User's Manual

MPR series User’s Manual: Draft version 0.95 11/4/04 page 21
RFID readers and tags operating in the microwave ISM band at 2.4-2.45 GHz are also widely used. The
2.4-2.45 GHz band is available for unlicensed operation in most jurisdictions worldwide. At this frequency
the wavelength is about 12 cm (5 inches). Very small tags can be used in the 2.45 GHz band, but because
of the consequent small antennas, the amount of power collected by a tag is reduced in comparison to UHF
tags. Passive 2.4 GHz tags have typical read ranges of around 1 to 3 meters (3 to 10 feet).
1.5.2 RFID vs. bar code
RFID tags and readers perform functions similar to those of bar codes and bar code scanners. How do they
differ? When should one use bar codes and when should RFID tags be employed? There are four key
distinctions to keep in mind:
• COST: bar codes can be printed on the surface of many existing packages at very low cost.
Separate bar-coded tags with adhesive backing are also inexpensive. Bar code scanners of various
types are widely available at modest cost, as is software to integrate bar code scanning into
standard business processes and enterprise planning. RFID (particularly at UHF and microwave
frequencies) is a relatively less widespread technology, and RFID tags are manufactured objects
containing an integrated circuit and antenna structure. RFID tags today cost significantly more
than bar codes, the exact value depending on type and quantity, though the cost of RFID tags is
falling rapidly as economies of scale are applied. Low-cost readers such as the MPR5000 are just
becoming available, but most readers are still expensive proprietary devices. When cost is the
only or a dominant issue, bar codes should be used.
• INFORMATION: Bar codes usually contain very limited information. Bar codes printed on
mass-produced packaging inevitably identify only the type of product and not the unique
individual package in hand. Bar codes containing unique identifying information such as serial
numbers can be used, but must be individually printed, raising cost, and separate codes are usually
needed to identify model number and the particular instance of the model. RFID tags generally
allow a 64-bit or 96-bit UID, the latter being more than adequate to identify manufacturer, model
or part number, and the specific physical instance of the model to which the tag is attached. More
advanced tags can contain additional user memory, which can be written to in the field, allowing
for versatile storage of information conveniently attached to an object when necessary. When
information storage capacity is a concern, RFID tags may be superior to bar codes.
• AUTOMATION: Bar codes require an optical line of sight between the reading device and the
code, and may also require that the code or reader be properly oriented. In many cases this means
that individual objects or tags must be handled by a human being in order to be reliable read.
UHF RFID tags can be read from a relatively long distance, and the path between the reader and
the tag can be visually obstructed (though certain obstructions will also affect radio frequency
devices, as will be discussed in more detail below). Bar codes are normally read one at a time,
particularly on randomly-oriented or stacked objects, whereas tens to hundreds of RFID tags can