Characteristics of RFID C-slot tag antenna on a coated metallic cylindrical surface

Abstract

Recently, the ultra-high frequency (UHF) radio frequency identification (RFID) is increasingly used for the automatic identification and tracking. The UHF RFID system consists of the RFID reader and the RFID tag. The RFID reader generates the radio wave energy into the air via the reader antenna [1]–[2]. The tag usually consists of the tag antenna element and the micro chip which includes the product information. The tag antenna is generally made from copper strip with a meander line shape (folded dipole concept). In order to activate the tag micro chip, the impedance of the tag antenna should be a complex conjugate of the micro chip impedance to obtain enough operating power for the chip [3]. The RFID tag antenna converts the RF energy from the RFID reader into the chip. The chip can send a signal back (product data) to the RFID reader via scattered fields, respectively. The RFID tag is generally attached on the surface of the product packet such as paper parcel, plastic box, metallic surface of the product, etc. The radiation pattern and impedance of the RFID tag are distorted due to the near field scattered from metallic objects nearby. Especially, the RFID tag attaches to the metallic surface of the product such the tank contained gas, gasoline, oil tank, etc. Typically, the UHF RFID tag antenna behaves like the electric source (dipole or meander line shapes). Therefore, the EM energy in the shadow zone (behind the product) is dramatically decreased when the RFID tag is directly attached on the curved metallic product due to the electric field parallel to the metallic surface. Moreover, the tank of a gas, gasoline and oil are usually coated with some color layers. The material layer will affect the radiation pattern of the tag. Importantly, the prediction of the EM field radiated from the source on a curved surface is very important in the RFID tag antenna design procedure. In order to avoid the degradation of the electric source from the impact of the metallic product, it is of interest to consider the magnetic source type such as slot shape attached on the metallic curved surface. Therefore, the slot type antenna is proposed to use as a tag antenna instead of the conventional dipole or meander line shapes.