Robust Wireless Interrogation of Fully-Passive RLC Sensors

Abstract

Fully passive sensors (FPS) are widely used as a simple and inexpensive alternative of their active counterparts in many applications. However, measurement of FPSs relies on extremely bulky and complicated reader circuitry. In some cases the readout method depends on measurement distance. In this paper, we propose a readout technique based on a two-mode LC-oscillator formed with two coupled resonators, i.e., the FPS and the LC tank in the reader. We show that such a configuration can offer robust measurement of fully passive resistive and capacitive sensors provided that the system operates under strong coupling. We examine measurement errors due to non-idealities of the system (finite coil <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> and frequency mismatch) and provide design guidelines to ameliorate these unwanted effects. Although applied to sensing in this work, this analysis can be extended to wireless power transfer and impedance transformation.