Title: Troubleshooting RFID Tags Problems with Metallic Objects Using Metamaterials
Abstract: Radiofrequency Identification (RFID) is a technology that is being rapidly developed and that uses radiofrequency (RF) signals for the automatic identification of objects or persons. Although the first article regarding modulated electromagnetic backscattering (basic principle of passive RFID) was published in 1948 (Stockman, 1948) it has been a long way to progress for reaching today levels (Rao, 1999; Finkenzeller, 2004; Pozar, 2004). Nowadays RFID finds many applications in logistics, supply chain management, access control, electronic toll systems, targets identification, vehicle security, animals tracking and patients’ identification in hospitals. An RFID system is composed of a reader, a reader antenna (usually circularly polarized patch antenna), RFID ‘tags’ or transponders and a middleware or subsystem of data processing. A passive RFID tag consists of an antenna and an application specific integrated circuit (ASIC) chip. IC chips have complex input impedances, and their impedances vary with frequency. A key point for tag antenna design is that it must be conjugately matched with the desired IC chip for the maximum power transfer (Gevi, 2004; Rao et al, 2005). The different types of RFID systems are distinguished by two major characteristics: the power source of the tag and the frequency of operation. With regards to the power source of the tag, they can either be active (powered by battery), passive (powered by the reader field) or semi-passive (battery assisted backscatter). According to the frequency of operation the RFID systems are generally distinguished into four frequency ranges; i.e., low frequency (LF) (125-134.2 kHz), high frequency (HF) (13.56 MHz), ultra high frequency (UHF) (433, 860-960 MHz) and microwave frequency (2.45, 5.8 GHz). In addition, the standards of the UHF RFID are different for each country: 866-869 MHz in Europe, 902-928 MHz in America and 950-956 MHz in Asia. The communication frequencies used depends to a large extent on the application. Regulations are imposed by most countries (grouped into 3 Regions: US, Europe and Asia) to control emissions and prevent interference with other Industrial, Scientific and Medical equipment (ISM). The higher the frequency band the faster the speed of tag reading and also the larger the information storage capacity. This is the reason why UHF RFID has gained popularity in many applications and it can be expected that the same will happen in the near future with microwave RFID. In a typical application tags are attached to objects (or persons). Each tag has a certain amount of internal memory (EEPROM) in the chip in which it stores information about the