I'm working on a practice question requiring me to find the total number of TM modes (including normal modes and SPP excitation modes) in a symmetric Metal-Insulator-Metal (MIM) waveguide only knowing it's thickness in terms of the plasma frequency of the metal.

I'm not sure how not knowing the frequency of excitation cannot affect the number of modes in the waveguide. More generally, how can we determine the number of modes in the waveguide?

  • $\begingroup$ The plasma frequency of the metal determines the upper cutoff frequency of the waveguide, i.e., frequencies above the metal plasma frequency will not be confined by the material and will escape. $\endgroup$ – honeste_vivere Mar 3 at 19:02

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