Abstract
The main objective of this paper is to model environmental effects on the read range of radio frequency identification (RFID) system. In order to evaluate the performance of an RFID system in real applications, electric and magnetic radiated fields (E or H) of a circular loop antenna should be derived. In this investigation, three cases are considered, free space model, the case that there is a perfect parallel or non-parallel surface, and finally the general model considering non-parallel non-perfect conductive/dielectric surface. In general model, besides the method of images, a new approach is proposed which model non-parallel main and image CLAs as two equivalent vertical and horizontal loops. According to this model, the radiated fields and also induced voltage are functions of the current intensity, wavenumber, reflection coefficient of the surface, both angle and the distance between antenna and surface, and the distance between the RFID tag and reader. To compare the analytical values extracted from E and B formulas of proposed model and associated results derived from computational methods, MATLAB and FEKO outputs are compared in the same conditions.
Using this new proposed model, the performance of an RFID system operating in metal environment and also effective read range can be evaluated. It is also able to show the environmental effects on radiated fields of reader as well as tag's antenna. In addition, the interference effect of different RFIDs can be easily modeled by these new formulas.