Security and safety control systems - Intelligent Buildings and Building Automation - page 229

system processor for verification, and if valid for entry at that point and that
time, the processor sends a signal to release the door.
Wiegand cards , which look like credit cards, are widely used in access-
control systems. They work according to a principle similar to that used
in magnetic-stripe cards. Instead of a band of ferromagnetic material, the
Wiegand card contains a set of embedded wires. The wires are made of a
special alloy with magnetic properties that are difficult to duplicate. The
set of wires can contain data such as the user's identification information,
credit card numbers, medical history and so on. The card is read by passing
it through, or bringing it near, a reader. The Wiegand effect occurs over a
wide range of temperatures, so access-control devices using this technology
can function in hostile environments. Other features include rapid response
time and portability. These features make Wiegand cards and readers ideal
for use in the field.
Proximity cards are another type of commonly used contactless cards using
integrated circuits (IC) embedded in a high-grade fibreglass-epoxy card. The
IC, capacitor and coil are connected in parallel. The card reader presents a
field that excites the coil and charges the capacitor, which then energizes
and powers the IC. The IC then transmits the card number via the coil to
the card reader. The card readers communicate in Wiegand protocol. The
earliest cards have 26 bits and the latest cards have an increased bit number
to provide unique numbers.
Smart cards are a new type of card. Each card contains an integrated
circuit chip embedded in the plastic of the card. This type of card has both
a coded memory and a microprocessor with inherent intelligence. The card
acts as a super-miniature computer as it records and stores information and
personal identification codes in its memory. Smart cards can have a stor-
age capacity of 8 KB up to 64 KB. The cards include contact smart cards
and contactless smart cards. Contactless smart cards have a working range
of 10 cm and are typically used for access-control applications. There are
benefits to using smart cards for access control. Contactless smart cards can
achieve a higher security level for the credential and the overall access-control
systems. They also provide more storage and secure reading and writing of
data. The capacity to add other applications to the cards, such as biometric
identities, is one of the most important advantages of contactless smart cards
over proximity cards. Radio-frequency identification (RFID) cards are a very
common type of card nowadays. Users often are confused as to the differ-
ence between RFID and contactless smart cards. However, RFID, specified
by a different standard, is usually used for low-security applications such
as a supply chain. The other important difference is that the RFID has four
options of working distance ranging from 10 cm to 10 m (corresponding to
four working frequencies of range between 125-135 kHz and 2.45 GHz).