Electrostatic Unsteady Thermal Energy Harvester Using Nematic Liquid Crystal

Abstract

A novel electrostatic unsteady thermal harvester is proposed using nematic liquid crystal as the temperature-sensitive dielectric. With its large anisotropic permittivity and relatively high resistivity, an early prototype is made using fluorinated liquid crystal BCH-5F.F.F. Temperature change of the liquid crystal induces its permittivity change, thereby output voltage is obtained. An effective circuit model is developed and the simulation results are compared with the experimental data for designing harvester with better performance.Keywords: Electrostatic, Thermal energy harvesting, Nematic liquid crystal, Resistivity IntroductionEnergy supply for low-power electronics is a big challenge with increasing demand of portable and wireless devices. Thermal energy harvesting can be a promising solution for self-powered electronics such as wireless sensing node [1], which is one of the essential components of the Internet of Things. Conventional thermal energy harvesting mostly utilizes constant temperature gradient based on the Seebeck effect [2]. More recently, time-dependent fluctuating ambient temperature has been reported to be an alternative thermal energy source for energy harvesting [3,4].We previously proposed electret-based unsteady thermal generator utilizing permittivity change of ferroelectric material [5]. By using potassium tantalate niobate (KTN) crystal, output power of 572 nJ has been obtained in 300 s [6]. However, relatively high operation temperature and long recovery time are the main drawbacks of the KTN-based system, which limit the actual application of unsteady energy harvester working in the room temperature range with rapid but small temperature fluctuations.In this paper, nematic liquid crystal with anisotropic permittivity is, for the first time, studied as temperature sensitive dielectric in the electret-based unsteady thermal energy harvester to improve the temperature sensitivity and fast-response to temperature variation.