Screen printed RFID antennas on low cost flexible substrates

Recently, more and more studies are carried out in the field of printed RFID tags. It is connected with rapid development of new electronic technology, i.e. printed electronics which utilizes printing techniques, like screen printing, inkjet, flexography or gravure, for production of electronic components. This method is on one hand environmentally friendly because it allows eliminating wastes emerging during etching process used commonly in electronics. On the other hand, components can be printed on low cost flexible substrates, like foil or paper. These two factors cause that such products are cheap and can be competitive with their equivalents used currently. In this study, investigations of RFID tag antennas working in UHF frequency range made with screen printing technique are described. Conductive polymer pastes containing silver nanopowder, silver flakes or carbon nanotubes were used for antenna fabrication. Each of them was deposited on foil and paper. Properties of printed antennas were investigated by return loss measurements performed in the frequency range 0.5 ÷ 1.5 GHz. Achieved results were compared with simulation carried out in CST Microwave Studio. Antenna surface profile was checked using optical profilometer or metallographic microscope. Its mechanical tests were also conducted. The obtained results showed that the best candidate for antenna printing on flexible substrate was the paste with silver nanopowder because it combined high conductivity and high mechanical durability.