(a) Waves propagating between two infinitely conducting metal slabs form a waveguide, or transmission line. Analogous transmission lines include coaxial cables and paired wires. (b) The two lowest order TM modes of this waveguide. The higher order mode (blue) has a dispersion that is functionally identical to that of waves propagating in a plasma. Near the cutoff frequency this mode behaves like an “epsilon-near-zero” (ENZ) material. The bounce angle approaches 90 degrees, the wavelength approaches infinity, and the electric field is longitudinal. The lowest order mode, on the other hand, has linear dispersion (red). The equivalent bounce angle is 0 degrees and the fields are purely transverse. This is the mode that propagates signals in conventional low-frequency wiring. (c) Even though the fields, energy, and power are entirely contained in the region between the metals, conduction currents are entirely contained within the metals. Currents travel along one “wire” and return to ground along the other. (d) Equivalent displacement current wires can be made by etching a groove into an ENZ material.