Design of a Label-Typed UHF RFID Tag Antenna for Metallic Objects

In this letter, we present a label-typed UHF RFID tag antenna for metallic objects. The antenna is fabricated on a thin flexible PET substrate with a thickness of 0.07 mm. In order to achieve good performance on metallic objects as well as in free space, the design of the proposed antenna is mainly considered for two factors; gain and impedance matching. To increase the gain of the proposed antenna, we place an additional loop, which has a line width of 2.5 mm and surrounds the original meandered folded dipole antenna. Also, the design is achieved by matching in frequency region where minimum impedance variation occurs on metallic objects, so that the change of the input impedance is small compared to free space case. The experimental results show that the maximum reading range of the proposed antenna is about 7.5 m in free space, and 3 m for 1-mm separation from the metallic surface. Furthermore, reading range has been compared among commercial and the proposed label-typed RFID tags, revealing about 3 times longer reading range than Alien M-tag when it is placed 1 mm above a metal surface.