1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Resonant Cavity, U(t) decay?

  1. Oct 9, 2009 #1
    Hey there, I recently solved for the resonant modes in a 3d metal box.

    Thats nice, but I was wondering about how to actually excite the modes (its a sealed metal box)
    Supposing I actually excited these modes by shining incident em radiation such that a portion [of the incident wave] penetrates by skin effect (assuming the thickness of the metal allows for penetration without too much attenuation).

    Will I subsequently have gradual decay of the energy stored in my box? I.e will my resonant mode 'leak' out by a similar process as they were originally excited with?

    Thanks-Hopefully that was cogent.
  2. jcsd
  3. Oct 9, 2009 #2


    User Avatar
    Science Advisor
    Gold Member

    Are you asking how to excite a cavity in your simulations? Or in the real world?
    If it is the latter the answer is that this can be done with a small antenna (a dipole of some sort) placed where the mode you want to excite has an anti-node.
    The idea is usually (but not always) to make the antenna so small that losses due to the coupling can be neglected (although if you actually want to measure what is inside your box you have no choice but to "tap" some of its energy).
    In the undercoupled case most of the losses will be due to the fact that the walls are made from a non-perfect conductor, i.e. just resistive losses.

    And yes, the energy in the box will decay exponentially,
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook