Those induced voltages are represented by the voltage drop in the inductor L.
The parameters Rl and Rr are loss and radiation resistances, respectively. Figure 4.1 is an
example of a magnetic ?¬?eld-sensitive label antenna.
In Figure 4.12, the source voltage is the voltage developed across the self-capacitance of
the antenna when it is open-circuited, as a result of the current injected into it, when it is
short-circuited, by the displacement current density of the electric ?¬?eld in which the
antenna is immersed. The parameters Rl and Rr are loss and radiation resistances, respectively.
Figure 4.4 is an example of an electric ?¬?eld-sensitive label antenna.
Calculating the parameters of the magnetic ?¬?eld-sensitive antenna is straightforward,
the relevant formulae being obvious and outlined in many elementary electromagnetic text
books (Stutzman and Thiele, 1988; Cheng, 1989; Balanis, 1996; Kraus and Marhefka, 2002).
For the electric ?¬?eld antennas, determination of the relevant parameters is sometimes not
so simple, as electrostatic ?¬?eld solutions for the relevant geometries are not readily
available. Therefore, empirical results or numerical modeling are more commonly
employed for useful shapes.
Thus far, the nature of RFID ICs and the nature of the impedance of label antennas have
been considered. Clearly, matching a label??™s input impedance to a label antenna??™s impedance
is vital.
Pages:
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162