Performance analysis of polymer based antenna-coils for RFID

Transponder-labels, -tags or -modules of inductively coupled RFID (Radio Frequency Identification)-systems commonly consist of a substrate with an appropriate transponder-chip or transponder-module mounted on top. The antenna coil is structured on this substrate, usually made of PET, PVC or polyimide and usually consists of a wound wire or etched copper or aluminium structures. As a low cost alternative, conductive polymeric thick film pastes can be used for the production of antenna coils for inductively coupled transponders. These pastes are applied by screen printing or dispensing. In mass production the consequence is a reduction of material costs and processing time. Most popular fillers of the conductive polymer pastes are silver flakes which get connected during the curing process. The conductivities of these compounds are lower in comparison with copper or aluminium. Therefore, the transponder coils made of conductive polymer pastes have substantially higher ohmic losses which influence the functionality of RFID transponders. In this paper, the minimum operating magnetic field strength and powering range of the transponder is considered in detail. A selected reference design with the size of a smart card inlay (47 /spl times/ 74 mm/sup 2/) is used.