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Tags
Historically, an RFID device that does not actively transmit to a reader was known as
a tag, while a device capable of actively transmission was known as a transponder
(TRANSmitter + resPONDER).Today the terminology has become interchangeable,
with RFID devices referred to variously as tags or transponders. For clarity, in this watch
report RFID devices that actively transmit to a reader will be termed active tags and
RFID devices that only reflect radio signals are termed passive tags. In general, active tags
use a battery to power the tag transmitter and receiver.The lifetime of such tags is direct-
ly related to battery life which is often in the range of three to 10 years)
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. Passive tags
generally obtain their power supply from the radio frequency signal generated by the
interrogation unit.The battery-free tag operation lasts the life of the product or system in
which it is embedded.
RFID tags can be divided into two further categories:
Chip-containing tags are fabricated as low-power integrated circuits suitable for interfac-
ing to external coils, or utilising `coil-on-chip' technology for data transfer and power
generation (passive mode).The basic components of a chip containing tag are:
- Digital circuitry (microprocessor, control logic, security logic);
- Memory (ROM, RAM, non­volatile EEPROM). ROM-based memory is used to
accommodate security data and the tag operating system instructions. RAM-based
memory is used to store temporary data during the processes of interrogation and
response.The non-volatile programmable memory may take various forms, with
EEPROM being typical. It is used to store the tag data and needs to be non-volatile
to ensure that the data is retained while the device is in power-saving mode;
- Analogue circuitry (data transfer, power supply);
- Tag antenna.This is the means through which the tag senses the interrogating field
and, where appropriate, the programming field.The antenna also serves as the means
of transmitting the tag response to interrogation.Tags will generally employ one of
the following types of antennae:
- Electric antenna.The antenna is of printed dipole
type and is used typically in the high frequency
range ­ 2.45 GHz;
- Inductive antenna.The antenna is made of etched
wire or copper/aluminium wire wound in a cir-
cular pattern on the tag.These coil antennae can
operate at 125­134 KHz as well as at 13.56
MHz;
- Capacitive antenna. In this case, a small amount of conductive carbon ink will
typically fulfil the duties of the antenna. It is applied to the paper substrate via
conventional printing methods.These antennas operate at low frequencies such
as 130 KHz;
- encapsulating material to protect the chip from harsh environments.
Smart Labels
and Smart Tags
75
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This longevity is appropriate in supply chain management, but not in the cultural heritage sector.
Inlay (Lucatron), Antenna with BiblioChipTM
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