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BELL SYSTEM TECHNICAL JOURNAL 



radius and the inside radius is 1.097. The shielding efficiency of this 

 combination is approximately the same as that of two cylinders having 

 the same ratio Rnlfi as given in Fig. 4, curve "5." This shows that 

 the condition that the radii of the cylinders should be in geometric 

 progression is not very critical, at least, not for the value of RnJTi 

 under consideration. 



100 

 95 



80 



uj 65 

 o 



Z 60 



O 55 



Z 



o 



40 



(0 30 



25 

 20 

 15 

 10 



10 20 30 40 50 60 70 80 90 100 



SEPARATION IN PER CENT (S/pXIOO) 



Fig. 6 — Shielding efficiency of two concentric cylinders versus the air-gap 

 between them. Overall thickness of the wall of the shield (P) kept constant. Zero 

 frequency. 



The curves of Fig. 6 also show the shielding efficiency of two con- 

 centric cylinders vs. the air-gap between them. In this case, however, 

 the total thickness F of the wall of the double cylindrical shield is 

 kept constant and the air-gap is increased from zero to F at the 

 expense of the cylinders. When the air-gap is zero, the shielding 

 efficiency is therefore that of a solid cylinder, the thickness of the 



