Shield for radio frequency ID tag or contactless smart card
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United States of America Patent
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May 3, 2011
Grant Date -
Mar 6, 2008
app pub date -
Aug 30, 2007
filing date -
Aug 30, 2006
priority date (Note) -
Expired
status (Latency Note)
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Abstract
We have found that to effectively shield inductively coupled RFID systems, the shield does not have to be present on all the sides of the device. It is also not required that one side be covered completely. In fact, a shield of any shape that allows a current to flow in a closed loop may be enough to shield the RFID. The only requirement is that the back electromagnetic field (EMF) from the shield induces sufficient flux to cancel all or part of the magnetic flux coming from the reader. It is possible for the shield to work even if the induced flux is small: the shift in the self-inductance of the RFID or contactless card coil due to the presence of the material in the shield can be enough to cause a shift in a resonant frequency of the circuit and thus in the power delivered to the chip. The current invention is a shield that does not completely cover a smartcard or RFID tag and/or has a hole or void within the shield. The advantage of this invention is that it will allow optical and mechanical access to the surface and the body of the smartcard or RFID tag and/or to parts of the smartcard/RFID coil. It also leads to significant cost savings since less shielding material is used.
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