A Compact Five-Band Omnidirectional RF Ambient Energy Harvesting System for IoT Applications

A compact multiband RF energy harvesting system designed for IoT applications is proposed, operating at 0.94 GHz, 1.8 GHz, 2.1 GHz, 2.6 GHz, and 3.5 GHz. The RF system consists of an omnidirectional modified monopole antenna, a compact multiband rectifier, and an energy management module. In order to achieve omnidirectional radiation patterns and compact size, the antenna current distribution is carefully controlled to avoid high-order modes of traditional monopoles. The overall size of the proposed rectenna is 0.24λ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i>×0.22λ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_L</i> (the wavelength at the lowest frequency), and the rectenna achieves the power conversion efficiency (PCE) of 19.2% at 0.94 GHz, 24% at 1.8 GHz, 24.5% at 2.1 GHz, 17.7% at 2.6 GHz, and 16.4% at 3.5 GHz with an incident power level of -20 dBm. In addition, the proposed RF system provides an 18.7 μW peaking output DC power in outdoor ambient environments and powers a commercial temperature sensor as a demonstration. The experimental results highlight that the proposed RF system achieves multiband operation and a stable omnidirectional radiation pattern, offering enhanced frequency coverage in a compact size and competitive efficiency. It has the potential for efficient ambient energy harvesting and powering IoT devices.