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BELL SYSTEM TECHNICAL JOURNAL 



zero to P keeping rijRi = r^jRi can be obtained by means of the 

 following equation 



g- 1/4m 



where 



1 -^ + 1/4m(i --^Xn,, 

 912 \ Vgi2/ 



" R2 



+ 1> 



(10) 



If Ri/r2 (that is Vgi2) is varied from 1 to R^/ri the desired result is 

 obtained. 



Assume in Fig. 3 the thickness of the two cylinders to be the same, 

 that is, R\ — r\ = R2 — ^2- The variation in shielding efficiency vs. 5 



FiR. 3. 



or Vgi2, is then given by equation (5), with §2 expressed in terms of 

 512 and q\ as follows : 



Vg2 = 



1 + Vgi2[l - Vgi] 



(11) 



In an article in the Philosophical Magazine of February 1933 L. V. 

 King has developed relations for the shielding efficiency of spherical 

 and cylindrical shells taking into account the effect of induced currents. 

 The following equations for an infinitely long metallic cylinder have 

 been picked from his paper. For a non-magnetic shell, the thickness 

 of which is small compared to its radius, the shielding ratio, g, is 

 given by 



g = 1 cosh {ka) + 1/2 ka sinh {kd) | , (12) 



