Enhancing Battery-Free Sensor Nodes: Integrating Passive Beamforming with Frequency Division Duplexing

This paper presents a novel node design for facilitating uplink communication and Radio Frequency (RF) power transfer in battery-free Internet of Things (IoT) devices. The proposed design utilizes a frequency-division duplex (FDD) approach, enabling sensor nodes to continuously receive wireless power in the downlink at a frequency of 2.4 GHz. Forward-and reverse-bias rectifiers were designed to provide differential outputs for the wireless power transfer (WPT) pathway. The two rectifiers are capable of harvesting
$214 \mu W$
from an incoming signal with a power level of −5 dBm. To enhance the RF communication range for backscattering uplinks, a bandpass filter was designed to create a phase shift of 0-180° over the frequency range of 2.472-2.625 GHz, allowing the uplink beam to be steered toward the base station.