Electromagnetic waves Poynting vector

There is a close similarity with planar electromagnetic cavities (H.-J. Stockmann, 1999). The basic equations take the same form and, in particular, the Poynting vector is the analog of the quantum mechanical current. It is therefore possible to experimentally observe currents, nodal points and streamlines in microwave billiards (M. Barth et.al., 2002 Y.-H. Kim et.al., 2003). The microwave measurements have confirmed many of the predictions of the random Gaussian wave fields described above. For example wave function statistics, current flow and... 

An electromagnetic wave transports energy. The energy flow per second per unit area (i.e., the intensity) is given by the Poynting vector S for an electromagnetic wave moving in vacuum,... 

Let us consider the propagation of electromagnetic waves with both fields nonzero E O and B 0. As usual, propagation is parallel to the Poynting vector G, defined in Eq. (17). Evidently, by definition, vector G is perpendicular to both fields E and B. Hence, there cannot exist components of the magnetic field B parallel to the instantaneous direction of propagation G. 

When the distance from the source exceeds the characteristic length Xo, the magnetic field is mainly defined by component be, and the electromagnetic field at the arrival moment corresponds to the wave zone components of the field are perpendicular to the direction of the Poynting vector, and the ratio of components of electric and magnetic field, does not depend on the distance to the dipole. 

We eonelude this seetion with a eaution. It is important to remember that whereas the Poynting veetor ean be defined for an arbitrary eleetromagnetie field, the Stokes parameters can only be defined for transverse fields such as plane waves discussed in the previous section or spherical waves discussed in Section 12. Quite often the electromagnetic field at an observation point is not a well-defined transverse electromagnetic wave, in which case the Stokes vector formalism cannot be applied directly. 

The flow of energy and the direction of the electromagnetic wave propagation are represented by the Poynting vector ... 

The flux density of an electromagnetic wave is described by the Poynting vector. For the case of the plane wave field one obtains for the time average in the direction of propagation... 

The energy flux propagated by the electromagnetic wave is give by P, the Poynting vector defined as P = E x H, or... 

It was shown in Section 2.8.3 that the energy transferred by an electromagnetic wave is proportional to the square of the wave amplitude E. Without proof, we state that the energy density carried by a wave is defined by the vector product [E B] = S vector S being referred to as the Poynting vector. 

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