A Batteryless Six-Port RFID-Based Wireless Sensor Architecture for IoT Applications

In this article, a novel architecture for batteryless wireless sensors is proposed and demonstrated. The proposed architecture uses a six-port structure to integrate a UHF radio-frequency identification (RFID) chip with a resistive sensing element to enable the reading of environmental conditions wirelessly, without using a battery at the sensor node. The six-port structure divides an incoming RFID interrogator signal into an in-phase and quadrature branch and implements signal mixing without the use of a lossy or an active mixer. The amplitude and phase of the mixed signal are dependent on the value of the attached sensing element. By reading the phase of this signal at the reader, the value of the element can be easily determined using a noncoherent IQ demodulator. The design can easily integrate any type of resistive sensing element for parameters, such as temperature, humidity, and water level. A pin diode is used to control the amplitude and phase of the backscattered signal to demonstrate the performance. These values are successfully read at a distance of 2 m.