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B Magnetic induction/ goal ref technology

  1. Jun 10, 2016 #1
    Hi,

    I am interested in the basics of "goal ref technology", but I was not able to find a lot of material. Just one very brief wikipedia page and some paragraphs at the Fraunhofer institute.

    Does this work a bit like the anti shoplifting RFID tags?

    As far as I understand, the coils in the ball are connected to a passive circuit. This should mean that the ball does not need power or electronics, right? Makes sense.

    Then I think the electronics attached to the pickup coils in the goalposts looks for perturbations of the magnetic field originally created in the goal area. These perturbations come from the coils in the ball: when the ball crosses the goal line its coils pick up the "original" magnetic field, whose flux changes (both because the magnetic field itself is varying, and because the ball is likely to move quickly). By Faraday law this generates an induced emf and current, which in turn generates an induced magnetic field, adding to the original one.

    I read that the "original" magnetic field is "low frequency".
    What does that mean, exactly? How many Hz, approximately? How does that compare with that of RFID technology?

    What is the need of having a varying magnetic field, anyway?

    My guess is that it is useful when the ball crosses the line at very low speed, or when it is inside the goal, not moving.

    Thanks a lot for any insight.

    Franz
     
  2. jcsd
  3. Jun 11, 2016 #2
    Here's a tube that is FIFA Quality.


    I guess understanding and explaining technology isn't one of their top priorities.
     
  4. Jun 11, 2016 #3
    Thanks,
    I did find this video, but it does not explain much, as the "webpage" at Fraunhofer Institute. I understand the fact that it is a patented technology, but I'd just like to understand the basics of it.

    I wanted some more detail, such as: what is the need of low frequency magnetic fields?
    I think that in principle one could use a static magneticic field. The flux through the coils in the ball would change anyway, due to the speed and rotation of the ball.
    Is this just a second-order improvement, or is it essential?
     
  5. Jun 14, 2016 #4
    After poking around I found some stuff.

    Complex Image Theory
    http://www.disneyresearch.com/wp-content/uploads/RWS_2012_Arumugam.pdf

    This is for football ( American style )
    One loop for the football, with a battery, so an active circuit.
    The soccer ball has three loops it looks like, probably because it can spin in any orientation.
    Is Goal Ref a passive circuit in the ball?

    https://www.disneyresearch.com/project/magnetoquasistatic-position-and-orientation-tracking-2/
    http://www.engr.ncsu.edu/magazine/fall-winter2014/field.php
    http://www.sciencealert.com/news/20140907-25847.html

    This isn't actually Goal ref, but it might help you, as it did me, with some insight into low frequency magnetic positioning.
     
  6. Jun 28, 2016 #5
    256bits,

    thank you very much for your help! This is very interesting!
    Also, apologies for the late reply. In the last couple of weeks I was very busy with something else, and I did not check PF.
    Thanks again!
    Franz
     
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