A major obstacle limiting the development of deployable sensing and actuation solutions is the scarcity of power. Converted energy from the vibrations of a host structure using devices (harvesters) based on piezoelectric materials has been shown to be a possible solution. However, these energy harvesters are only efficient at a narrow range of vibration frequencies and/or under high deformation conditions. This considerably limits the levels of harvestable power. While several approaches have been developed to broaden the frequencies at which these vibration-based harvesters can operate, their input still needs to be vibratory. The aim of the proposed research is to be able to harness the energy from quasi-static (very low frequency) structural deformations through novel micro-mechanical devices that use multiple instabilities (sudden transitions in geometry while resisting a compressive load) in elastic elements (strips, plates and shells). The sudden transitions (snap-through instabilities) are recoverable (elastic) and generate high-rate motion that amplify and increase the input frequency and deformation amplitude to scavengers that are attached to the deforming elements. These devices then become mechanical analogs to electrical components (that is, amplifiers and frequency modulators). The research will develop methods to control (occurrence instance and number of events) the snap-through instabilities by optimizing material and geometric configurations on elastic elements, which will in turn allow maximizing the energy transfer from piezoelectric energy harvesters. The investigation will also demonstrate the integration of the developed energy harvesting devices into structural elements, as well as power management and storage approaches to maximize use of locally harvested energy. The introduced methods will allow energy generation and conversion from the unexplored range of quasi-static structural response. The project will allow multidisciplinary training of two graduate students and will be integrated with educational and outreach activities focused on promoting the multidisciplinary training of engineering undergraduate students.
The hypothesis behind the proposed research is that energy harvesting within the unexplored structural response range of << 1Hz can be achieved through devices that amplify the amplitude and frequency of the input signal by means of instability transitions in the post-buckling response of elastic elements. The high rate motion input to the harvester depends on the postbuckling characteristics of the mechanical transducers, which can be controlled through material tailoring, boundary conditions, and system arrangements. Regulation of the post-buckling behavior can lead to controlled acceleration input to the piezoelectric vibrators. The research objective is to advance the knowledge and technology needed to create the noted devices to enhance the power conversion capabilities of piezoelectric materials for energy harvesting under quasi-static structural deformations. The research tasks are: 1) theoretical and experimental studies on the postbuckling response of isotropic and anisotropic columns and cylinders, 2) enhancement and control of the high rate motion of the mechanical transducers by material tailoring, boundary conditions and system assemblies, 3) optimization of the piezoelectric harvesters materials and geometry to tailor the amplitude and magnitude of the output voltage signal, and 4) system integration and evaluation in prototype structural components and evaluation of power management and storage technology. The research work will lead to new concepts and mechanisms for materials and structures that utilize the energy that develops within them (strain) form transient and low magnitude loads and convert it to electrical power for local use or storage. The research will expand the useable range of piezoelectric materials as power harvesters and will also open new possibilities for their use in hybrid material systems s and structures for local powering of sensing and actuating devices as well as displacement-power cogeneration structures.
