Time–temperature excursion monitoring using chipless RFID tags and organic oils.

A food-safe cost-effective time-temperature indicator (TTI) sensor for cold chain disruption detection at the item level is proposed. The sensor is based on the radar cross section (RCS) readout from a chipless square split ring resonator (SSRR) exposed to organic oils with customizable melting temperatures and defined flow paths. The inclusion of several oil mixtures into the same sensor allows for the determination of a range of configurable temperatures/times. The same sensor has two modes of operation: one for threshold detection and another for gradual change detection. These modes depend on the orientation of the sensor on the packaging and the influence of gravity. The provided design, along with a convenient signal conditioning strategy, accurately detects four time exposure thresholds in the 7-30 min range when placed in upright position at ambient temperature, while it exhibits linear response between 10 and 30 min just by turning it by 90 degrees. Prospective future directions are also discussed

SDR-based monostatic Chipless RFID Reader with Vector Background Subtraction Capabilities

This article presents a high-performance frequency-domain chipless RFID reader with vector background subtraction capabilities, implemented in a software-defined radio (SDR) for the first time. The proposed reader is low-cost, compact size, and versatile. It is implemented in a USRP N210 paired to a modified CBX-40 daughterboard, enabling magnitude and phase data acquisition in a monostatic (one antenna) set up. The reader can perform a vector background subtraction operation between two complex measurements (with and without a chipless tag) to suppress the self-interference (SI) that hinders the response of the tag and provide 40 dB of dynamic range. To demonstrate the performance of the reader, the spectral signatures of three frequency-coded (FC) tags with four resonant frequencies are captured over the 1.5-4-GHz band scanned with 10-MHz resolution in 251 ms, obtaining comparable measurements to those of an expensive laboratory vector network analyzer (VNA) from 20 to 40 cm. The detected resonant frequency offset between both devices is Delta f(r) <= 4.18% . It is also demonstrated that the proposed reader can track a resonant frequency shift and therefore be used in real-time sensing applications