FERRITES IN MK.'UOWAVE APPLICATIONS 



1341 



Curve A. Broad resonance absorption line. 



Curve B. A loss which disappears when the material is maRnotizod 

 called ''Low Field Loss". 



Curve C. Loss which goes to zero for one component and rises for the 

 other. 



Curve D. A loss which appears to be independent of magnetic Held 

 over a wide range and can be related to the dielectric lo.ss tangent of the 

 material, hence called dielectric loss. 



Curve E. Higher order modes causing erratic v^ariation- in l(».s.s. 



Curve F. Double peaks due to "Cavity Resonances". 



Qualitative and semiquantitative explanations have been developed 

 to explain all of these phenomena. Some of them follow from a simple 

 extension of the plane wave theory and the rest are based upon con- 

 siderations of the special case of a partially filled waveguide. 



Curve A J Fig. 5 



Associated with the precessional resonance there is a damping term 

 by which power is dissipated in the lattice. The exact nature of this 

 damping term is not fully understood, and measured line widths are 

 always greater than those predicted by present theory. Nevertheless 

 we have at our disposal empirical damping constants which can be used 

 to predict resonance absorption losses as was done in the calculation of 

 the curves of Figs. 1 and 4. 



These apply, however, only to small ellipsoidal samples which are 

 ground from single crystal ferrites. In polycrystalline ferrites the ab- 

 sorption line is generally broader for three reasons, namely; crystalline 

 anisotropy, strain anisotropy and varying internal demagnetizing fields 

 due to the variety of shapes of the constituent crystallites. 



Many ferrites have a high crystalline anisotropy which behaves in 



-CIRCULAR POLARIZATION ^CIRCULAR POLARIZATION 



MAGNETIC FIELD 



Fig 5 — Typical loss characteristics encountered in the measurement of van- 

 ous ferrite samples in cylindrical waveguides with longitudinal static field. 



