Posts Tagged UHF
Most RFID systems operate in the radio spectrum’s unlicensed portion, where regulations
govern power output for readers. This characteristic, combined with physical
limitations, limits the reading range for passive tags, which are powered by the radio
signal that reads them. Some passive tags operate in the low-frequency band
(125–134.2 KHz), such as proximity cards and implantable glass-covered transponders.
These devices have a typical read-range of less than two feet. Passive tags operating
in the UHF band (915MHz in North America) can typically be read at 10 meters or more
in free space, but the range diminishes when tags are attached to everyday objects.
Also, human beings absorb UHF radiation and disrupt the communication between passive
tags and readers. Active tags are battery-equipped and have longer ranges, but they
are also significantly more expensive and have a limited shelf life. Although
different RFID systems have been in use for years, popular accounts of RFID
technology typically refer to the Electronic Product Code. The EPC was developed by
the Auto-ID Center in collaboration with the Massachusetts Institute of Technology
and other universities, and is now managed by EPC global. The center’s goal was to
make RFID tags as simple as possible, with the aim of driving the chips’ price
below five cents. Working with industry partners such as Procter & Gamble, the
Auto-ID Center developed an RFID system that many in the industry hope will
replace the ubiquitous Universal Product Code bar codes present on many
Figure 1. An abstract view of the EPC Network
Each EPC tag has a serial number of at least 96 bits divided into sections
identifying the tagged item’s manufacturer, product, version, and serial number.
In addition to being an identification code, this number can serve as a pointer
to a database entry for the tag that contains a detailed transactional history
for the associated object. For example, EPCglobal is in the process of
elaborating a universally accessible Object Name Service (ONS) database; this
service will provide information about tagged objects. Unlike today’s
proprietary and mutually incompatible RFID systems, EPC is being promoted as a
single, open worldwide RFID standard that will dramatically lower costs and
increase adoption. Figure 1 shows an abstract view of the EPC Network. EPC
tags contain several thousand transistors and a small antenna. Given the small
size, the most inexpensive emerging generations of these tags will likely have
only between 250 and 1,000 gates available for security features. 9 As a result,
they won’t implement encryption algorithms or other traditional security
features. EPCglobal has recently completed its Class-1 Generation-2 EPC tag
standard, which is likely to see widespread deployment in the coming years.
In this standard, tags contain a kill self destruct feature. When an EPC tag
successfully receives the kill command, it renders itself permanently inoperable.
To prevent inadvertent or malicious disablement of tags, the EPC-standard kill
command requires readers to use a tag-specific, 32-bit password.
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