A 960pW Co-Integrated-Antenna Wireless Energy Harvester for WiFi Backchannel Wireless Powering

Abstract

Leveraging the ubiquitous WiFi infrastructure to wirelessly power sensors can enable perpetually powered sensors for several monitoring and asset-tracking IoT applications. Small form factor is often desirable to ensure unobtrusive sensors. However, typical 2.4GHz WiFi output power of <+20dBm implies ∼−30dBm (μW) incident power (assuming free space path loss) at a ∼3m range. This presents a fundamental trade-off since small antenna area can further restrict the wireless power available to the rectifier/harvester. In addition, the time-varying nature of RF wireless powering implies that the energy-harvesting approach must accommodate cold start. In this work, we address the challenge of simultaneously achieving small form factor, μW-scale wireless input sensitivity, and operation at relatively high frequency (2.4GHz) by co-designing the antenna, rectifier, and DC-DC converter, achieving −36dBm input sensitivity for a 0.8V output in primary operating mode and −33dBm sensitivity from cold start with overall 1.97cm2 area (including antenna). In contrast to prior work, the proposed wireless harvesting approach optimally extracts energy from the wireless beacon even with < −30dBm (μW) incident power levels. The harvester consumes 960pW quiescent power while supporting cold start. The feasibility of the proposed approach is demonstrated by harvesting energy from a commercial WiFi node.