User's Manual

MPR series User’s Manual: Draft version 0.95 11/4/04 page 19
6) If an MPR is properly seated in the PC Card port, and the driver is installed, one of the resident COM
Ports will say something like "MPR5000 Series (COM9)". In this example, the card is enumerating itself
as COM9.
1.5 RFID overview
1.5.1 RFID operating principles
Radio-frequency identification (RFID) is an auto-identification technology, similar in concept to other
common auto-identification technologies such as bar code scanners, magnetic strip readers, or magnetic ink
readers. Like other auto-ID techniques. RFID associates an identifying number with a physical object. In
RFID, the unique identifying number (UID or, as will be explained below, EPC) is incorporated in a
special system, an RFID transponder (often simply known as a tag). An RFID Interrogator (usually
known as a reader) is used to obtain the UID from the tag using electromagnetic waves. The tag is usually
attached to a physical object that is to be identified, such as a carton, a pallet, or a container filled with a
product.
In order to reduce the cost of the tag, most tags do not incorporate a battery or other source of power, but
instead operate using DC power derived from the radio frequency signal they receive from the reader. In
addition, low-cost tags do not incorporate a radio transmitter, but instead use varying reflection of the
received signal from the reader to communicate back to it. Such tags are known as passive tags. Since
passive tags are the most common type, the description below will assume their use. Variants are also
available: semi-active tags incorporate a battery to power the integrated circuit, but still use reflected
waves (backscattering) to communicate with the reader. Active tags incorporate both a battery and a radio
transmitter, and are much more costly than passive tags, but also more versatile.
RFID systems can operate at different radio frequencies. The frequency chosen has important effects on
the way tags and readers interact and on what applications are appropriate.
Low-frequency (LF) tags and readers typically operate at 125 or 134 KHz. This is a very low frequency,
with a wavelength of about 2.4 kilometers (1.5 miles). Low-frequency radiation is very effective at
penetrating water and living tissues, so that LF tags can be used to identify livestock. However, because
the tags and readers are very much smaller than a wavelength, they cannot radiate effectively, so LF readers
and tags depend on inductive coupling to operate. In effect, the reader and tag form the primary and
secondary windings of a transformer. The tag must be in close proximity to the reader antenna to be read;
read ranges are comparable to the size of the reader antenna, typically a few 10’s of cm (5-10 inches) for a
small reader antenna. Because the induced voltage per coil winding is also very small at these frequencies,
the tags are composed of many turns of wire, often wound around a ferrite core to increase coupling. Since