Analysis of a polycarbonate RFID tag for blood chain tracking

In this paper we describe an antenna especially designed for a RFID passive tag working at UHF (867 MHz), for healthcare applications. In particular for the transfusional medicine and the blood supply chain. The tag has to be able to work placed on the top of a blood bag, while the bag is full of blood, and the antenna has been designed with this goal in mind. Therefore we require an antenna able to work close to a (relatively large amount of) lossy medium with high permittivity. Moreover, the bag shape is curved but its shape cannot be predicted exactly, so that the antenna must retain its behavior for a large set of different environments. In order to comply with all those requirements, a printed slot antenna built with a exible substrate has been selected, so that the whole tag can be exible too. The first step was the optimization of the working parameters of the antenna while placed on a perfect planar surface (i.e., assuming the blood bag to be a parallelepiped). Since the actual bag shape is not known, this choice allows to take into account the lossy material, but using a simple geometry. The antenna has been optimized to get the maximum reading distance. Then we consider the effects of a real blood bag (i.e., a curved one), filled with blood, on the antenna behavior. We consider a bag with a transverse section bounded by two arc of circles (with a radius quite larger than the bag size). Since we found a reasonable agreement with the planar antenna we can assume that the antenna behavior is quite insensitive to the bag shape. A robustness analysis, respect to the bag curvature radius, has been performed, too, to assess the antenna use in real environments.