Differentiation Features of RFID Systems - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 12

of the silicon chip. In practice, this means redesigning the chip layout, with all the
associated expense.
The use of a microprocessor improves upon this situation considerably. An operating
system for the management of application data is incorporated into the processor during
manufacture using a mask. Changes are thus cheaper to implement and, in addition,
the software can be specifically adapted to perform very different applications.
In the context of contactless smart cards, writable data carriers with a state machine
are also known as 'memory cards', to distinguish them from 'processor cards'.
In this context, we should also mention transponders that can store data by utilis-
ing physical effects. This includes the read-only surface wave transponder and 1-bit
transponders that can usually be deactivated (set to 0), but can rarely be reactivated
(set to 1).
One very important feature of RFID systems is the power supply to the transpon-
der. Passive transponders do not have their own power supply, and therefore all power
required for the operation of a passive transponder must be drawn from the (electri-
cal/magnetic) field of the reader. Conversely, active transponders incorporate a battery,
which supplies all or part of the power for the operation of a microchip.
One of the most important characteristics of RFID systems is the operating frequency
and the resulting range of the system. The operating frequency of an RFID system is the
frequency at which the reader transmits. The transmission frequency of the transponder
is disregarded. In most cases it is the same as the transmission frequency of the reader
(load modulation, backscatter). However, the transponder's 'transmitting power' may
be set several powers of ten lower than that of the reader.
The different transmission frequencies are classified into the three basic ranges, LF
(low frequency, 30 - 300 kHz), HF (high frequency)/RF radio frequency (3 - 30 MHz)
and UHF (ultra high frequency, 300 MHz - 3 GHz)/microwave ( > 3 GHz). A further
subdivision of RFID systems according to range allows us to differentiate between
close-coupling (0 - 1 cm), remote-coupling (0 - 1 m), and long-range ( > 1m) systems.
The different procedures for sending data from the transponder back to the reader
can be classified into three groups: (i) the use of reflection or backscatter (the frequency
of the reflected wave corresponds with the transmission frequency of the reader →
frequency ratio 1:1) or (ii) load modulation (the reader's field is influenced by the
transponder → frequency ratio 1:1), and (iii) the use of subharmonics (1 /n fold) and
the generation of harmonic waves ( n -fold) in the transponder.
2.2 Transponder Construction Formats
2.2.1 Disks and coins
The most common construction format is the so-called disk (coin), a transponder
in a round (ABS) injection moulded housing, with a diameter ranging from a few
millimetres to 10 cm (Figure 2.2). There is usually a hole for a fastening screw in the
centre. As an alternative to (ABS) injection moulding, polystyrol or even epoxy resin
may be used to achieve a wider operating temperature range.