Balluff BIS M-370-000-A02, Manual, Page: 189 / 198

BIS M REFERENCE MANUAL
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RFID OPERATING PRINCIPLES
RFID OVERVIEW
BIS M products are designed for use with passive RFID tags, which do not require batteries
or contain an internal power supply. Through a process called
inductive coupling , passive
RFID tags obtain power from the RFID antenna.
When a passive tag comes in contact with the RF field from an RFID antenna, the incoming
radio frequency signal generates a small, but sufficient, electrical current that powers the
passive tag’s integrated circuit (IC) and antenna.
Similar to a transformer, the efficiency of the energy transferred is directly related to the size
and number of turns of the transmitting antenna (primary winding) and the size and number
of turns of the RFID tag’s antenna (secondary winding). The resonant frequency and Q-factor
(quality factor) of each antenna coil are the primary concerns when producing efficient
antenna coil and tag coil designs. The Q-factor defines how broad the energy bandwidth is
spread.
Antenna and tag coils that are optimally tuned will achieve the most efficient energy transfer.
Although, RF output power is fixed within legal limits, the higher the peak energy at the
resonant frequency, the higher the Q-factor value and the narrower the bandwidth. Inversely,
the lower the peak energy at the resonant frequency, the lower the Q-factor value (resulting
in a wider bandwidth). In general, raising the Q-factor value of the two antenna coils
produces better overall range results. However, when the Q-factor value becomes too high,
the system may become less tolerant to shifts in resonant frequency. When the Q-factor is
low, bandwidth becomes wider which increases system tolerance to a shift in resonant
frequency.
Tuned antenna circuits can be affected by many materials. Metal, liquid, plastic, cement and
even organic substances can cause an upward shift in the resonant frequency, which can
negatively affect an antenna’s tuning (certain other materials can cause a downward shift in
resonant frequency as well). However, the lower the operating frequency, the less
pronounced the influence would be to the antenna’s performance. BIS M products are
manufactured using optimal antenna designs that exhibit Q-factor values within the required
range of most applications.
BIS M Controllers operate at the internationally accepted ISM (
Industrial, Scientific and
Medical ) frequency of 13.56 MHz. Residing in the High Frequency RF spectrum, 13.56 MHz
provides an excellent compromise between range, speed and immunity to environmental
materials, as opposed to 864 MHz or 915 MHz, which fall under the Ultra-High Frequency
(UHF) spectrum or 2.4GHz, which resides in the microwave range spectrum. For reference,
13.56 MHz falls between the AM and FM radio bands.
When mounting RFID antennas and tags, it is important to understanding certain principals.
If your RFID application requires that the tag be attached directly to a metal surface, always
use a non-metallic tag spacer to avoid a possible reduction in read/write range.
In addition, motors, conveyors and other automation equipment can produce excessive
electrical noise that may also negatively affect RF performance. BIS M products should only
be used with well-grounded systems. Conveyor equipment should be tied directly to an earth
ground by an electrician. All cables used on or around BIS M devices must be shielded.
Cable
shields typically should be grounded at only one end.