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Transcript 
A Near Field Simulation on a
UHF RFID Reader Problem
Gert Doodeman
Netherlands Organisation for Applied
Scientific Research
The conveyor belt problem
A conveyor belt with parcels, equipped with an
UHF RFID reader directly under the belt
2
CST meeting Tegernsee 2007
The conveyor belt problem (2)
The antenna is e.g. a cross dipole or a circular polarized patch.
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CST meeting Tegernsee 2007
The conveyor belt problem (3)
The antenna is circular polarized.
Due to the metal of the conveyer
belt, the antenna polarisation is
oval.
With a phase correction, nearly
circular polarization should be
recovered.
4
CST meeting Tegernsee 2007
The conveyor belt problem (4)
Sometimes parcell B is recognized while
parcell A should be readed by the antenna.
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CST meeting Tegernsee 2007
The conveyor belt problem (5)
Simple instruments can be very helpful
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CST meeting Tegernsee 2007
Understanding the problem (1)
• Part of the conveyor belt with antenna was simulated in CST.
• The E-field is calculated in both RFID-tag orientations.
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CST meeting Tegernsee 2007
Understanding the problem (2)
The E-fields in the y-direction (the belt moving direction) has a
nice field strength distribution
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CST meeting Tegernsee 2007
CST simulation (3)
The E-fields in the x-direction (perpendicular to the belt moving
direction) propagates between the two metal side carriers.
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CST meeting Tegernsee 2007
The solution
•
•
•
•
Understanding the problem
Variable power level can not be avoided
Placing Reflectors
Placing Absorbers
Thanks to CST simulation software
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CST meeting Tegernsee 2007
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