Design and modeling of embedded 13.56 MHz RFID antennas

Radio frequency identification (RFID) tags have become quite widespread in many services. In these applications, data are transferred, contact-free, to a local querying system (reader or interrogator) from a remote transponder (tag) which includes an antenna and a microchip transmitter. A suitable antenna for these tags must have low cost, low profile and, especially, small size, whereas the bandwidth requirement (few kilohertz) is less critical. There has been much interest in the 13.56 MHz frequency in the last decade, more than in the VLF, LF and UHF bands. The use of the 13.56 MHz frequency has proven to be advantageous over these other bands. With the aid of IE3D software, which is based on the method of moments (MoM), a single-layer 13.56 MHz RFID tag has been designed and modeled, and a double-layer design has been developed to reduce size. The antenna challenges, which include port matching, efficiency, and size at 13.56 MHz, and the performance advantages over the UHF band are addressed.