The idea of “non-Hertzian” EM energy goes back to the 19th century. I’ll try to give a short summary.
At the end of the 19th century, physicists believed that light was a mechanical oscillation in a mechanical medium, the aether. But such a medium could in principle sustain two kinds of waves: transversal and longitudinal. Those readers who are unfamiliar with physics should think of water for illustration: transversal waves are the surface waves which wave in a fashion perpendicular to their axis of propagation, while longitudinal waves are the sounds waves or pressure waves that propagate underneath the surface. The latter oscillate in the direction of propagation.
Transversal waves generally move at a different speed than longitudinal waves.
The history books of physics tell us that Heinrich Hertz was the first person to demonstrate experimentally the generation of transversal EM waves. Those are the EM waves that mainstream science deals with exclusively today; in fact, based on the standard Maxwell equations, it can be mathematically proved that only transversal waves are possible in a vacuum. Of course, in a material medium such as an ionized gas, longitudinal waves are accepted by and well known to mainstream physics (as plasma waves).
What mainstream physics has forgotten is that Nikola Tesla claimed to have generated longitudinal EM waves. He also claimed that his waves cannot be shielded by a Faraday cage, can move at superluminal speed, do not decay with the inverse square of the distance and can be used for the wireless transmission of energy (even at over-unity).
Since Tesla’s claims were at odds with the Maxwell theory, and further contradicted the speed limit c of the new special theory of relativity, they were subsequently dismissed and forgotten.
Today, however, a number of new theoretical developments exist that once again makes it a relevant question whether or not longitudinal waves exist in the vacuum. The terms “longitudinal” and “scalar” waves are used synonymously.
In the past decade, several theorists have pointed out empirical and theoretical reasons to doubt the completeness of Maxwell’s theory, and proposed an extended theory of electromagnetism that allows for novel EM phenomena, such as “pressure waves” of the vacuum. The literature on this subject is substantial.
T. W. Barret argues in  that “a number of physical effects strongly suggest that the Maxwell field theory of electromagnetism is incomplete.” He subsequently proposes a modified EM theory based on the non-abelian symmetry group SU(2) instead of the abelian U(1) of Maxwell’s theory . In the same theoretical spirit, M.W. Evans has proposed O(3) Electrodynamics . B. Lehnert writes in :
“An extended Lorentz invariant form of Maxwell’s equations has been developed on the hypothesis that the densities of electric charge and current can be interpreted as intrinsic properties of the electromagnetic field in vacuo. As consequences of this proposal, longitudinal electric space charge waves and steady electromagnetic equilibria are predicted to exist in vacuo.”
These proposed extensions have in common that they treat the potentials of the EM field as physically real, while the Maxwell theory treats them as mere mathematical conveniences without physical meaning.
The implications of longitudinal EM are vast. Since the frequency and wavelength of such waves can be modulated independently, they could provide virtually infinite bandwidth for communication. They would provide for instantaneous (superluminal) communication and thus utterly destroy Einstein’s relativity theory.
 Terence W. Barret: Maxwell’s Theory Extended (Part 1) – Empirical Reasons for Questioning the Completeness of Maxwell’s Theory- Effects demonstrating the Physical Significance of the A potentials. Annales de la Fondation Louis de Broglie, Vol. 15, 2, 1990 p. 143-183.
 Terence W. Barret: Maxwell’s Theory Extended (Part 2) – Theoretical and Pragmatic Reasons for Questioning the completeness of Maxwell’s Theory. Annales de la Fondation Louis de Broglie, Vol. 15, 3, 1990 p.253-283.
 M.W. Evans: O(3) Electrodynamics. Modern Nonlinear Optics, Part 2, Second Edition, Advances in Chemical Physics Volume 119, ISBN 0-471-38931-5, p. 79-267
 B. Lehnert: Basic Concepts of an Extended Electromagnetic Field Theory. Speculations in Science and Technology, Vol 17, 4, 1994 p. 259-266.