Let us assume that the electron density varies only in space (inhomogeneous isotropic plasma). One can then construct basic solutions by assuming that the field variables vary harmonically in time. The incident wave is completely reflected by the semi-infinite plasma. However, in the case of a plasma slab, some power gets transmitted through it even in this frequency band. It can be shown that this tunneling effect is due to the interaction of the electric field of the positive wave with the magnetic field of the negative wave and vice versa. Surface waves can also exist at the interface of a dielectric with a plasma layer or a plasma cylinder. Moissan achieved plasma generation through surface plasmons in a device called a surfatron. The surfatron is a highly efficient device for launching surface plasmons that produce plasma at a microwave frequency.