Miniaturized and battery-free temperature and humidity sensor for smart pharmaceutical packaging

Temperature and humidity levels inside pharmaceutical packaging can significantly affect the shelf life of the enclosed medications. The RFID technology in the UHF band is promising to address this issue as it permits to wirelessly monitor the inner environment at the item level. This work presents the design and experimental characterization of a miniaturized battery-less RFID sensor, able to simultaneously measure temperature and humidity. The proposed sensor includes a helical antenna and is compatible with the insertion into a capsule, similar to common drugs. A first prototype of the miniaturized sensor was realized and tested in terms of both communication and sensing performance. Despite variable boundary conditions, a reading distance greater than 40 cm was demonstrated. A realistic readability analysis under uncontrolled conditions estimated a probability of 65% to read the sensor from more than 20 cm. Furthermore, the humidity sensor performance was extensively characterized in a climate chamber through several tests, resulting in an accuracy of ±5% in the RH range 40-80% that is compliant with the requirements of several pharma applications.