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It would depend on the types of tags you are using. If you wanted to read tags from a distance of 10 feet or more, you would need to use passive UHF RFID transponders, and it would be difficult to read those consistently if the tags were stacked one on top of another or back to back. The metallic antenna of one tag would likely block the energy from reaching the tag below it.
However, Magellan Technology developed a technique called phased jitter modulation, enabling HF tags to be read even if they were stacked one on top of another. These tags can be read from a distance of 1 or 2 feet. If that is all the read distance you require, I would suggest you contact SATO Holdings Corp., which acquired Magellan in 2013.
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Thanks for that explanation Mark. I will contact SATO Global Solutions as you suggest.
I have used the Magellan / SATO solution to successfully read (100% accuracy) about 200 items loosely placed in a plastic bin when passed thru a Magellan Tunnel reader. That solution is used by many Hospitals across Aust and NZ to receipt Orthopaedic surgical loan kits from Orthopaedic Joint suppliers prior to joint replacement surgery.
However I was told that by Magellan that their HF RFID tech struggled with perfectly stacked items, with the HF RFID tag in identical locations, That is back to back RFID tags that are aligned over the next items RFID tag . They told me that the best way to avoid this was to alternate the location of the RFID tag so they were not back to back.
I was testing this just yesterday as I have a use case to apply tags in the same location on each page of a booklet.
I used several different Type 2 tags sourced from Amazon and both NTAG213 and NTAG216 I sourced myself from China. My first thought was the use of tags that can be surface mounted onto metal as each one is backed with shielding. Indeed, two back-to-back shielded tags one on to[p of the other with nothing else between them enabled me to read the topmost tag without error.
I replicated witha set of NTAG213 and a set of NTAG216 unshielded tags and discovered no conflict with them either. I repeated the excersize three times with different tags and had no conflict at all. Very interesting…
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