Transverse electromagnetic mode ($E_z=B_z=0$)

A transverse electromagnetic mode has both electric field and magnetic field transverse to its propagation axis. An ideal two-conductor guide can support such a mode without a geometric waveguide cutoff frequency; an empty simply connected perfect conductor pipe cannot.

In a matched lossless parallel-plate transmission line, a single travelling wave obeys $V/I=Z_0=(d/a)\sqrt{{\mu }_0/\epsilon }$. The electric attraction per unit length is $f_E=\epsilon a{V}_{\mathrm{rms}}^2/(2d^2)$; each plate feels the field of the other plate, excluding its self-field. Opposite sheet currents give magnetic repulsion $f_B={\mu }_0{I}_{\mathrm{rms}}^2/(2a)$. Substituting the travelling-wave impedance proves their equality, so the ideal net transverse electromagnetic force is zero at every phase. A standing wave or independent voltage and current need not have this cancellation.