Abstract
The Internet of Things (IoT) infrastructure requires billions of devices that must ideally be self-powered. Ambient RF and thermal energy have great potential since they are both available continuously throughout the day. An RF harvester is a rectenna that is a combination of a receiving antenna and a rectifier. Thermal energy harvesters (TEH) are typically static type, with a fixed hot source at one end and a cold source at the other. Here, we present a transient type TEH that generates energy from diurnal cycle temperature fluctuations. Smart integration is achieved by designing the antenna to also act as the heatsink for the TEH. The antenna must be optimized while considering the electromagnetic radiation as well as the heat transfer performances. Thus, two simulators, Ansys HFSS and Ansys Fluent, were employed. The antenna operates at GSM900, GSM1800, and 3G bands simultaneously, with measured gains of 3.8, 4, and 5.3 dB, respectively, which have increased by ~3–4 dB (radiation efficiency doubled from ~40% to ~80%) compared to the flat antenna (with no heatsink fins). The TEH is in the form of a square box where two identical rectennas cover the four sides. Through RF field testing, ~250 mV is consistently collected at any instance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.25 {\mu }\text{W}$ </tex-math></inline-formula> for a 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> load). Without the heatsink antenna, the average power collected from the TEH is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$13.6 {\mu }\text{W}$ </tex-math></inline-formula> , which increases by 2.3 times when the heatsink antenna is integrated, highlighting the utility of this co-design and monolithic integration, which enhances both RF and thermal harvested powers.
Highlights
The Internet of Things (IoT) infrastructure requires billions of devices that must ideally be self-powered
The heatsink antenna in this work is designed for the multi-source ambient energy harvester, which consists of the RFEH and the Thermal energy harvesters (TEH)
We presented a dual-function triple-band (900 MHz, 100 MHz and 2100 MHz) heatsink antenna for smart integration of the RFEH and the TEH
Summary
The Internet of Things (IoT) is a fast-growing global infrastructure of physical objects connected through the Internet. A heatsink is used in [14] which is connected to the ground plane of the patch antenna, cooptimization of the heatsink has not been done since the heatsink is not part of the antenna’s radiating element This kind of concept where the two harvesters, multi-band RFEH and transient TEH, are co-designed by optimization of EM radiation and heat transfer performances through a single component, has never been done before. We alleviated the above-mentioned shortcomings by carefully designing a dual-purpose heatsink antenna, where the design has been optimized for both EM and thermal performances to demonstrate a novel monolithically integrated multi-source ambient energy harvester. Through this design optimization, both the RFEH as well as the TEH energy collection have been significantly enhanced.
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