iCLASS SE Reader Module Hardware Developer’s Guide, SE3200-902, Rev. C.1
Page 33 of 52 February 2014
7.1.2 Load Modulation
As previously mentioned, interpret the inductively coupled system as a transformer.
Putting a transponder (with a SRF around 13.56 MHz) into the magnetic field of a
reader absorbs energy from the field. This loading of the reader’s antenna, caused by
the transponder, is represented as transformed impedance at the antenna.
To communicate with the reader, the transponder switches an additional load resistor
across its own antenna. This results in a further impedance / voltage change at the
reader’s antenna. Therefore, the credential does not actually transmit.
Figure 14: Load Modulation Principle
7.2 Antenna Integration
Magnetic field antennas operate optimally within a free-air environment because the
magnetic field propagates perpendicularly with equal magnitude to the back and front
of the antenna. Antenna performance degradation due to Eddy Current loss begins at
the point where a metallic plate begins to enter the periphery of the magnetic flux
lines of the magnetic field.
Note: Magnetic field losses due to Eddy Currents are not
recoverable.
Magnetic field loss is extremely important. As loss increases, the available magnetic
field to power a credential and for the credential to load modulate is reduced, thus,
affecting RF performance of the system.
7.2.1 Steps to Integration
Due to antenna parasitic shift and eddy current losses, RF implementation should be
fully planned out prior to an industrial/mechanical design. This requires
experimentation to be completed including the proximity of metal obstructions in the
proximity of the antenna (including the LF antenna for HF+LF applications).
7.2.2 Antenna Interconnect Cable
The antenna interconnect cable is also designed to be routed in a free air environment.
Routing the antenna interconnect cable across metal structures shifts the antenna
characteristics and requires optimization.
7.2.3 Training and Assistance
HID Connect Applications Engineering staff will provide RF integration review and
conceptual training for integrators. In addition, HID provides antenna optimization and
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