Water Motion Active Transducer for Energy Harvesting

Abstract

As effective methods to convert mechanical motion to electrical power, various transducers, such as electromagnetic inductive transducers, piezoelectric transducers, and variable capacitive transducers have been developed. The electromagnetic inductive transducers defined by Faradays law are predominantly used for electric energy harvesting from mechanical motion. Furthermore, the piezoelectric transducers are becoming an emerging technology for self-powered portable devices. Otherwise, in spite of the potential for energy transducing by variable capacitance, it remains in an infant state for energy harvesting, because it needs additional external bias-voltage sources for the accumulation of charge at the electrodes, which requires a passive transducer, or toxic liquid metals for effective induction. Also, their sources for energy harvesting are restricted only to artificial intermittent stimulation, like pushing or vibration. To overcome the limitations, I propose a water active capacitive transducer (WMAT) as an energy harvester to effectively generate electric power from the natural motion of water without any external bias voltage sources. One of the most significant limitations in applying capacitive transducers as energy harvesters is that they need an external bias-voltage source to accumulate charge at the electrodes. In my research, two types of WMAT devices are proposed according to various applications. First, I designed the WMAT with a simple structure consisting of PVP dielectric layer, hydrophobic layer on the rigid substrate. This simple structure has considerable advantages for the process and manufacturing cost. All fabrication processes for the WMAT were solely conducted by solution processes without any vacuum or high-cost processes. Second, I introduced a fabric-based WMAT using fabric materials with flexible and stretchable for wearable electronics. In this experiment, core materials for electrification and EDL to generate the electricity are PVP and PMMA energy conversion layers. I studied an effective fabrication method using newly adopted fabric-based materials and polymer materials to find easy and simple method differ from the conventional complex process. Furthermore, I carried out spray coating and transfer process with fabric material to overcome the limitation of spin coating and lithography process of high temperature and chemical treatment. The simple and low-cost process is the most attractive of all of the advantages of the WMAT in comparison to other energy harvesters with complex structures and cumbersome processes. With variation of the overlapping areas between the water and electrodes, this energy transducer could sufficiently convert the energy from the water's mechanical motion to electric energy. From a simple structure, we successfully generated electricity enough to turn on an LED using various kinds of natural water motion. The WMAT, which has wide applicability, has good potential to be a candidate for generating sustainable electric energy.