Investigation of RFID tag antennas printed on flexible substrates using two types of conductive pastes

The most important obstacle of becoming widespread for RFID tags is its cost which should be decreased after bringing in market its printed equivalents. In this study, screen-printed RFID tag antennas were investigated. It was used a semi-automatic screen printer and polyester screen selected for the tested pastes. RFID tags were printed on flexible substrate (polyimide foil) using silver and graphite pastes and then cured at 120°C for 15 min and at 150°C for 30 min, relatively. Printed antennas work in HF or UHF frequency range. To characterize the printed patterns its resistance using a 2-point probe method was measured. Moreover, the measurement of antennas thickness was performed. In this order, two methods were evaluated: optical profilometer and cross-sections. Apart from the measurements of antenna thickness the profilometer made possible to determine a pattern's XY profile. The profiles were compared in order to verify differences in printing quality of tested patterns. Furthermore, the printed RFID antennas were characterized using a network analyzer. It allows measuring the reflection coefficient S
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, so to verify if the printed antennas work on the proper frequency.