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E-textiles EMC/FCC and durability issues

  1. Jul 4, 2013 #1
    I am trying to build a keyboard sewn into a shirt and I wonder if I need to worry about EMC/FCC issues with the conductive thread to the keys? For each key I use a normal (but very thin) pushbutton, the wire length to the arduino controller will be no more than 150 mm and I will use DC 3-5v. Because I debounce the signals from the buttons I assume that EMC won't be an issue for my stuff, but what about other devices?

    It will most likely be a low volume product (no more than 100 units) and I don't think I can afford to do proper EMC/FCC certification so my plan is to shield everything that needs shielding and then keep my fingers crossed that the FCC won't show up at my door.

    If shielding is needed then I think I can do it by adding conductive fabric or paint over and under the conductive wires.

    1. How big is the risk that my device will effect other devices and thus potentially anger the FCC?
    2. How big is the risk that my device will be effected despite debouncing?
    3. If I have a "hole" in my shielding that is 1-2mm wide and 150mm long will that allow RF signals do go through and cause EMC/FCC issues?
    4. What is the most durable choice of material for the conductive thread? From what I've read it is supposed to be stainless steel fibers but perhaps there is a better choice? Clothing means it will go through lots and lots of flexing and stretching.
  2. jcsd
  3. Jul 4, 2013 #2
    A slot with longest linear dimension, L = 150mm, in a shield is a perfect slot antenna for EM waves with wavelength λ = 2L = 300mm, or 1 GHz. In other words, the slot will pass anything above 1 GHz without attenuation. Below 1 GHz, the Shield Effectiveness (SE) increases with 20dB per decade according to SE = 20 log (λ/2L).


    Source: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CCwQFjAA&url=http%3A%2F%2Fwww.lairdtech.com%2FWorkArea%2Flinkit.aspx%3FLinkIdentifier%3Did%26ItemID%3D3400&ei=Bt7VUbrkLaGn4gSdmYCQCA&usg=AFQjCNGcU7gzJdO6s7PK9BOV51BBuJVLYA&sig2=ZrtyPU28KJ3hLtPV2Yk1lQ&bvm=bv.48705608,d.bGE [pdf]
    Last edited: Jul 4, 2013
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