
68 CHAPTER THREE
absence of a tag; they cannot identify individual items. On the other hand, some tags may
store kilobytes of data. Larger capacities usually require active tags, and even among pas-
sive tags, larger memory capacity directly increases the cost per tag.
This section examines storage and processing capacities for 1-bit EAS tags, surface acoustic
wave (SAW) tags, and state machines and microprocessors.
One-Bit EAS Tags
Electronic Article Surveillance (EAS) tags are typically used to prevent theft. Rented vid-
eos and library books typically have EAS tags attached in the form of thin strips or labels.
Stores often tag clothing with EAS tags inside hard plastic clips or buttons that are difficult
to remove without the correct tool. Some EAS tags are even designed to damage an item if
removed incorrectly and so discourage theft.
EAS tags are often called “1-bit” tags because they are capable of communicating 1 bit of
information. One bit may be used to store the answer to a yes or no question—in this case,
the question is, “Is there a tag present?” If a tag is detected, the answer is “1” or “yes.” If a
HOW MANY BITS DO I NEED?
Some of the latest active tags ordered by the U.S. Department of Defense will be able tostore as much
as 256bytes of information. How much storage do you need for your application? To getan idea, let’s
look at some numbers:
• Number of people on Earth: 6.3 * 10^9 ...