ABSTRACTS OF TECHNICAL ARTICLES 335 



Impedance Concept in Wave Guides.* S. A. ScHELKUNorr. The im- 

 pedance concept is the foundation of engineering transmission theory. If 

 wave guides are to be fully utilized as transmission systems or parts thereof, 

 their properties must be expressed in terms of appropriately chosen im- 

 pedances or else a new transmission theory must be developed. The gradual 

 extension of the concept has necessitated a broader point of view without 

 which an exploitation of its full potentialities would be impossible. 



In the course of various private discussions it has been noted that there 

 exists some uneasiness with regard to the applicability of the concept at very 

 high frequencies. In part this may be attributed to relative unfamiliarity 

 with the wave guide phenomena and in part to the evolution of the concept 

 itself. Some particular aspects of the concept have to be sacrificed in the 

 process of generalization and although these aspects may be logically un- 

 important, they frequently become psychological obstacles to understanding 

 in the early stages of the development. For this reason several sections of 

 this paper are devoted to a general discussion of the impedance concept be- 

 fore more specific applications are given; then by way of illustration it is 

 proved that an infinitely thin perfectly conducting iris between two different 

 wave guides behaves as if between the admittances of its faces there existed 

 an ideal transformer. This theorem is a generalization of another theorem 

 to the effect that when the two wave guides are alike, the iris behaves as a 

 shunt reactor. Actual calculation of the admittances and the transformer 

 ratio depends on the solution of an appropriate boundary value problem. 



More generally, wave guide discontinuities are representable by T-net- 

 works. In some special cases these networks lack series branches, and in 

 other cases the shunt branch. 



Theory of Cathode Sputtering in Low Voltage Gaseous Discharges.^ 

 Charles Hard Townes. To determine the amount of sputtering in a 

 glow discharge three functions must be known: the number of ions of a given 

 energy striking the cathode, the amount of cathode material released from 

 the cathode by each ion, and the fraction of material released from the 

 cathode which diffuses away. Expressions derived for these allow deter- 

 mination of the dependence of total rate of sputtering on the geometry of 

 the discharge, pressure, cathode fall, current, and constants of the gas and 

 cathode surface. The result is most accurate for very low voltage, high 

 pressure discharges. Comparison with experimental data shows quanti- 

 tative agreement under these conditions. 



^Quarterly of Applied Malhentctics, April 1944. 

 ^Phys. Rev., June 1 and 15, 1944. 



