RFID reader design

I am trying to build a RFID reader for passive RFID tags like

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These tags has got read/write range upto 10m.

My reader must be capable of reading tags at a minimum distance of 6m( also the maximum).

I got few questions regarding this

1) Is it possible to read passive tags at a distance of 6m

2) Is it possible to build this reader.

3)What would be the size of reader

4)What would be the power requirement of this reader

5)Is it possible to detect direction and distance of RFID tag from the reader

Thanks.

Reply to
Alchemist
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Not sure. The general rule of thumb is that the diameter of the coil is equal or twice the required reading distance. Also the required power increases quickly with distance while the received signal decreases quickly with distance. And all that has to be done on one antenna. My contacts with a manufacturer of RFID systems once told me that it is already tricky to receive signals when the loop runs around a door opening.

Meindert

Reply to
Meindert Sprang

On 17 May 2006 23:32:28 -0700, "Alchemist" Gave us:

Not likely.

It would have to be more than an RFID tag. It would have to be able to report back directional data other than merely the RFID packet.

Reply to
Roy L. Fuchs
1) Is it possible to read passive tags at a distance of 6m

That depends on the field strength required to activate the passive tag. That should be a part of the passive tag specifications, and is your starting point for the reader design. Generally, the answer is , yes.

2) Is it possible to build this reader.

Yes. However, you will need the passive tag specs before you can start the design.

3)What would be the size of reader

I suspect it would be easy to put in a cigar box unless you need a specific beamwidth for the antenna. It depends upon your application, and what type of signal processing is needed in the reader, i.e. does it merely pass the data to and from another external computer.

4)What would be the power requirement of this reader

It must supply activation energy for the passive tag at the required distance. That's why you need the tag specifications. You also need the frequency, since it will be different for all of the possibles ( 140khz, 13 Mhz, 915 Mhz, 5800 Mhz)

5)Is it possible to detect direction and distance of RFID tag from the reader

( It depends on the spec requirements. Distance is very difficult and I would say probably not. Direction can be done using directional antennae, which rules it out pretty well below 915 Mhz.) A 915 antenna such as the TIRIS antenna is about 5 feet long and 1.5 ft wide and will support beamwidths of 25-30 degrees..... approx. ball park.. 5800 directional antenna are about 6 inches in diameter if made with multiple patches and microstrip................... Don't even think about using short pulses for distance --- passive tags can't do that by a long shot and a reader design would be impractical )

Andy in Eureka , Tex ( retired RFID engineer )

Reply to
Andy

From my experience with 15MHz passive tags, the reach is about the diameter of the stationary antenna. Also note that the field must not exceed a certain field strength.

Rene

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Reply to
Rene Tschaggelar

Yes, our reader/tag combination (Palomar and its derivatives) has approximately such a range. But for a practical system you need to use a freguency at which the radiation is in the freely-propagating regime (far field). Ours operate at 868 MHz. I don't think a practical-sized near-field reader can ever reach such ranges.

Not only the reader affects the maximum range; you also need a good optimized tag.

Now you are groping into the area of trade secrets...

Regards, Mikko

Reply to
Mikko Kiviranta

Andy asks Mikko,

Mikko, is your tag a completely passive tag, without a battery of any kind ?

If so, I'd like to discuss it more with you via email.....

Andy in Eureka, Texas

Reply to
Andy

Yes it is a completely passive one. There is a paper about the early tag IC in the IEEE Journal of Solid State Circuits vol 38 no 10 p 1602, whose derivatives include the Atmel ATA5590. Unfortunately I cannot talk beyond what has been published, so you may find it easier to just google around with keywords "Palomar" or "Mimosa".

Regards, Mikko

Reply to
Kiviranta, Mikko

I want passive tags because they will be small and i can attach these tags to tracked items very easily.

I got two papers which describes how to measure direction and distance of tag from the reader.

I am not sure whether we can implement this for passive tags.

