Field Conditions of Interrogation Zone in Anticollision Radio Frequency Identification Systems with Inductive Coupling

Abstract

Passive Radio Frequency IDentification (RFID) systems with inductive coupling are the most widespread nowadays (Yan et al., 2008; Wolfram et al., 2008). These systems operate thanks to direct inductive coupling between antenna units of the communication system which consist of Read/Write Device (RWD) and electronic identifier (called a tag or transponder). The communication in transmitter – receiver set is carried out in two ways. In the first case, only one object with electronic tag can be placed in the correct working area called interrogation zone of the RFID system. This arrangement is called a single identification system or also single system. In the second case of multiple identification system, called anticollision system, the communication process is carried out simultaneously with multiple RFID tags. In this process, the algorithms of multi-access to the radio channel are used, what provides an effective way to distinguish simultaneously between multiple objects (Yeh et al., 2009; Dobkin & Wandinger, 2005). It should be note that synthesis procedure of interrogation zone includes the simultaneous analysis of electromagnetic field (presented in this paper), communication protocols and electric aspects of operation conditions in the process of system efficiency identification. The typical applications of anticollision RFID systems are concentrated on different economic and public activity in industry, commerce, science, medicine and others (Harrison, 2009, Donaljdson, 2009; Steden, 2005; Wyld, 2009 and 2005; Ahlstrom, 2005). When determining the interrogation zone for the given automatic identification process, it is necessary to define a maximum working distance of the RFID system. This parameter determines the distance between the specified point of the RWD’s and the midpoint of the tag’s antenna loop. It is very important because the magnetic field generated around the RWD’s antenna loop is not only medium of information signal but also provides passive tags with energy. The proper supply is essential to carry out operations of recording and reading information which is stored in the transponder’s semiconductor memory (Fig. 1). The basic parameter, which determines the working area and characterizes the maximum working distance of the RFID system, is Hmin minimum value of magnetic field strength or more often used Bmin minimum value of magnetic induction at which the correct data transmission between the RWD and the tag takes place (Jankowski-M. & Kalita, 2008). The minimum value of magnetic induction required in the process of writing data to the