An RFID Tag Antenna Tolerant to Mounting on Materials

This paper presents a novel UHF RFID tag antenna for mass-retailed products. The tag is realized on low-cost material. The antenna is composed of two elements: a planar dipole-based antenna, matched with a small inductive coil. In particular, it is able to work when directly mounted on different materials. When the permittivity or the thickness of the material on which it is mounted changes, the antenna´s impedance varies around a fixed impedance on the Smith chart. This impedance is close to the conjugate of the RFID chip´s input impedance. The different mounting materials tested were cardboard, a paper block, plastic, wood, a bottle of tap water, and a glass bottle. The measurement results indicated a maximum range of eight meters for materials with a low permittivity, and a maximum range close to two meters for denser materials or materials with a higher permittivity.