I wondering about the feasibility of making a 13.56 MHz antenna that would occupy the entire rack of a shelf (5'x2'). The range would need to be small so that it only identifies entities that are sitting on the shelf. I was thinking of using 13.56 because anti collision is more widely used in HF. Is it possible to design this antenna at 13.56 MHz or is it better to do it at a low frequency and find a way to implement anti collision on that? Thanks for the help
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\$\begingroup\$ 13.56 milli - Hz?????? \$\endgroup\$– Leon HellerCommented Aug 23, 2019 at 18:41
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\$\begingroup\$ @Kevin Dias 13.56MHz is an allocated band \$\endgroup\$– Voltage Spike ♦Commented Aug 23, 2019 at 18:45
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\$\begingroup\$ sorry for the confusion i updated the post to show MHz \$\endgroup\$– Kevin DiasCommented Aug 23, 2019 at 19:59
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1\$\begingroup\$ The NFC coil should not need to be the same size as the shelf, it can be smaller, as it will still be able to read tags adjacent, above and below itself, its hard to make a coil read much more than about half its diameter above and below, but they can read about 30% of its diameter surrounding the coil, for the ones I have made in the past (6x6cm square antenna) As for making it resonant, that is still possible, its just a game of working with capacitance and inductance, briefcase size coils are common enough, \$\endgroup\$– RerouteCommented Aug 26, 2019 at 12:39
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2 Answers
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What your're suggesting could likely be done with a bunch of loop antennas, like NFC type antennas, but one single antenna that size will likely not work, it would probably be way off on its resonant frequency.
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5'x2' is now 5 feet x 2 feet? That would be 0.92 m2 area, which is quite large. I have made a round near-field coil for HF RFID with a radius of 0.15 m (area of 0.071 m2) and two loops, which was still quite easy to match to 50 Ω. I also tried doing one with a radius of 0.25 m and two loops, but that was already very hard to match. Based on that I'd say you'll have hard time trying to match the very large coil. Even if you are matching to some other value than 50 Ω.
Maybe it could be achieved with overlapping coils, like in MRI? I do not know if it could be done, but it's a possibility. The mutual inductance of the overlapping coils is something that needs to be taken care of. A lot to think about.
