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RFID reader design

Discussion in 'Electronic Design' started by Alchemist, May 18, 2006.

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  1. Alchemist

    Alchemist Guest

    I am trying to build a RFID reader for passive RFID tags like
    http://availabletechnologies.pnl.gov/securityelectronics/rftagsdescription.stm.
    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.
     
  2. 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
     
  3. Roy L. Fuchs

    Roy L. Fuchs Guest

    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.
     
  4. Andy

    Andy Guest

    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 )
     
  5. 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
     
  6. 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
     
  7. Andy

    Andy Guest

    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
     
  8. 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
     
  9. Alchemist

    Alchemist Guest

    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"
    http://www.unl.im.dendai.ac.jp/INSS2004/INSS2004_papers/OralPresentations/D2.pdf


    "A 3-axis Orthogonal Antenna for Indoor Localization"
    http://www.unl.im.dendai.ac.jp/INSS2004/INSS2004_papers/OralPresentations/D1.pdf


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


    Thanks.
     
  10. Alchemist

    Alchemist Guest

    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"
    http://www.unl.im.dendai.ac.jp/INSS2004/INSS2004_papers/OralPresentat...



    "A 3-axis Orthogonal Antenna for Indoor Localization"
    http://www.unl.im.dendai.ac.jp/INSS2004/INSS2004_papers/OralPresentat...



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


    Thanks.
     
  11. Andy

    Andy Guest

    Andy writes:

    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)
     
  12. Roy L. Fuchs

    Roy L. Fuchs Guest

    Then shoot for a smaller sensing area than several meters.

    Change your design to meet what is physically possible.
     
  13. Alchemist

    Alchemist Guest

    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.
     
  14. Jim Thompson

    Jim Thompson Guest

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

    ...Jim Thompson
     
  15. Andy

    Andy Guest

    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


    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 )
     
  16. Have a look at http://www.rfid-radar.com/

    Reinier
     
  17. Roy L. Fuchs

    Roy L. Fuchs Guest

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