The  Physics

THE PHYSICS

Characteristics of Zenneck Surface Waves


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.

THE PHYSICS

The primary field component for a ZSW is a time-varying, transverse magnetic field that encircles the ZSW launch structure.

Coverage area of a ViZiv Surface Wave versus a Hertzian Radiated Wave at a specified frequency. Illustration only.

High-power energy transfer requires that the ZSW completely spans the globe. To achieve global coverage, the frequency of the ZSW needs to be in the low kHz (kilohertz) frequency range, typically 10 kHz or less. This low frequency requirement is driven by the amount of attenuation experienced as the wave travels along the surface of the earth. At higher frequencies, the attenuation factor is so large that all of the energy put in the ZSW, not captured by a receiver, gets absorbed by the earth. At the lower frequencies, a global standing wave can be established such that a very small amount of energy gets lost due to heat in the earth and a receiver can extract energy from the standing wave when and where needed.

The launch structure for a ZSW is not an antenna, rather it is a coupling probe connecting the energy source to the surface waveguide, i.e. the air in contact with and immediately above the surface of the earth. While the size of the coupling probe does depend upon the frequency of operation, it would be much smaller than an equivalent radiating antenna would be, if the antenna were designed to transmit the same level of power with the same efficiency. The energy radiated from such an antenna would further be dispersed in all directions and unavailable for capture by a receiver located on the earth. Small size, controlled dispersion, low attenuation and efficient operation are all features of ZSW systems that make them attractive for a wide range of applications that require moving energy and information from one point to another over the surface of the earth.

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