Jonathan Zenneck - Middle Years

Middle Years

Zenneck, in 1907, was the first to analyze a solution of Maxwell's equations that had a "surface wave" property. This so-called Zenneck wave is simply a vertically polarized plane wave solution to Maxwell's equations in the presence of a planar boundary that separates free space from a half space with a finite conductivity. For large conductivity -- this depends on the frequency and dielectric constant, too -- such a wave has a Poynting vector that is approximately parallel to the planar boundary. The amplitude of this wave decays exponentially in the directions both parallel and perpendicular to the boundary (with differing decay constants).

It is worth emphasizing at the outset that the term "surface wave" is often a misnomer. We should attach no more significance to the phenomenon than the equations that describe it imply. The term surface wave conjures up an image of energy flow that is confined to a region that is localized at or near the surface. Whereas this is true for acoustic surface waves or certain classes of seismic waves, for example, it is generally not true for the phenomenon that we are discussing here. In our case, the boundary generally does not serve to localize the energy associated with the phenomenon; rather it just serves to guide the wave. Most of the energy of the wave is not near the surface. More accurately, for the case of vertical polarization, the presence of the conducting boundary allows the energy of the wave to extend down to the boundary in a significant manner (in contrast to the horizontally polarized case where the boundary condition mostly excludes the wave from the region near the surface). When we allow the boundary to be curved, as in the case of propagation around a sphere, the curvature of the surface leads to diffraction effects, yielding propagation of the wave beyond the geometrical horizon. The electromagnetic surface waves that we are discussing are no more magical than these phenomena. Their analysis is, however, somewhat complicated.

1895 Zenneck left zoology and turned over to the new field of radio science, He became assistant to Ferdinand Braun and lecturer at "Physikalisches Institut" in Strasbourg, Alsace. Nikola Tesla lectures introduced him to the wireless sciences. In 1899, Zenneck started propagation studies of wireless telegraphy, first over land, but then became more interested in the larger ranges that were reached over sea. In 1900 he started ship-to-coast experiments in the Northern Sea near Cuxhaven, Germany. in 1902 he conducted tests of directional antennas. In 1905, Zenneck left Strasbourg since he was appointed assistant-professor at the Danzig Technische Hochschule and in 1906, he became professor of experimental physics in the Braunschweig Technische Hochschule. Also in 1906, Zenneck wrote "Electromagnetic Oscillations and Wireless Telegraphy", the then standard textbook on the subject). In 1909, he joined Badische Anilin und Sodafabrik in Ludwigshafen to experiment with electrical discharges in air to produce bound nitrogen as fertilizer.