24-08-2012, 04:16 PM
ENERGY HARVESTING BY PYROELECTRIC EFFECT USING PZT
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ABSTRACT
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.
INTRODUCTION
Due to recent advances in low-power portable electronics
and the fact that batteries in general provide a finite amount of
power, attention has been given to explore methods for energy
harvesting and scavenging. Energy can be recovered from mechanical
vibration [1], light, and spatial and temporal temperature
variations [2, 3].
Thermal energy in the environment is a potential source of
energy for low-power electronics. For example, a recent commercial
product, a wristwatch, uses thermoelectric modules to
generate enough power to run the clock’s mechanical components
[3]. The thermoelectric modules work on the thermal gradient
provided by body heat. A recent patent was issued for
energy harvesting using novel thermoelectric materials [4],
THE EXPERIMENTAL SYSTEM
An experimental system was created to validate the simplified
model to predict the power generated for a sample pyroelectric
element. The pyroelectric element was PZT-5A, with area
A = 1.44 cm2 (1.20 cm × 1.20 cm), thickness of 150 μm, measured
pyroelectric coefficient p = 238 μCm−2K−1, and capacitance
Cp = 45 nF.
The experimental system is pictured in Fig. 2, where the
PZT element was bonded to a thin resistance heater (Minco
HK5578 R35.0L12B, 1.91 cm × 1.91 cm). The heater was used
to control the temperature of the pyroelectric element and a Type
K thermocouple sensor was attached to the backside of the resistance
heater to measure the temperature of the heater. The
measured temperature was assumed to be the temperature of the
PZT. Also, the thermocouple sensor was passed through an Analog
Devices AD595 monolithic thermocouple amplifier and the
signal was recorded by a desktop computer with a data acquisition
system (National Instruments, LabPC+, 12-bit).
THE MEASURED AND PREDICTED RESULTS
The control system was tuned to achieve a relatively-high
temperature rate, where the maximum was 15.65 ◦Cs−1 [see
dash-line plot in Fig. 4(a)] over a temperature range between
29.79 to 102.78◦C. The resulting measured and predicted output
voltage Vp for the PZT element are shown in Fig. 4(b). The
measured and predicted peak voltages were 0.58 V and 0.53 V,
respectively. Both the voltage profile and peak voltage for the
measured and predicted results compared well [see Fig. 4(b)].
Finally, the measured and predicted power densities (normalized
with area of PZT element) are depicted in Fig. 4©, where the
peak values for the measured and predicted results were 0.23
μWcm−2 and 0.20 μWcm−2, respectively. Like the voltage results,
the measured and predicted power densities were also in
good agreement.
CONCLUSIONS
The potential for energy harvesting via the pyroelectric effect
was studied for a PZT-5A sample and a simple model was
developed to predict the power generated. Measured and predicted
results show good agreement and the measured peak
power density was 0.23 μWcm−2 for approximately 15◦Cs−1
temperature rate. Using the model, a thin-film with significantly
higher pyroelectric coefficient showed nearly three orders
of magnitude improvement in the peak power density.