Frequency Shifts in Cavities with Longitudinally Magnetized Small Ferrite Discs

A possible experimental determination of the elements of the permeability tensor of a magnetized ferrite at any frequency and magnetic field rests 011 the measurement of the frequency shift that the sample produces in a resonant cavity.1 From this measurement and from the theoretical relation among frequency shift, ferrite and cavity geometry and ferrite properties, we may deduce the diagonal and off-diagonal components, N and K, of the Polder tensor. The theoretical relation referred to above is the result of the assumption usually made that the ferrite has small volume compared to the 637 638 T H E B E L L SYSTEM T E C H N I C A L J O U R N A L , MAY 1958 cavity volume and produces a small perturbation of the fields in the cavity:1, 2Ao wo = W.lu) + WsiB) wTM · ^ m ; Here Wc is the total energy stored in the empty cavity at resonance, W,(M) the additional magnetic energy stored in the sample, Wa(E) the additional electric energy stored in the sample, du the shift of resonance frequency upon introduction of the sample and co() the resonant frequency of the empty cavity. The quantities TFC£), W,,(M) and IF/^ are given by WC(K) =