Physical Principles of RFID Systems - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 131

1

X T = Im (4.98)

1
R L +

1
Z mod

jωC 2 +

4.2.6.2 Power supplyof passive transponders

A passive transponder does not have its own power supply from an internal voltage
source, such as a battery or solar cell. If the transponder is within range of the reader
a voltage U 0 is induced in the transponder antenna by the field strength E that occurs
at distance r . Part of this voltage is available at the terminals of the antenna as voltage
U T . Only this voltage U T is rectified and is available to the transponder as supply
voltage (rectenna) (Jurianto and Chia, n.d. a, b).
In the case of power matching between the radiation resistor R r and the input
impedance Z T of the transponder, power P 2 = P e can be derived from equation (4.87).
Figure 4.76 shows the power available in RFID systems at different distances at the

30

20

10

0

− 10

20

−

− 30

0.1 1 10

Distance r (m)

Pe(868 MHz, 0.5 W ERP (0.82 W EIRP))
Pe(2.45 GHz, 0.5 W EIRP)
Pe(915 MHz, 0.5 W EIRP)

Figure 4.76 1mW ) available for the operation of the

transponder, in the case of power matching at the distance r , using a dipole antenna at the
transponder

The maximum power P e ( 0dBm =