User's Manual

CHAPTER 1: GETTING STARTED
COBALT HF RFID CONTROLLERS OPERATOR’S MANUAL
P/N: 17-1320 REV 01 (03-06) PAGE 26 OF 116
1.7 RFID OVERVIEW
The Cobalt HF-series products are designed for use with passive RFID tags. Passive
tags require no batteries and are energized by the magnetic field of the Cobalt HF
controller’s antenna. Through inductive coupling, power is induced from the controller’s
antenna into the antenna of the RFID tag. Similar to a transformer, the efficiency of the
energy transferred is a result of the size and number of turns on the transmit antenna
(primary winding) and size and number of turns on the tag’s antenna (secondary
winding). The resonant frequency of each antenna coil and its Q-factor (quality factor)
are primary design concerns for efficient antenna coil and tag coil designs.
Optimum tuned coils for both the antenna and tag will achieve the best energy transfer.
The Q-factor defines how wide of bandwidth the energy is spread over. The RF output
power is fixed within the legal limits, the higher the peak energy at the resonant
frequency the higher the Q value and the narrower the bandwidth. Inversely, the lower
the peak energy at the resonant frequency the lower the Q value and the wider the
bandwidth. Higher the Q values of the two antenna coils will produce the greatest range.
However the with too high a Q value the less tolerant the system will be of shifts of the
resonant frequency. The lower the Q value, the wider the bandwidth and the greater
tolerance the system will have to shifting of the resonant frequency.
Tuned antenna circuits are affected by virtually all materials, whether they are metal,
water, plastic, cement or even the human touch. Some materials will shift the resonant
frequency up, and other materials will shift the frequency down and some have more
affect than others. Metal and water will have the most serious affect on antenna tuning,
metal more so than water. The lower the frequency the less affect metal and water have
on the performance. The 13.56MHz HF frequency provides the best compromise
between range, speed, and immunity to environmental affects. The HF-series products
are designed with optimum antenna designs with Q values required for most applications.
The Cobalt HF-series operates at the ISM (Industrial, Scientific, Medical) internationally
accepted frequency of 13.56MHz. 13.56MHz is considered to be in the High Frequency
spectrum as opposed to 864MHz or 915MHz which fall under the Ultra-High Frequency
or UHF spectrum, or 2.4GHz in the microwave range spectrum. For reference,
13.56MHz falls between the AM and FM radio bands.
Understanding these principals is important when considering the mounting of the HF
Controller’s antenna and the RFID tag. Unless the tag or antenna is designed specifically
for mounting close to metal, non-metallic mounting brackets and non-metallic tag spacers
are required to achieve optimum read and write ranges.
Electrical noise generated by motors, conveyors and other automation equipment can
produce excessive electrical noise which can negatively affect the RF communications.
The Cobalt HF series products should only be used on well grounded systems.
Conveyors systems should be tied directly to earth ground by an electrician. All cables
used on and around the RFID system must be shielded cables. Cable shields should
typically be grounded at both ends, however, differences in ground potentials can
produce “ground loops” and in those cases the ground connection may need to be lifted
at one end of the cable.
The range performance specified in this and other Escort Memory Systems publications
refer to the free air measurement, meaning there is no metal in the field. Because the
proximity to metal and other environmental conditions affect read and write range, it is
impossible for Escort Memory Systems to state the absolute range that will be achieved