Physical Principles of RFID Systems - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 83

Reader antenna

x

Transponder antenna

Figure 4.23 Cross-section through reader and transponder antennas. The transponder antenna
is tilted at an angle ϑ in relation to the reader antenna

Reading range with
parallel transponder coil

Reading range with
vertical transponder coil

Transponder coil
cross-section

Transponder coil

Reader antenna
(cross-section)

Magnetic field line H

Figure 4.24 Interrogation zone of a reader at different alignments of the transponder coil

R — for example, exactly above and below the coil windings — exhibit a significantly
reduced read range. If the transponder itself is tilted through 90 ◦ a completely different
picture of the interrogation zone emerges (Figure 4.24, dotted line). Field lines that
run parallel to the R -plane of the reader coil now penetrate the transponder coil at an
angle ϑ =

0 ◦ and thus lead to an optimal range in this area.