Core Electronics Forum

UHF RFID tag identification limitations around steel

Hi, I need to identify when an object passes over a point on the other side of a 10mm thick steel plate. I know that RFID struggles to penetrate through steel; however, I do have the ability to drill a hole directly below the line that the RFID tag passes over (see attached sketch).

Questions:

  • Has anyone dealt with a similar use case and resolved the issue using either UHF RFID tags or an alternative?
  • Does any one know what size hole would be required to allow the RFID reader to adequately transmit and receive a signal?
  • Is there a particular technology that I should focus my attention on outside of RFID?

Restraints:

  • Tags are to be passive
  • Tags need to have a max width/diameter of 5mm
  • Transmitter/Receiver needs to be able to be supported by battery power

NOTE: I am a beginner in this space and hoping to gain some direction to reduce the time to develop a solution. Open to thoughts and suggestions.

Cheers, Chris

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Hi Chris.
What are you trying to detect, the tag or the block of material. If it is the block of polymer material an infrared system may be simpler. The transmitter could be mounted below shining through a hole and if a receiver can be mounted above a through beam detector system would probably be OK or if the bottom of the polymer is shiny or smooth then a reflective system may work.
Cheers Bob

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Thanks for your input Rob. Unfortunately, due to the application I cannot use light. I really need to be able to detect the presence of an embedded tag/sensor so that I can gain positive presence of the item. I anticipate having a series of sensors at different heights come across this point and would like to be able to also determine the height based on signal strength in addition to present yes/no. If you’ve got any other thoughts would be keen to hear them. Cheers

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Hi Chris.
I am by no means the full bottle on RFID systems but I do know the tags are powered solely by the energy received by the fixed unit. You might appreciate then that they do not have a great deal of spare power to do much more that reply with their ID. With this in mind I think your idea of measuring signal strength might be a bit over the limit of capability. To measure the thickness an acoustic reflective system mounted overhead may work. You may even be able to measure the presence of a block or not with such a system unless you need to identify particular blocks passing this point but you could use a barcode reader for this. There are possibly several alternatives
Cheers Bob

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Hi Chris
Add on to above
As a matter of interest why can’t you use light?
Cheers Bob

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Hi Bob and Chris,

To expand on Bob’s point, depending on packaging constraints, if you needed identification as well as prescence detection, a barcode scanner might work as long as your system gives enough time to read it.
Something like this might be what you’re looking for:

Keen to find out more about this one!
-James

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Hi Bob, for this application (although not shown in the schematic) the hole needs to be ‘plugged’ to ensure no leakage. The plug cannot be transparent; hence the need to be able to ID a tag without visual means. I am also considering pivoting and using small Rare Earth magnets (Dia 4mmx4mm) and then using a magnetometer on the underside to ID magnetic strength…just a thought?!

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Hi Chris,

I’d assume that a Reed Switch or Hall Effect Sensor might be a good pick if you can mount strong magnets to the underside of the tagged object, however it’d only detect presence, rather than identify, your objects.

Maybe a bit more info about the context of your project might help us think up an alternate system?
-James

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Hi Chris

Don’t quite understand, “plugged” from what and what with. I would assume with some plastic material and from light (from earlier comments).
The steel plate will certainly upset magnetic fields. By the way how is this material to be detected transported across this steel plate?
You may well look at some of these little acoustic radar units as used on robots if you can’t use any form of light.
Cheers Bob

Good idea James

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