Improvement of Pyroelectric Cells for Thermal Energy Harvesting

Abstract

This study proposes trenching piezoelectric (PZT) material in a thicker PZT pyroelectric cell to improve the temperature variation rate to enhance the efficiency of thermal energy-harvesting conversion by pyroelectricity. A thicker pyroelectric cell is beneficial in generating electricity pyroelectrically, but it hinders rapid temperature variations. Therefore, the PZT sheet was fabricated to produce deeper trenches to cause lateral temperature gradients induced by the trenched electrode, enhancing the temperature variation rate under homogeneous heat irradiation. When the trenched electrode type with an electrode width of 200 μm and a cutting depth of 150 μm was used to fabricate a PZT pyroelectric cell with a 200 μm thick PZT sheet, the temperature variation rate was improved by about 55%. Therefore, the trenched electrode design did indeed enhance the temperature variation rate and the efficiency of pyroelectric energy converters.

Pyroelectric Harvesters for Generating Cyclic Energy

“…Using the temperature variation rate at the point near the top electrode could not discriminate the properties of the pyroelectric sensors with various thicknesses of the ZnO films. Therefore, a conservative consideration was to adopt the properties at the point near the bottom electrode for inspecting the sensors because the temperature variation rate at this point could display differences of the ZnO films with various thicknesses [5,6]. As the ZnO films at the point near the bottom electrode possess the lowest temperature variation rates, this position could certainly enhance the responsivity of the pyroelectric devices.…”

“…Although thin film deposition technology can be used to grow films with lesser thickness, the pyroelectric properties usually decrease quickly. Commercial PZT bulk materials possessing excellent pyroelectric properties, together with the designs of trench and groove structures fabricated using a dicing saw apparatus, as well as a sandblast etching technique, were useful for improving the temperature variation rate and thus enhancing the efficiency of pyroelectric harvesters [6,7]. The cyclic heating system was mainly meant to achieve a periodic temperature profile for generating temperature fluctuations in the pyroelectric cells.…”

“…Furthermore, thermal isolation was applied to the rear side of the PZT pyroelectric cells, and the two lateral sides of the model were symmetric, in order to serve as boundary conditions. The top border of the model was applied to the incident irradiation power of about 1.228 × 10 −12 W/μm 2 [5][6][7], with various unit step functions for the resulting various frequencies or work cycles. In fact, the PZT pyroelectric cells used the current responsivity and induced charge in the performance of the harvesters.…”

“…Thermoelectric generators need a temperature difference, as they cannot work in an environment with spatially uniform and time-dependent temperature fluctuations [1]. Alternatively, pyroelectric devices directly convert temperature fluctuations into electrical energy [1][2][3][4][5][6][7]. Pyroelectric materials have the potential to operate with high thermodynamic efficiency and, compared to thermoelectric generators, do not require bulky heat sinks to maintain the temperature gradient.…”

“…When the dimensions and the materials of pyroelectric elements are determined, creating a larger temperature variation rate in the pyroelectric element is useful for harvesting pyroelectric energy, however, the temperature variation rate is difficult to extract from pyroelectric layers by experimental measurements. Some finite element models were built using the commercial software package COMSOL to explore the temperature variation rate in pyroelectric cells, with some designs of cavities created by wet etching, trenches made with a precision dicing saw, and grooves generated by a sandblast etching technique, in order to improve the energy conversion efficiency of PZT cells by pyroelectricity [5][6][7]. Cyclic heat energy harvesting mainly uses the pyroelectric elements to convert temperature fluctuations into electricity.…”