Miniaturized Battery-Less RFID Patch for Temperature and Humidity Monitoring Inside Alu/PVC Pharmaceutical Blister

Aluminum-polyvinyl chloride (Alu/PVC) blister packs are the most common packaging solution for solid oral pharmaceuticals due to their good barrier properties and low cost. However, this format may not always guarantee adequate protection of the drug against environmental conditions, such as temperature (T) and relative humidity (RH), which directly impact the stability and efficacy of pharmaceuticals. In this scenario, the capability to monitor these parameters directly at the level of each individual cavity becomes essential for early detection of microenvironmental alterations and for preserving drug quality. This work presents a miniaturized passive Ultra-High Frequency (UHF) Radiofrequency Identification (RFID) sensor for T/RH monitoring inside individual cavities of Alu/PVC blister packs. The device, a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$14 \times 9 \times 3 ~\text{mm}^{3}$</tex> patch antenna, is designed to operate in direct contact with the aluminum foil and optimized to maximize the realized gain, reaching -15.3 dB at 868 MHz. This enables a theoretical read range of 1.2 m. A first prototype was fabricated and experimentally characterized in terms of communication performance. A long-lasting measurement has validated the device's capability to track the T/RH evolution of the internal microenvironment over prolonged monitoring sessions, confirming its suitability for advanced monitoring in pharmaceutical packaging applications.