Mohammed Daqaq Clemson University The goal of this award is to investigate and delineate the physical underpinnings of a scalable concept for micro power generation for wireless sensing and communication. Inspired by music-playing harmonicas that create tones via oscillations of reeds when subjected to air blow, the proposed concept exploits flow-induced self-excited oscillations of piezoelectric cantilever beams embedded within a cavity to transform wind energy into electricity. To achieve this goal, the specific investigations include i) integrating theories in continuous-systems vibrations, piezoelectricity, and fluid dynamics with computational analysis to develop a reduced-order mathematical model that governs the nonlinear aero-electro-mechanical response of the system; and ii) implementing analytical, semi-analytical, and numerical methodologies from nonlinear systems dynamics to understand the interconnected role that the design parameters play in the electromechanical transduction and how to optimize them for enhanced performance . Results of this research will build the fundamental understanding necessary for energy harvesting from flow-induced oscillations and will provide the tools to determine the unknown role that the design parameters play in the limit-cycle oscillations necessary for energy harvesting. Micro-power generators based on the proposed concept will aid in powering and extending the autonomous operations of many vital electronic systems such as those used in wireless communications, remote sensing, and health-monitoring networks. Research results are tied to a myriad of educational activities and will result in new graduate course offerings. These include a creative inquiry project and an outreach initiative to the local community. Extensive efforts are also proposed to provide underrepresented and minority students with similar experiences.
Motivated by the obvious need for a compact, scalable, low-maintenance, cheap, and low-maintenance micro-power generators (MPGs), we proposed and implemented a novel concept for a MPG which uses wind energy to maintain remote low-power consumption sensors. Inspired by music playing harmonica (Fig. 1), the harvester shown in Fig. 2 consists of a piezoelectric cantilever structure embedded within a cavity to mimic the vibration of the reeds in a harmonica when subjected to air blow. The operation principle of the harvester is simple. Wind blows into the chamber and the air pressure in the chamber increases. The increased air pressure bends the beam and opens an air path between the chamber and the environment. As the air passes through the aperture, the pressure in the chamber decreases. The mechanical restoring force pulls the beam back decreasing the aperture area and the process is repeated. These periodic fluctuations in the pressure cause the beam to undergo self-sustained oscillations. The resulting periodic strain in the piezoelectric layer produces an electric field which can be channeled as a current to an electric device. Figure 3 depicts the experimental configuration employed to investigate the feasibility of the proposed concept. Figures 4 and 5 depict variation in the voltage and output power of the device with the chamber air pressure and the corresponding wind speed over an electric load of 49.65 kOhm. The significance of this novel concept for micro power generation stems from its simplicity and scalability without sacrificing power density. This concept has the ability to eliminate the shortcomings of traditional vibration-based energy harvesters and small size wind turbines while, at the same time, combining flow-induced vibrations to generate the necessary power. On one hand, it is based on transforming vibrations to electricity but does not require an external vibration source eliminating the bandwidth issues associated with resonant vibratory energy harvesters. On the other hand, while this device depends on the presence of air flow, it does not suffer from the scalability issues that hinder the performance of small size wind turbines. This stems from the simplicity of the design which only requires a cavity, a cantilever beam, a small aperture, and a piezoelectric layer. In fact, using a very simple and inexpensive etching process, a MPG consisting of an array of such cantilevers can be easily fabricated at the microscale. In addition to providing a novel concept for micro power generation, this research marks the first attempt to build the fundamental understanding necessary for energy harvesting from flow-induced oscillations. Validated mathematical and computational models that describe the basic physics of the driving mechanism in such systems have been developed. A systematic nonlinear study has been conducted to determine the complex and unknown role that the design parameters play in the onset of oscillations necessary for energy harvesting. Design charts have been generated for choosing the optimal design parameters that maximize the output power for a given average wind speed. This research provides the necessary tools to design a compact, scalable, cheap, and low-maintenance wind energy harvester. MPGs based on this concept will become readily available to power many vital electronic systems such as wireless and health-monitoring sensor networks. Autonomous operation of these sensors will help avoid catastrophic failures of structures similar to the 500 bridge failures reported in the US over the last two decades. In addition, their successful implementation will lower our dependence on batteries whose continuous replacement can be a cumbersome and expensive process. This research is also tied to a myriad of educational activities. Several graduate students have been supported by this project. Undergraduate students were recruited through the Clemson Calhoun's honor program to undertake state-of-the-art work on the design, construction, and testing of energy harvesting devices. Weekly meetings have been arranged with the recruited students to expose them to the basic elements of vibratory energy harvesting. In addition to involving undergraduate students in research on energy harvesting, Dr. Daqaq has developed a course module on vibratory energy harvesting and taught it in the structural vibrations class (ME 845) in Fall 2011 at Clemson. The student feedback was very rewarding and indicated their deep interest in new application/research topics involving the theory of vibrations and smart materials. Dr. Daqaq has also been invited by Wiley to co-author a graduate text-book titled ``Nonlinear Energy Harvesting'' with Professor Brian Mann from Duke University. A chapter on energy harvesting using fluid-structural interactions which is closely related to this research will be included in the book.