"Localization of RFID Tags from Measurement of Complex Gradients of Electromagnetic Fields"

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"A 3-axis Orthogonal Antenna for Indoor Localization"

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Now i am trying to get the specification of the tags.

Thanks.

Reply to
Alchemist

I want passive tags because they will be small and i can attach these tags to tracked items very easily.

I got two papers which describes how to measure direction and distance of tag from the reader.

I am not sure whether we can implement this for passive tags.

"Localization of RFID Tags from Measurement of Complex Gradients of Electromagnetic Fields"

formatting link

"A 3-axis Orthogonal Antenna for Indoor Localization"

formatting link

Now i am trying to get the specification of the tags.

Thanks.

Reply to
Alchemist

Having done extensive measurements and plotting of the fields produced by Readers in the presence of vehicles, roadway reflections and grazing angles, I can tell you without a doubt that using "field strength" to determine distance has NO chance of being a practical sytem. Regardless of any academic papers you may have read, or written, unless it is backed up with real world measurement, it is all a bunch of crap.

Please refer to " Data Communications by Means of Reflective Transmission" which I wrote for Microwaves and Electronics a dozen years ago. It contains E-field footprints made on a roadway by state of art measurement techniques, which I did on the antenna range of Texas Instruments in McKinney, Texas. It shows that one can easily get a 20 db variation in field strength in just a few INCHES of movement when the tag is moved in the presence of reflections.

I suspect that neither of the articles you quoted used actual measurement in a competitive environment. It simply isn't a practical way to make precision measurement.... In free space maybe, but not in a morass of radio waves at the same frequency coming from 10 directions at once, all within a few db of the same field strength..... It's like putting a flashlight in a hall of mirrors and trying to shoot out the one light source with one shot.

...... based on years of field experience in toll tag systems. On the other hand, you can probably put up a system at a Walmart entrance to read clothing tags within a few inches. That's NOT a competitive environment.

Andy in Eureka, (retired RFID engineer from Texas Instruments)

Reply to
Andy

On 19 May 2006 03:56:42 -0700, "Alchemist" Gave us:

Then shoot for a smaller sensing area than several meters.

Change your design to meet what is physically possible.

Reply to
Roy L. Fuchs

Hi Andy ,

Thanks a lot for your positive comments.

I want to explain my project a little more.

This system is for tracking objects inside a house, what i am doing is i will attach a passive RFID tag with each tracked item. If i want to find one item then i will use reader to find the location of missing item.

I am using passive tags because i can attach tags to small items like sun glass etc.

Thanks.

Reply to
Alchemist

That's what wives are for, "Someone has stolen my socks" ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Andy comments:

Here's a suggestion.... Just put a reader on each doorway and keep track of whether the tag has passed thru the doorway.... It wouldn't require direction OR distance, and a simple software routine would tell you which room the TAG is in....( If it was in room A, and the door on room A then registers a "hit" it is no longer in room A but has moved to room B --- that sort of thing , not foolproof but reasonable ) Also the read distance would need to be less than a meter, so you could use a LOT less power --- the reader has to continually illuminate for a passive tag, so low power is a big plus for avoiding brain cancer and bad stuff.....

Also, battery life in a semi-passive or active tag is in the neighborhood of 5 years, and the batteries are very cheap, so that would cut the illuminator power down even more since the tag doesn't have to draw power energy from the illuminator field, only "wake-up" energy....

Just a suggestion... I really miss working on those kinds of projects, but everyone has to hang it up sometime....

If you would like to throw ideas around, I'd be please to correspond... My email is snipped-for-privacy@juno.com

Andy in Eureka, Texas

( If you have more owls in your yard than dogs, and all the cats have disappeared, you probably live in Eureka, Texas )

Reply to
Andy

Have a look at

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Reinier

Reply to
Reinier Gerritsen

On Mon, 22 May 2006 23:20:15 +0200, Reinier Gerritsen Gave us:

Cool find!

Reply to
Roy L. Fuchs

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