Fundamental Operating Principles - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 40

Procedure:
FDX:
Energy transfer:
downlink:
uplink:
HDX:
Energy transfer:
downlink:
uplink:
SEQ:
Energy transfer:
downlink:
uplink:
t
Figure 3.12 Representation of full duplex, half duplex and sequential systems over time. Data
transfer from the reader to the transponder is termed downlink, while data transfer from the
transponder to the reader is termed uplink
operation → pulsed system ). Data transfer from the transponder to the reader occurs
in the pauses between the power supply to the transponder. See Figure 3.12 for a
representation of full duplex, half duplex and sequential systems.
Unfortunately, the literature relating to RFID has not yet been able to agree a con-
sistent nomenclature for these system variants. Rather, there has been a confusing and
inconsistent classification of individual systems into full and half duplex procedures.
Thus pulsed systems are often termed half duplex systems — this is correct from the
point of view of data transfer — and all unpulsed systems are falsely classified as
full duplex systems. For this reason, in this topic pulsed systems — for differentiation
from other procedures, and unlike most RFID literature(!) — are termed sequential
systems (SEQ).
3.2.1 Inductive coupling
3.2.1.1 Power supply topassive transponders
An inductively coupled transponder comprises an electronic data-carrying device, usu-
ally a single microchip, and a large area coil that functions as an antenna.
Inductively coupled transponders are almost always operated passively. This means
that all the energy needed for the operation of the microchip has to be provided by
the reader (Figure 3.13). For this purpose, the reader's antenna coil generates a strong,
high frequency electromagnetic field, which penetrates the cross-section of the coil
area and the area around the coil. Because the wavelength of the frequency range used
( < 135 kHz: 2400 m, 13.56 MHz: 22.1 m) is several times greater than the distance
between the reader's antenna and the transponder, the electromagnetic field may be
treated as a simple magnetic alternating field with regard to the distance between
transponder and antenna (see Section 4.2.1.1 for further details).