Electromagnetic modeling strategy supporting the fabrication of inkjet-printed chipless RFID sensors

Inkjet-printing fabrication techniques can be used for the manufacturing process of chipless radio frequency identification (RFID) sensors. With respect to traditional silicon-based fabrication, flexible electronics induce the possibility to experiment with new substrates and conductive materials. With the development of high-conductive nano-inks, the low sintering temperature required to process them results in compatibility with a large variety of substrates. However, the requirements for the conductivity of the metalized printed patterns are particularly stringent for applications where the working frequency is high, like in the case of common chipless RFID tags working in the frequency range of 3–10 GHz. In chipless RFID systems, the higher the conductivity of the conductive parts, the better the signal response of the tag. However, in printed chipless RFIDs, the conductivity can only give a partial indication of the goodness of the tag. The tag response is dependent on the sheet resistance, which is not only related to the conductivity of the ink, but also to the thickness of the printed pattern. Therefore, if a sufficiently high-conductive nano-ink is selected, the signal efficiency of the printed tag can be further improved by making an evaluation based on the thickness of the patterns. The objective of this study is to propose a strategy for evaluating the signal response efficiency in inkjet-printed chipless tags by means of a first quantification of the average thickness of the printed layer, which is used to feed a finite-element method (FEM) simulation model to give the manufacturer an idea of the optimal number of layers to be printed to have a strong signal response.