Fabrication and analytical modeling of transverse mode piezoelectric energy harvesters
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Fabrication and analytical modeling of transverse mode piezoelectric energy harvesters Seon-Bae Kim1, Jung-Hyun Park2, Seung-Hyun Kim3, Hosang Ahn1, H. Clyde Wikle1 and Dong-Joo Kim1 1 Materials Research and Education Center, Auburn University, Auburn, AL 36849, U.S.A. 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439, U.S.A. 3 School of Engineering, Brown University, Providence, RI 02919, U.S.A.
ABSTRACT A transverse (d33) mode piezoelectric cantilever was fabricated for energy harvesting. Various dimensions of interdigital electrodes (IDE) were deposited on a piezoelectric layer to examine the effects of electrode design on the performance of energy harvesters. Modeling was performed to calculate the output power of the devices. The estimation was based on Roundy’s analytical modeling derived for a d31 mode piezoelectric energy harvester (PEH). In order to apply the Roundy’s model to d33 mode PEH, the IDE configuration was converted to the area of top and bottom electrodes (TBE). The power conversion in d33 mode PEH was commonly estimated by the product of piezoelectric layer’s thickness and finger electrode’s length. In addition, the spacing between fingers was regarded as gap between top and bottom electrodes. However, the output power in a transverse mode PEH increases continuously with the increase of finger spacing, which does not correspond to experimental results. In this research, the dimension of IDE was converted to that of TBE using conformal mapping, and variation of power of PEH was remodeled. The modified model suggests that the maximum power in a transverse mode PEH is obtained when the finger spacing is identical with effective finger spacing. The output power then decreases when finger spacing is larger than effective finger spacing. The decrease of efficiency may result from insufficient degree of poling and increased charged defect with increasing finger spacing. INTRODUCTION Lots of mobile and wireless devices are powered by battery that is based on chemical reaction and has limitation in capacity. Battery should be replaced for continuous operation of the devices. In addition to such inconvenience, battery causes environmental issues for disposal. Therefore, there are efforts to replace battery by regenerative energy sources such as solar, geothermal, and wind energy. Among them, vibration energy can be easily obtained from ambient without limitation in weather, place and time. The vibration energy can be converted to electric energy by electromagnetic and piezoelectric devices, and the latter has higher efficiency and is compatible with miniaturization [1-3]. The output power of piezoelectric energy harvester (PEH) is proportional to piezoelectric constant and strain. PEH can be operated by means of three different piezoelectric modes; d31, d33, or d15 mode. A piezoelectric constant d15 is the largest, but it is hard to realize d15 mode device. A d31 mode device has been widely investigated due to simple structure and easy fabrication, and precise electrode pat
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