1344 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



wave rotating counterclockwise is positive circularly polarized in domains 

 numbered 2. In the absence of any other effects the resonance fre- 

 quency of all of these domains would be determined by the anisotropy 

 field. However, if we excite both circular polarizations simultaneously 

 and if the relative phase of the two circular polarizations is as shown in 

 Fig. 7(a) poles will be set up at the domain walls as indicated in the 

 figure. The demagnetizing fields associated with these will cause the 

 resonance for both circular components to occur at a frequency given by: 



/ = T^cff ^ yM, 



(13) 



On the other hand, if the phase of the two circular polarizations is as 

 shown in Fig. 7(b), no poles will be set up on the walls and the re- 

 sonance will be determined primarily by the anisotropy field. 



/ = T^eff ^ yH, 



(14) 



These two examples of the relative phase of the circular waves cor- 

 respond to linear polarizations in the x and y directions respectively. 



This simplified derivation gives the maximum and minimum fre- 

 quencies at which resonances can occur. In a material containing a large 

 number of randomly shaped and randomly oriented crystallites, res- 

 onances can occur at all frequencies between these limits. Most ferrites 

 have values of M^ between 80,000 and 240,000 and anisotropy fields 

 which probably range from 8000 to 80,000 amp. turns/meter with per- 



(a) 



POLES ON WALL 



^LINEAR POLARIZATION^ 

 V IN X DIRECTION , 



(b) 



NO POLES ON WALL 

 ^LINEAR POLARIZATION' 

 \ IN y DIRECTION 



Fig. 7 — Model used by Smit and Polder to illustrate their theory for the "low- 

 field loss." 



