A method of continuously harvesting energy from pyroelectric materials is demonstrated using an innovative cyclic heating scheme. In traditional pyroelectric energy harvesting methods, static heating sources are used, and most of the available energy has to be harvested at once. A cyclic heating system is developed such that the temperature varies between hot and cold regions. Although the energy harvested during each period of the heating cycle is small, the accumulated total energy over time may exceed traditional methods. Three materials are studied: a commonly available soft lead zirconate titanate (PZT), a pre-stressed PZT composite, and single-crystal PMN-30PT. Radiation heating and natural cooling are used such that, at smaller cyclic frequencies, the temporal rate of change in temperature is large enough to produce high power densities. The maximum power density of 8.64 μW/cm3 is generated with a PMN-30PT single crystal at an angular velocity of 0.64 rad/s with a rate of 8.5°C/s. The pre-stressed PZT composite generated a power density of 6.31 μW/cm(3), which is 40% larger than the density of 4.48 μW/cm3 obtained from standard PZT.
This paper considers energy harvesting using pyroelectric materials such as PZT-5A and thin-films. A simple model is used to predict the power generated based on the measured temperature of the material as a function of time. The measured and predicted results are presented and compared. In particular, the measured peak power density for a PZT-5A sample was 0.23 μWcm−2 for a maximum temperature rate of approximately 15 °Cs−1. The predicted peak power density under the same boundary conditions for thin-film lead scandium tantalate was over 125 μWcm−2. The power density is shown to be highly dependent upon the surface area and the pyroelectric coefficient, underlining the importance of maximizing these parameters.
An understanding of the power that can be harvested from pyroelectric materials and its dependence on material properties, geometry and boundary condition is crucial to the design of energy harvesting devices using these materials. In this paper, simple analytical expressions are developed for ideal voltage, power and power densities as a function of pyroelectric constant, permittivity, surface area, thickness, temperature variation and rate of change for unclamped samples. Experiments are performed to specifically study the effect of geometry and are compared with theoretical predictions.
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