Abstract
Pyroelectric harvesters convert time-dependent temperature variations into electric current. The appropriate geometry of the pyroelectric cells, coupled with the optimal period of temperature fluctuations, is key to driving the optimal load resistance, which enhances the performance of pyroelectric harvesters. The induced charge increases when the thickness of the pyroelectric cells decreases. Moreover, the induced charge is extremely reduced for the thinner pyroelectric cell when not used for the optimal period. The maximum harvested power is achieved when a 100 μm-thick PZT (Lead zirconate titanate) cell is used to drive the optimal load resistance of about 40 MΩ. Moreover, the harvested power is greatly reduced when the working resistance diverges even slightly from the optimal load resistance. The stored voltage generated from the 75 μm-thick PZT cell is less than that from the 400 μm-thick PZT cell for a period longer than 64 s. Although the thinner PZT cell is advantageous in that it enhances the efficiency of the pyroelectric harvester, the much thinner 75 μm-thick PZT cell and the divergence from the optimal period further diminish the performance of the pyroelectric cell. Therefore, the designers of pyroelectric harvesters need to consider the coupling effect between the geometry of the pyroelectric cells and the optimal period of temperature fluctuations to drive the optimal load resistance.
Highlights
Environmental energy harvesting has become the hot topic with regard to driving low-energy consumption systems, such as wireless sensor networks
The optimal period of temperature fluctuations is directly related to the geometry of the pyroelectric cells
The stored voltage generated from the 75 μm-thick PZT cell was less than that from the 400 μm-thick PZT cell for a period longer than 64 s
Summary
Environmental energy harvesting has become the hot topic with regard to driving low-energy consumption systems, such as wireless sensor networks. Thermoelectric modules are the main way for harvesting waste heat energy from temperature fluctuations. Thermoelectric generators rely mainly on the Seebeck effect to convert a steady-state temperature difference at the junction of two dissimilar metals or semiconductors into an electromagnetic force or electrical energy. Thermoelectric elements need temperature gradients leading to heat flow in fixed temperature differences, which cannot work in the environment temperature with spatially-uniform and time-dependent temperature fluctuations within short periods [1,2]. Pyroelectric devices directly convert time-dependent temperature fluctuations into electricity [1,2,3,4,5,6,7,8,9]. The pyroelectric effect is the change produced in the spontaneous polarization of a non-centrosymmetric dielectric material as a consequence of the change in its temperature. The change in polarization stems from the shift in the degree of non-centrosymmetry owing to thermal fluctuations corresponding to different temperatures
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