
36 CHAPTER TWO
Information storage capacity
Tags provide varying amounts of storage capacity. Read-only tags are set to store a par-
ticular value at the factory. Users can set a value to write-once tags one time, while the
value stored by a write-many tag may be changed many times. Some tags are also able
to gather new information, such as temperature or pressure readings, on their own.
Tags range in storage capacity from the 1-bit tags used for theft prevention to tags used
in auto assembly lines, which may store thousands of bytes.
Standards compliance
Many types of RFID systems conform to particular national and international standards.
A developer working on “an ISO 11785 system” is actually working on a system com-
patible with that standard. Some standards, such as the Class system used by EPCglobal,
specify frequencies, coupling type, information storage capacity, and more.
Selecting tags
Many considerations are involved in selecting tags. They include the following:
Required read range
Active tags provide a longer read range than passive tags. For retail applications, the
read ranges offered by passive tags are usually sufficient.
Material and packaging
Different materials have differing RF characteristics. For example, liquids may impede
the flow of radio waves. Metal containers also pose interference challenges to the
readers.
Form factors
RFID tags come in different sizes. The form factor ...