passive RFID tag detection from all directions

Hello,

I have following kind of question: Is there a solution to detect passive tags, for example RFID tags from multiple directions? I would need some kind of simple technology by which tag could be detected from any direction from certain distance, let's say 2 centimeters. So basically, what I am looking for is detection of some kind of passive element from certain distance from any direction. Any ideas how to solve this problem?

Thanks already for answers and follow up questions,

- Dknot

You mean all directions viewn from the tag, so the tag should have a kind of isotropic antenna?

In case of inductively coupled RFID, this would require multiple decoupled coils. A UHF or microwave RFID tag with circular polarized antenna should basically work for this purpose.

Depending on maximum costs, you may use three receiver coils (in x. y and z plane) and use three 13.56 MHz or 125 kHz chips (or just complete 125 kHz transponders). The only thing is that you need to learn the host application to merge three tag ID into one.

It doesn't work to put these coils in series and feed one chip.

Other option can be to accept some larger distance and use several antennas that are multiplexed (in time). Several vendors have readers (both RF and UHF) with internal multiplexers (at more cost). More elaborate solution can be one reader antenna that contains 2 coils/antennas that are fed out of phase to get a more or less 3D field component.

Do you really need full 3D sensitivity?

Thank you for your replies WimRFP and FvM!

Maybe I should first tell more details about the use of RFID in my project: My idea is to make very low cost proximity detection system. So, if I would put inexpensive RFID sticker on for example dish plate or any other common household object and I would have a small RFID reader in my hand, reader would always alarm when my hand is close to object. RFID stickers would be great for this kind of project, because they are very low cost, and you can put them easily on many objects. They are thin and handy.

However, objects with odd geometries such as a plate are a problem. If my hand comes from wrong angle, RFID stickers do not normally operate well. In case of the plate, approaching with sensor from the side of the plate does not trigger reader. It is unfortunately not possible to put stickers to all corners in common case scerio.

So what I am looking for is some kind of small sticker type of thing, which has 3d-sensitivity. I'm so excited about the idea, but maybe my idea is technologically impossible? Circular polarized antenna is, at least if I have understood right, never very slim, handy sticker and all corners of the objects simply can not be covered. Is there any way to have a slim sticker and reader with 3-d sensitivity? Using many readers is not excluded, but they should be small (Let's say not more than size of the finger). I'm new with electronics, but quite recentness, so doing some work is fine .


Thanks again for your replies,

-Dknot