Looking for waveguide failure info

Discussion in 'Physics' started by SupaTreadz, Sep 22, 2014.

  1. SupaTreadz

    Thread Starter New Member

    Jan 9, 2013
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    I don't know much about waveguides, but I would like to find out what the possible result of a particle impacting a waveguide could be. Would a particle penetrating a waveguide cause failure of the waveguide, or just degraded performance? What about if the particle did not penetrate the waveguide but the impact resulted in spalling of the waveguide interior surface?

    Any insight would be much appreciated.
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    minor distortion of the interior surface would have very minimal impact on transmission. larger defects would increase reflection and create localized heating.
    what size "particle" are we discussing? high energy electron size, or depleted uranium munition size?
     
  3. SupaTreadz

    Thread Starter New Member

    Jan 9, 2013
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    Roughly 0.1mm to 5mm diameter particles, impacting at hypervelocity speeds (~7km/s). Waveguide is of the WR62 type, I imagine the size of the hole/damage relative to the waveguide dimensions plays a significant role in the degradation. What is "minor" distortion? Any rough ideas on the type of degradation (dB loss?) that the signal might experience from a 1mm hole? Or from a couple mm attached spall sticking off the interior surface? Which would likely be worse, complete perforation or just damage from interior spallation?

    Thanks for the help
     
  4. studiot

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    Nov 9, 2007
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    You would also need to describe how rigidly the waveguide is held under those conditions.
    Are you thinking of one in space?

    The reason I am asking is that there will be considerable momentum associated with such particles and their effect will be quite different on a piece of metal that is free to rotate or bend as it is buffeted by the impactors compared to one that is held rigidly in their path.
     
  5. Kermit2

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    complete perforation, if the hole is less than 10% of the interior dia. would be better. projections and deformity may or may not be detrimental depending on power levels and transmitter type. neither would good for the equipment in the long run

    what freq? My experience is mostly radar, radio freq and round flexible types of waveguides are less familiar
     
    Last edited: Sep 22, 2014
  6. SupaTreadz

    Thread Starter New Member

    Jan 9, 2013
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    Yes, the waveguide in question is in space, exposed to the meteoroid/orbital debris environment. The waveguide is quite rigidly constrained, however momentum transfer is typically not a concern with hypervelocity impacts as the impact time is too low for that to have a major effect. Really just trying to understand what type of damage might cause "failure" of the waveguide.

    Does "would be better" mean better as in worse signal degradation, or actually better? If the waveguide dimensions are 0.622in x 0.311in, then a particle in that range could easily exceed 10% of any dimension. Typically, a 10% degradation of signal is considered a "failure".

    Frequency is Ku-band range.
     
  7. BR-549

    Well-Known Member

    Sep 22, 2013
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    That is the smallest antenna I ever saw. The horn is cute too.
    I don't think it will survive.
    Can you construct a semi-sphere of antennas and select which one to feed?
    With that size of ant. and that environment.....redundancy is one answer.
    Maybe mount ants. in multiple planes of craft?
    Momentum can be a b...other.
     
  8. SupaTreadz

    Thread Starter New Member

    Jan 9, 2013
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    The dish itself is quite massive, and luckily the waveguide is covered along most of its entire length. The assembly is already on orbit though, I am simply trying to generate a probability of failure for a certain duration.
     
  9. BR-549

    Well-Known Member

    Sep 22, 2013
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    Oh that's great. I'm glad you answered.
    Does NASA or somebody give you a probability of impact per area figure or something?
    How high is your craft?
    How much pwr out of horn?
     
  10. SupaTreadz

    Thread Starter New Member

    Jan 9, 2013
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    Yeah this is just an updated risk assessment for an antenna on the ISS, we have meteoroid/otbital debris flux info to predict the particle population but it's tricky to assign failure risk to objects like this that lose performance capabilities rather than just failing immediately
     
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  11. Kermit2

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    Feb 5, 2010
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    the best way to detect increasing losses in your waveguide would be by way of the receiver using a signal injection port for a way to force a signal in that has a trusted dbm level. downward deviation in rx signal strength being a direct reading of increasing waveguide damage. everything else here is glorified guess work. probability of damage and amount of probable damage cumulatively. 100% likely to be possible IF it happens. :)
     
  12. studiot

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    Nov 9, 2007
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    I can't see how you can divorce the mounting mechanics from the impact damage.
    If the guide is truly rigidly restrained then impacts will cause shearing failure to separation of parts, for larger particle impactors, and punching failure for small ones.

    That is you plate will end up sheared off or punctured.

    If the guide is loosely mounted than bending and/or twisting effects will arise leading to possible warping of the guide.

    This may be worse since the guide may end up looking like a swiss cheese but still be 90%+ functional,
    But if the geometry is disturbed the waveguide properties change dramatically.
     
  13. SupaTreadz

    Thread Starter New Member

    Jan 9, 2013
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    Thanks for the info, guesswork is sufficient for this stage of the analysis. Testing could potentially occur in the future.

    And studiot, hypervelocity impact mechanics get a little bizarre, since the particle tends to get instantly vaporized upon impact and most of the impact energy is depleted in this process. For the size of particles expected in the population, I would expect very little actual deformation of the waveguide, especially since it has an aluminum cover at a small standoff from the waveguide, allowing the debris cloud to expand a bit. The guide is very securely mounted, I would at worst expect a small penetration at some point and from what you guys have indicated, I don't think that will be a serious concern.
     
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