By ether concept the space is physical substance that has known (electric constant e and magnet constant m) and unknown yet properties. In any substance can be created so called longitudinal waves. In general case it is oscillations of the energy density in the direction of the wave spreading.

     In Alexander Chernetsky's paper "On Physical Nature of Bioenergy Phenomenons and on their modeling", published in 1989, it is described the properties of longitudinal waves these are created in so called "working body" (superconducting metal, plasma  and biological plasma). The theory of 1960 for it named as "charge equivalent theory" was proposed by V.I.Dokutchaev, Russia (1932 - 1990).
    Relative motion of charges, according to Lorentz scale transformations, produce the change of distance between charges of moving frame of reference that is equivalent to some increase of charge density of the current. By this way, additional equivalent charge is created in moving system:

                            q₀         u 
                  q = -------- (---------)      by Dokutchaev
                             2         c

where q₀ is charge in motionless system, u is velocity of system, c is velocity of light.

     Dokutchaev's dissertation of 1970 described some experiments: superconductors were placed in electromagnetically screened box (Faraday cage) but some signal was detected outside of the box when current was created in superconductor. Main conclusion is: longitudinal waves can be created in space (in vacuum) by means of electric energy  and such sort waves is not screening by metal screen.

     Alexander Chernetsky also described some experiments in which longitudinal waves are created. In his version "the working body" is electric discharge. There is known pinch - effect (interaction between electric current and magnetic field of this current) that lead to high frequency oscillations of the plasma. Radial component of the density current oscillations is responsible for longitudinal waves these are spreading in radial direction also [ 1 ].
 
    More 60 years ago Nikola Tesla wrote: " I showed that the universal medium is a gaseous body in which only longitudinal pulses can be propagated, involving alternating compressions and expansions similar to those produced by sound waves in the air. Thus, a wireless transmitter does not Hertz waves which are a myth, but sound waves in the ether, behaving in every respect like those in the air, except that, owing to the great elastic force and extremely small density of the medium, their speed is that of light." It is part of N.Tesla's article "Pioneer Radio Engineer Gives Views on Power", published in  New York Herald Tribune, Sept. 11, 1932, [ 2, p.94 ].  American scientist Thomas E. Bearden explained this statement of Tesla in next way: Ordinary receiver use so called "precessia of electrons" phenomenon that is result of interaction between electron gas of  antenna wires metal and longitudinal waves [ 2 ]. Tesla wrote about great mistake of modern science: "The Hertz wave theory of wireless transmission may be kept up for a while, but I do not hesitate to say that in a short time it will recognized as one of most remarkable and inexplicable aberrations of the scientific mind which has ever been recorded in history", article "The True Wireless" [ 2, p.95 ].

     Technology of Tesla require high potential source (up to millions Volts) that produce high frequency oscillations. Terminal that create the longitudinal wave is the spherical metal surface (sphere capacitor). The synthesis of Tesla's scheme and Dokutchaev's concept allow us to conclude: longitudinal wave is generated by means of changing energy density (electric charge density). Let's name it as function r(t). In Hertz transmitter there is changing energy density also, but it is linear density r₁(t): density of electric current in wire of antenna. It is one-dimensional density of energy. In Tesla's sphere capacitor there is change of charge value that is placed on the surface of the capacitor. So, it is two-dimensional density of energy r₂(t).

     N.Kozyrev [ 3 ] created so called "waves of density of time" by means of non-electrical methods: rotation plus axial vibration of gyroscope, deformation of material body, diffusion and  dissolving or crystallization of the matter,  fading of plants and so on. Different detectors for such sort waves were used: electrical component of the wave was detected by means of galvanometer, gravitational component of the wave was detected by means of the weighing machine, chronal component of the wave was detected by means of electronic scheme that used so called "Winston bridge" since electrical properties of electronics components are changing in wave area. These three methods showed the next: any type change of matter structure that can be presented as r(t) ( i.e. change of density of energy ) is the way for generation of the longitudinal wave. For example, if it is change of volume density of matter, we can write three-dimensional density function r₃(t). It is connected with well-known Poisson equation for gravitation.
 
    There are more complex methods for longitudinal wave creation. R.Ziolkovsky, Physical Review A, vol.39, p.2005, wrote in the paper "Localized Transmission of Electromagnetic Energy" about his experiments. Before electromagnetic version, R. Ziolkovsky created the analogy in liquid to study the properties of wave to create the optimum antenna system.

     What is the best method of the energy density modulation  for telecommunication systems? There are some experiments to prove the biological possibility to create  the longitudinal waves [1, p. 50]. By this analogy, I think, there is the way to produce longitudinal waves by means of technical system where the volumetrical density of plasma is changing.