Electromagnetic Waves: Review of S. A. Schelkunoff's Book

p H I S new addition to a well-known series has been awaited with much interest by all those acquainted with Dr. SchelkunofTs contributions to propagation theory, and it will be found t h a t their expectations have been entirely fulfilled. T h i s monumental piece of work is equally remarkable for the originality and consistency of its approach as for the wealth of information contained in its five hundred densely packed pages. The a u t h o r ' s systematic use of the harmonic oscillation, with complex variables and coefficients, is in line with the marvelous development which has occurred in the communication field during the last fifty years. Alternating current theory, then acoustics, then vibrational mechanics successively dropped the differential equations which physics offered as a basis and systematically restricted themselves to harmonic oscillations. This has resulted in the replacement of the differential operator by io>, leading to a tremendous simplification of steady-state analysis, which has been reduced to the calculation of amplitude ratios and phase differences. T h e genuinely difficjlt problems have not disappeared for all t h a t but are now relegated to Fourier or Laplace transform theory, and it has become apparent t h a t an enormous field of application can be covered by purely algebraic processes. Net the least advantage of this method has been the unification brought into the three chapters of technical science mentioned above. Electrical impedanccs gave the model a f t e r which acoustical and mechanical impedances were fashioned; and mixed m u t u a l impedanccs, thereafter, made it possible to write the equations of electro-mechanical or acoustico-mechanical transducers.