frame of the project EnerVib (Innovative Energy Generation Concepts from Vibrating Flight Structures) between the Institute of Structural Mechanics and Lightweight Design (SLA) at RWTH Aachen University and the Research group System Reliability, Adaptive Structures, and Machine Acoustics (SAM) at TU Darmstadt is aimed at answering the central question of how electrical energy can locally be generated, processed and stored from vibration-kinetic energy.
This kind of energy harvesting is realized in EnerVib by using the piezoelectric effect. Materials with piezoelectric properties can generate an electric voltage under elastic deformation and vice versa. On the one hand, the project focuses on biogenic wood-based materials which, as sustainable, eco-efficient raw materials, combine an advantageous load-bearing behaviour with piezoelectric properties. On the other hand, the project also focuses on novel piezoelectrets which, compared to classical piezocrystals and ceramics, have a higher (weight-specific) performance in the conversion of mechanical into electrical energy.
In this context, the SLA investigates in particular the electro-mechanical properties of biogenic wood-based materials. In addition to the higher eco-efficiency, the fatigue strength and the advantageous load-bearing properties qualify this biogenic material. The piezoelectric properties of wood are made possible by the crystalline structure of cellulose. The innovation consists in exploiting the combination of the advantageous mechanical properties of wood with piezoelectric conversion for energy harvesting.
Within the framework of EnerVib, a comprehensive characterization of the electro-mechanical properties of biogenic wood-based materials is carried out first. Specific characteristic values for the description of the performance are determined and a material selection is made. From the monolithic structure of the samples on coupon level the possibilities of a multi-layer structure are investigated. With this basic research the basis for the conception of multifunctional structures and mechanisms made of fibre composites with integrated wood layers shall be created.
Load-bearing hybrid structures made of fibre composites and wood-based materials, as well as absorber mechanisms as resonators, whose spring elements consist of the above-mentioned piezoelectric transducer materials (hybrid structures and/or monolithic structures), are to be integrated into the aircraft as energy harvesters in order to realize a local supply of electrical consumers. Besides the reduction of complex cabling for the power supply, a direct supply of electrical consumers such as sensors, microelectronics etc. can be achieved. This opens up additional possibilities for new technological fields of application through local electrical supply at previously unreachable locations. As an additional synergy effect, coordinated absorber mechanisms can contribute to vibration suppression.