Digital Electronics as RFID Tags: Impedance Estimation and Propagation Characterization at 26.5 GHz and 300 GHz

This article presents a circuit impedance model and results of propagation characterization at 26.5 GHz and 300 GHz for a new type of RFID tag that is based on digital electronics. This RFID tag leverages the backscatter radio generated from switching of transistors inside digital circuits, which does not need antennas or RF front-end circuits thereby further reducing the device's form factor. Moreover, the proposed RFID tag is compatible with a wide range of interrogating frequencies and can be implemented on existing electronics without additional cost. The proposed circuit impedance model explains the modulation mechanism of this new backscatter radio and provides an estimation of digital circuits' impedance using SPICE model parameters. Based on the proposed circuit impedance model, we develop a modified modulation loss factor to estimate the modulation loss resulting from the switching activity of the digital electronics. Furthermore, propagation characterization is conducted at 26.5 GHz and 300 GHz, where the shadowing gain for the carrier power and the backscattered power is characterized as 3.93 dB and 0.96 dB at 26.5 GHz, and 1.01 dB and 0.52 dB at 300 GHz, respectively, showing that the backscatter channel can provide a more reliable link that is resistant to the constructive and destructive interference from the multipaths as compared to the carrier channel.