Bimetal-and-electret-based thermal energy harvesters - Application to a battery-free Wireless Sensor Node

TL;DR

This paper presents a novel bimetal-electret thermal energy harvester that efficiently converts thermal gradients into electricity without forced convection, enabling battery-free wireless sensor nodes in industrial environments.

Contribution

Introduction of a bimetal-electret harvester that operates under standard conditions and powers a wireless sensor node without batteries.

Findings

Output power of 5.4μW at 70°C

No forced convection needed for operation

Successful powering of a wireless sensor node

Abstract

This paper introduces a thermal energy harvester turning thermal gradients into electricity by coupling a bimetallic strip to an electret-based converter: the bimetallic strip behaves as a thermal-to-mechanical power converter turning thermal gradients into mechanical oscillations that are finally converted into electricity with the electret. Output powers of 5.4uW were reached on a hot source at 70{\deg}C, and, contrary to the previous proofs of concept, the new devices presented in this paper do not require forced convection to work, making them compatible with standard conditions of thermal energy harvesting and environments such as hot pipes, pumps and more generally industrial equipment. Finally, ten energy harvesters have been parallelized and combined to a self-starting power management circuit made of a flyback converter to supply a battery-free Wireless Temperature Sensor Node, sending information every 100 seconds after its startup state.