A Battery-Less Non-Hybrid Six-Port RFID-Based Wireless Sensor Architecture for IoT Applications

Abstract

This paper introduces a novel battery-less wireless sensor architecture, which is based on the principle of direct frequency conversion. The proposed architecture uses a non-hybrid six-port structure to integrate a UHF RFID chip with sensing elements to create a sensor node. The RFID chip provides a unique identification to the sensor node and the sensing element enables the reading of environmental conditions. The non-hybrid six-port structure unequally divides an incoming RFID interrogator signal into an in-phase and quadrature branch. Using the novel unequal distribution in a six-port allows higher power being directed to the RFID chip to ensure a longer read range. The I and Q signals reflected by the RFID chip and the sensing element, respectively, are mixed without the use of a lossy or an active mixer. The mixed signal’s amplitude and phase are directly dependent on the values of the attached sensing element. To read the value of the sensing element wirelessly at a reader, an IQ demodulator is used, which determines the phase of the backscattered signal. As a result, various sensed parameters such as light intensity, voltage, or force may be read wirelessly without requiring a battery at the node. To demonstrate the performance, a pin diode is used as a sensing element to read voltages wirelessly at a distance of up to 2.45 m.