# 6.9. Relative Effective Permeability¶

A simple model of the relative effective permeability of the ferrite core $$\mu_{cer}$$ is related to the relative permeability of the unbounded ferrite material $$\mu_r = \mu / \mu_0$$ by [8]. This was explained as a step-up in flux and hence of emf due to the core by Burgess in 1946 [11].

• $$D_F$$: Demagnetization factor of ferrite core
• $$\mu_r$$ Relative permeability of the unbounded ferrite material

For most ferrite material, $$\mu_r$$ is very large ( $$\mu_r \gg 1$$ ) so that $$\mu_{cer}$$ is approximately inversely proportional to the demagnetization factor:

$\mu_{cer} \cong D_F^{-1}$

Devore and Bohley mentioned that a improved model of relative effective permeability in the equation of radiation resistance [16].

• $$D_w$$ is demagnetization factor of winding
• $$l_F$$ is length of ferrite core
• $$l_w$$ is length of winding
• $$A_F$$ is cross section area of ferrite core
• $$A_w$$ is cross section area of winding