11. OTHER ELECTROMAGNETIC RADIATION 



L. N. LlEBERMANN 



1. Introduction 



The theory of propagation of electromagnetic energy in the sea is contained 

 completely in the remarkable electromagnetic equations given by Maxwell in 

 1873. Surprisingly the large amount of experimentation with undersea electro- 

 magnetic propagation, particularly during World War II and the post-war era, 

 has contributed negligibly to our basic understanding over that given by 

 Maxwell in his theoretical tour de force ; experiments have simply confirmed 

 principles which were already known and inherent in Maxwell's equations. 



As is well known, Maxwell's equations predict the propagation of electro- 

 magnetic waves in the form of a periodically varying electric field and magnetic 

 field in the form 



E = Eo exp (icut — yz) 



(1) 



H = //o exp {icot — yz). 



The quantity y, termed the propagation constant, is given immediately from 

 Maxwell's equations in the form 



y = iio\/{ejx — ia^la)). (2) 



The quantities e, /z and a are electromagnetic properties of the medium, which 

 are discussed in detail immediately below. Inasmuch as these are always real 

 quantities the propagation constant, y, can be complex. It is seen from (1) 

 that the real part of y leads to attenuation of the electric and magnetic fields 

 with propagation of the wave. 



2. Electromagnetic Properties of Sea-Water 



The physical significance of the characteristic constants of the medium are as 

 follows : the quantity a is the conductivity of the medium ; /x is the permeability ; 

 and e is the dielectric constant. Table I gives values for these constants for 

 typical media. 



Table I 



O, €, 



mhos/m farads/m 



\_MS received July, 1960] 469 



