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 easily decoded, but more difficult to duplicate. The encoding is
manufacturer processed, but custom printing must account for specific ink
colors which are critical to the read technique.
d) Hollerith. Rectangular punched holes similar to a computer
keypunch card are the means of storing information on the Hollerith card.
The amount of information which can be stored is quite limited. The storage
space available is even less where a photograph or other printing are also
required on the card. This card is extremely vulnerable to copying with
inexpensive tools.
e) Electric Circuit. This card is essentially a plug-in printed
circuit which can present a limited number of unique codes. The unique
codes are values of continuity or electrical pathways on the card. The card
is decoded and simulated easily with inexpensive, unsophisticated tools.
This card is encoded in the factory but may be assembled by users.
f) Metallic Strip. This badge consists of a matrix of metal
(usually copper) strips which are laminated to a badge core. A moderate
amount of information can be encoded by the presence or absence of strips.
The card is easily simulated. This card is factory encoded but may be
assembled locally to add custom artwork and photographic images.
g) Wiegand Effect. The Wiegand badge contains a series of small
parallel wires laminated within the card. These wires are manufactured from
ferromagnetic materials which produce a sharp change in magnetic flux when
exposed to a slowly changing magnetic field. The wires' placement above and
below a critical centerline determines the specific information in binary
code. This technology is factory-encoded and therefore impossible to erase
and difficult to alter or duplicate.
h) Proximity. Proximity badges are essentially tuned antennas
laminated within the core of a card. A weak radio signal is spectrum
generated by the card reader and is attenuated and reflected to the reader
as specific information. The information on the badge can be decoded, but
the card is difficult to alter or duplicate.
i) Capacitance. The capacitance badge contains an array of
capacitor plates which are connected (or not) to a specific pattern. This
pattern is the limited information code. Although affected by wetness, this
factory-encoded badge is difficult to read, alter, or duplicate.
j) Active Electronic. This miniature transmitter contains the
individual code which is sent when energized by the reader. The media is
characterized by the very limited amount of information storage. This card
can be decoded with instruments, although it is moderately difficult to
duplicate.
13.02-72
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