Balluff BIS U Basishandbuch Seite 39

BIS U Basic Manual
3
Basic Physical Information
3.2 Physics of the Due to their shape and size, the antennas on the data carriers are capable of reflecting as well as
Transponder
absorbing electromagnetic waves transmitted by the identification system BIS U.
The passive transponder (data carrier) does not have its own power supply (e.g. battery) and
must therefore draw the energy it needs to operate from the electromagnetic field. A portion of
the RF voltage present at the antenna connections is commutated and used to supply the IC.
However, the much larger portion of dispersed power is reflected. A time-controlled change in
the reflection characteristics of the dipole antenna generates a backscattered electromagnetic
wave with a modulated amplitude (intensity). The wave is detected by the antenna on the
processor unit and then demodulated.
This type of information exchange between the partners of an identification system is known as
electromagnetic backscatter.
Figure 3:
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Processor unit Transmitting/receiving antenna
Directional
coupler
Emitter/receiver
Schematic diagram of backscatter
Data carriers
Dipole antenna transponder
Emitted
wave
Reflected wave
Free space wave Z
0
Load resistance
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