428 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1957 



K in the region below resonance because the effects of polycrystalUne 

 structure and anisotropy forces were neglected in Polder's and Hogan's^ 

 analysis. Furthermore, it was assumed in the derivation of the perme- 

 tihility tensor that the ferrite is saturated with a biasing dc magnetic 

 field which is large compared to Ihe microwave magnetic field. 



There exists a great need for experimental data for all those conditions 

 where some of the above assumptions do not hold. In particular, the 

 region of biasing magnetization between zero and ferromagnetic reso- 

 nance is of interest because it is the operating region for many ferrite 

 devices such as phase shifters, modulators, and field displacement iso- 

 lators. Techniques for the measurement of ferrite parameters below 

 resonance were investigated and it was found that the measurement of 

 the perturbation of a degenerate cylindrical cavity by a thin ferrite disc 

 yielded accurate results, whereas observation of the cavity perturbation 

 caused by a small sphere produced less accurate data. 



It is the purpose of this paper to describe and discuss the thin disc 

 method and to compare it with other techniques described in the litera- 

 ture.^' ^ After defining the ferrite parameters as constants in Maxwell's 

 equations it is shown how these parameters can be obtained from 

 various measuring techniques. Instrumentation for the thin disc tech- 

 nique is described and a few remarks are made pertaining to experi- 

 mental difficulties. Finally, some measurements of low-loss ferrites are 

 reported and compared with values predicted bj^ Polder's relations. 



2. DESCRIPTION OF FERRITE PARAMETERS 



It is customary^ to define the electric and magnetic polarization vec- 

 tors P and M in terms of the field vectors E (electric field intensity), 

 T) (electric displacement), l} (magnetic field intensity), and B (mag- 

 netic induction). In the M.K.S. system we have: 



P =D - £oE 



M = B/fio - S 



€o = 8.854 X 10"^^ farad/meter, permittivity of free space 



Mo = 4x X 10~^ henry/meter, permeability of free space 



Then, the intrinsic parameters of a ferrite medium are defined as those 

 quantities which relate P and M to the electric and magnetic fields in 

 the medium respectively. 



P = fox J 



ill = Tn^ 



Whereas the electric susceptibility Xe is a scalar quantity in ferrites the 



