Low-Cost Portable Readout System Design for Inductively Coupled Resonant Sensors

Abstract

Spiral coil-based inductor–capacitor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> ) resonant sensors have seen many applications in agriculture, healthcare, biomanufacturing, and consumer electronics. Traditional techniques to interrogate such sensors using vector network analyzers (VNAs) are expensive and often not portable, whereas custom readouts suffer from high cost, low range of usable interrogation distances, or low frequency range. This article proposes a new simple, low-cost, and portable readout design based on the technique of coherent demodulation. A complete theoretical analysis examining how the interrogation distance is related to other circuit parameters is presented. Finally, a complete readout system was implemented using printed circuit board technology and commercially available off-the-shelf components. The system operates between 1 and 100 MHz and the fabricated system consumes 1.26 W. Measurements show that the system operates reliably and repeatably with interrogation distances up to 5 cm.