Enhanced pyroelectric effect through product property and its applications

• Main Author: Chang, Harrison Hoon Seok
• Other Authors: Huang, Zhaorong
• Published: Cranfield University 2009
• Subjects: 621.3815
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519132

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.