Abstract:
Pyroelectric materials have the ability to generate electrical response when they experience
a thermal stimulus. This has lead to their deployment in applications such as
Infra-Red detectors/sensors, energy harvesting, and ferroelectric electron emission cathodes,
among others. All the “Figures of merit” presented in the literature for assessing
pyroelectric materials are proportional to the pyroelectric coefficient. Hence, enhancing
this coefficient should improve the performance of the pyroelectric element in any application.
This research has been conducted to find ways of enhancing the pyroelectric
coefficient of a given material through product property in the secondary pyroelectric
effect arising from thermal expansion coefficient mismatch.
Analytical model for describing such enhancement in 2-2 connectivity laminate composites
has been developed and simulated on Mathematics package Maple, while Finite
Element Analysis package ANSYSR⃝ was used to perform thermo-structural analysis investigating
the effect of bonding/interfacial layer on the strain transfer between the laminate
layers. Indicators for judging the credentials of various pyroelectric materials in
pyroelectric coefficient enhancement have been identified and evaluated for six different
pyroelectric materials. These six pyroelectric materials were paired with six different
non-pyroelectric materials to form thirty-six 2-2 connectivity laminate composites for
the purpose of comparing pyroelectric coefficient enhancements, whereby various factors
affecting the enhancement have been determined. Potential applications of this enhancement
and what it may mean in terms of improvement in the outputs of these applications
has been reviewed. In particular, two electrical boundary conditions, namely short and
open circuit conditions, have been explored while the effects of thermal mass variation
due to the introduction of non-pyroelectric layer have also been inspected.
Experimental verification of pyroelectric coefficient enhancement under short circuit
condition in Lead zirconate titanate/Stainless steel 2-2 connectivity laminate composites
has been conducted with observed pyroelectric coefficient enhancements of more
than 100 % while theoretical enhancements of up to 800 % is predicted in certain laminate
composites of Lead zirconate titanate/Chlorinated polyvinyl chloride thermoplastic.
Consideration of the open circuit condition pyroelectric coefficients and their enhancements
revealed significant dissimilarities from their short circuit condition counterparts,
prompting the need for more distinction to be made between the two than it has previously
been thought. For instance, appraising employment credentials of pyroelectric
elements in applications such as pyroelectric X-ray generation, electron accelerator, and
nuclear fusion should involve the use of open circuit pyroelectric coefficient rather than
the short circuit one.
The effects of thermal mass has also been considered using quantities termed “Figures
of merit for efficiency”, comparing the laminate composite’s thermal-to-electrical
conversion efficiency to that of stand alone pyroelectric material. Up to twenty fold increase
in thermal-to-electrical conversion efficiency under short circuit condition has been
predicted in laminate composites of Lead zirconate titanate/Chlorinated polyvinyl chloride
thermoplastic, insinuating a potential for increased employment of Lead zirconate
titanate in areas such as pyroelectric sensors and pyroelectric energy harvesting.
Pyroelectric energy harvesting application has been examined in detail as a potential
beneficiary of this enhancement, with various analysis tools for assessing pyroelectric energy
harvesting performance of a given pyroelectric element presented and evaluated. A
pyroelectric energy harvesting system was designed as a hypothetical application of pyroelectricity
and pyroelectric coefficient enhanced 2-2 connectivity laminate composites.
Theoretical analysis confirms that large improvement in pyroelectric energy harvesting
performance can be expected in Lead zirconate titanate materials by converting them
into 2-2 connectivity laminate composites. The use of newly defined “New electrothermal
coupling factor for composites” (k2
N ew) for assessing credentials of particular pyroelectric
element in pyroelectric energy harvesting application has been proposed and vindicated
while the experimental samples from the pyroelectric coefficient enhancement study were
demonstrated to show significant improvement in their pyroelectric energy harvesting
performance via pyroelectric coefficient enhancement.
The analysis techniques used in this dissertation provide a methodology for assessing
the potentials of particular pyroelectric material and its 2-2 connectivity laminate
composites for applications under both short and open circuit conditions.