The term “Zenneck surface wave” (ZSW) refers to a unique mode of wave propagation wherein electromagnetic energy is guided from point to point by and along the interface between the earth and air. Conventional power-line delivery of electrical energy is accomplished through electromagnetic waves that are guided by the transmission line wires that span from tower to tower or pole to pole. Radiated electrical energy, like that used for radio, television and cell phones, is unguided and spreads out in all directions as it travels, being reflected and refracted in multiple directions as it encounters the surface of the earth and other objects.
ZSW’s exist in the domain between conductor-guided waves and waves launched and propagated from antennas. Specifically, a ZSW takes advantage of the electrical current densities induced in the surface of the earth whenever a wave strikes the earth at a precisely defined angle called the complex Brewster’s angle.
The primary field component for a ZSW is a time-varying, transverse magnetic field that encircles the ZSW launch structure. According to Maxwell’s equations, this time-varying magnetic field, which is typically designated by the symbol Hφ, creates time-varying electric fields that are everywhere perpendicular to the magnetic field. There are two electric fields created. One field, called Ez, points perpendicular to the surface of the earth. A much smaller secondary field, denoted by Eρ, points in the radial travel direction of the ZSW. Electrical power that moves from point to point along the surface of the earth is carried by Ez and Hφ. Even though Eρ is much smaller than Ez, establishing the correct Eρ is critical to launching a ZSW. When the required Eρ is achieved, the energy in the wave follows the contours of the earth rather than radiating off into space.
Coverage area of a ViZiv Surface Wave versus a Hertzian Radiated Wave at a specified frequency. Illustration only.