Characteristics of passive UHF RFID tags on metal slabs

The characterization of passive UHF radio frequency identification (RFID) tags is a field that has previously garnered a tremendous amount of interest. Passive UHF RFID tags operate at the Industrial, Science, and Medicine (ISM) allowed band of 902 MHz to 928 MHz in the United States, and is limited to 4W of effective isotropic radiated power (EIRP) by the Federal Communications Commission (FCC). The main characteristics of the typical passive UHF RFID tag is the gain of the tag throughout the frequency range of operation, the transmission and reflection coefficients, the application specific integrated circuit (ASIC), and the mechanical or physical limitations caused by the construction of the tag itself. From a broader perspective, the performance as a whole of the typical tag is dependent on the frequencies, number of tags in the field, obstacles in the environment, humidity, temperature, radio frequency (RF) interference (noise), tag to reader separation, polarization mismatches, effective radar cross-section (RCS), and reader identification algorithm [1]. Similarly, the factors that are used to describe the governing effect of the typical tag communication rate (or read rate) are the tag antenna design, as well as the tag design and implementation [1, 2]. Here, the tag antenna is typically derived by responses due to the antenna size, polarization, and directionality [1]. The free space characteristics of passive UHF RFID tags are well known [1-5]. However, their operation on metal plates or slabs has not previously produced significant research. Passive UHF RFID tags are known to be less operable around metallic slabs due to the detuning of the tag frequency response, as well as the power of the tag reply.