Optimizing Processes with RFID and Auto ID, 2009
Optimizing Processes with RFID and Auto ID, 2009
Optimizing Processes with RFID and Auto ID, 2009
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2 <strong>RF<strong>ID</strong></strong> technology<br />
2.3 Classification of <strong>RF<strong>ID</strong></strong> systems<br />
2.3.1 Passive systems<br />
For passive <strong>RF<strong>ID</strong></strong> systems, the transponder does not have its own energy<br />
source: energy is fed to most systems externally. Normally this<br />
takes place via high-frequency transmission, in rare cases also via<br />
light, sound, pressure, temperature, or other mechanisms. Special<br />
models of passive systems require no energy at all, in which they are<br />
simply based on physical effects.<br />
While the development of a high-performance passive transponder<br />
requires quite some effort, this principle provides a number of advantages:<br />
• It is easy to produce the transponder (only a chip <strong>and</strong> an antenna<br />
are required)<br />
• They have a virtually unrestricted life cycle <strong>and</strong> are service-free<br />
(no battery)<br />
• They can be extremely miniaturized<br />
• Very low costs are possible (to the order of < 0.10 euros)<br />
Systems <strong>with</strong> inductive coupling in the LF/HF range<br />
The oldest <strong>RF<strong>ID</strong></strong> systems are based on energy transfer via a high-frequency<br />
magnetic field <strong>with</strong> inductive coupling, i.e. using the transformation<br />
principle. Fig. 2.6 shows the principle: The transmitter in<br />
the reading device drives current through the antenna coil, thereby<br />
creating a high-frequency magnetic field. Alternating voltage is produced<br />
in the transponder coil by induction <strong>and</strong> is available for operating<br />
the transponder chip after rectification. Data is transferred to<br />
the reader via load modulation. At the same time, a resistive load is<br />
switched to the antenna coil in the transponder according to the modulation<br />
of data. This results in a voltage drop at the reader’s transmission<br />
coil – albeit minimal – can be detected <strong>and</strong> analyzed in the reader<br />
electronics (receiver).<br />
The frequencies that are usually used are 125 kHz (LF) or 13.56 MHz<br />
(HF), as these b<strong>and</strong>s are especially attractive combined <strong>with</strong> the high<br />
permissible output power <strong>and</strong> they can be used worldwide. Read<br />
ranges in excess of one meter can be accomplished. However, at the<br />
same time large antenna coils are required (e.g. 60 × 80 cm), which<br />
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