I am working on a smart shopping system and would like to know if a UHF rfid signal can pass through few layers of clothes in a bag as multiple clothes would be present in a bag and system has to detect it correctly.
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\$\begingroup\$ atre you considering EPCGlobal? \$\endgroup\$– Jasen Слава УкраїніSep 14, 2018 at 23:57
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1\$\begingroup\$ You may need control over the bag to prevent customers from shielding them if you're trying to detect theft. \$\endgroup\$– K HSep 15, 2018 at 1:20
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\$\begingroup\$ RF shielding requires atoms that can be polarized under the force of E&M fields. Cotton does not have that type of atoms. \$\endgroup\$– analogsystemsrfSep 15, 2018 at 4:24
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2 Answers
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RF will pass though ordinary fabric with no measurable effect.
answered Sep 14, 2018 at 23:55
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1\$\begingroup\$ This is the correct answer, but it could be improved with some supporting material. \$\endgroup\$ Sep 15, 2018 at 0:14
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\$\begingroup\$ Yet Polyester has a higher Dk than cotton so as long as it does not detune the antenna, ok \$\endgroup\$ Sep 15, 2018 at 2:23
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\$\begingroup\$ yeah, but clothes are mostly air, and RFID tags have a fairly low Q to start with, so a little dt-tuning will not cause a big loss in range. \$\endgroup\$ Sep 15, 2018 at 6:15
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I have experience only with some very simple RFID systems about 10 years ago, so I don't know what advances have been made recently, but from what experience I have, I can say that it'll pass through the fabric, but it's probably an ineffective mechanism against theft as the customers can shield their bags.
Furthermore, I think most RFID tags need very close distance between the reader and the tag (a few centimeters) so you'd need to choose a tag that can be read from further away. And then it might be difficult to be sure exactly who has the item in his/her bag when they walk out the store. Also, you must make sure that if you have several RFID tags in the bag, you can still read them separately without them interfering with each other.
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\$\begingroup\$ passive tags can be read at about 1m range if you have a large enough antenna, but now the reader costs $1000 instead of $20 \$\endgroup\$ Sep 15, 2018 at 6:04