1168 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER, 1953 



Fig. 7 — Real part (/*') of permeability of a ferrite versus applied magnetic 

 field for the two circularly polarized components into which an incident plane 

 wave may be resolved. The useful region for the Faraday effect is that for low H, 

 where the two curves are approximately parallel. 



one sample at 9,000 mc, Hogan found a rotation of 60 degrees per cm of 

 path and an attenuation of about 0.5 db per cm. 



X. EFFECT OF CROSS FIELD 



When a steady magnetic field is applied to a ferrite in a direction per- 

 pendicular to the path of transmission of electromagnetic waves through 

 the material, the effective ac permeability of the material varies with 

 the applied magnetic field. For a given frequency, the permeability starts 

 out positive. As the magnetic field increases the permeability goes 

 through zero and approaches a large negative value as ferromagnetic 

 resonance is reached. Above resonance the permeability is positive and 

 gradually decreases with increase in magnetic field. 



Since the characteristic impedance of the ferrite relative to an empty 

 waveguide is 



-/'. 



it is apparent that Z may be varied by changing the applied field. When 

 /x is zero, the ferrite appears to be a perfect reflector, while when m = «, 

 it provides a perfect match to the empty guide. Since it is possible to 



