A Finite Element Model of Self-Resonating Bimorph Microcantilever for Fast Temperature Cycling in A Pyroelectric Energy
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A Finite Element Model of Self-Resonating Bimorph Microcantilever for Fast Temperature Cycling in A Pyroelectric Energy Harvester. Salwa Mostafa1, Nicolay Lavrik2, Thirumalesh Bannuru2, Slo Rajic2, Syed K. Islam1, Panos G. Datskos2 and Scott R. Hunter2 1 Depapartment of Electrical Engineering and Computer Science, The University of Tennessee, Knoxville, TN 37996-2100, U.S.A. 2 Measurement Science and Systems Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, U.S.A. ABSTRACT A self resonating bimorph cantilever structure for fast temperature cycling in a pyroelectric energy harvester has been modeled using finite element method. Effect of constituting material properties and system parameters on the frequency and magnitude of temperature cycling and the efficiency of energy recycling using the proposed structure has been investigated. Results show that thermal contact conductance and heat source temperature play a key role in dominating the cycling frequency and efficiency of energy recycling. Studying the performance trend with various parameters such as thermal contact conductance, heat source temperature, device aspect ratio and constituent material of varying thermal conductivity and expansion coefficient, an optimal solution for most efficient energy scavenging process has been sought. INTRODUCTION Energy scavenging utilizing ferroelectric properties of material by means of novel transducers is a growing research field. A relatively new approach in this regard is using the pyroelectric property of certain materials to convert waste heat into electrical energy [1-6]. The efficiency of pyroelectric energy converter depends highly on the rate of change of temperature in the pyroelectric material because electrical current is only generated when the temperature in the material is varying and the magnitude is proportional to the rate of temperature change. Low conversion efficiency in the previously reported attempts was discouraging but they were limited due to lack of efficient and fast thermal cycling methods. Recent work presents model of thermally actuated MEMS with external heat source which are capable temperature cycling with 1.2 second periods[7]. In this study a MEMS based self-resonating bimorph cantilever structure is presented that can be used for faster temperature cycling compared to previous MEMS or pyroelectric energy scavenging efforts. The relation between the frequency and range of temperature cycling to thermal contact conductance, heat source temperature, aspect ratio of the device and other material properties such as thermal conductivity, thermal expansion coefficient has been studied. From the observed performance patterns in relation to different parameter variation optimized parameter choices are sought for maximum energy scavenging.
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THEORY The proposed device in this study is a basic bimaterial bi-layer cantilever anchored to a heat sink at its base. The tip of the cantilever is initially brought in contact with a heat source to initiate the self-resonance. As
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