EM waves are transmitted through Space,but the Signals at the Transmitter and the Receiver are earthed completing the circuit .Like.the return current through Ground wire or Ground are there Return EM waves through Ground? Just as we consider Image Conductors in Transmission lines to make the Electric or Magnetic fields at Ground to be zero do we have to consider Image waves at equal depth below the Ground(equal to height )? Or similar to the Corpuscular and wave theory of light should we consider charge flow and electric Field Radiation and associated Magnetic Field or Waves?
Dear Pisupati. This is an interesting question. I may only contribute to the answer. First, reviewing the different situations in which imaging was used may be a good start for all. One situation, you mentioned, is that of transmission line parameters calculation such as its capacitance per unit length. To calculate transmission line capacitance, which is the capacity of holding positive and negative charges on two plates insulated from each other, it was appropriate to assume the presence of conductors holding the opposite charge below earth surface at a depth equals the height of the conductors above ground. Now ground is the zero voltage of the electric field in between. This helped the calculation of the capacitance as outlined in textbooks. Another case of image theory was the case of a monopole antenna parameters and radiation pattern calculations. In this case, the reflecting ground is as if a signal is coming out from a monopole below ground forming together a (virtual) dipole with double the gain and lower radiation resistance. In these 2 cases, imaging was used as a mathematical tool and of course no signals or conductors below the ground. Imaging like this is used to apply formulas known for dual items (e.g. a dipole or EMF between two oppositely charged particles) to solve problems of single items ( a monopole or a single charged conductor). In the case of electromagnetic waves, beside the case of the dipole, the use of imaging can be used for mathematical convenience only, e.g. to represent reflection in communication channels as signals coming from below ground, or else, others may suggest to solve single body issue whenever the double one is known. This is a good reminder of such a powerful tool.
For the first part of the question, the return EM wave through ground. Cases in which we have grounded communication like telegraphy or else can be treated in the same way as we treat electric power distribution. The ground in power distribution is considered as an infinite source or sink of charge which can be applied to grounded communication signals as well. On the other hand, wireless communication does not require a return path as we are not transferring charges but rather a wave front composed of an electric and magnetic fields that may induce small emf/ currents in receiving antennas. Thanks again for the interesting question. @AlDmour.
Prof.Ismat Aldmore is right in saying that we use image conductors, only for calculating the capacitance of Transmission Lines with image conductors carrying charges opposite to that of transmission line charges making ground to be at zero potential.
In the case of EHV Lines we use image conductors having the same type of charges to calculate the Inductance of the line making the net Magnetic flux density zero at ground.
Actually there is no image conductors existing at all below the ground.
His statement , " wireless communication does not require a return path as we are not transferring charges but rather a wave front composed of an electric and magnetic fields that may induce small emf/ currents in receiving antennas " can be elaborated as follows.
In the case of propagation of EM waves we don't have or we don't consider Image Em Waves for the following reasons.
Production and Prorogation of EM waves is due to Electromagnetic waves created by the vibration of an electric charge, and not due to flow of charges. This vibration creates a wave which has both an electric and a magnetic component. An electromagnetic wave transports its energy through a vacuum at a speed of 3.00 x 108 m/s (a speed value commonly represented by the symbol c). The propagation of an electromagnetic wave through a material medium occurs at a net speed which is less than 3.00 x 108 m/s. This is depicted in the animation below. LINK :
http://www.physicsclassroom.com/mmedia/waves/em.cfm
Electromagnetic radiation is a particular form of the more general electromagnetic field (EM field), which is produced by moving charges. Electromagnetic radiation is associated with EM fields that are far enough away from the moving charges that produced them that absorption of the EM radiation no longer affects the behavior of these moving charges. These two types or behaviors of EM field are sometimes referred to as the near and far field. In this language, EMR is merely another name for the far-field. Charges and currents directly produce the near-field. However, charges and currents produce EMR only indirectly—rather, in EMR, both the magnetic and electric fields are associated with changes in the other type of field, not directly by charges and currents. LINK :
http://en.wikipedia.org/wiki/Electromagnetic_radiation
Also, Induction and Radiation Fields in an antenna are explained in the LINK :
http://www.tpub.com/neets/book10/40.htm
The Links given below will also be of interest.
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35
The animation and the You tube Video URL :
http://www.youtube.com/watch?feature=player_embedded&v=sS2ZyUvfUco
Excitation of an atom wherein an electron raised to a higher energy level while returning back to its previous level causes radiation of energy equal to that it received in going to the higher energy level,as the excited state is unstable lasting only for
10 ^ (-8) seconds and if the radiation falls under visible spectrum it appears in the form of light,which is the principle of LEDs....
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