If a tag's antenna (45mm x 75mm) is larger than the reader's antenna (20mm x 26mm), could this pose coupling problems when trying to read the tag?
The reader functions correctly with tags similar to its size.
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\$\begingroup\$ the maximum read range will be about 50mm, is that a problem? \$\endgroup\$– Jasen Слава УкраїніMay 24, 2019 at 3:46
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\$\begingroup\$ @Jasen not at all, even if the reader and card have to touch its is not an issue. Is your 50mm based on computations or simply intuition? \$\endgroup\$– Charles GervaisMay 24, 2019 at 18:02
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\$\begingroup\$ based on experience. with the roles reversed large reader, small tag, but the coupling would be about the same. \$\endgroup\$– Jasen Слава УкраїніMay 24, 2019 at 19:42
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2 Answers
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After testing the actual setup, I was able to get a successful exchange between the smaller reader and the larger tag. Comparing the same tag on another, larger reader show that the smaller tends to have more erroneous transactions and the range is very limited, but I am still able to get valid transactions with a valid CRC.
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It all depends on the coupling factor. Different coil sizes for reader and tag will lead to a reduced coupling factor between the coils which will lead to reduced communication distance. The situation is worse for smaller reader and bigger tag antennas because in passive RFID coupling, it is the reader that powers the tag and this is often the limiting cause of reading range. If you have a given big tag antenna with a given small reader antenna, you could add a third resonant coupling coil with medium size in-between. Some people call these additional coils „RFID boosters“, but there‘s nothing really boosted, the RFID magnetic field field is just deflected in the right direction.
answered May 27, 2019 at 16:56