Readout Range and Sensing Resolution Optimization of a Reader for Fully Passive Wireless Sensors

The zero-power sensor network is a platform that facilitates fully passive wireless sensing based on third-order intermodulation. This article describes the development, optimization, and evaluation of the reader for the interrogation of zero-power sensor devices. Detailed hardware architecture of the reader is included, along with the introduction of two different signal synthesis techniques for applications that require long readout range with lower resolution, or high resolution with shorter range. The reader is characterized with respect to the two critical limitations: 1) maximal readout distance due to the readers' own self-intermodulation and 2) sensor readout resolution based on the minimal synchronized intermediate frequency step. The readout range is extended by applying signal isolation strategies, and the system is evaluated with respect to the signal-to-noise ratio demonstrating an extension of the readout range to a maximum of 15 m. A new approach to signal synthesis is implemented, which enhances the readout resolution of a sensor capacitance from 2.2% to 0.3% resolution. The enhancement is demonstrated at a readout distance of 5 m.